Euornithes Sereno, 1998 non Stejneger, 1884
Official Definition- (Vultur gryphus <- Enantiornis leali, Cathayornis yandica) (Benito, Chen, Wilson, Bhullar, Burnham and Field, 2022: Registration Number 553)
Other definitions- (Iberomesornis romerali + Passer domesticus) (modified from Sanz and Buscalioni, 1992)
(Passer domesticus <- Sinornis santensis) (Sereno, online 2005; modified from Sereno, 1998)
(Passer domesticus <- Enantiornis leali) (modified from Longrich, 2009)
(Passer domesticus <- Cathayornis yandica) (Turner, Makovicky and Norell, 2012)
= Ornithurae sensu Gauthier and de Queiroz, 2001
Definition- (tail shorter than the femur and with an upturned and ploughshare-shaped compressed pygostyle in the adult, composed of less than six segments, and shorter than the less than eight free caudals homologous with Vultur gryphus)
= Euornithes sensu Sereno, 1998 (modified)
Definition- (Passer domesticus <- Sinornis santensis)
= Euornithes sensu Longrich, 2009
Definition- (Passer domesticus <- Enantiornis leali) (modified)
= Euornithes sensu Turner, Makovicky and Norell, 2012
Definition- (Passer domesticus <- Cathayornis yandica)
= Ornithuromorpha sensu O'Connor, Wang and Hu, 2016
Definition- (Passer domesticus <- Enantiornis leali) (modified)
Diagnosis- (proposed) less than six caudal vertebrae fused into pygostyle; mobile scapulocoracoid articulation convex on scapular side; procoracoid process (absent in Patagopteryx and Apsaravis); coracoid not laterally convex (absent in Piscivornis, Bellulornis and Apsaravis); anterior edge of humeral head not concave in proximal view (absent in Patagopteryx and Ambiortus); lateral edge of manual phalanx II-1 deeply convex (absent in Schizooura, some Gansus and Xinghaiornis+Mengciusornis); metacarpal III does not extend much past metacarpal II (absent in Schizooura and Xinghaiornis); tarsometatarsus fused distally (absent in Archaeorhynchus and Xinghaiornis+Mengciusornis); pedal ungual I not strongly curved (absent in Tianyuornis).
Comments- Euornithes was first used by Stejneger (1884; not Cope, 1889, contra Sereno, online 2005 and Turner et al., 2012) as a superorder containing living birds besides palaeognaths (his Dromaeognathae) and penguins (his Impennes). Sanz and Buscalioni (1992) later erected the homonym Euornithes as a new subclass, "the most recent common ancestor of Iberomesornis and Ornithurae (sensu Gauthier 1986 and Cracraft 1986) and all of its descendants", which is equivalent to a modern Ornithothoraces. These were both largely ignored. In the 1990s, birds intermediate between enantiornithines and ornithurines began to be recognized, with Chinese and BAND authors generally expanding the concept of Ornithurae to include those taxa they studied (Chaoyangia, Gansus, Liaoningornis incorrectly, Songlingornis) while Western cladists created Ornithuromorpha for the taxa they studied (Patagopteryx, Vorona possibly incorrectly, Gargantuavis). Unfortunately, Ornithuromorpha was given node-based definitions dependant on Patagopteryx (and sometimes Vorona), which had an uncertain placement relative to the numerous Chinese taxa described in the early 2000s (yanornithids, hongshanornithids, schizoourids, etc.). Thus Ornithuromorpha became an unstable clade content-wise instead of the clade of birds closer to Aves than Enantiornithes that most people wanted to refer to. One solution was to use the expanded Ornithurae of Chinese authors, but formally define it, which unfortunately led to an apomorphy-based definition dependant on pygostyle anatomy (Gauthier and de Queiroz, 2001). This was problematic because several relevant taxa (Patagopteryx, Vorona, Chaoyangia, the types of Yanornis and Archaeorhynchus) don't preserve pygostyles, a classic example of why apomorphy-based definitions should be avoided. Another solution proposed by O'Connor et al. (2016) was to redefine Ornithuromorpha to be "The first ancestor of Neornithes that is not also an ancestor of the Enantiornithes, and all of its descendants." These definitions were not used widely outside of Clarke's and O'Connor's works respectively. Sereno (1998) had instead proposed Euornithes as a new taxon with the definition "All ornithothoracines closer to Neornithes than to Sinornis", followed by Longrich's (2009) definition "all birds closer to Passer than to Enantiornis" and Turner et al.'s (2012) "Passer domesticus (Linnaeus, 1758) and all coelurosaurs closer to it than to Cathayornis yandica Zhou et al., 1992." These are all equivalent in modern topologies as Sinornis and Cathayornis have been universally recognized as enantiornithines since 2000. The resolution of what to call the clade was made by Benito et al.'s (2022) use of Phylocode to establish the definition as "The largest clade containing Vultur gryphus Linnaeus, 1758 (Aves or Neornithes) but not Enantiornis leali Walker, 1981 (Enantiornithes) and Cathayornis yandica Zhou, Jin & Zhang, 1992 (Enantiornithes)", which is followed here. As Benito et al. state, Phylocode Note 9.15A.2 says "In order for two uses of identically spelled preexisting names to be considered the same name rather than homonyms, one use must have been derived from the other or both derived from a third use of the name. If later uses of a name are not accompanied by a reference to an earlier use, absence of any overlap in the compositions associated with identically spelled names can be taken as evidence that they are homonyms", and Sereno (1998) lists Euornithes as "new taxon" and states it is "a taxon coined here" while also claiming to be "Unaware of Sanz and Buscalioni (1992)" in 1998 (Sereno, online 2005) and was evidently unaware of Stejneger's work even in 2005 as he cites Cope, 1889 instead. Thus Euornithes Stegnejer, 1884 and Euornithes Sanz and Buscalioni, 1988 are homonyms of Euornithes Sereno, 1998 and the latter should be cited as the proper author.
References- Stejneger, 1884. Classification of birds. The Illustrated Science Monthly. 2, 45.
Cope, 1889. Synopsis of the families of Vertebrata. The American Naturalist. 23, 849-877.
Sanz and Buscalioni, 1992. A new bird from the Early Cretaceous of Las Hoyas, Spain, and the early radiation of birds. Palaeontology. 35, 829-845.
Sereno, 1998. A rationale for phylogenetic definitions, with application to the higher-level taxonomy of Dinosauria. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen. 210(1), 41-83.
Gauthier and de Quieroz, 2001. Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and the name "Aves." In Gauthier and Gall (eds.). New Perspectives on the Origin and Early Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom. Peabody Museum of Natural History. 7-41.
Sereno, online 2005. Stem Archosauria - TaxonSearch. http://www.taxonsearch.org/dev/file_home.php [version 1.0, 2005 November 7]
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Turner, Makovicky and Norell, 2012. A review of dromaeosaurid systematics and paravian phylogeny. Bulletin of the American Museum of Natural History. 371, 1-206.
O'Connor, Wang and Hu, 2016. A new ornithuromorph (Aves) with an elongate rostrum from the Jehol Biota, and the early evolution of rostralization in birds. Journal of Systematic Palaeontology. 14(11), 939-948.
Benito, Chen, Wilson, Bhullar, Burnham and Field, 2022. Forty new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds. PeerJ. 10:e13919.

unnamed probable Euornithes (Morrison, Dyke and Chiappe, 2005)
Late Campanian, Late Cretaceous
Northumberland Formation of the Nanaimo Group, British Columbia, Canada
Material- (RBCM.EH2005.003.0001.C) distal ulna (Morrison, Dyke and Chiappe, 2005)
(RBCM.EH2005.003.0001.D) distal ulna (Morrison, Dyke and Chiappe, 2005)
(RBCM.EH2005.003.0001.E) tibiotarsus (95 mm) (Morrison, Dyke and Chiappe, 2005)
(TMP 1999.081.0001) carpometacarpus (57 mm) (Dyke, Wang and Kaiser, 2011)
Comments- These were tentatively referred to Ornithurae by Morrison et al. (2005) and (in the case of the carpometacarpus) Dyke et al. (2011). Note that other ornithurine specimens described in these publications are here placed in Aves- tarsometatarsi RBCM.EH2005.003.0001.A and RBCM.EH2005.003.0001.B, and coracoid RBCM.EH2008.011.01120 that was later made part of the holotype of Maaqwi.
References- Morrison, Dyke and Chiappe, 2005. Cretaceous fossil birds from Hornby Island (British Columbia). Canadian Journal of Earth Sciences. 42(12), 2097-2101.
Dyke, Wang and Kaiser, 2011. Large fossil birds from a Late Cretaceous marine turbidite sequence on Hornby Island (British Columbia). Canadian Journal of Earth Sciences. 48(11), 1489-1496.

undescribed Euornithes (DePalma, 2010)
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, South Dakota, US
Material- (multiple individuals, at least two taxa) over twenty elements including incomplete mandibles and coracoid
twelve cervical vertebrae, nine dorsal vertebrae, fragmentary synsacrum, scapula, coracoid, partial pelves, phalanx I-1, pedal ungual I, tarsometatarsus
Comments- This material is in preparation for description and referred to Ornithurae by DePalma (2010).
Reference- DePalma, 2010. Geology, taphonomy, and paleoecology of a unique Upper Cretaceous bonebed near the Cretaceous-Tertiary boundary in South Dakota. Masters thesis, University of Kansas. 227 pp.

undescribed euornithine (Galton, Dyke and Kurochkin, 2009)
Late Albian, Early Cretaceous
Cambridge Greensand, England
Material- (Booth Museum coll?) humerus
Comments- Galton et al. (2009) note an ornithurine humerus from the Cambridge Greensand, though which definition of Ornithurae they use is uncertain. This may be one of the seven bird elements from the Booth Museum (mentioned as "Enaliornis and Aves incertae sedis, including ends of humeri") to be described by Galton (in prep.).
References- Galton, Dyke and Kurochkin, 2009. Re-analysis of Lower Cretaceous fossil birds from the UK reveals an unexpected diversity. Journal of Vertebrate Paleontology. 29(3), 102A.
Galton, in prep. Additional bird bones (Hesperornithiformes Enaliornis and Aves incertae sedis) from the Early Cretaceous of England. Revue Paleobiologie.

unnamed euornithine (Hurum, Roberts, Dyke, Grundvåg, Nakrem, Midtkandal, Śliwińska and Olaussen, 2016)
Early-Mid Albian, Early Cretaceous
Zillerberget Member, Carolinefjellet Formation, Norway
Material- (PMO 228.582) femur (35 mm)
Comments- This was discovered in 1962 and tentatively assigned to ?Avialae. Hartman et al. (2019) recovered it as a euornithine sister to Schizooura, but with only the femur known a more exact position than basal Euornithes is not advocated for here.
References- Hurum, Roberts, Dyke, Grundvåg, Nakrem, Midtkandal, Śliwińska and Olaussen, 2016. Bird or maniraptoran dinosaur? A femur from the Albian strata of Spitsbergen. Palaeontologia Polonica. 67, 137-147.

unnamed euornithine (Nesov, 1984)
Early Cenomanian, Late Cretaceous
Khodzhakul Formation, Uzbekistan
Material- (TsNIGRI 57/11915) distal tarsometatarsus(?)
Comments- This was discovered in 1975 and briefly described and illustrated by Nesov (1984) as a possible distal tarsometatarsus of an aquatic bird. Nesov identified it as coming from the Beshtyuba Formation, but later (1992) determined that locality (Cholpyk or Tcelpyk) belongs to the Khodzhakul Formation instead. If it is indeed a fused distal tarsometatarsus, it is probably an euornithine. Nessov notes metatarsal II ends more proximally than III and IV.
References- Nesov, 1984a. Pterozavry i ptitsy pozdnego mela Sredney Azii. Paleontologicheskii Zhurnal. 1, 47-57.
Nesov, 1984b. Upper Cretaceous pterosaurs and birds from central Asia. Paleontological Journal. 1, 38-49.
Nessov, 1992. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. In Campbell (ed.). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478..

unnamed euornithine (Nesov, 1984)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Materal- (TsNIGRI 44/11915; paratype of Zhyraornis kashkarovi) proximal scapula
Comments- This scapula was originally a paratype of Zhyraornis kashkarovi (Nesov, 1984). Kurochkin (1996) later noted the acromion and glenoid showed "a certain similarity" to enantiornithines, but could not refer to to Zhyraornis itself (which he regarded as an enantiornithine). The elongate anteriorly projecting acromion and limited coracoid articulation indicates it is ornithothoracine, while Nesov noted the coracoid articular surface was weakly convex, unlike enantiornitines. Patagopteryx differs in having a transversely expanded acromion which is also ventrally constricted, distally flat and dorsally angled. That of Archaeorhynchus is smaller and more separated from the scapula ventrally. That of Yixianornis is slightly more slender and dorsally projected, and is separated ventrally from the bulbous coracoid tubercle. Ambiortus' acromion is different in being dorsoventrally compressed and having a dorsal tubercle, though the length and low coracoid tubercle are roughly similar. Apsaravis has a more elongate and hooked acromion, though the coracoid tubercle is similarly low. The scapulae of hesperornithines are highly reduced, while Ichthyornis has an apomorphically reduced acromion. Iaceornis' is narrower and hooked, with a bulbous coracoid tubercle. Those of Aves sensu stricto are generally dorsoventrally compressed. TsNIGRI 44/11915 is here referred to Euornithes incertae sedis, though it may belong to Zhyraornis.
References- Nesov, 1984a. Pterozavry i ptitsy pozdnego mela Sredney Azii. Paleontologicheskii Zhurnal. 1, 47-57.
Nesov, 1984b. Upper Cretaceous pterosaurs and birds from central Asia. Paleontological Journal. 1, 38-49.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.

unnamed euornithine (Nessov, 1992)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Material- (ZIN PO 4605) proximal coracoid
Comments- Nessov (1992a) noted a coracoid with a "deep, round scapular facet", which seems to be the one later figured by him as possibly an ichthyornithiform (Nessov, 1992b). Note the specimen number is the same as a distal coracoid now referred to Abavornis species and labeled Aves in the same figure. Compared to Ichthyornis, it has a more proximolateral-distomedially oriented scapular cotyla, and a more laterally and less ventrally angled acrocoracoid which is dorsoventrally flatter. The concave scapular cotyla does indicate referral to Euornithes however.
References- Nessov, 1992a. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. In Campbell (ed.). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.
Nessov, 1992b. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.

unnamed euornithine (Nessov, 1992)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Material- (ZIN PO 3434b) distal tarsometatarsus
Comments- This specimen was listed as Aves indet. by Nessov (1992), but can be identified as a euornithine by the high degree of distal fusion, including a distal vascular foramen. It is not hesperornithine, since metatarsal IV is less robust than III.
Reference- Nessov, 1992. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. In Campbell (ed.). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.

unnamed probable euornithine (Nessov, 1992)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Material- (ZIN PO 4607) dorsal vertebra (7 mm)
Comments- Nessov (1992a) noted an ichthyornithiform vertebra discovered in 1989, which seems to be a dorsal vertebra (ZIN PO 4607) later figured by him as Ichthyornis sp. (Nessov, 1992b). It is roughly similar to Ichthyornis, but the dorsals of that taxon are not diagnostic, and ZIN PO 4607 could come from another related taxon as well. It is from an avebrevicaudan due to its large lateral central fossae, probably an ornithothoracine based on its age. It is not an enantiornithine, as the parapophyses are anteriorly placed, and can be excluded from Hesperornithes and Aves sensu stricto due to its amphicoely.
References- Nessov, 1992a. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. In Campbell (ed.). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.
Nessov, 1992b. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.

unnamed possible euornithine (Clarke and Norell, 2004)
Early Maastrichtian, Late Cretaceous
Tsaagan Khushu, Nemegt Formation, Mongolia
Material- (IGM 100/1310) proximal tibiotarsus
Comments- Diuscovered in 2001, IGM 100/1310 was described by Clarke and Norell (2004) and recovered as a member of Ornithurae using Clarke's avialan matrix. This is based on the presence of a medial cnemial crest, which is also known in more basal euornithines as well as a few enantiornithines (Hollanda, Gobipteryx, Alexornis) and some alvarezsaurids (though it differs from the contemporaneous Mononykus in the larger anterior cnemial crest, tuberculated medial scar and other proportions).
Reference- Clarke and Norell, 2004. New avialan remains and a review of the known avifauna from the Late Cretaceous Nemegt Formation of Mongolia. American Museum Novitates. 3447. 12 pp.

unnamed euornithine (Hou, Martin, Zhou and Feduccia, 1996)
Early Albian, Early Cretaceous
Boluochi, Jiufotang Formation, Liaoning, China
Material- (IVPP V9937) partial tibia, partial fibula, phalanx I-1 (~5 mm), pedal ungual I (~3 mm), distal tarsometatarsus, phalanx II-1 (~9 mm), phalanx II-2 (~7 mm), pedal ungual II (~6 mm), phalanx III-1 (~9 mm), phalanx III-2 (~7 mm), phalanx III-3 (~6 mm), pedal ungual III (~7 mm), phalanx IV-? (~6 mm), phalanx IV-? (~5 mm), phalanx IV-4 (~5 mm), pedal ungual IV (~4 mm)
Comments- First mentioned as "a partial foot" referred to Chaoyangia by Hou et al. (1996) and used in their skeletal reconstruction. The specimen number was listed as a referred specimen by Zhou and Hou (2002) without detail, and it was finally described and illustrated by O'Connor and Zhou (2013) as Euornithes indet. (their Ornithuromorpha). A position in Euornithes is suggested based on the distally fused metatarsus.
References- Hou, Martin, Zhou and Feduccia, 1996. Early adaptive radiation of birds: evidence from fossils from northeastern China. Science. 274, 1164-1167.
Zhou and Hou, 2002. The discovery and study of Mesozoic birds in China. In Chiappe and Witmer (eds.). Mesozoic Birds - Above the Heads of Dinosaurs. University of California Press. 160-183.
O'Connor and Zhou (online 2012), 2013. A redescription of Chaoyangia beishanensis (Aves) and a comprehensive phylogeny of Mesozoic birds. Journal of Systematic Palaeontology. 11(7), 889-906.

Euornithes indet. (Harris, Lamanna, Li and You, 2009)
Late Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Material- ?(IVPP V26194; Ornithuromorpha indet. A) posterior skull, sclerotic ossicles, posterior mandibles(?), altantal neural arch, axis (5.42 mm), third cervical vertebra (3.10 mm), fourth cervical vertebra (4.59 mm), fifth cervical vertebra (5.17 mm), sixth cervical vertebra (5.66 mm), seventh cervical vertebra, eighth cervical vertebra, partial ninth cervical vertebra
(IVPP V26195; Ornithuromorpha indet. B) posterior braincase, altantal neural arch, axis, third cervical vertebra (3.28 mm), fourth cervical vertebra (3.41 mm), fifth cervical vertebra (4.47 mm), sixth cervical vertebra, seventh cervical vertebra (5.54 mm), eighth cervical vertebra (5.46 mm), partial ninth cervical vertebra
?(IVPP V26196; Ornithuromorpha indet. C) posterior skull, posterior mandibles, altas, axis, third cervical vertebra (4.29 mm), fourth cervical vertebra (5.22 mm), fifth cervical vertebra (6.21 mm), sixth cervical vertebra (5.89 mm), seventh cervical vertebra, eighth cervical vertebra, ninth cervical vertebra, tenth cervical vertebra (4.86 mm), first dorsal vertebra (5.09 mm), second dorsal vertebra, third dorsal vertebra, fourth dorsal vertebra, fifth dorsal vertebra, dorsal rib fragment
Comments- IVPP V26194 was initially mentioned by Harris et al. (2009) as likely belonging to Gansus, noted as the posterior cranial half exposed in dorsal view. O'Connor et al. (2021, 2022) described it as an indeterminate euornithine (ornithuromorph in their usage), as it was not easily comparable to probable Gansus skull IVPP V26199 which is preserved in ventral view and only the first three cervicals. O'Connor et al. used O'Connor's bird analysis to recover it as an avialan in a trichotomy with Jeholornis and Pygostylia, which they attributed "to the limited number of morphological characters that could be confidently scored into the current matrix." Adding it to Hartman et al.'s maniraptoromorph analysis places it in Enantiornithes, but only a single step moves it to Euornithes. Among Xiagou taxa, it takes 0 steps to be Avimaia, 1 step to be Dunhuangia or Feitianius, 3 steps to be Qiliania, 4 steps to be Gansus, Meemannavis or Yumenornis, 5 steps to be Changmaornis, and 8 steps to be Jiuquanornis. Cervical proportions indicate it is not Brevidentavis.
IVPP V26195 was also first mentioned by Harris et al. (2009) as a likely Gansus specimen, as the one which "preserves a caudal fragment of the braincase that exhibits an intricate series of curvilinear impressions that may correspond to portions of the brain or neural vasculature." O'Connor et al. (2021, 2022) also described this as an indeterminate euornithine (ornithuromorph) as only the first three cervicals are comparable to Gansus, and used O'Connor's bird analysis to recover it in a polytomy with Schizooura, Xinghaiornis and Zhongjianornis (note the trees in their figure 9 are majority rule and implied weighting). In Hartman et al.'s matrix it resolves as an avian, and takes 1 more step to be Changmaornis, Gansus, Meemannavis or Yumenornis, 3 steps to be Avimaia, Dunhuangia or Feitianius, 4 steps to be Jiuquanornis, and 5 steps to be Qiliania. As for the above specimen, cervical proportions indicate it is not Brevidentavis.
IVPP V26196 is the last specimen noted by Harris et al. (2009) as probably Gansus, one of the "caudal halves of crania" preserved in right lateral view. Again, O'Connor et al. (2021, 2022) describe this as an indeterminate euornithine (ornithuromorph), which is again difficult to compare to the Gansus specimen preserved in ventral view. They recovered this specimen in a polytomy with other euornithines (again, the more precise positions in their figure 9 are due to majority rule consensus and implied weighting). In Hartman et al.'s matrix it resolves as an enantiornithine, taking no steps to be Avimaia, 1 step to be Dunhuangia, Feitianius or Meemannavis, 2 steps to be Qiliania, Gansus or Yumenavis, 3 to be Changmaornis, 4 to be Brevidentavis and 6 to be Jiuquanornis.
References- Harris, Lamanna, Li and You, 2009. Avian cranial material and cranial cervical vertebrae from the Lower Cretaceous Xiagou Formation of Gansu Province, China. Journal of Vertebrate Paleontology. 29(3), 111A.
O'Connor, Lamanna, Harris, Hu, Bailleul, Wang and You, 2021. First avian skulls from the Lower Cretaceous Xiagou Formation, Gansu, China. The Society of Vertebrate Paleontology Virtual Meeting Conference Program, 81st Annual Meeting. 196.
O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2022 (online 2021). Avian skulls represent a diverse ornithuromorph fauna from the Lower Cretaceous Xiagou Formation, Gansu Province, China. Journal of Systematics and Evolution. 60(5), 1172-1198.

undescribed Euornithes (Gao, Li, Wei, Pak and Pak, 2009)
Barremian-Albian, Early Cretaceous
Sinuiju Series, North Korea
Comments- Gao et al. (2009) report "even more advanced ornithurine birds" from the Sinuiju Series, though these remain undescribed. It is assumed Gao et al. use Martin's concept of Ornithurae that is equivalent to Euornithes.
References- Gao, Li, Wei, Pak and Pak, 2009. Early Cretaceous birds and pterosaurs from the Sinuiju series, and geographic extension of the Jehol biota into the Korean peninsula. Journal of the Paleontological Society of Korea. 25(1), 57-61.

unnamed possible euornithine (Buffetaut, Dyke, Suteethorn and Tong, 2005)
Late Barremian, Early Cretaceous
Kalasin 3, Sao Khua Formation, Thailand
Material- (K3-1) distal humerus
Comments- This was discovered in 1992 and "may be an early ornithurine" according to Buffetaut et al. (2005). That was based on two characters, the transversely oriented dorsal condyle and the brachial fossa, which are both present in many theropods. It is provisionally listed here pending further study.
Reference- Buffetaut, Dyke, Suteethorn and Tong, 2005. First record of a fossil bird from the Early Cretaceous of Thailand. Comptes Rendus Palevol. 4(8), 681-686.

undescribed possible euornithine (Close and Vickers-Rich, 2009)
Aptian, Early Cretaceous
Wonthaggi Formation of the Strzelecki Group, Victoria, Australia
Material- cervical vertebra
Comments- This was mentioned as "a small, heterocoelous cervical vertebra, which has been tentatively identified as an ornithuromorph." It is here placed in Euornithes as Ornithuromorpha was often used as a rough synonym at the time, and taxa basal to Patagopteryx (e.g. Jianchangornis, Archaeorhynchus) also have fully heterocoelous cervicals.
Reference- Close and Vickers-Rich, 2009. Australia's Mesozoic birds: New material from the Early Cretaceous of Victoria. Journal of Vertebrate Paleontology. 29(3), 80A.

Jianchangornis Zhou, Zhang and Li, 2009b
= "Jianchangornis" Zhou, Zhang and Li, 2009a
J. microdonta Zhou, Zhang and Li, 2009b
= "Jianchangornis microdonta" Zhou, Zhang and Li, 2009a
Early Albian, Early Cretaceous
Jianchang, Jiufotang Formation, Liaoning, China
Holotype- (IVPP V16708) (820 g, subadult) incomplete skull (72 mm), nine sclerotic plates, mandibles (one partial), hyoid, eight cervical vertebrae, seven dorsal vertebrae, eleven dorsal ribs, four gastralia, synsacrum (34 mm), pygostyle (5.5 mm), scapulae (53, ~47mm), coracoids (~30, 32 mm), furcula, sternum, humeri (75, 76 mm), radii (81, 78 mm), ulnae (82, 83 mm), scapholunare, pisiform, semilunate carpals, metacarpals I (10, 10 mm), phalanges I-1 (~25, 29 mm), manual unguals I (~9, ~9 mm), metacarpals II+III (mcII 34, 33 mm, mcIII ~32, 36 mm), phalanges II-1 (~20, ~18 mm), phalanges II-2 (~16, ~16 mm), manual unguals II (~4.5, ~6 mm), manual ungual III (~5.5 mm), ilia (38 mm), pubes (~51 mm), femora (59, 60 mm), tibiotarsi (75, 76 mm), fibulae (one proximal; 26 mm), pedal ungual I (~5.5 mm), tarsometatarsi (one incomplete; ~35, 37 mm), phalanx II-1 (12 mm), phalanges II-2 (11 mm), pedal unguals II (~6 mm), phalanges III-1 (15 mm), phalanges III-2 (11 mm), phalanges III-3 (10 mm), pedal ungual III (~7 mm), phalanx IV-1, phalanges IV-2 (8 mm), phalanges IV-3 (6 mm), phalanges IV-4 (7 mm), pedal ungual IV (~6 mm), feathers, fish fragments
Diagnosis- (after Zhou et al., 2009) at least 16 small, conical dentary teeth; strongly curved scapula; robust U-shaped furcula; robust and wide metacarpal I; manual digit I extends beyond metacarpal II; humerus+ulna+carpometacarpus / femur+tibiotarsus+tarsometatarsus ratio ~1.1.
Comments- This specimen was briefly described in an abstract (Zhou et al., 2009a) before being named and fully described later that year (Zhou et al., 2009b), though the former use is a nomen nudum due to ICZN Article 9.9. Including it in a version of Clarke's analysis, the authors found a basal euornithine polytomy consisting of Vorona, Archaeorhynchus, Jianchangornis, Hongshanornis, Patagopteryx, songlingornithids and more derived birds.
References- Zhou, Zhang and Li, 2009a. A new basal ornithurine bird from the Lower Cretaceous of China. Journal of Vertebrate Paleontology. 29(3), 207A.
Zhou, Zhang and Li, 2009b. A new basal ornithurine bird (Jianchangornis microdonta gen. et sp. nov.) from the Lower Cretaceous of China. Vertebrata PalAsiatica. 47(4), 299-310.

unnamed clade (Archaeorhynchus + Aves)
Diagnosis- (proposed) medial cnemial crest (absent in patagopterygiforms).

Schizoouridae Zelenkov in Zelenkov and Kurochkin, 2015
Definition- (Schizooura lii <- Apsaravis ukhaana) (Zelenkov and Kurochkin, 2015)
Other definitions- (Mengciusornis dentatus, Schizooura lii <- Jianchangornis microdonta, Bellulornis rectusunguis) (modified after Wang et al., 2019 online)
Diagnosis- (proposed) toothless premaxilla (also in ambiortiforms, Xinghaiornis and Odontornithes+Carinatae); toothless maxilla (also in Xinghaiornis+Mengciusornis and Aves); nasal contacts antorbital fenestra (also in toothless dentary (also in Odontornithes+Carinatae); Xinghaiornis+Mengciusornis, Apsaravis and Aves); dentary symphysis <45 degrees in lateral view (also in Juehuaornis and Xinghaiornis).
Comments- Schizoouridae was named by Zelenkov in a Russian book chapter by Zelenkov and Kurochkin (2015) as a sister taxon to Apsaravidae in Euornithes (his Ornithurae). This was not based on a numerical phylogenetic analysis and a pairing of Schizooura and Apsaravis has not been recovered to my knowledge in such analyses. However, as Apsaravis is near universally found to be closer to Aves than Schizooura their phylogenetic definition serves as a name for whichever taxa group with Schizooura to the exclusion of Aves.
Wang et al. (2019 online) were unaware of Zelenkov's work so tried to create the name Schizoouridae themselves. They intended it to include Schizooura and Mengciusornis, but the latter falls out closer to Bellulornis using the Hartman et al. maniraptoromorph matrix, so that their phylogenetic definition self destructs. At least six steps are necessary to make the definition valid.
References- Zelenkov and Kurochkin, 2015. Class Aves. In Kurochkin, Lopatin and Zelenkov (eds.). Fossil vertebrates of Russia and adjacent countries. Part 3. Fossil Reptiles and Birds. GEOS. 86-290.
Wang, O'Connor, Zhou and Zhou, 2020 (online 2019). New toothed Early Cretaceous ornithuromorph bird reveals intraclade diversity in pattern of tooth loss. Journal of Systematic Palaeontology. 18(8), 631-645.

Schizooura Zhou, Zhou and O'Connor, 2012
= "Eoornithura" O'Connor and Zhou, 2013
S. lii Zhou, Zhou and O'Connor, 2012
= "Eoornithura lii" O'Connor and Zhou, 2013
Early Albian, Early Cretaceous
Jianchang, Jiufotang Formation, Liaoning, China
Holotype- (IVPP V16861) skull (50.01 mm), mandibles, eleven cervical vertebrae, posterior six dorsal vertebrae, partial dorsal ribs fused to uncinate process, gastralia, synsacrum, eight caudal vertebrae, pygostyle (6.45 mm), scapulae (one partial; 50 mm), coracoids (27.47 mm), furcula, sternum, sternal ribs, humeri (56.40 mm), radii (57.32 mm), ulnae (65.90 mm), scapholunares, pisiforms, metacarpals I (6.67 mm), phalanges I-1 (one partial; 11.77 mm), manual unguals I (3.83 mm), carpometacarpi (31.14 mm; mcII 22, mcIII 23 mm), phalanges II-1 (one incomplete; 14.41 mm), phalanges II-2 (14.70 mm), manual unguals II (2.16 mm), phalanx III-1 (5.52 mm), ilia (one incomplete, one partial), incomplete pubes (~40.94 mm), ischium, femora (49.00 mm), tibiotarsi (61.17 mm), partial fibula, metatarsals I, phalanges I-1 (4.63 mm), pedal unguals I (3.25 mm), tarsometatarsi (35.60 mm), phalanges II-1 (9.65 mm), phalanges II-2 (7.64 mm), pedal unguals II (5.20 mm), phalanges III-1 (9.36 mm), phalanges III-2 (7.72 mm), phalanges III-3 (6.50 mm), pedal unguals III (6.25 mm), phalanx IV-1 (5.92 mm), phalanges IV-2 (4.99 mm), phalanges IV-3 (4.34 mm), phalanges IV-4 (4.31 mm), pedal unguals IV (5 mm), body feathers, remiges, retrices
Diagnosis- (after Zhou et al., 2012) toothless; dorsal premaxilla process contacts frontals; jugal slender; robust, V-shaped furcula with short hypocleidium; robust humerus with large deltopectoral crest that extends ~50% of humeral length; (humerus+ulna+mcII)/(femur+tibiotarsus+tarsometatarsus) ratio ~1.01; tarsometatarsotibiotarsal ratio high (0.58).
Comments- O'Connor and Zhou (2013; first online in 2012) used the name "Eoornithura lii" in their supplementary information, which based on its absence in the main paper where Schizooura liiis present, and similarity to that name, is near certainly an early name for the taxon. Zhou et al. (2012) list the pygostyle length as 20 mm, but this includes all eight associated distal vertebrae, while Wang et al. (2017) lists it as 6.45 mm, presumably only including the fused distal three elements. Wang et al. (2020) determined "CT scanning clearly shows that the upper and lower jaws of Schizooura are toothless" and provided revised measurements.
References- Zhou, Zhou and O'Connor, 2010. A new toothless ornithurine bird from the Lower Cretaceous of China. Journal of Vertebrate Paleontology. Program and Abstracts 2010, 192A.
Zhou, Zhou and O'Connor, 2012. A new basal beaked ornithurine bird from the Lower Cretaceous of Western Liaoning, China. Vertebrata PalAsiatica. 50(1), 9-24.
O'Connor and Zhou, 2013. A redescription of Chaoyangia beishanensis (Aves) and a comprehensive phylogeny of Mesozoic birds. Journal of Systematic Palaeontology. 11(7), 889-906.
Wang, O'Connor, Pan and Zhou, 2017. A bizarre Early Cretaceous enantiornithine bird with unique crural feathers and an ornithuromorph plough-shaped pygostyle. Nature Communications. 8:14141.
Wang, O'Connor, Zhou and Zhou, 2020 (online 2019). New toothed Early Cretaceous ornithuromorph bird reveals intraclade diversity in pattern of tooth loss. Journal of Systematic Palaeontology. 18(8), 631-645.

Archaeorhynchus Zhou and Zhang, 2006
= "Archaeorhychus" Zhou and Zhang, 2005 online
A. spathula Zhou and Zhang, 2006
"Archaeorhynchus spathula" Zhou and Zhang, 2005 online
Late Valanginian-Middle Aptian, Early Cretaceous
Yixian, Yixian Formation, Liaoning, China
Holotype- (IVPP V14287) (270 g, subadult) skull, sclerotic plates, mandibles, ten cervical vertebrae, several dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, sacrum, nine caudal vertebrae, scapulae (46 mm), coracoids (20 mm), furcula, sternum, sternal ribs, humeri (54 mm), radii (56 mm), ulnae (57 mm), scapholunare, pisiform, carpometacarpi (27mm; mcI 6, mcII 25, mcIII 24 mm), phalanx I-1 (10.5 mm), phalanx II-1, phalanx II-2, manual ungual, ilia, pubes (37 mm), ischia (~20 mm), femora (37 mm), tibiae (43 mm), fibulae, astragali, metatarsal I, tarsometatarsus (20 mm; one partial), thirteen pedal phalanges, seven pedal unguals, body feathers, remiges, gastroliths
Late Valanginian-Middle Aptian, Early Cretaceous
Linyuan, Yixian Formation, Liaoning, China
Referred- (IVPP V20312) (adult) partial skull, mandibles, hyoid, eight postaxial cervical vertebrae, four dorsal vertebrae, several dorsal ribs, four caudal vertebrae, pygostyle (5.40 mm), scapulae (one incomplete), coracoids, furcula, sternum, humeri (59.1 mm), radii (60.3 mm), ulnae (61.3 mm), pisiform, carpometacarpi (28.3 mm, mcI 7.2 mm), phalanges I-1, manual ungual I, partial pubes, distal ischia, incomplete femora, tibiotarsi (44.9 mm), fibulae, tarsometatarsi (21.6 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, gastroliths (Wang and Zhou, 2017)
Early Albian, Early Cretaceous
Jianchang, Jiufotang Formation, Liaoning, China
(IVPP V17075) (subadult) incomplete skull, partial sclerotic rings, hyoid, atlantal arches, axis, seven cervical vertebrae, cervical ribs, three posterior dorsal vertebrae, dorsal ribs, gastralia, fused first to fourth sacral vertebrae, fifth to seventh sacral vertebrae, seven caudal vertebrae, pygostyle, incomplete scapulae (46 mm), partial coracoids (20 mm), furcula, partial sternum, sternal ribs, humeri (one incomplete; 53 mm), radii (one partial; 55 mm) ulnae (58 mm), scapholunares, pisiforms, (carpometacarpus 28.5 mm) semilunate carpals, distal carpal III, metacarpals I (6 mm), phalanges I-1 (10 mm), manual unguals I (6 mm), metacarpals II (25 mm), phalanges II-1 (12 mm), phalanges II-2 (12 mm), manual ungual II (3.5 mm), metacarpals III (23 mm), phalanges III-1 (4 mm), phalanx III-2, ilia (one partial), pubes (~28 mm), ischia (~17 mm), femora (36 mm), tibiae (42 mm), fibulae (one incomplete; ~21 mm), astragali, calcaneum, distal tarsus, metatarsal II, phalanges II-1 (6 mm), phalanges II-2 (one fragmentary; 5 mm), pedal unguals II (5 mm), metatarsals III (one partial; 22 mm), phalanges III-1 (6.5 mm), phalanges III-2 (5 mm), phalanges III-3 (4 mm), pedal unguals III (5 mm), metatarsals IV (one partial), phalanges IV-1 (5 mm), phalanges IV-2 (one partial; 3 mm), phalanx IV-3 (2.5 mm), phalanges IV-4 (one partial; 2 mm), pedal unguals IV (4 mm), gastroliths (Zhou et al., 2013)
(IVPP V17091) (subadult) skull, sclerotic plates, mandibles, hyoids, eight cervical vertebrae, cervical ribs, three dorsal vertebrae, dorsal ribs, gastralia, synsacrum, six caudal vertebrae, pygostyle, scapulae (~43 mm), coracoids (19 mm), furcula, sternum, sternal ribs, humeri (one incomplete; 49 mm)), radii (one partial; 52 mm) ulnae (one partial; 54 mm), scapholunare, pisiform, (carpometacarpus 25 mm) semilunate carpal, metacarpal I (5 mm), phalanges I-1 (one fragmentary; 9 mm), manual unguals I (4 mm), metacarpals II (one fragmentary; 23 mm), phalanx II-1 (11 mm), phalanx II-2 (10 mm), manual ungual II (2.5 mm), metacarpals III (one partial; 21 mm), phalanx III-1 (5 mm), phalanx III-2, ilia, pubes (~30 mm), ischia (~14 mm), femora (34 mm), tibiae (one incomplete; 39 mm), fibulae (one partial; 28 mm), astragali, calcanea, distal tarsi, metatarsals II, phalanges II-1 (5.5 mm), phalanges II-2 (4 mm), pedal unguals II (4 mm), metatarsals III (19 mm), phalanges III-1 (6 mm), phalanges III-2 (5 mm), phalanges III-3 (4 mm), pedal unguals III (4 mm), metatarsals IV, phalanges IV-1 (4.5 mm), phalanges IV-2 (3.5 mm), phalanx IV-3 (2 mm), phalanx IV-4 (2 mm), pedal ungual IV (3.5 mm), body feathers, remiges, gastroliths (Zhou et al., 2013)
Early Albian, Early Cretaceous
Toudaoyingzi, Jiufotang Formation, Liaoning, China
(STM 7-11) (subadult) fragmentary skull, dentaries, several cervical vertebrae, fragmentary dorsal vertebrae, dorsal ribs, uncinate processes, caudal vertebrae, pygostyle, scapulae, coracoids, humeri, radii, ulnae, pisiform, semilunate carpal, metacarpals I, phalanges I-1, manual unguals I, metacarpals II, phalanx II-1, phalanx II-2, metacarpals III, phalanx III-1, pubes, femora, tibiae, fibulae, astragali, calcaneum, metatarsals I, phalanges I-1, pedal unguals I, metatarsals II, phalanges II-1, phalanges II-2, pedal unguals II, metatarsals III, phalanges III-1, phalanges III-2, phalanges III-3, pedal ungual III, metatarsals IV, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal ungual IV, lungs, body feathers, remiges, retrices, ~100 gastroliths (Wang, O'Connor, Maina, Pan, Wang, Wang, Zheng and Zhou, 2018)
Diagnosis- (after Zhou and Zhang, 2006) premaxilla toothless (also in Ichthyornis+Passer); maxilla toothless (also in Aves); dentary toothless (also in Longicrusavis and Carinatae); premaxillae broad with slightly rounded tips; dentary spatulate; strong longitudinal medial ridge on dentary dorsal to Meckelian groove; pointed omal tips of furcula (also in Yixianornis); forelimb elongate (humerus+ulna / femur+tibiotarsus ratio of 138%) (also large in Ichthyornis- ~176%); tibiotarsofemoral ratio 1.14.
(after Wang and Zhou, 2017) glenoid facet of coracoid strongly projects laterally; lateral margin of coracoid longer than medial margin; posterior surface of furcula excavated by deep furrow.
Other diagnoses- Zhou and Zhang (2006) also included the elongate foramina and grooves on the lateral dentary as a diagnostic character, but this is correlated with the lack of teeth. The broad sternum with deep posterior notches and elongate posterolateral processes are symplesiomorphies shared with enantiornithines. The character "hindlimb shortened" is already covered in forelimb/hindlimb ratio and tibiotarsal length. Metatarsals II and IV of Patagopteryx, songlingornithids and Apsaravis are also nearly equal in length.
Comments- This taxon first appeared as a nomen nudum OTU in Zhou and Zhang's (2005) online matrix, though it did not appear in their cladogram. If the matrix is run in PAUP, Archaeorhynchus forms an unresolved polytomy with Hongshanornis, Liaoningornis and more derived euornithines (Apsaravis, songlingornithids and Ornithurae). This is the same as the published tree in Zhou and Zhang (2006). In both papers, Patagopteryx was coded but excluded for no stated reason, yet emerges as the most basal euornithine when the matrix is run with it.
References- Zhou and Zhang, 2005. Discovery of an ornithurine bird and its implication for Early Cretaceous avian radiation. Proceedings of the National Academy of Sciences. 102(52), 18998-19002.
Zhou and Zhang, 2006. A beaked basal ornithurine bird (Aves, Ornithurae) from the Lower Cretaceous of China. Zoologica Scripta. 35, 363-373.
Zhou, Zhou and O'Connor, 2013. Anatomy of the basal ornithuromorph bird Archaeorhynchus spathula from the Early Cretaceous of Liaoning, China. Journal of Vertebrate Paleontology. 33(1), 141-152.
Wang and Zhou, 2017 (online 2016). A new adult specimen of the basalmost ornithuromorph bird Archaeorhynchus spathula (Aves: Ornithuromorpha) and its implications for early avian ontogeny. Journal of Systematic Palaeontology. 15(1), 1-18.
Wang, O'Connor, Pan and Zhou, 2017. A bizarre Early Cretaceous enantiornithine bird with unique crural feathers and an ornithuromorph plough-shaped pygostyle. Nature Communications. 8:14141.
Wang, O'Connor, Maina, Pan, Wang, Wang, Zheng and Zhou, 2018. Archaeorhynchus preserving significant soft tissue including probable fossilized lungs. Proceedings of the National Academy of Sciences of the United States of America. 115(45), 11555-11560.

Meemannavis O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2022
= "Meemannavis" O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2021a online
M. ductrix O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2022
= "Meemannavis ductrix" O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2021a online
Late Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Material- (IVPP V26198) incomplete premaxillae, ?maxilla, frontals, braincase, ?palatines (20.6 mm), ?pterygoid, mandibles (45.9 mm), ?third cervical vertebra (4.86 mm), ?fourth cervical vertebra, ?fifth cervical vertebra (7.01 mm), ?sixth cervical vertebra (5.16 mm), ?seventh cervical vertebra (6.4 mm), ?eighth cervical vertebra, ?ninth cervical vertebra, posterior cervical vertebra, two dorsal vertebrae (3.73 mm), dorsal rib fragments
Diagnosis- (after O'Connor et al., 2022) premaxillae fused anteriorly; toothless dentary that is dorsoventrally shallow, gently curved, and that gradually tapers anteriorly; quadrate cotyles of mandible anteroposteriorly narrow.
Differs from Archaeorhynchus in- anteroventral expansion of dentary absent; dentary more elongate.
Differs from Eogranivora in- dentary symphysis unfused.
Differs from Xinghaiornis in- dorsal surface of the dentary is gently concave instead of striaght.
Comments- Discovered in 2004 or 2005, this was first mentioned by Harris et al. (2009) as likely referrable to Gansus, it being one of three specimens which "consist primarily of the caudal halves of crania", in left lateral view that "also preserves portions of dentaries that, although toothless, may possess very small alveoli." O'Connor et al. (2021) presented it at a later SVP presentation as a new taxon "Meemannavis ductrix", mentioned in the abstract as that specimen with the edentulous dentary. It was named and described by O'Connor et al. (2021 online), but the paper had no mention of ZooBank and "Meemannavis" lacked an entry on the ZooBank website. Thus according to ICZN Article 8.5.3 (an electronic work must "be registered in the Official Register of Zoological Nomenclature (ZooBank) (see Article 78.2.4) and contain evidence in the work itself that such registration has occurred"), "Meemannavis ductrix" O'Connor et al., 2021 was a nomen nudum that became valid in September 2022 once the volume was published. O'Connor et al. (2022) suggest that one of the possible palatines may be a prearticular, and that part of the possible pterygid may be a quadrate.
O'Connor et al. (2021, 2022) added it to O'Connor's bird matrix and recovered it in a large polytomy of euornithines, excluded from Neognathae, Schizhoouridae and several pairs of OTUs. Note the trees in their figure are majority rule and implied weighting. Adding it to Hartman et al.'s maniraptoromorph analysis results in a sister group relationship with Archaeorhynchus.
References- Harris, Lamanna, Li and You, 2009. Avian cranial material and cranial cervical vertebrae from the Lower Cretaceous Xiagou Formation of Gansu Province, China. Journal of Vertebrate Paleontology. 29(3), 111A.
O'Connor, Lamanna, Harris, Hu, Bailleul, Wang and You, 2021. First avian skulls from the Lower Cretaceous Xiagou Formation, Gansu, China. The Society of Vertebrate Paleontology Virtual Meeting Conference Program, 81st Annual Meeting. 196.
O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2022 (online 2021). Avian skulls represent a diverse ornithuromorph fauna from the Lower Cretaceous Xiagou Formation, Gansu Province, China. Journal of Systematics and Evolution. 60(5), 1172-1198.

Piscivoravis Zhou, Zhou and O'Connor, 2013 online
P. lii Zhou, Zhou and O'Connor, 2013 online
Early Albian, Early Cretaceous
Xiaotaizi, Jiufotang Formation, Liaoning, China
Holotype- (IVPP V17078) (subadult) posterior skull, posterior mandible, partial hyoids, ten cervical vertebrae, twelve dorsal vertebrae, thirteen dorsal ribs (some partial), uncinate processes, several gastralia, synsacrum, three caudal vertebrae, pygostyle (14.58 mm), scapula (61 mm), coracoid (35 mm), incomplete furcula, sternum, humerus (74 mm), radius (75 mm), ulna (77 mm), scapholunare, pisiform, carpometacarpus (mcI 7, mcII 34, mcIII 34 mm), phalanx I-1 (17 mm), manual ungual I (10 mm), phalanx II-1 (15 mm), phalanx II-2 (15 mm), manual ungual II (6 mm), phalanx III-1 (9 mm), ilia, pubes (~63 mm), ischia, femora (56 mm), tibiotarsi (71 mm), fibulae (one incomplete; 33 mm), metatarsals I (6 mm), phalanges I-1 98 mm), pedal unguals I (5 mm), tarsometatarsi (35.6 mm), phalanges II-1 (12 mm), phalanges II-2 (11 mm), pedal unguals II (7 mm), phalanges III-1 (13 mm), phalanges III-2 (one partial; 10 mm), phalanx III-3 (10 mm), pedal ungual III (7 mm), phalanges IV-1 (10 mm), phalanges IV-2 (8 mm), phalanges IV-3 (6 mm), phalanx IV-4 (7 mm), pedal ungual IV (6 mm), body feathers, remiges, retrices, fish bones
Diagnosis- (after Zhou et al., 2014) anterior 1/3-1/2 of pubis dorsomedially excavated by deep groove; synsacrum with tall spinous crest that diminishes posteriorly; furcula with strongly tapered omal tips; sternum broad, width greater than length; scapula long, tapered and distally constricted; deltopectoral crest anteriorly deflected; large and strongly curved manual unguals; (humerus+ulna+mcII)/(femur+tibiotarsus+mtIII) ~ 1.14; two well-developed cnemial crests on tibiotarsus.
Comments- Zhou et al.'s article describing the taxon was published online in 2013 with a ZooBank registration, though the physical version was not published until 2014. A better photo of the skull and cervicals is present in Wang et al. (2016).
Zhou et al. (2014) added Piscivoravis to a version of Clarke's analysis and found it to be a basal ornithoromorph in a polytomy with Patagopteryx, Jianchangornis and more derived taxa.
References- Zhou, Zhou and O'Connor, 2014 (online 2013). A new piscivorous ornithuromorph from the Jehol Biota. Historical Biology. 26(5), 608-618.
Wang, Zhou and Sullivan, 2016. A fish-eating enantiornithine bird from the Early Cretaceous of China provides evidence of modern avian digestive features. Current Biology. 26, 1170-1176.

Ornithuromorpha Chiappe et al., 1999
Definition- (Patagopteryx deferrariisi + Passer domesticus) (modified from Chiappe, 2002)
Other definitions- (Vorona berivotrensis + Patagopteryx deferrariisi + Passer domesticus) (modified from Chiappe, 2001)
(Passer domesticus <- Enantiornis leali) (modified from O'Connor, Wang and Hu, 2016)
Diagnosis- (proposed) peg and socket quadrate-quadratojugal articulation; quadrate pneumatic (absent in Hesperornithes); eleven or less dorsal vertebrae (unknown in Archaeorhynchus and Chaoyangia); nine or more sacral vertebrae; less than twelve caudal vertebrae (unknown in Archaeorhynchus and Chaoyangia); pygostyle less than four vertebrae in length; scapula longer than humerus (absent in Jianchangornis, Yanornis, Gansus and Hesperornis regalis); carpometacarpus fused distally; metacarpal I distal articulation shelf-like; pelvis completely fused; posterior trochanter absent on femur (unknown in Archaeorhynchus and Chaoyangia); distal vascular foramen enclosed by fusion of metatarsals III and IV (absent in basal Hesperornithes); hypotarsus present (unknown in Archaeorhynchus and Chaoyangia); at least one proximal vascular foramen in tarsometatarsus; metatarsal II ginglymoid (absent in Yanornis, some hesperornithines and Apsaravis).
References- Clarke, 2009. The Mesozoic record of ornithurine birds and the origin of Aves. Journal of Vertebrate Paleontology. 29(3), 79A.
O'Connor, Wang and Hu, 2016. A new ornithuromorph (Aves) with an elongate rostrum from the Jehol Biota, and the early evolution of rostralization in birds. Journal of Systematic Palaeontology. 14(11), 939-948.

Patagopterygiformes Alvarenga and Bonaparte, 1992
Definition- (Patagopteryx deferrariisi <- Passer domesticus) (Martyniuk, 2012)
= Patagopterygidae Alvarenga and Bonaparte, 1992
= Chaoyangiformes Hou, 1997
Definition- (Chaoyangia beishanensis <- Passer domesticus) (Martyniuk, 2012)
= "Chaoyangidae" Hou, 1997
= Chaoyangithiformes Zhou and Zhang, 2006
= "Chaoyangornithidae" Zhou and Zhang, 2006
Diagnosis-
Comments- Hou (1997) erected Chaoyangiformes for his new families Chaoyangidae and Songlingornithidae within basal Euornithes (his Ornithurae). As noted below in the Songlingornis section of the comments, there are no synapomorphies that suggest grouping Songlingornis with Chaoyangia. Zhou and Zhang (2006) later erected the taxa Chaoyangithiformes (credited to Hou, 1997) and Chaoyangornithidae (this time containing both Chaoyangia and Songlingornis). Both of these are malformed, as there is no "Chaoyangithes" or "Chaoyangornis". Moreover, both "Chaoyangidae" and "Chaoyangornithidae" are nomina nuda, as they were neither diagnosed nor defined (ICZN Article 13.1.1).
References- Alvarenga and Bonaparte, 1992. A new flightless landbird from the Cretaceous of Patagonia. Los Angeles County Museum of Natural History, Science Series. 36, 51-64.
Hou, 1997. Mesozoic birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou, 228 pp.
Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

unnamed possible patagopterygiforms (Forster and O'Connor, 2000; described by O'Connor and Forster, 2010)
Middle Maastrichtian, Late Cretaceous
Anembalemba Member of Maevarano Formation, Madagascar
Material- (FMNH PA 779) incomplete coracoid (50.1 mm)
(UA 9602) incomplete coracoid
Comments- The coracoids differ from each other, so are from different taxa. UA 9602 was found close to the Vorona holotype and is of similar size, so may belong to that individual. Both specimens seem closer to Aves than enantiornithines based on the concave scapular articulation, but are primitive in lacking procoracoid processes as in Patagopteryx and apsaraviforms. Adding them to Hartman et al.'s maniraptoromorph analysis results in them being patagopterygiform, with two steps needed to make them apsaraviform.
References- Forster and O'Connor, 2000. The avifauna of the Upper Cretaceous Maevarano Formation, Madagascar. Journal of Vertebrate Paleontology. 20(3), 41A-42A.
O'Connor and Forster, 2010. A Late Cretaceous (Maastrichtian) avifauna from the Maevarano Formation, Madagascar. Journal of Vertebrate Paleontology. 30(4), 1178-1201.

Chaoyangia Hou and Zhang, 1993
C. beishanensis Hou and Zhang, 1993
Early Albian, Early Cretaceous
Boluochi, Jiufotang Formation, Liaoning, China
Holotype- (IVPP V9934) (~235 mm) eleven dorsal vertebrae, eight dorsal ribs, dorsal rib fragments, three uncinate processes, gastralia(?), synsacrum, about five caudal vertebrae, ilia (one partial; 32 mm), pubes (51 mm), ischia (30 mm), femora (one incomplete; 45 mm), tibiotarsus, proximal fibula, tarsometatarsal fragment
Diagnosis- (after O'Connor and Zhou, 2013) uncinate processes expanded basally, forming a 55 degree angle with the rib; ischium with two, gradually expanding, dorsal processes; ischia distally contacting; femoral neck poorly defined.
Other diagnoses- Of the characters listed in the diagnosis by Hou and Zhang (1993), most are symplesiomorphies (non-heterocoelous dorsal vertebrae; uncinate processes; sacrum not fused to ilia; unfused pelvis; pelvis opisthopubic; preacetabular process longer than postacetabular process; pubic symphysis; femoral head well developed; fourth trochanter absent). The longitudinally grooved dorsal ribs are also present in Archaeorhynchus, Yanornis and Yixianornis, so are more widely distributed. More than eight sacral vertebrae are present in most euornithines. The ilium is described as "nephroid" and the femoral shaft "well developed", which are too vague to elaborate. The postacetabular process was described as expanded, but Hou and Zhang included portions of the sacrum in the postacetabular process (O'Connor and Zhou, 2013). The postacetabular process is actually tapered as in most maniraptorans. The pubis is reported to be pneumatized, which is otherwise only reported in Archaeopteryx among Mesozoic theropods, but difficult to determine in most specimens and of uncertain validity in Chaoyangia (perhaps the pubic shaft is hollow but non-pneumatic). The cnemial crest is equally well developed in Yixianornis and Yanornis.
Hou (1997) adds a few supposedly diagnostic characters. The thin-walled long bones (femur and presumably tibia) and fibula unfused to the tibia are symplesiomorphic for theropods. The femur is said to be pneumatized via a foramen on the proximolateral side, but this is only reported for Shixinggia among Mesozoic theropods. Hou's record of erroneous morphological interpretation makes me wary of accepting this character as valid.
Zhou and Hou (2002) add the character "uncinate processes long, slender and ventrally distributed to their diagnosis, but they are longer and more slender in Confuciusornis and similarly placed as well. They also state the postacetabular process is slightly rounded, but the posterior curvature is similar to Archaeorhynchus, though taller. A pubic symphysis of about a third of pubic length (30%) falls within the range of variation in Confuciusornis, and is not that different from Hongshanornis (26%) or Yanornis (35%). The trochanteric crest is equally high in taxa like Confuciusornis and Vorona. The rest of their new diagnostic characters are based on Songlingornis.
Comments- The holotype was discovered in 1990 and was merely referred to Aves order indet. by Hou and Zhang (1993). Other specimens were subsequently referred by Hou et al. (1996), but "a partial foot" was later found to be from an indeterminate euornithine (IVPP V9937), while "a shoulder girdle including the furcula, coracoids, and sternum" was made the holotype of a new genus (IVPP V10913- Songlingornis). Hou (1997) states there are three cervicals and seven dorsals preserved, but such a low number of dorsals would be unheard of in a non-avian theropod, and it is more likely all ten presacral vertebrae are dorsals as agreed by O'Connor and Zhou (2013).
Chaoyangia a basal euornithine? Hou et al. (1996) referred Chaoyangia to basal Euornithes (their Ornithurae) due to the uncinate processes (now known to be present in many maniraptorans) and several characters preserved only in IVPP V10913.
Hou (1997) followed Hou et al.'s phylogenetic scheme, with additional evidence for Chaoyangia being a euornithine being ossified, pneumatized and elongated gastralia and a well developed cnemial crest. The gastralial characters are confusing, since no other euornithines known at the time preserved gastralia besides perhaps a couple elements in the probably incorrectly referred Liaoningornis. In any case, gastralia are symplesiomorphic for theropods, and are more elongate in basal taxa like Changchengornis (39% of femoral length) than in euornithines like Yixianornis (18%). Chaoyangia's are intermediate (28%). The only theropod with verified pneumatic gastralia is Aerosteon, and I am doubtful it can be verified in Chaoyangia, especially given Hou's history of misinterpretation and his additional claims of pneumaticity in the taxon (femur, pubis, etc.). The cnemial crest is as anteriorly elevated and pointed in some enantiornithines like Eoenantiornis and has yet to be analyzed on a broad scale in bird phylogeny.
Zhou (1999) found Chaoyangia to be a basal euornithine (his Ornithurae) in his thesis. Additional characters not based on Songlingornis include- proximodorsal ischial process absent; ischium expanded distally due to low mid dorsal process (not present in Apsaravis, but seems valid); tall trochanteric crest (miscoded as absent in Confuciusornis and enantiornithines).
Zhang and Zhou (2000) included Chaoyangia in a version of Chiappe's bird matrix, finding it to be a basal euornithine. In addition to the uncinate processes and characters based on Songlingornis, this was also due to the supposedly subparallel pelvic elements (miscoded as present in Chaoyangia), compressed pubic shaft (miscoded as present in Chaoyangia- Clarke, 2002), trochanteric crest (miscoded as absent in Confuciusornis, Protopteryx and Sinornis), and medial cnemial crest (somewhat questionable, as it may be taphonomic- O'Connor and Zhou, 2013).
Thus despite several miscodings and problematic characters, two characters support placing Chaoyangia in Euornithes- proximodorsal ischial process absent; ischium expanded distally due to low mid dorsal process. Using Hartman et al.'s maniraptoromorph dataset, Chaoyangia falls out sister to Patagopteryx
Chaoyangia a basal pygostylian? Clarke (2002) is one of the few Western authors to comment on Chaoyangia. She found it to fall out as a pygostylian outside Ornithuromorpha. This was based on four characters, of which two were misinterpreted in Chaoyangia. Clarke suggested it had seven sacrals, but O'Connor and Zhou (2013) more recently show it has at least nine, and possibly up to eleven, sacrals. Clarke also claimed its pelvic elements were incompletely fused, but all three elements were fused together in the holotype. Additionally newly discovered taxa have shown most basal euornithines are equally primitive in the remaining characters- all euornithines except Patagopteryx and Apsaravis plus ornithurines have pubic symphyses; and Archaeorhynchus, Schizooura, Yanornis, hongshanornithids, Iteravis and Gansus have pubic boots. Clarke further claimed that Chaoyangia was identical to Confuciusornis in all scored characters, and may be synonymous, but Confuciusornis differs in lacking a pubic boot, having a narrower postacetabular process, and a shorter ischium with a proximodorsal process and no mid dorsal process. Forcing Chaoyangia to be outside Ornithothoraces in the Hartman et al. maniraptoromorph dataset results in trees 7 steps longer where it falls out by Balaur.
Songlingornis- Hou et al. (1996) referred at least one additional specimen to Chaoyangia (IVPP V10913), which was later made the holotype of the new genus Songlingornis (Hou, 1997). The reference of IVPP V10913 to Chaoyangia was followed by Hou and Zhou (1999) and Zhou and Hou (2002), though the latter did indicate it had also been used as the holotype of Songlingornis. The specimens preserve few elements in common (though not none, as claimed by Clarke and Norell, 2001)- several dorsal vertebrae, dorsal ribs and proximal femur. The dorsals are alike in being non-heterocoelous, but this is similar to all non-hesperornithine, non-avian birds. Both femora are described as having proximally projecting trochanteric crests, shallow trochanteric fossae and large heads. These features are comparable to many basal birds including Confuciusornis and Vorona. The only point of difference in their descriptions in that Chaoyangia is said to have a "basically absent" neck, while Songlingornis has a "relatively well developed neck." Yet Chaoyangia's proximal femur has a near identical shape to Songlingornis'. Thus the taxa cannot be distinguished, but also share no synapomorphies that would allow them to be synonymized. Forcing them to be sister taxa in the Hartman et al. dataset results in trees only one step longer, where Songlingornis moves to Patagopterygiformes
References- Hou and Zhang, 1993. A new fossil bird from Lower Cretaceous of Liaoning. Vertebrata PalAsiatica. 31, 217-224.
Hou, Martin, Zhou and Feduccia, 1996. Early adaptive radiation of birds: evidence from fossils from northeastern China. Science. 274, 1164-1167.
Hou, 1997. Mesozoic birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou, 228 pp.
Hou and Zhou, 1999. Paleornithology of China: A general review. Chinese Science Bulletin. 44(23), 2113-2116.
Zhou, 1999. Early evolution of birds and avian flight-evidence from Mesozoic fossils and modern birds. PhD Dissertation, Department of Systematics and Ecology, University of Kansas. 216 pp.
Zhang and Zhou, 2000. A primitive enantiornithine bird and the origin of feathers. Science. 290, 1955-1959.
Clarke and Norell, 2001. Fossils and avian evolution. Nature. 414, 508.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Zhou and Hou, 2002. The discovery and study of Mesozoic birds in China. In Chiappe and Witmer (eds.). Mesozoic Birds - Above the Heads of Dinosaurs. University of California Press. 160-183.
Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.
O'Connor and Zhou (online 2012), 2013. A redescription of Chaoyangia beishanensis (Aves) and a comprehensive phylogeny of Mesozoic birds. Journal of Systematic Palaeontology. 11(7), 889-906.

Patagopteryx Alvarenga and Bonaparte, 1992
P. deferrariisi Alvarenga and Bonaparte, 1992
Santonian, Late Cretaceous
Bajo de la Carpa Formation of the Rio Colorado Subgroup, Neuquen, Argentina
Holotype- (MACN-N-03) (~545 mm) ninth cervical vertebra (~20 mm), tenth cervical vertebra (20.0 mm), eleventh cervical vertebra (19.9 mm), twelfth cervical vertebra (~20 mm), thirteenth cervical vertebra (16.0 mm), first dorsal vertebra (14.4 mm), second dorsal vertebra (13.0 mm), third dorsal vertebra (12.4 mm), fourth dorsal vertebra (10.8 mm), fifth dorsal vertebra (14.5 mm), sixth dorsal vertebra (~12 mm), seventh dorsal vertebra (~12 mm), eighth dorsal vertebra (12.6 mm), ninth dorsal vertebra (13.2 mm), tenth dorsal vertebra (~13 mm), eleventh dorsal vertebra (~12 mm), synsacrum (52.6 mm), two caudal vertebrae (9.0, 8.6 mm), proximal scapulae, proximal coracoids, humeri (one incomplete; 66.3 mm), proximal radius, proximal ulna, ilia (one incomplete; 68.4 mm), femora (one partial; ~99 mm), incomplete tibiotarsus (~138 mm), partial tarsometatarsus, phalanx II-1, phalanx III-1, phalanx IV-1, phalanx IV-2, phalanx IV-3
Paratypes- (MACN-N-10) (at least three individuals) metatarsal I, proximal tarsometatarsus, four distal tarsometatarsi, phalanx II-1 (~16 mm), phalanx III-1 (~20 mm), phalanx IV-1 (~9 mm), phalanx IV-2 (7.0 mm)
(MACN-N-11) posterior skull, posterior mandibles, proatlas, atlas, axis, third cervical vertebra, fourth cervical vertebra, fifth cervical vertebra, sixth cervical vertebra, seventh cervical vertebra, eighth cervical vertebra, four dorsal vertebrae, two dorsal ribs, five caudal vertebrae, scapula (~73 mm), incomplete coracoids (38.0, 38.0 mm), partial sternum, incomplete humeri (~59, 59.8 mm), radius (46.0 mm), incomplete ulnae (~52 mm), carpometacarpus (~23 mm), partial phalanx II-1 (8.4 mm), phalanx II-2 (11.6 mm), manual ungual II (~7 mm), partial ilia, pubes (one incomplete; ~50 mm), incomplete ischia (50.4, 52.5 mm), femur (~100 mm), tibiotarsus (~137, ~136 mm), partial fibula, metatarsals I (14.8 mm), phalanges I-1 (11.9, 11.9 mm), pedal unguals I (~18 mm), tarsometatarsi (~49, 50.8 mm), phalanges II-1 (~16, 15.8 mm), phalanges II-2 (12.6 mm), pedal ungual II (18.0 mm), phalanges III-1 (20.3, 20.3 mm), phalanx III-2 (14.4 mm), phalanx III-3 (11.6 mm), pedal ungual III (~17 mm), phalanx IV-1 (~10 mm), phalanx IV-2 (7.3 mm), phalanx IV-3 (6.0 mm), phalanx IV-4 (7.5 mm), pedal ungual IV (~16 mm)
Referred- (MACN-N-14) six cervical vertebral fragments, ?first dorsal vertebral fragment, second dorsal vertebra (11.6 mm), third dorsal vertebra (9.1 mm), fourth dorsal vertebra (12.8 mm), fifth dorsal vertebra (~12 mm) (Chiappe, 1992)
(MUCPv-48) skull fragments including braincase, two posterior dorsal vertebrae, mid caudal vertebra (10.3 mm), partial ilium, incomplete femur (~98 mm), tibiotarsi (~141 mm; one incomplete, one distal), fibula (~112 mm), metatarsals I, phalanx I-1 (11.8 mm), pedal ungual I, tarsometatarsi (51 mm; one fragmentary), phalanx II-1 (15.8 mm), phalanx II-2 (12.8 mm), proximal pedal ungual II, phalanx III-1 (~20 mm), distal phalanx III-2, phalanx III-3 (10.6 mm), pedal ungual III (~20 mm), phalanx IV-1 (8.8 mm), phalanx IV-2 (6.1 mm), phalanx IV-3 (5.9 mm), phalanx IV-4 (7.4 mm), partial pedal ungual IV (Chiappe, 1991)
(MUCPv-207) several vertebrae, partial synsacrum, mid caudal vertebrae, partial hindlimb (Chiappe, 2002a)
Diagnosis- (after Alvarenga and Bonaparte, 1992) cervical vertebrae completely heterocoelous (also in Ornithurae); dorsal vertebrae 6-11 procoelous; reduced forelimbs; large lateral process on distal postacetabular process; medial process on distal postacetabular process.
(after Chiappe, 1996a) quadrate fused to pterygoid; quadrate foramen present laterally; fifth dorsal vertebra biconvex; posterior dorsal vertebrae with very wide reniform centra; posterior articular surface of synsacrum convex; acromion transversely expanded anteriorly; proximal end of coracoid with dorsally projecting section for scapular articulation; two prominent intermuscular lines on dorsal shaft of humerus; distal ulna extremely anteroposteriorly compressed; metacarpal III more robust than metacarpal II; strong medial laminar process on metacarpal II (a reduced metacarpal I?); pubis anteroposteriorly compressed; distal pubis anteriorly curved; prominent m. iliofibularis tubercle on fibula; distal fibula fused to anterior side of tibiotarsus; minimum width of tarsometatarsus over 20% of length; untwisted metatarsal I.
(after Chiappe, 2002a) acromion dorsoventrally expanded at tip (also in Apsaravis).
Other diagnoses- Some of Alvarenga and Bonaparte's (1992) diagnostic characters are symplesiomorphic- notarium absent; anterior articular surface of synsacrum strongly concave; synsacrum dorsoventrally compressed; synsacrum transversely wide; humerus lacks pneumotricipital foramen; ilium weakly fused to synsacrum; preacetabular process vertically oriented; preacetabular process laterally far from synsacrum; iliac crest single and extends to posterior margin of ilium; opisthopubic pelvis; ilioischial fenestra open; iliopubic fenestra open; lateral cnemial crest anteriorly developed; supratendinal bridge absent on tibiotarsus.
Of Chiappe's (2002a) diagnostic characters, the prominent iliac crest is plesiomorphic for avepods and the "well developed caudolateral spine" seems to be the supratrochanteric process common in basal birds. The ischium is also paddle-shaped in Yixianornis, Gansus, Ichthyornis and Iaceornis.
Comments- The holotype and MACN-N-10 were discovered in 1984, while MACN-N-11 was discovered in 1985. They were first commented on by Bonaparte (1986), who described them as ratite-like. Chiappe (1991) noted the description of the then unnamed taxon was in press, also mentioning MUCPv-48 as "housed in the UNC". The taxon was formally described by Alvarenga and Bonaparte (1992), and redescribed by Chiappe, first in his unpublished thesis (1992), then in 1996a, and finally in depth in 2002a. Chinsamy et al. (1994, 1995) described its histology.
Alvarenga and Bonaparte (1992) stated there are indications that the then unprepared MACN-N-11 lacked a pygostyle, but this cannot be confirmed. The supposed furcular epicleidia in the holotype were later determined to be proximal coracoids (Chiappe, 1996). The supposed distal coracoid preserved in the holotype is probably not a Patagopteryx element (Chiappe, 1996). Hutchinson (2001) identified a proximodorsal ischial process and an obturator flange.
Patagopteryx a palaeognath? Alvarenga and Bonaparte (1992) and Alvarenga (1993) proposed a close relationship to palaeognaths, rheiforms in particular, but also lithornithiforms, tinamiforms, casuariiforms and apterygiforms. Characters supporting this are largely symplesiomorphic for birds- elongate acromion on scapula; pneumotricipital foramen absent (a reversal in ratites); open ischiopubic fenestra; open ilioischiadic fenestra; deep and triangular popliteal fossa; robust and anteriorly developed lateral cnemial crest; supratendinal bridge absent (probably a reversal in some lithornithids and ratites); round lateral tibiotarsal condyle; reduced hypotarsus (a reversal in ratites). "General form and proportions" of cervical vertebrae being similar to tinamiforms is too vague to evaulate. The supposedly horizontal postacetabular process would be primitive for carinates, but seems to be untrue in Patagopteryx in any case. Patagopteryx's trochanteric crest is not wide and planar laterally, as it has a lateral ridge and ITCR insertion scar. The trochanteric crest does not appear more anteriorly expanded than enantiornithines or Vorona. The supposedly medially placed tendinal groove is instead a depression formed by the extensor retinaculum ridges as in Apsaravis (Clarke and Norell, 2002), so is not homologous to the condition in palaeognaths. The tibiotarsal intercondylar groove is not particularly shallow or wide, contra Alvarenga and Bonaparte. Chiappe (1995) noted there is no "tendency for the ischia to become horizontal and approach each other medially", though the latter would be primitive for birds. Chiappe also notes Patagopteryx has a single cnemial crest, not two in which the "inner is formed over the outer" as is apparently the case in some ratites. The dorsoventrally flattened posterior dorsal centra and anteroposteriorly compressed ulna are apparently similar to rheiforms and are otherwise unknown in basal euornithines.
Kurochkin (1995) placed Patagopteryx within Ratitae based on several characters. The heterocoelous cervical vertebrae are symplesiomorphic for avians, and are found in some basal euornithines like Apsaravis and hesperornithines as well. The dorsals are said to be "transitional to heterocoely or procoelous", but Patagopteryx also has opisthocoelous and biconvex dorsals. Heterocoelous dorsals are similar to Aves and Hesperornithes, but no palaeognaths seem to have procoelous dorsals. Contra Kurochkin, the tibiotarsus lacks an anterior cnemial crest, which would be symplesiomorphic for a more inclusive clade than Ratitae in any case. The completely fused tarsometatarsus is symplesiomorphic for euornithines. A hallux with two phalanges is symplesiomorphic for all reptiles.
There are a few additional Aves characters which Patagopteryx does possess- a tricondylar quadrate articulation; the deltopectoral crest is oriented anteriorly (also in Alamitornis); the deltopectoral crest is lower than shaft width (also in Alamitornis and hesperornithines); pubic symphysis absent (also in Apsaravis, hesperornithines and Carinatae). While there are several characters shared with Aves and a couple apparently shared with Rheiformes, these are outweighed by the large number of characters suggesting a more basal position, as described below.
Patagopteryx a hesperornithine? Chatterjee (1999) performed a phylogenetic analysis which found Patagopteryx to be the sister taxon of Hesperornithiformes. This was only based on the ulna being shorter than the humerus (miscoded in Ichthyornis and now also known to be true in Hongshanornis and Apsaravis) and the supposedly absent distal trochlear surface on the ulna (actually unknown in Patagopteryx). In addition, Patagopteryx has to reverse the spherical head found in ornithurines in Chatterjee's cladogram. Thus there is basically no support for placing Patagopteryx in Hesperornithes.
Patagopteryx an enantiornithine? Feduccia (1999) listed Patagopteryx under Enantiornithes, though he did not mention reasons besides noting both Patagopteryx and Lecho Formation enantiornithines have LAGS in their femoral histology. However, these are also present in Rahonavis, so are probably plesiomorphic. While Patagopteryx does share a few characters with enantiornithines (e.g. some of the latter have tarsometatarsi which are excavated posteriorly), it has many more euornithine characters.
Patagopteryx a basal euornithine? Chiappe (1991) first suggested the then unnamed Patagopteryx was unrelated to any ornithurine. His 1992 thesis proposed it was basal to Ornithurae, though this was not published until Chiappe and Calvo (1994) (elaborated on in Chiappe, 1995). That phylogenetic analysis supported excluding Patagopteryx from Ornithurae as the basalmost euornithine based on- pterygoid process of quadrate rounded; more than ten dorsal vertebrae (now also known to be more primitive than songlingornithids, Apsaravis and Gansus); uncinate processes absent (probably untrue, as only a few ribs are preserved and uncinates are primitive for maniraptorans); procoracoid process absent (now also known to be more primitive than Archaeorhynchus, Hongshanornis, Ambiortus, songlingornithids and Gansus); humeral head anteriorly concave (now also known to also be more primitive than Hongshanornis, Ambiortus, songlingornithids, Apsaravis and Gansus); acetabulum >11% of ilial length (now also known to be more primitive than songlingornithids and Gansus); pubis and ischium not parallel to ilium (now also known to be more primitive than Apsaravis and Gansus); pubis not laterally compressed (now known also to be more primitive than Apsaravis); femur lacks patellar groove (now also known to be more primitive than Apsaravis and Gansus); anterior cnemial crest absent (now also known to be more primitive than Archaeorhynchus and Gansus); m. iliofibularis tubercle of fibula not posteriorly oriented (now also known to be more primitive than Gansus); metatarsal III not plantarily displaced proximally (now also known to be more primitive than songlingornithids, Apsaravis and Gansus); intercotylar eminence of tarsometatarsus poorly developed. In 1996a, Chiappe performed another analysis which added an additional character to support this- articular not pneumatic (now also known to be more primitive than Archaeorhynchus). In 2001 (repeated in 2002b), Chiappe expanded the analysis once more, finding Patagopteryx and Vorona to be basal to ornithurines. Added characters which supported excluding Patagopteryx from the latter clade are- anterior articular surface of synsacrum strongly concave (somewhat ambiguous, as it is somewhat concave in most coelurosaurs); extensor canal absent on tibiotarsus (now also known to be more primitive than Archaeorhynchus, songlingornithids and Apsaravis); wide medial condyle on tibiotarsus (now also known to be more primitive than Apsaravis and Gansus); transverse groove proximally undercuts tibiotarsal condyles (now also known to be more primitive than Gansus and probably Archaeorhynchus).
Norell and Clarke (2001) first published Clarke's matrix, which found Patagopteryx was not only basal to ornithurines, but also their new taxon Apsaravis. Additional basal euornithines have subsequently been added to the matrix (Hongshanornis, Archaeorhynchus, Ambiortus, songlingornithids, Gansus), which have all ended up more derived than Patagopteryx as well. New characters which support placing Patagopteryx outside Ornithurae are- less than ten sacral vertebrae (also more primitive than Apsaravis and Gansus); humerus not domed proximally (also more primitive than Archaeorhynchus, Hongshanornis, Ambiortus, songlingornithids, Apsaravis and Gansus); radius without muscle impression along ventroposterior surface (also more primitive than Archaeorhynchus and Apsaravis); metacarpal III >50% of width of metacarpal II (also more primitive than Yanornis, Yixianornis and Apsaravis); manual phalanx II-1 not strongly compressed dorsoventrally (also more primitive than Archaeorhynchus, Hongshanornis, Ambiortus, songlingornithids, Apsaravis and Gansus); antitrochanter directly posterior to acetabulum (probably a reversal, as more basal avialans have the opposite state); only one proximal vascular foramen on tarsometatarsus; fossa for metatarsal I on tarsometatarsus absent. In addition, Patagopteryx can be excluded from Carinatae due to- dorsal vertebrae lack ossified tendons on transverse processes; sacral vertebrae lack a series with short dorsally oriented transverse processes (also more primitive than Gansus). Finally, it can be excluded from Aves based on- quadrate foramen not located posteromedially; less than fifteen sacral vertebrae; no pneumatic foramen in humerus; the ilium does not overlap any dorsal ribs (also more primitive than Gansus); distal vascular foramen with one exit.
Cau and Arduini (2008) found Patagopteryx in a similar position, basal to all euornithines except Vorona. New characters influencing this position are- large hypapophyses absent in mid dorsals (also more primitive than Gansus); mid sacral centra not transversely compressed (also more primitive than Gansus); coracoid lateral process absent (this is miscoded in Patagopteryx); sternal keel absent (probably a reversal due to flightlessness, as Confuciusornis sometimes has a keel); manual phalanx II-2 longer than II-1 (also more primitive than Ambiortus, songlingornithids and Gansus); proximodorsal process on ischium (also more primitive than Archaeorhynchus, Chaoyangia, songlingornithids, Apsaravis and Gansus); fibula longer than half tibiotarsal length (also more primitive than Hongshanornis, songlingornithids and Gansus). Additionally, it is excluded from Carinatae based on- acrocoracoid process not hooked medially; coracoid foramen absent (miscoded in Aves, as it is absent in most, so not valid for excluding Patagopteryx); metatarsal II ginglymoid (miscoded in Ichthyornis and polymorphic in Aves, so not very useful for excluding Patagopteryx).
Gao et al. (2008) also found Patagopteryx to be a euornithine basal to Aves and Gansus. O'Connor et al. (2009) later used the same matrix with other euornithines added (Hongshanornis, PKUP V1069, Apsaravis, Yanornis, Hesperornis, Ichthyornis) and found Patagopteryx to be basal to all of them. New characters supporting this include- well developed olecranon fossa absent in humerus (also absent in Apsaravis, Hesperornithes and Ichthyornis; so probably convergent in Yixianornis and Aves, but does exclude Patagopteryx from the latter); m. scapulotriceps groove absent in humerus (also absent in Apsaravis, some Ichthyornis and palaeognaths; so probably convergent in Yixianornis and Neognathae); ischium >66% of pubic length (highly homoplasic once taxa that aren't included by have long ischia like Apsaravis, Hesperornithes and Iaceornis are taken into account); metatarsal I not twisted. In addition, the ungual on manual digit II excludes it from Iaceornis+Aves and lack of hypotarsal grooves excludes it from Aves. Some other characters (e.g. open iliosacral canals) are listed as avian (their neornithine) synapomorphies but not considered here, as they are actually neognath characters which only appear as avian characters since no palaeognaths were included.
Thus there are about 29 valid characters excluding Patagopteryx from Ornithurae, three additional characters excluding it from Carinatae and six others exclude it from Aves.
References- Bonaparte, 1986. History of terrestrial Cretaceous vertebrates of Gondwana. Simposio Bioestratigrafía del Paleozoico Inferior: IV Congreso Argentino de Paleontología y Bioestratigrafía, Mendoza, Argentina. 2, 63-95.
Chiappe, 1989. Flightless birds from the Late Cretaceous of Patagonia. Archosaurian Articulations. 1(10), 73-77.
Chiappe, 1991. Cretaceous birds of Latin-America. Cretaceous Research. 12, 55-63.
Alvarenga and Bonaparte, 1992. A new flightless landbird from the Cretaceous of Patagonia. Los Angeles County Museum of Natural History, Science Series. 36, 51-64.
Chiappe, 1992. Osteologia y sistematica de Patagopteryx deferrariisi Alvarenga y Bonaparte (Aves) del Cretacico de Patagonia. Filogenia e historia biogeografica de las aves Cretacicas de America del Sur. PhD Thesis. Universidad de Buenos Aires. 429 pp.
Alvarenga, 1993. A origem das aves seus fosseis. In Andrade (ed.). A Vida das Aves. 16-26.
Chiappe and Calvo, 1994. Neuquenornis volans, a new Upper Cretaceous bird (Enantiornithes: Avisauridae) from Patagonia, Argentina. Journal of Vertebrate Paleontology. 14(2), 230-246.
Chinsamy, Chiappe and Dodson, 1994. Growth rings in Mesozoic birds. Nature. 368, 196-197.
Chiappe, 1995. The phylogenetic position of the Cretaceous birds of Argentina: Enantiornithes and Patagopteryx deferrariisi. Courier Forschungsinstitut-Senckenberg. 181, 55-63.
Chinsamy, Chiappe and Dodson, 1995. Mesozoic avian bone microstructure: Physiological implications. Paleobiology. 21(4), 561-574.
Kurochkin, 1995. Synopsis of Mesozoic birds and early evolution of class Aves. Archaeopteryx. 13, 47-66.
Chiappe, 1996a. Late Cretaceous birds of Southern South America: Anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. In Arratia (ed.). Contributions of Southern South America to Vertebrate Paleontology. Münchner Geowissenschaftliche Abhandlungen (A). 30, 203-244.
Chiappe, 1996b. Early avian evolution in the southern hemisphere: Fossil record of birds in the Mesozoic of Gondwana. Memoirs of the Queensland Museum. 39, 533-556.
Chatterjee, 1999. Protoavis and the early evolution of birds. Palaeontographica A. 254, 1-100.
Feduccia, 1999. The Origin and Evolution of Birds. Yale University Press, New Haven, CT. 466 pp.
Chiappe, 2001. Phylogenetic relationships among basal birds. In Gauthier and Gall (eds.). New perspectives on the origin and early evolution of birds: Proceedings of the international symposium in honor of John H. Ostrom. Peabody Museum of Natural History. 125-139.
Hutchinson, 2001. The evolution of pelvic osteology and soft tissues on the line to extant birds (Neornithes). Zoological Journal of the Linnean Society. 131, 123-168.
Norell and Clarke, 2001. Fossil that fills a critical gap in avian evolution. Nature. 409, 181-184.
Chiappe, 2002a. Osteology of the flightless Patagopteryx deferrariisi from the Late Cretaceous of Patagonia (Argentina). Mesozoic Birds: Above the Heads of Dinosaurs. University of California Press. 281-316.
Chiappe, 2002b. Basal bird phylogeny: Problems and solutions. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 448-472.
Clarke and Norell, 2002. The morphology and phylogenetic position of Apsaravis ukhaana from the Late Cretaceous of Mongolia. American Museum Novitates. 3387, 46 pp.
Cau and Arduini, 2008. Enantiophoenix electrophyla gen. et sp. nov. (Aves, Enantiornithes) from the Upper Cretaceous (Cenomanian) of Lebanon and its phylogenetic relationships. Atti della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale in Milano. 149(2), 293-324.
Gao, Chiappe, Meng, O'Conner, Wang, Cheng and Liu, 2008. A new basal lineage of Early Cretaceous birds from China and its implications on the evolution of the avian tail. Palaeontology. 51(4), 775-791.
O'Conner, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009. Phylogenetic support for a specialized clade of Cretaceous enantiornithine birds with information from a new species. Journal of Vertebrate Paleontology. 29(1), 188-204.

Yanornithiformes Zhou and Zhang, 2001
Definition- (Yanornis martini <- Passer domesticus) (Martyniuk, 2012)
= Yanornithidae Zhou and Zhang, 2001
Definition- (Yanornis martini, Abitusavis lii <- Yixianornis grabaui, Piscivoravis lii, Passer domesticus) (Wang, Li, Liu and Zhou, 2020)
Comments- Zhou and Zhang (2001) named Yanornithidae and Yanornithiformes for Yanornis, while placing Yixianornis in Chaoyangornithiformes. Clarke et al. (2002) were the first to suggest placing the these taxa plus Songlingornis into a single clade at their SVP talk, though this was not published until 2006. You et al. (2006) independently coded Yanornis and Yixianornis and found the taxa to form a monophyletic clade in some of their most parsimonious trees, though in others Yanornis was more derived and sister to Apsaravis. The monophyletic clade of Yanornis, Yixianornis and/or Songlingornis has been called Songlingornithidae by many recent authors, but here Yanornis is recovered as further from Aves than Yixianornis and Songlingornis based on Hartman et al.'s maniraptoromorph matrix.
References- Zhou and Zhang, 2001. [Two new genera of ornithurine birds from the Early Cretaceous of Liaoxi involved in the origin of modern birds.] Kexue Tongbao. 46(5), 371-377.
Clarke, Zhou and Zhang, 2002. An ornithurine from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(3), 45A.
Clarke, Zhou and Zhang, 2006. Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui. Journal of Anatomy. 208, 287-308.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Wang, Li, Liu and Zhou, 2020. Two new Early Cretaceous ornithuromorph birds provide insights into the taxonomy and divergence of Yanornithidae (Aves: Ornithothoraces). Journal of Systematic Palaeontology. 18(21), 1805-1827.

Yanornithiformes indet. (Zhou and Zhang, 2001)
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Material- (IVPP V10996; paratype of Yanornis martini) (620 g) anterior skull, incomplete dentary, few cervical vertebrae, several dorsal vertebrae, incomplete coracoids, furcula, fragmentary sternum?, incomplete humeri (~78.5 mm), radii, ulnae (~78.5 mm), carpometacarpi (~38.1 mm), phalanx II-1?, femur (~53.7 mm), tibiotarsus (~72.6 mm), tarsometatarsi (one fragmentary), few pedal phalanges (Zhou and Zhang, 2001)
Barremian-Albian, Early Cretaceous
Jehol Group, Liaoning, China
(STM 9-5) scapula, incomplete humeri, partial radii, partial ulnae, femora, tibiotarsi, phalanx I-1, tarsometatarsi, phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanx IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal ungual IV, pedal claw sheaths, pedal scales, body feathers, remiges (Zheng et al., 2013)
(STM 9-18) skull (60 mm), mandibles, cervical series, dorsal vertebrae, dorsal ribs, gastralia, scapula (~50 mm), coracoids (35 mm), sternal ribs, humeri (73 mm), radii, ulnae (79 mm), carpometacarpus (35 mm), phalanx I-1, phalanx II-1 (~17 mm), phalanx II-2, pubes, femora (49 mm), tibiotarsi (~70 mm), fibula, metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsi (~31 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanx III-3, pedal ungual III, phalanges IV-1, phalanges IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, actinopterygian, actinopterygian fragments (Zheng et al., 2014)
(STM 9-31) skull (60 mm), mandibles, hyoids, cervical series with fused ribs, dorsal vertebrae, caudal vertebrae, pygostyle, scapula, coracoid, furcula, partial humerus, femora, tibiotarsi, tarsometatarsi (~52 mm), pedal phalanges, pedal unguals, cf. Jinanichthys, actinopterygian fragments (Zheng et al., 2014)
(STM 9-51) skull (~64 mm), mandibles, hyoids, cervical series, dorsal series, dorsal ribs, three uncinate processes, gastralia, synsacrum, caudal series, pygostyle, scapulae (42 mm), coracoid (~30 mm), sternal fragments, humeri (67 mm), radii, ulnae (~71 mm), scapholunare, pisiform, partial carpometacarpus, partial phalanx I-1, manual ungual II, manual claw sheath, ilia, pubes, ischia, femora (57 mm), tibiotarsi (75 mm), fibulae, metatarsal I, phalanges I-1, pedal unguals I, tarsometatarsi (35 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, body feathers, retrices, actinopterygian fragments, 3-5 gastroliths (1.1-1.9 mm) (Zheng et al., 2014)
Comments- The paratype of Yanornis martini (IVPP V10996) has yet to be described but was figured by Wang et al. (2020), who correctly noted "few diagnostic features can be identified from this specimen" and referred it to Yanornithidae indet.. Indeed no characters of Yanornis or Similiyanornis can be seen, so it is placed in Yanornithiformes indet. here.
Zheng et al. (2013) briefly described the feathers and pedal scales of STM 9-5 which they referred to Yanornis based on "carina approaching sternal anterior limit, scapula shorter than humerus, pubic symphysis relatively long, distal tarsals fused to metatarsals and metatarsals co-ossified proximally and distally, pedal digits relatively short and robust, and proximal pedal phalanges relatively long but unguals short", but these are also present (where known) in Similiyanornis and no characters distinguishing the taxa can be seen in STM 9-5. It is referred to Yanornithiformes indet. here.
Zheng et al. (2014) figured STM 9-18, which although poorly prepared appears to have a short manual phalanx II-1 like Yanornis (48% of carpometacarpal length versus 67%) but an unexpanded procoracoid process like Similiyanornis. Dentary morphology should be scorable but is not determinable in the figure. This should help support potential hypotheses such as Similiyanornis' elongate phalanx or unexpanded procoracoid process being individual variation, or even synonymy of the genera.
References- Zhou and Zhang, 2001. Two new ornithurine birds from the Early Cretaceous of western Liaoning, China. Chinese Science Bulletin. 46(1), 1-7.
Zheng, Zhou, Wang, Zhang, Zhang, Wang, Wei, Wang and Xu, 2013. Hind wings in basal birds and the evolution of leg feathers. Science. 339, 1309-1312.
Zheng, O'Connor, Huchzermeyer, Wang, Wang, Zhang and Zhou, 2014. New specimens of Yanornis indicate a piscivorous diet and modern alimentary canal. PLoS ONE. 9(4), e95036.

Yanornis Zhou and Zhang, 2001
= "Archaeoraptor" sensu Sloan, 1999 in part
= Archaeovolans Czerkas and Xu, 2002
= Abitusavis Wang, Li, Liu and Zhou, 2020
Y. martini Zhou and Zhang, 2001
= "Archaeoraptor liaoningensis" Sloan, 1999 in part
= Archaeovolans repatriates Czerkas and Xu, 2002
= Yanornis guozhangi Wang, Ji, Teng and Jin, 2013
= Abitusavis lii Wang, Li, Liu and Zhou, 2020
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V12558) (~275 mm, 770 g) skull (72.47 mm), mandibles, hyoid, ten cervical vertebrae, several dorsal vertebrae (6.3 mm), five dorsal ribs, gastralia?, synsacrum (37.43 mm), pygostyle (15.02 mm), scapulae (~55 mm), coracoids (34.21 mm), furcula, sternum (48.4 mm), humeri (85.31 mm), radii (85.97 mm), ulnae (90.32 mm), scapholunare, pisiform, carpometacarpus (39.24 mm, mcI 8.58 mm), phalanx I-1 (19.05 mm), manual ungual I (10.31 mm), phalanx II-1 (18.64 mm), phalanx II-2 (17.42 mm), manual ungual II (7.28 mm), phalanx III-1, ilia, pubes (~67 mm), ischium, femora (55.77 mm), tibiotarsi (82.42 mm), fibulae (32 mm), metatarsals I (6.33 mm), phalanges I-1 (8.41 mm), pedal unguals I (5 mm), tarsometatarsi (37.87 mm), phalanges II-1 (14.27 mm), phalanx II-2 (10.5 mm), pedal ungual II (5.76 mm), phalanx III-1 (13.86 mm), phalanx III-2 (10.71 mm), phalanx III-3 (10.56 mm), pedal ungual III (5.25 mm), phalanges IV-1 (9.19 mm), phalanges IV-2 (5.38 mm), phalanges IV-3 (5.58 mm), phalanges IV-4 (5.82 mm), pedal unguals IV (3.85 mm)
Referred- (IVPP V12444; specimen of "Archaeoraptor liaoningensis" in part; holotype of Archaeovolans repatriates) incomplete skull (~60 mm), partial mandibles, hyoid, several cervical vertebrae, few dorsal vertebrae (6.4 mm), several dorsal ribs, synsacrum, partial scapulae (57 mm), partial coracoids (38 mm), furcula (23 mm), sternum (48.2 mm), sternal ribs, humeri (~78.4 mm), radii (72.7 mm), ulnae (78.1 mm), scapholunare, pisiform, distal carpal III, carpometacarpi (one partial; mc I 7 mm, mc II ~36.9 mm), phalanx I-1 (~17 mm), manual ungual I (8 mm), phalanges II-1 (one partial; 17 mm), phalanges II-2 (18 mm), manual unguals II, phalanx III-1, partial ilia, proximal pubis, ischium, femur (~66 mm), tibiotarsus (78.1 mm), fibula, phalanx I-1 (8.4 mm), tarsometatarsus (38.8 mm), phalanx II-1 (14.1 mm), phalanx II-2 (12.1 mm), phalanx III-1 (14.7 mm), six pedal phalanges, three pedal unguals, body feathers, remiges (Sloan, 1999)
(IVPP V13358) skull, mandibles, hyoid, seven cervical vertebrae, several dorsal vertebrae, several dorsal ribs, gastralia, sacrum, two proximal caudal vertebrae, scapulae, coracoids, furcula, sternum, humeri, radii, ulnae (74.3 mm), scapholunare, pisiform, carpometacarpi, phalanges I-1, manual unguals I, phalanges II-1 (16.9 mm), phalanges II-2 (15.5 mm), manual unguals II, phalanx III-1, ilium, pubes, ischium, femur, tibiotarsi, tarsal?, metatarsal I, phalanges I-1, pedal unguals I, tarsometatarsi, phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, gastroliths (<2 to 2.7 mm), body feathers (Zhou et al., 2004)
(LHZA02-0008) partial skull (61.9 mm), anterior dentary, eighth cervical vertebrae, three dorsal vertebrae, fragmentary synsacrum (34.5 mm), scapulae (49.5 mm), coracoid (30.3 mm), furcula, humeri (70.1 mm), radii (69.4 mm), ulnae (70.2 mm), scapholunare, pisiform, carpometacarpi (mc I 5.5 mm, mc II 30 mm, mc III 29 mm), phalanges I-1 (15.5 mm), manual unguals I (8.5 mm), phalanges II-1 (16.3 mm), phalanges II-2 (15.8 mm), manual unguals II (7 mm), phalanx III-1 (8 mm), pubes (51.4 mm), ischium (20 mm), femora (53 mm), tibiotarsi (68.7 mm), fibula (19 mm), metatarsal I, phalanx I-1 (8.2 mm), pedal unguals I (5.5 mm), tarsometatarsi (35.5 mm), phalanges II-1 (13 mm), phalanges II-2 (10.3 mm), phalanges II-3 (9.5 mm), pedal unguals II (6.2 mm), phalanges III-1 (13.5 mm), phalanges III-2 (10.7 mm), phalanges III-3 (9.8 mm), pedal unguals III (7.5 mm), phalanges IV-1 (9.7 mm), phalanges IV-2 (9.3 mm), phalanges IV-3 (7.1 mm), phalanges IV-4 (6.1 mm), pedal unguals IV (5 mm) (Yuan, 2004)
Late Barremian-Early Aptian, Early Cretaceous
Jianshangou Beds of Yixian Formation, Liaoning, China
Holotype- (xhpm1205; holotype of Yanornis guozhangi) skull (55 mm), mandibles, hyoids, cervical series, several dorsal vertebrae, dorsal ribs, uncinate processes, synsacrum (32 mm), few caudal vertebrae, pygostyle (12 mm), partial scapulae (45 mm), coracoid, furcula, sternum, humeri (72 mm), radii (74 mm), ulnae (74 mm), pisiform, carpometacarpi (36 mm), phalanges I-1 (19 mm), manual unguals I (10 mm), phalanges II-1 (15 mm), phalanges II-2 (15 mm), manual unguals II (6 mm), phalanges III-1 (8 mm), ilia, pubes (75 mm), ischia, femora (55 mm), tibiotarsi (68 mm), fibulae (44 mm), metatarsals I, phalanges I-1 (7 mm), pedal unguals I (5 mm), tarsometatarsi (33 mm), phalanges II-1 (12 mm), phalanges II-2 (10 mm), pedal unguals II (6 mm), phalanges III-1 (14 mm), phalanges III-2 (10 mm), phalanges III-3 (8 mm), pedal unguals III (6 mm), phalanges IV-1 (9 mm), phalanges IV-2 (7 mm), phalanx IV-3 (6 mm), phalanx IV-4 (6 mm), pedal ungual IV (5 mm), three fish (Wang, Ji, Teng and Jin, 2013)
Late Valanginian-Middle Aptian, Early Cretaceous
Ningcheng, Yixian Formation, Inner Mongolia, China
Holotype- (IVPP V14606; holotype of Abitusavis lii) fragmentary skull, incomplete mandibles, atlas, axis, eight cervical vertebrae, eight dorsal vertebrae, dorsal ribs, uncinate processes, synsacrum (30.76 mm), four caudal vertebrae, pygostyle (12.27 mm), scapulae, coracoids (29.75 mm), furcula, incomplete sternum, sternal ribs, humeri (75.19 mm), radii (72.22 mm), ulnae (76.56 mm), pisiform, carpometacarpi (35.66 mm, mcI 6.67 mm), phalanx I-1, manual unguals I, phalanges II-1 (17.15 mm), phalanges II-2 (14.89 mm), manual unguals II (5.13 mm), phalanges III-1 (8.26 mm), ilia (one incomplete, one fragmentary), pubes, femora (54.76 mm), tibiotarsi (71.44 mm), fibulae, metatarsal I (5.75 mm), tarsometatarsi (37.28 mm), twelve pedal phalanges, five partial pedal phalanges, four pedal unguals (Liu, 2008)
Barremian-Albian, Early Cretaceous
Jehol Group, Liaoning?, China
?(IMMNH-PV00021) (adult) skull, mandibles, hyoid, cervical series, dorsal vertebrae, partial dorsal ribs?, sacrum, caudal series, pygostyle, scapulae, coracoids, partial furcula, fragmentary sternum, humeri, radii, ulnae, pisiform, carpometacarpi, phalanx I-1, manual ungual I, phalanges II-1, phalanges II-2, manual unguals II, phalanx III-1, incomplete pubes, femora, tibiotarsi, metatarsal I,. phalanges I-1, tarsometatarsi, pedal digits II, pedal digits III, pedal digits IV, body feathers, remiges (Wang et al., 2020a)
?(IVPP V13259; paratype of Abitusavis lii) skull, incomplete mandibles, hyoids, cervical vertebrae, dorsal vertebrae, dorsal ribs, synsacrum, partial sternum, fragmentary pectoral elements, humeri (75.4 mm), radii, ulnae (78.20 mm), proximal carpal, carpometacarpi (36.10 mm), phalanges I-1, phalanges II-1 (~18.6 mm), phalanges III-1, pubes, femora (56.10 mm), tibiotarsi (71.70 mm), fibulae, metatarsals I, phalanges I-1, pedal unguals I, tarsometatarsi (38.90 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, feathers, teleost elements (Zhou, Clarke and Zhang, 2002)
?(STM 9-15) skull (72.2 mm), mandibles, hyoids, cervical series, dorsal series, dorsal ribs, gastralia, synsacrum, caudal vertebrae, scapula (~57.8 mm), coracoids (39 mm), partial furcula, sternal fragments, humeri (80 mm), radii, ulnae (85 mm), scapholunare, pisiform, carpometacarpi (~34 mm), phalanges I-1, manual unguals I, phalanges II-1 (~16 mm), phalanges II-2, manual unguals II, phalanges III-1, phalanges III-2, manual claw sheaths, partial ilia, pubes, ischium, femora (~51 mm; one partial), incomplete tibiotarsi (~78 mm), fibulae (one partial), metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsus (39 mm), phalanx II-1, phalanx II-2, pedal ungual II, phalanx III-1, proximal phalanx III-2, phalanx IV-1, phalanx IV-2, phalanx IV-3, proximal phalanx IV-4, body feathers, two cf. Jinanichthys, actinopterygian fragments (Zheng et al., 2014)
?(STM 9-19) skull (~62 mm), cervical series fused to cervical ribs, dorsal series, dorsal ribs, synsacrum, caudal vertebrae, pygostyle, scapulae, coracoid, furcula, humeri (76 mm), radii, ulnae (80 mm), pisiform, carpometacarpi (34.5 mm), phalanges I-1, manual ungual I, phalanges II-1, phalanges II-2, manual unguals II, phalanges III-1, pubes, femora (58 mm), tibiotarsi (73 mm), metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsi (38 mm), phalanges II-1, phalanges II-2, pedal unguals II, pedal digits III, pedal phalanges IV, retrices, body feathers, Protopspherus scales (Zheng et al., 2014)
(STM 9-26) skull (72 mm), sclerotic plates, mandibles, hyoid, cervical series, dorsal series, dorsal ribs, caudal vertebrae, pygostyle, partial humerus (~78 mm), partial radius, partial ulna (~80 mm), incomplete manus, pubes, femur, tibiotarsi, phalanx I-1, pedal ungual I, tarsometatarsi, pedal phalangeal fragments, cf. Jinanichthys (Zheng et al., 2014)
(STM 9-37) skull (68 mm), sclerotic plates, mandibles, hyoids, cervical vertebrae, dorsal vertebrae, dorsal ribs, gastralia, scapula (~45 mm), furcula, sternum, humeri (79 mm), radii, ulnae (86 mm), carpometacarpi (~38 mm), phalanges I-1, manual unguals I, phalanges II-1 (~18 mm), phalanx II-2, phalanx III-1, pubes, femora (~55 mm), tibiotarsi (74 mm), proximal tarsometatarsi, actinopterygian fragments (Zheng et al., 2014)
?(STM 9-46) skull (~68 mm), several posterior cervical vertebrae, dorsal series, dorsal ribs, synsacrum, caudal vertebrae, pygostyle, scapulae (50 mm), coracoids (34 mm), partial furcula, partial sternum, humeri (80 mm), radii, ulnae (86 mm), scapholunares, pisiform, carpometacarpi (~39 mm), phalanx I-1, phalanges II-1 (~19 mm), ilia, pubes, partial ischium, femora (57 mm), tibiotarsi (74 mm), fibula, metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsi (40 mm), phalanx II-1, phalanx II-2, pedal ungual II, phalanx III-1, phalanx III-2, phalanx III-3, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, actinopterygian fragments (Zheng et al., 2014)
?(STM 9-49) skull (~61 mm), mandible, cervical series, dorsal series, dorsal ribs, gastralia, humeri (72 mm), radii, ulnae (~80 mm), carpometacarpi, phalanges I-1, manual unguals I, phalanges II-1, phalanges II-2, manual unguals II, phalanges III-1, phalanges III-2, pubes, femora (~50 mm), tibiotarsi (~75 mm), fibulae (one partial), phalanges I-1, pedal unguals I, tarsometatarsi, phalanx II-1, phalanx II-2, pedal ungual II, phalanx III-1, phalanx III-2, phalanx III-3, pedal ungual III, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, pedal digits, cf. Jinanichthys, actinopterygian fragments (Zheng et al., 2014)
?(STM 9-52) skull (68 mm), sclerotic ring, mandibles, cervical series, dorsal series, dorsal ribs, scapula (48 mm), coracoid (31 mm), furcula, humeri (~68 mm), radii, ulnae (72 mm), pisiform, carpometacarpi (41 mm), phalanges I-1, manual unguals I, phalanx II-1 (~22 mm), phalanx II-2, manual ungual II, phalanx III-1, ilium, pubes, femora (50 mm), tibiotarsi (68 mm), pedal ungual I, tarsometatarsi (35 mm), phalanges II-1, phalanges II-2, pedal unguals II, pedal phalanges, pedal unguals, remiges, actinopterygian fragments (Zheng et al., 2014)
Diagnosis- (after Wang et al., 2020b) dentary with [more] vertically oriented anterior margin (actually about 61-64 degrees in the holotype, 68 percent in IVPP V12444 and 60-63 degrees in IVPP V13358 versus about 42-50 degrees in Similiyanornis); synsacrum with ventral groove; coracoid with distally expanded procoracoid process (also in Schizooura, Yixianornis).
Other diagnoses- Zhou and Zhang (2001) listed several characters in their diagnosis. A straight dentary is also present in Songlingornis, Ichthyornis, Similiyanornis and hesperornithids. According to their figure, the dentary is only 43% of skull length (which is similar to other basal euornithines), not 66%. The number of dentary teeth (20) is similar to Similiyanornis (~20) and Ichthyornis (21-24). Elongate cervical vertebrae are also present in Patagopteryx, Similiyanornis, hesperornithines and ambiortiforms. While stated to be heterocoelous by Zhou and Zhang (2001), the cervicals were coded as semiheterocoelous by Zhou and Zhang (2005) and amphicelous by Clarke et al. (2006). Their true state remains to be determined. A synsacrum with nine vertebrae is also known in Similiyanornis, Mengciusornis, Yixianornis and Patagopteryx. The short pygostyle is similar to most euornithines. Posterior sternal fenestrae are present in Piscivoravis, Iteravis, Gansus, Yixianornis and Songlingornis as well. The posterolateral sternal process is not distally semicircular, but rather slightly convex as in Yixianornis and Archaeorhynchus. A forelimb/hindlimb ratio (hum+uln+carp/fem+tib+tars) of ~110% (actually 106-122%) is also present in Similiyanornis (107%). The manus is shorter than the ulna, but contra Zhou and Zhang is not shorter than the radius. In any case, the carpometacarpo-ulnar ratio (43-49%) is very similar to Similiyanornis (46%), Yixianornis (42%), Patagopteryx (44%), Archaeorhynchus (45%), and Gansus (48%). The tarsometatarsus is completely fused in almost all euornithiness. The third pedal digit is similar in length (107-115% of tarsometatarsal length) to Patagopteryx (~106%) and Gansus (102-116%). Proximal pedal phalanges are longer and more robust than distal phalanges in other basal euornithines where known.
Czerkas and Xu (2002) diagnosed Archaeovolans based on several characters. The number of premaxillary teeth (four) is plesiomorphic, as is them being larger than dentary teeth. The large number of dentary teeth (at least eighteen) is dealt with above. While they claim uncinate processes were absent, the ribcage is only partially articulated and has several small transverse elements which could be uncinates. The "strikingly modern" pectoral girdle is vague but is shared with more derived birds in any case. The supposedly short sternal keel as illustrated is not present in the specimen, which shows an elongate keel as in other Yanornis specimens and basal euornithines. The scapholunare and pisiform are said to be "well developed", but this is vague and they are comparable to other basal euornithines. The lack of a long ventral ramus is plesiomorphic and shared with Similiyanornis, Yixianornis and Gansus. Finally, the lack of a projected ventral carpal trochlea is plesiomorphic and shared with other basal euornithines such as Yixianornis and Patagopteryx.
Clarke et al. (2006) listed humerus longer than scapula as diagnostic, but this is present in all basal euornithines except Patagopteryx, Yixianornis and Apsaravis.
Wang et al. (2020b) listed several characters differing from their new yanornithiforms Abitusavis (here synonymized with Yanornis) and/or Similiyanornis but a premaxillary body anterior to the naris shorter than the subnarial process of the premaxilla is not present in some specimens (e.g. xhpm1205). Two sternal characters listed as differing from Abitusavis are just adult characters compared to the latter and are present in many other basal ornithouromorphs- sternum bearing a pair of anterolateral processes (also in e.g. Similiyanornis, Jianchangornis, Archaeorhynchus, songlingornithids, Yumenornis); posterolateral sternal processes distally expanded (also in e.g. Jianchangornis, Archaeorhynchus, Piscivoravis, songlingornithids, Yumenornis; unknown in Similiyanornis). An elongate forelimb with an intermembral index (hum+uln/fem+tib) of 1.27 only refers to the holotype, with the range of ratios actually 1.09-1.27, which overlaps 1.12 in Similiyanornis. A bicipital crest of the humerus with a pit-shaped fossa [anteriorly] is also present in Similiyanornis, Jianchangornis, Schizooura, Iteravis and Apsaravis.
The "Archaeoraptor" debacle- The specimen IVPP V12444 was fraudulently combined with the tail of the Microraptor zhaoianus holotype by a Chinese farmer. It was smuggled out of the country then sold at the 1998 Tuscon Gem Show to Czerkas. Currie recognized the legs were part and counterpart slabs of the same bones, while Rowe and Aulenback independently verified the composite nature of the specimen. National Geographic announced the specimen in a press conference in October, and in November, Sloan (1999) published a paper using the name "Archaeoraptor liaoningensis". This was a nomen nudum because it explicitely stated the taxon was to be described formerly in an official publication. That official publication was to have been in Science or Nature, but both journals rejected it. In April, Olson (2000) published an article purporting to officially describe "Archaeoraptor" and attach that name to the dromaeosaurid tail (with the latter as the lectotype). Several months later in December, Xu et al. (2000) officially named Microraptor zhaoianus based on the dromaeosaurid tail and associated anterior part of the skeleton Xu had discovered. At this time, Olshevsky (DML, 2000) noted that Olson's publication predated Xu et al.'s, and he believed that this made Microraptor a junior synonym of "Archaeoraptor". Several days later, Creisler (DML, 2001) pointed out the Olson's attempt to name "Archaeoraptor" was invalid because the ICZN requires a diagnosis in a valid publication, while Olson merely referenced the invalid article by Sloan. Creisler further indicated Olson cannot designate a lectotype without a valid publication defining a holotype first. Thus "Archaeoraptor" is still a nomen nudum, despite Olson's efforts, and Microraptor zhaoianus is the valid name for the IVPP V 12330 dromaeosaurid. The specimen was returned to the IVPP in May, 2000 and Zhou and Zhang were asked to work on the euornithine section. They noticed the similarity with Yanornis shortly before completing their paper on that taxon in December 2000. Rowe et al. (2001) detailed the composite nature of the specimen, recognizing it was from at least two, and possibly up to five animals. They noted the euornithine section (IVPP V 12444) was to be described by Xu (in prep.), which later appeared as Czerkas and Xu (2002). These authors described the specimen as a new taxon of euornithine (as Ornithurae) bird- Archaeovolans repatriates. Czerkas and Xu noted in an addendum that the recently described Yanornis martini was extremely similar and might be congeneric, though they also thought differences were present. Zhou et al. published their work in 2002, noting that both anatomy and proportions were nearly identical in the holotypes for the two species and synonymized them. Given the recent description of Similiyanornis, IVPP V12444 can be referred to Yanornis based on the vertical anterior dentary margin, expanded procoracoid process (also noted by Wang et al., 2020b), and lack of Similiyanornis' enlarged anterior dentary tooth, anterior dentary foramen, and elongate manual phalanx II-1 (46% of carpometacarpus versus 67% in Similiyanornis). While Rowe et al. found no evidence the right femur and both tibiotarsi, fibulae and pes belong to the same individual as the body, Zhou et al. (2002) confirmed they do.
Yanornis gouzhangi- Wang et al. (2013) described a supposedly new Yanornis species, Y. guozhangi, based on complete skeleton xhpm1205. Contra their diagnosis, the "large and strong deltoid crest, which is almost half the length of the shaft" is the same as in Yanornis martini. The pubic symphysis is noted to be shorter than the Y. martini holotype, at 24% compared to 35%, but it falls within the range of variation of Y. martini with LHZA02-0008 having a 37% ratio and IVPP V13259 having a 21% ratio. The fibula was stated to be longer, at "2/3 the length of the tibiotarsus" (actual ratio 65%) compared to 39% in the Y. martini holotype. Most specimens cannot be checked but the ratio in LHZA02-0008 is 28% and that of IVPP V14606 at least 39%. Wang et al. state "the tarsometatarsus is short and completely fused, less than half the length of the tibiotarsus", but all euornithines have completely fused tarsometatarsi and the tarsometatarsotibiotarsal ratio (49%) is actually greater than the ratio in the Y. martini type (46%) and falls within the range of other specimens (49-54%). With the longer fibula being the only valid proposed difference, Y. guozhangi is synonymized with Y. martini. It also shares Yanornis' dentary with a vertically oriented anterior margin and lacks Similiyanornis' large anterior dentary tooth and long manual phalanx II-1 (67% of carpometacarpus versus 42% in xhpm1205). Wang et al. reached the same conclusion, stating "all of the features originally used to diagnose this taxon are present in Yanornis martini", "putative differences between these two taxa pertain to subtle limb proportions" and "our re-examination indicates that the former is morphologically identical to Yanornis martini."
Abitusavis- Liu (2008) described IVPP V14606 in their thesis as an example of Yanornis martini. It was later described by Wang et al. (2020b) as a new taxon of yanornithid, Abitusavis lii. However, most of their listed diagnostic characters compared to Yanornis are flawed. Two characters are listed as differing from Similiyanornis, but being shared with Yanornis- synsacrum bearing a ventral groove; coracoid with distally expanded procoracoid process. Wang et al. also list intercotylar eminence of tarsometatarsus absent in their diagnosis, but the weak convexity is only slightly less prominent than in Similiyanornis while Yanornis (e.g. IVPP V12558, xhpm1205) lacks any convexity. A distal vascular foramen which is proximally located is listed in supposed contrast with Similiyanornis, but the labeled distal vascular foramen in the latter is just the gap between trochlea III and IV also seen in Abitusavis. The area around the true distal vascular foramen is too poorly preserved to score in other yanornithiforms. They also list margins of pedal ungual flexor tubercles step-like instead of circular but this is similar to some Yanornis (e.g. IVPP V13358) so is probably individual variation. Two sternal characters (sternum without anterolateral processes; posterolateral processes of sternum not expanded distally) are typical of young ornithothoracines, which agrees with the smaller size of Abitusavis (humerus 88% of Yanornis holotype). Notably the intermediate-sized IVPP V12444 (92%) only has slightly expanded posterolateral processes. The supposed posterodorsally elongate retroarticular process strongly reseembles the medial articular process of Ichthyornis, down to the slight anteromedial convexity for the medial condyle, suggesting the posterior mandible rotated into ventral exposure. This would not differ from Yanornis specimens preserved in lateral view but is similar to the Similiyanornis type as interpreted by Liu. The synsacrum having one less vertebra incorporated than the Yanornis holotype is a character known to vary individually in Ichthyornis. The potentially most diagnostic character is the paired M. cranialis tibialis tubercles on metatarsals II and III, unlike the Yanornis holotype with its proximodistally poorly defined tubercle on metatarsal II and at best very small tubercles on metatarsal III. Given the individual variation in other Mesozoic birds, this is considered insufficient to support a new species, and Abitusavis lii is here placed as a junior synonym of Yanornis martini.
Zhou et al. (2002) stated "a recently discovered specimen of Yanornis (IVPP V13259) contains preserved macerated fish remains, including a teleost vertebra, fin rays and opercular fragments" and figured a small section of it. Wang et al. (2020b) referred it to their new taxon Abitusavis based on the intermembral index (hum+uln/fem+tib of 1.20 in both), femoral/tibiotarsal ratio (0.78 vs. 0.77 in holotype) and absent intercotylar eminence. However, the ratios fall within the range of variation of Yanornis while the intercotylar eminence is also absent in that taxon as noted above. It is assigned to Yanornis here based on the short manual phalanx II-1 unlike Similiyanornis.
Referred specimens- The paratype (IVPP V10996) has yet to be described but was figured by Wang et al. (2020b), who correctly noted "few diagnostic features can be identified from this specimen" and referred it to Yanornithidae indet.. Indeed no characters of Yanornis or Similiyanornis can be seen, so it is placed in Yanornithiformes indet. here.
Yuan (2004) described another specimen (LHZA02-0008) as Yanornis martini which is notable in having four phalanges on each pedal digit II and a specimen of the osteoglossomorph Jinanichthys in its mouth. It is not Similiyanornis based on the lack of an enlarged dentary tooth and short manual phalanx II-1 (54% of carpometacarpus), so is referred to Yanornis here.
Zhou et al. (2004) briefly described a specimen with gastroliths (IVPP V13358), which was later illustrated by Zhou and Zhang (2006) and mentioned another specimen (IVPP V13278) which was later made the holotype of Similiyanornis brevipectus. Wang et al. (2020b) correctly concluded IVPP V13358 was Yanornis instead of Similiyanornis based on the more vertical anterior dentary edge, lack of Similiyanornis' enlarged dentary tooth and anterior foramen and short manual phalanx II-1.
Zheng et al. (2013) briefly described STM 9-5 which they referred to Yanornis, but it is referred to Yanornithiformes indet. here.
Zheng et al. (2014) described fish remains in ten new specimens. Of these, note STM 9-52 has only one large phalanx in digit II of its right manus, which if not a developmental anomaly is likely to be a forgery. Most of right pedal digit III seems to be fake, lending credence to the latter possibility. Wang et al. (2020b) stated "until adequate preparation and detailed comparative study are conducted, we suggest the aforementioned 10 specimens are tentatively referred to Yanornithidae indet." However, STM 9-15, 9-19, 9-46, 9-49 and 9-52 can be tentatively referred to Yanornis based on the short manual phalanx II-1 (46%, ~45%, 48%, ~53% and 52% of carpometacarpus respectively; but see STM 9-18), while STM 9-26 can be referred to it based on the more vertical anterior dentary margin and lack of an enlarged tooth, STM 9-37 based on the lack of an enlarged anterior dentary tooth and short phalanx II-1 (48%). STM 9-18, 9-31 and 9-51 are placed in Yanornithiformes indet. here though, with the caveat 9-18 appears to show a mix of Yanornis and Similiyanornis characters.
Wang et al. (2020) described the hsitology of IMMNH-PV00021 (perhaps from Inner Mongolia like IVPP V14606 based on it being in the Inner Mongolia Museum of Natural
History) as Yanornis, which it may be based on the short manual phalanx II-1 (~51% of carpometacarpal length).
Miscoded originally? Zhou and Zhang (2005) were the first authors to code Yanornis, but You et al. (2006) changed numerous codings based on personal observation of the holotype by Chiappe and O'Connor. Clarke et al. (2006) later coded Yanornis again based on the holotype, IVPP V12444, V13259 and V13358. These include making the following states uncertain- anterior premaxillary fusion (stated to be present by Zhou et al., 2002 and coded so by Clarke et al.); fusion of frontoparietal suture (appears absent in the figure of the holotype; also uncertain in Clarke et al.); quadrate pneumaticity including cluster of foramina on dorsal process (also uncertain in Clarke et al.); presence of external mandibular fenestra (appears absent in the figure of the holotype; also uncertain in Clarke et al.); coely of cervical vertebrae (stated to be heterocoelous by Zhou and Zhang, 2001; coded as semihetercoelous by Zhou and Zhang, 2005; coded as amphicoelous by Clarke et al.); presence of large hypapophyses on mid dorsal vertebrae (appears absent in IVPP V12444; coded as absent by Clarke et al.); number of dorsal vertebrae (also uncertain in Clarke et al.); presence of notarium (seems absent from figures of holotype and IVPP V12444; coded as absent by Clarke et al.); number of sacral vertebrae (stated to be and illustrated as nine by Zhou and Zhang, 2001; coded as nine by Clarke et al.); number of sacrals with dorsally directed diapophyses (stated to be and illustrated as none by Zhou and Zhang, 2001; coded as none by Clarke et al.); length and presence of pygostyle (the supposed pygostyle of the holotype has no features identifying it as such- Senter, pers. comm.); median proximity of coracoid sulci on sternum (coded as close or overlapping by Clarke et al.); presence of intermuscular lines on sternum (also uncertain in Clarke et al.); lateral excavation of furcula (coded as absent by both Clarke et al. and Nesbitt et al., 2009); pointed epicleidea (coded as absent by both Clarke et al. and Nesbitt et al., 2009; but seemingly present in IVPP V12444 and V13358); concavity of dorsal coracoid surface (stated to be deeply concave distally by Zhou and Zhang, 2001; coded as flat by Clarke et al.); pneumaticity of coracoid (coded as absent by Clarke et al.); position of glenoid relative to acrocoracoid (stated to be ventral by Czerkas and Xu and coded as such by Clarke et al.); curvature of acrocoracoid (coded as medially hooked by Clarke et al.); presence of supracoracoid foramen (also uncertain in Clarke et al.); whether the supracoracoid foramen opens into a medial groove (unknown since the foramen's presence is uncertain); angle between scapula and coracoid (less than 90 degrees in IVPP V13358; coded as such by Clarke et al.); length of acromion (illustrated as long in the holotype, but as short in IVPP V12444 and V13358; coded as long by Clarke et al.); curvature of acromion (stated to be curved by Zhou et al., 2002; coded as straight by Clarke et al.); presence and morphology of capital groove and ventral tubercle (also uncertain in Clarke et al.; all specimens seem to be preserved with humeri in anterior view); presence of anterior concavity on humeral head (actually already coded unknown by Zhou and Zhang, 2005; but coded absent by Clarke et al.); development of bicipital crest (stated to be ball-shaped by Zhou and Zhang, 2001 and well developed by Czerkas and Xu; coded as enlarged by Zhou and Zhang and moderate by Clarke et al.); presence of brachial fossa on humerus (also uncertain in Clarke et al.); demarkation of muscle origins on the dorsodistal humerus (also uncertain in Clarke et al.); presence of scapulotricipital and humerotricipital grooves (also uncertain in Clarke et al.; all specimens seem to be preserved with humeri in anterior view); separation of ulnar cotyla (also uncertain in Clarke et al.); semilunar morphology of dorsal ulnar condyle (visible in IVPP V12444; stated to be present by Zhou and Zhang, 2001 and coded as such by Clarke et al.); morphology of ventroposterior surface of radius (apparently grooved in both IVPP V12444 and V13358; coded as flat or scarred by Clarke et al.); length of pisiform rami (poorly developed in IVPP V12444 and coded as such by Clarke et al.); comparative lengths of dorsal and ventral pisiform rami (coded as subequal by Clarke et al.); width of metacarpal III (is approximately 50% in the holotype and IVPP V12444; seems much narrower in Zhou and Zhang's illustration of IVPP V13358, but is wider in the photo; coded as narrower by Clarke et al.); convexity of medial metacarpal I edge (concave in IVPP V12444; also coded uncertain in Clarke et al.); presence of internal index process of manual phalanx II-2 (absent in IVPP V13358 and coded as such by Clarke et al.); dorsal fusion of ilia (clearly absent in the holotype and coded as such by Clarke et al.); anterior extent of ilium (does not overlap last dorsal vertebra in the holotype and coded as such by Clarke et al.); presence of cuppedicus fossa on ilium (also coded uncertain in Clarke et al.); size and presence of posterior trochanter (also coded uncertain in Clarke et al.); fusion of tibiotarsus (coded as completely fused by Clarke et al.); comparative anterior projection of tibiotarsal condyles (also coded uncertain in Clarke et al.); presence of supratendinal groove (coded as absent by Clarke et al.); presence of retinaculi extensor tubercle on distal tibiotarsus (also coded uncertain in Clarke et al.); comparative width of tibiotarsal condyles (also coded uncertain in Clarke et al.); medial constriction of tibiotarsal condyles in distal view (coded as constricted by Clarke et al.); width of tibiotarsal intercondylar groove in distal view (coded as wide by Clarke et al.); extent of cartilaginous tibial sulcus (actually already coded unknown by Zhou and Zhang, 2005); distal tibiotarsal width compared to midshaft width (coded as subequal by Clarke et al., but this seems untrue in most birds including Yanornis, making interpretation of Clarke's character problematic); distal contact between fibula and tarsus (absent in all specimens; as coded by Clarke et al.); hypotarsal development (coded as absent or lacking crests and foramina by Clarke et al.); development of fossa for metatarsal I (also coded uncertain in Clarke et al.); ginglymoidy of metatarsal II (seems rounded in IVPP V13358); relative transverse width of metatarsals (subequal in IVPP V13358 and coded as such by Clarke et al.); number of distal vascular foramen exits in tarsometatarsus (also coded uncertain in Clarke et al.).
They also changed several codings- dentary symphysis without broad dorsally facing surface (which agrees with Czerkas and Xu, 2002); posterior dentary unforked (as it appears in the figure of the holotype); Meckelian groove not covered by splenial (which agrees with Czerkas and Xu, 2002); presence of lateral foramina in the dorsal centra (though described as pleurocoels by Zhou and Zhang and Czerkas and Xu, their size makes them more likely to be fossae as coded by Clarke et al.); lateral coracoid process absent (illustrated as present by Zhou and Zhang, 2001 and Zhou et al., 2002; coded as present by Clarke et al., 2006); ulna shorter than humerus (longer in specimens with exactly measured elements; as coded by Clarke et al.); dorsal ulnar cotyla not convex (coded uncertain by Clarke et al.); ulnar brachial scar present (also coded as present by Clarke et al.); intermetacarpal space reaches proximally to metacarpal I (present in all specimens; as coded by Clarke et al.); manual phalanx II-2 shorter than II-1 (coded as longer by Clarke et al., but actually varies from 97-106%, making it polymorphic); one proximal vascular foramen in tarsometatarsus (coded uncertain by Clarke et al.); metatarsal I straight (coded as curved by Clarke et al.); laterally placed m. tibialis cranialis tubercle on tarsometatarsus (as coded by Clarke et al.); metatarsal trochlea II subequal or wider than trochlea III and/or IV (Zhang and Zhou, 2001 state metatarsal II's trochlea is intermediate in width between III and IV; which state this represents is confusing, as Clarke's character has states compared to trochlea III AND/OR IV, so it agrees with parts of states 1 and 2); metatarsal II shorter than metatarsal IV, but reaching distally farther than base of metatarsal IV trochlea (as coded by Clarke et al; while Zhou and Zhang's illustration appears to show subequal lengths, their text states II is shorter).
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Similiyanornis Wang, Li, Liu and Zhou, 2020
S. brevipectus Wang, Li, Liu and Zhou, 2020
= Yanornis "brevipectis" Liu, 2008
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V13278) skull (51.44 mm), mandibles (49.4 mm), hyoids, nine postaxial cervical vertebrae (9.7, 9.8, 11.7, 12.4, 13.8, ~9.1, ~9.6, ~8.4 mm), two posteriormost dorsal vertebrae, partial dorsal ribs, synsacrum (31.4 mm), several caudal vertebrae, pygostyle (9.92 mm), scapula, coracoids (28.74 mm), partial furcula, incomplete sternum, sternal ribs, humeri (67.7, 64.8 mm), radii (65.38, 65.4 mm), ulnae (67.9, 68.0 mm), scapholunare, pisiform, carpometacarpus (31.05 mm, mcI 6.85 mm), phalanx I-1 (15.37 mm), manual ungual I (8.29 mm), phalanx II-1 (20.65 mm), phalanx II-2 (10.17 mm), manual ungual II (5.86 mm), phalanx III-1 (8.39 mm), ilia (30.3 mm), pubes (49.7, 46.1 mm), ischia (18.3, 20.2 mm), femora (54.97, 49.3 mm), tibiotarsi (61.5, 59.2 mm), fibula (~34.3 mm), metatarsal I, incomplete phalanx I-1 (~8.3 mm), tarsometatarsi (34.3, 31.8 mm), incomplete phalanges II-1 (11.05 mm), phalanx II-2 (8.95 mm), incomplete pedal ungual II, phalanges III-1 (one incomplete; 12.79 mm), phalanges III-2 (8.97, 9.2 mm), phalanges III-3 (8.51, 8.6 mm), pedal unguals III (3.72 mm), phalanges IV-1 (one partial; 8.24 mm), phalanges IV-2 (7.23, 7.2 mm), phalanges IV-3 (6.08, 6.1 mm), phalanges IV-4 (6.29, 6.1 mm), pedal unguals IV (4.83, 5.0 mm), body feathers, remiges, retrices
Diagnosis- (after Wang et al., 2020) dentary having a minute alveolus near the anterior tip (also in Hesperornis); first dentary tooth hypertrophied; tapered procoracoid process on coracoid; manual phalanx II-1 over two-thirds of carpometacarpus length (67% vs. 42-52% in Yanornis).
Other diagnoses- Wang et al. (2020) listed a lateral foramen at the anterior tip of the premaxilla, but this is also present in some Yanornis (e.g. xhpm1205). A subnarial process of the premaxilla shorter than the premaxillary body anterior to the naris was said to be diagnostic, but is also present in some Yanornis (IVPP V13259, xhpm1205). Contra their statement "The lacrimal is poorly preserved in all the specimens that can be confidently referred to Yanornis martini", the supposedly diagnostic T-shaped lacrimal bearing a slender posterodorsal process is also present in xhpm1205. They listed two surangular foramina as diagnostic, but Yanornis may have these as well based on xhpm1205. They stated cervical prezygapophyses longer than postzygapophyses as diagnostic, but this is only visible in two anterior cervicals and absent in the last preserved cervical, comparable to IVPP V13259 where two anterior cervicals have longer prezygapophyses, a mid cervical is intermediate and three posterior cervicals have longer postzygapophyses. A large femorotibiotarsal ratio of 85% was listed as diagnostic, but while the type of Yanornis has a 68% ratio, other specimens have ratios of 81% (xhpm1205) and 85% (IVPP V12444). Wang et al. listed bicipital crest of humerus without a pit-shaped fossa but the right humerus seems to have an anterior fossa, albeit larger and more triangular than Yanornis' holotype. They also listed an enlarged flexor tuber of pedal ungual IV, but this minor difference is similar to some Yanornis (e.g. xhpm1205) but not others (e.g. IVPP V13358) so is probably individual variation.
Comments- Zhou et al. (2004) first mention IVPP V13278 as one of the several Yanornis martini "completely, or partially, articulated specimens with minimal or no evidence of postmortem disturbance. No gastroliths are known from any of these specimens." Liu (2008) described this as a new species of Yanornis, Y. "brevipectis", in their MS thesis. Wang et al. (2020) officially described it as a new genus as well, Similiyanornis brevipectus. Differences in interpretation from the thesis include longer posterodorsal premaxillary processes, reidentifying the mesethmoid as a lacrimal, recognizing a mandible without an external fenestra, and recognizing the sternum is broken posteriorly instead of being shorter than in Yanornis (despite retaining a version of its original species name "brevipectis"). Notably, Liu's Table 3.1 shows the forelimb measurements in Wang et al. are averages of right and left sides.
References- Zhou, Clarke, Zhang and Wings, 2004. Gastroliths in Yanornis: An indication of the earliest radical diet-switching and gizzard plasticity in the lineage leading to living birds? Naturwissenschaften. 91(12), 571-574.
Liu, 2008. A new species of Yanornis and its phylogenic relationships. MS thesis, Chinese Academy of Sciences. 51 pp.
Wang, Li, Liu and Zhou, 2020. Two new Early Cretaceous ornithuromorph birds provide insights into the taxonomy and divergence of Yanornithidae (Aves: Ornithothoraces). Journal of Systematic Palaeontology. 18(21), 1805-1827.

unnamed clade (Yixianornis grabaui + Gansus yumenensis + Passer domesticus)

Guildavis Clarke, 2004
Definition- (Guildavis tener <- Ichthyornis dispar, Struthio camelus, Tetrao major, Vultur gryphus) (modified from Clarke, 2004)
= "Guildavis" Clarke, 2002
G. tener (Marsh, 1880) Clarke, 2004
Definition- (the species that includes YPM 1760) (Clarke, 2004)
= Ichthyornis tener Marsh, 1880
= "Guildavis" tener (Marsh, 1880) Clarke, 2002
Cretaceous
Wallace County, Kansas, US
Holotype- (YPM 1760) partial synsacrum (~17 mm)
Other diagnoses- Clarke (2004) distinguished this taxon from Ichthyornis based on two characters. The first is the presence of parapophyses on the first sacral, which are also found in Gansus and Aves. The second is the presence of wider iliosacral sulci, but this is also seen in Patagopteryx, Gargantuavis, Zhyraornis and Gansus.
Comments- Marsh (1880) named this as a new species of Ichthyornis based on a synsacrum discovered in 1879, but never illustrated or described the species. He referred a distal humerus (YPM 1738) and coracoid (YPM 1766) to Ichthyornis tener without comment, but Clarke (2004) showed these are referrable to I. dispar. Brodkorb (1967) incorrectly believed the humerus was YPM 1760, as Marsh never states which element YPM 1760 is and references a figure of the humerus. Clarke (2002) removed the holotype from Ichthyornis and described it as the new genus "Guildavis", which was published by her in 2004. Clarke noted Guildavis could not be compared to the probably contemporaneous Apatornis and Iaceornis besides being smaller, so may be synonymous with either of these taxa.
Clarke (2004) found Guildavis to be more derived than Ichthyornis based on the parapophysis on the first sacral, but this is now known to be present in the more basal Gansus as well. Similarly, Clarke found Guildavis to be excluded from Aves due to its amphicoelous anterior sacral articular surface, but some crown birds including most charadriiforms have this as well, and Clarke did not include any neoavians in her analysis.
References- Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Brodkorb, 1967. Catalogue of fossil birds: part 3 (Ralliformes, Ichthyornithiformes, Charadriiformes). Bulletin of the Florida State Museum (Biological Sciences). 11, 99-220.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT, 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.

unnamed ornithuromorph (Parris and Hope, 2002)
Late Maastrichtian-Early Danian, Late Cretaceous-Early Paleocene
Hornerstown Formation, New Jersey, US
Material- (NJSM 15065) proximal scapula
Comments- This specimen closely resembles both Ambiortus and Lithornis in the flattened, styloid, ventrally bent acromion. It may resemble the former in fusing the coracoid tubercle to the cranial end of the humeral facet. Parris and Hope (2002) tentatively referred it to Palaeognathae, but based on Clarke's (2002) placement of Ambiortus outside that clade, it is assigned to a more inclusive clade here.
References- Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT, 532 pp.
Parris and Hope, 2002. New interpretations of the birds from the Navesink and Hornerstown Formations, New Jersey, USA (Aves: Neornithes). In Zhou and Zhang (eds.). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing, 1-4 June 2000. 113-124.

unnamed Ornithuromorpha (Forster and O'Connor, 2000; described by O'Connor and Forster, 2010)
Middle Maastrichtian, Late Cretaceous
Anembalemba Member of Maevarano Formation, Madagascar
Material- (FMNH PA 748) distal humerus (O'Connor and Forster, 2010)
(UA 9601) synsacrum (25 mm) (Forster and O'Connor, 2000; described by O'Connor and Forster, 2010)
(UA 9607) distal humerus (O'Connor and Forster, 2010)
Comments- The synsacrum UA 9601 was reported by Forster and O'Connor (2000), then by O'Connor and Forster (2009) as an ornithurine sensu Gauthier and de Queiroz. It was later described by O'Connor and Forster (2010) as an ornithurine sensu Gauthier and de Queiroz based on having ten vertebrae, while the distal humeri were described as ornithurines sensu Gauthier and de Queirozbased on "a well-defined dorsal supracondylar tubercle, an incipient scapulotricipital sulcus, and the assortment of small fossae on the distal end (e.g., fossae associated with the ventral epicondyle)."
References- Forster and O'Connor, 2000. The avifauna of the Upper Cretaceous Maevarano Formation, Madagascar. Journal of Vertebrate Paleontology. 20(3), 41A-42A.
O'Connor and Forster, 2009. The Late Cretaceous (Maastrichtian) avifauna from the Maevarano Formation, Northwestern Madagascar: Recent discoveries and new insights related to avian anatomical diversification. Journal of Vertebrate Paleontology. 29(3), 157A.
O'Connor and Forster, 2010. A Late Cretaceous (Maastrichtian) avifauna from the Maevarano Formation, Madagascar. Journal of Vertebrate Paleontology. 30(4), 1178-1201.

unnamed Ornithuromorpha (Agnolin and Martinelli, 2009)
Campanian-Maastrichtian, Late Cretaceous
Los Alamitos Formation, Río Negro, Argentina
Material- (MACN PV RN 1111) distal tibiotarsus
(MACN PV RN 1112) distal tibiotarsus
(MACN PV RN 1113) distal tibiotarsus
Comments- These have a non-bridged extensor groove.
Reference- Agnolin and Martinelli, 2009. Fossil birds from the Late Cretaceous Los Alamitos Formation, Río Negro province, Argentina. Journal of South American Earth Sciences. 27, 42-49.

Songlingornithidae Hou, 1997
Definition- (Songlingornis linghensis <- Chaoyangia beishanensis, Passer domesticus) (Martyniuk, 2012)
= Yixianorniformes Zhang and Zhou, 2006
= Yixianornithidae Zhang and Zhou, 2006
Other diagnoses- Clarke et al. (2006) found four characters to unambiguously diagnose this clade in a version including Yanornis. Yanornis has not been shown to lack completely heterocoelous cervicals. A posteromedial sternal process joining distally to the posteromedian process to form a fenestra is also seen in Piscivoravis, Iteravis and Gansus. A procoracoid process is now known in all basal euornithines except Patagopteryx and Apsaravis. The lack of a medially concave coracoid surface (where the supracoracoid foramen exits if it is present) is more parsimoniously primitive to euornithines, as it is present in Bellulornis and Arcaheornithura, while the concavity in Apsaravis is considered a reversal.
Zhou and Zhang's (2006) diagnosis for Yixianornis' eponymous family and order was the same as their 2001 diagnosis for the genus. Most of those characters are apomorphic for Yixianornis or otherwise problematic (see Yixianornis diagnosis), except the femoro-tarsometatarsal ratio of ~150-170%, which is also present in e.g. Jianchangornis (162-169%), Archaeorhynchus (164-185%) and Piscivoravis (157%).
Comments- Hou (1997) originally named Songlingornithidae for Songlingornis within the Chaoyangiformes, while Zhou and Zhang (2001) later placed Yixianornis in Chaoyangornithiformes. Zhou and Zhang (2006) created Yixianornithidae and Yixianornithiformes for Yixianornis, and placed Songlingornis in the Chaoyangornithiformes and "Chaoyangornithidae". Clarke et al. (2002) were the first to suggest placing these taxa and Yanornis into a single clade at their SVP talk, though this was not published until 2006. You et al. (2006) independently coded Yanornis and Yixianornis and found the taxa to form a monophyletic clade in some of their most parsimonious trees, though in others Yanornis was more derived and sister to Apsaravis. The monophyletic clade of Yanornis, Yixianornis and/or Songlingornis has been called Songlingornithidae by many recent authors, but here Yanornis is recovered as further from Aves than Yixianornis and Songlingornis based on Hartman et al.'s maniraptoromorph matrix.
References- Hou, 1997. Mesozoic birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou. 228 pp.
Zhou and Zhang, 2001. [Two new genera of ornithurine birds from the Early Cretaceous of Liaoxi involved in the origin of modern birds.] Kexue Tongbao. 46(5), 371-377.
Clarke, Zhou and Zhang, 2002. An ornithurine from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(3), 45A.
Clarke, Zhou and Zhang, 2006. Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui. Journal of Anatomy. 208, 287-308.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.
Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Yixianornis Zhou and Zhang, 2001
Y. grabaui Zhou and Zhang, 2001
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V12631) (~215 mm, 320 g) skull (~39 mm), mandibles, sclerotic ring, atlas, axis, third cervical vertebra, fourth cervical vertebra, fifth cervical vertebra, sixth cervical vertebra, seventh cervical vertebra, eighth cervical vertebra, ninth cervical vertebra, tenth cervical vertebra, eleventh cervical vertebra, twelfth cervical vertebra, ten dorsal vertebrae (5.8 mm), dorsal ribs, uncinate processes, fifteen rows of gastralia, synsacrum (25 mm), five caudal vertebrae, pygostyle (7.92 mm), scapulae (48.1 mm), coracoids (23.3 mm), furcula, sternum (43.1 mm), sternal ribs, humeri (49.3 mm), radii (48 mm), ulnae (50.3 mm), scapholunare, pisiforms, carpometacarpi (mc I 5 mm, mc II 21 mm, mc III 21 mm), phalanges I-1 (10.8 mm), manual unguals I (6.1 mm), phalanges II-1 (12.5 mm), phalanges II-2 (12.3 mm), manual unguals II (5 mm), phalanges III-1 (6 mm), ilia (23.5 mm), pubes (~42.2 mm), ischium (~20.5 mm), femora (41 mm), tibiotarsi (52.8 mm), fibula (~15 mm), metatarsal I (4 mm), phalanges I-1 (7.8 mm), pedal unguals I (5 mm), tarsometatarsi (27.30 mm), phalanges II-1 (11.3 mm), phalanges II-2 (9.4 mm), pedal unguals II (6 mm), phalanges III-1 (11.5 mm), phalanges III-2 (8.7 mm), phalanges III-3 (8.3 mm), pedal unguals III (6 mm), phalanges IV-1 (7 mm), phalanges IV-2 (5.8 mm), phalanges IV-3 (5.6 mm), phalanges IV-4 (6.2 mm), pedal unguals IV (5 mm), body feathers, eleven remiges (to 67 mm), eight retrices (~75-~92 mm)
Diagnosis- (after Zhou and Zhang, 2001) snout anterior to frontal margin of orbit 41% of skull length; metacarpal III 32% the width of metacarpal II (unknown in Songlingornis); pubic symphysis ~16% the length of pubis (unknown in Songlingornis); ratio of pedal digit III to tarsometatarsus length 128% (unknown in Songlingornis).
Other diagnoses- Zhou and Zhang (2001) included a few other characters in their diagnosis. The short snout was expressed as a ratio of skull length to width (stated to be 150%, but in actuality 175% as preserved). However, the width is exaggerated by crushing the mandibles and jugals laterally, and the true ratio based on the postorbital processes is 235%. This makes it probably comparable to Hongshanornis, and Songlingornis is probably also short-snouted based on its dentary proportions, though difficult to quantify thanks to a lack of posterior skull material and good illustration. Clarke et al. (2006) use another measure of this feature, namely dentary length, which they state is shorter than in Songlingornis. One measure which can be compared in both Yixianornis and Hongshanornis is length anterior to the frontal margin of the orbit, which is shorter in Yixianornis (41% vs. 51%). It could be assumed Songlingornis' apparently longer dentary indicates it had a larger ratio. "Postcranial long bones slender" is unspecific and unquantified, but seems to be even more true of Hongshanornis and Gansus. Most euornithines have protruding elliptical humeral heads. While Zhou and Zhang use a pubic symphysis length of 20% pubic length in their diagnosis, their measurement table indicates a ratio of 26%, and Clarke et al.'s measurements indicate a smaller ratio of 16% (based on a pubis estimated to be 7 mm longer). While the proximal pubis is hidden by the femur, I find Clarke et al.'s estimate more likely based on the general length of basal bird pubic peduncles. The femoro-tarsometatarsal ratio (stated to be 160%, but actually 152%) is overlapped by Yanornis (149-170%).
Clarke et al. state the xiphoid process (just posterior to the costal margin) of the sternum has a greater extent along the sternal margin than in Yanornis or Songlingornis, but that of Hongshanornis and Gansus are longer (Songlingornis' seems to be also, at least in Hou's illustration). They also stated the interclavicular angle was longer than in Yanornis or Songlingornis, but this is also true in Hongshanornis, Archaeorhynchus and Gansus.
Comments- The holotype is misidentified as IVPP V13631 in Clarke et al.'s (2006) redescription. Their measurement of 12.5 mm for pedal phalanx IV-1 is also in error.
References- Zhou and Zhang, 2001. [Two new genera of ornithurine birds from the Early Cretaceous of Liaoxi involved in the origin of modern birds.] Kexue Tongbao. 46(5), 371-377.
Zhou and Zhang, 2001. Two new ornithurine birds from the Early Cretaceous of western Liaoning, China. Chinese Science Bulletin. 46(1), 1-7.
Clarke, Zhou and Zhang, 2002. An ornithurine from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(3), 45A.
Clarke, Zhou and Zhang, 2006. Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui. Journal of Anatomy. 208, 287-308.
Wang, O'Connor, Pan and Zhou, 2017. A bizarre Early Cretaceous enantiornithine bird with unique crural feathers and an ornithuromorph plough-shaped pygostyle. Nature Communications. 8:14141.
Bailleul, Li, O'Connor and Zhou, 2019. Origin of the avian predentary and evidence of a unique form of cranial kinesis in Cretaceous ornithuromorphs. Proceedings of the National Academy of Sciences. 116(49), 24696-24706.

Songlingornis Hou, 1997
S. linghensis Hou, 1997
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V10913) (~190 mm) premaxilla, maxilla, nasals, quadrate, mandibles (25.5 mm), cervical vertebrae, several dorsal vertebrae, two dorsal ribs (31 mm), two dorsal rib fragments, scapula, coracoids (22.5 mm), furcula, sternum (35 mm), proximal radius, distal ulnae, carpometacarpus (25 mm), proximal femur, partial tarsometatarsus?
Diagnosis- (after Hou, 1997) dorsal edge of scapula almost straight.
(after Clarke et al., 2006) width of distal expansion of posterolateral sternal process 28% of sternal length.
Other diagnoses- Hou (1997) included numerous characters in his diagnosis, but many are vague (mandible slender and elongate; ribs slender and elongate; well developed coracoid head; relatively well developed carpometacarpus; well developed femoral head) or primitive (dorsal vertebrae not heterocoelous; concave coracoid facet for scapula; procoracoid process present; supracoracoid foramen present; distal fossa on posterior coracoid; hypocleidium absent; elongate and broad sternum; deep coracoid grooves on sternum; distinct sternal carina). Others are found in other songlingornithids (teeth closely packed; more than nine dentary teeth; large anterolateral sternal process; well developed xiphoid sternal process; posterolateral sternal process with expanded tip; posterolateral sternal process extends posteriorly far beyond posteromedian process; posteromedial sternal process joins distally to posteromedian process forming fenestra).While Hou says the sternal rostrum ("manubrium") is well developed in the diagnosis, he later states it is damaged and cannot be described.
Zhou and Hou (2002) diagnose Chaoyangia partly using characters from Songlingornis. Most of the characters are repeated from Hou's earlier Songlingornis diagnosis. The remainder are plesiomorphic (premaxillary and dentary teeth present; U-shaped furcula; sternal keel extends along full length of sternum; short posterolateral sternal process).
Comments- This specimen was collected in 1992 and mentioned by Zhou (1995) as being probably referrable to Chaoyangia. Hou et al. (1995) say it is at least referrable to Euornithes (their Ornithurae), and later (1996) refer it to Chaoyangia due to the similar size and rarity of euornithine birds in the deposits. Hou (1997) described it as the new taxon Songlingornis linghensis, while Zhou and Hou (2002) referred it to Chaoyangia but did indicate it had also been used as the holotype of Songlingornis. The holotypes of both specimens preserve few elements in common (though not none, as claimed by Clarke and Norell, 2001)- several dorsal vertebrae, dorsal ribs and proximal femur. The dorsals are alike in being non-heterocoelous, but this is similar to all non-hesperornithine, non-avian birds. Both femora are described as having proximally projecting trochanteric crests, shallow trochanteric fossae and large heads. These features are comparable to many basal birds including Confuciusornis and Vorona. The only point of difference in their descriptions in that Chaoyangia is said to have a "basically absent" neck, while Songlingornis has a "relatively well developed neck." Yet Chaoyangia's proximal femur has a near identical shape to Patagopteryx's, which has a neck, and Songlingornis' illustration is too schematic for proper comparison. Thus the taxa cannot be distinguished, but also share no synapomorphies that would allow them to be synonymized.
Songlingornis was originally described as a basal euornithine (Ornithurae of Hou) by Hou (1997), placed on his phylogram more derived than Liaoningornis but less than Gansus and Ornithurae sensu Chiappe. Clarke (2002) was the first author to include the taxon in a cladistic analysis, finding it to be a carinate in an unresolved polytomy with Ichthyornis and more derived birds. More recently, Clarke et al. included Yanornis and Yixianornis in their matrix and found Songlingornis to clade with these taxa in a group more derived than Patagopteryx, but less than Apsaravis and Ornithurae. This was first announced at their SVP 2002 talk, but only published in 2006.
References- Hou, Zhou, Gu and Sun, 1995. Introduction to Mesozoic birds from Liaoning, China. Vertebrata PalAsiatica. 33(4), 261-271.
Zhou, 1995. New understanding of the evolution of the limb and girdle elements in early birds - evidences from Chinese fossils. In Sun and Wang (eds.). Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota. Short papers, 209-214.
Hou, Martin, Zhou and Feduccia, 1996. Early adaptive radiation of birds: evidence from fossils from northeastern China. Science. 274, 1164-1167.
Hou, 1997. Mesozoic birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou. 228 pp.
Clarke and Norell, 2001. Fossils and avian evolution. Nature. 414, 508.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, Zhou and Zhang, 2002. An ornithurine from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(3), 45A.
Zhou and Hou, 2002. The Discovery and Study of Mesozoic Birds in China. in Chiappe and Witmer, (eds.). Mesozoic Birds- Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London. 160-183.
Clarke, Zhou and Zhang, 2006. Insight into the evolution of avian flight from a new clade of Early Cretaceous ornithurines from China and the morphology of Yixianornis grabaui. Journal of Anatomy. 208, 287-308.

Ambiortiformes Kurochkin, 1982
Definition- (Ambiortus dementjevi <- Passer domesticus) (Martyniuk, 2012)
= Ambiortidae Kurochkin, 1982
= Gansuiformes Hou and Liu, 1984
Definition- (Gansus yumenensis <- Passer domesticus, Hesperornis regalis, Ichthyornis anceps, Enantiornis leali) (Martyniuk, 2012)
= Gansuidae Hou and Liu, 1984
= Gansuiornithiformes Zhou and Zhang, 2006
= "Gansuiornithidae" Zhou and Zhang, 2006
= Ambiortes Zelenkov in Zelenkov and Kurochkin, 2015
Comments- Kurochkin (1982) established the monotypic Ambiortiformes and Ambiortidae, but later (1999) assigned Otogornis to the Ambiortiformes as well, and even later (2000) to the Ambiortidae. This was based on several problematic characters. The acrocoracoid of Otogornis is not noticably thicker than Enantiornis, which also shares the "three edged" morphology. The proximal tip of Otogornis' acrocoracoid is not necessarily acute (compare medial view of left coracoid to other figures). The glenoid on the scapula is no wider in Ambiortus than Enantiornis and appears concave in Hou's original illustration, but is flat in some enantiornithines (e.g. Gobipteryx) anyway. Otogornis' humeral head is no more ventrally placed than Sinornis', and is not smaller or shorter. Nor is it oval, having a proximally concave margin as in enantiornithines. Finally, the long and thin manual phalanx II-2 is symplesiomorphic, being found in most basal birds. Otogornis seems to be an enantiornithine instead. Martyniuk (2012) later defined the clade. Ambiortes was created by Zelenkov in a book chapter by Zelenkov and Kurochkin (2015) to only include Ambiortiformes.
Zhou and Zhang (2006) listed Gansuiornithiformes and "Gansuiornithidae", which are incorrectly formed as there is no genus "Gansuiornis". Furthermore, "Gansuiornithidae" is a nomen nudum since it was not defined or diagnosed (ICZN Article 13.1.1).
References- Kurochkin, 1982. Novyy otryad ptits iz nizhnego mela Mongolii. Doklandy Akademii Nauk SSSR. 262(2), 452-455.
Hou and Liu, 1984. A new fossil bird from Lower Cretaceous of Gansu and early evolution of birds. Scientia Sinica. 27, 1296-1302.
Kurochkin, 1999. The relationships of the Early Cretaceous Ambiortus and Otogornis (Aves: Ambiortiformes). in Olson (ed). Avian Paleontology at the Close of the 20th Century: Proceedings of the 4th International Meeting of the Society of Avian Paleontology and Evolution. Smithsonian Contributions to Paleobiology. 89, 275-284.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Zelenkov and Kurochkin, 2015. Class Aves. In Kurochkin, Lopatin and Zelenkov (eds.). Fossil vertebrates of Russia and adjacent countries. Part 3. Fossil Reptiles and Birds. GEOS. 86-290.

Yumenornis Wang, O'Connor, Li and You, 2013
Y. huangi Wang, O'Connor, Li and You, 2013
Late Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Holotype- (GSGM-06-CM-013) scapula, coracoid, partial furcula, partial sternum, sternal ribs, humerus (49.9 mm), radius (49.7 mm), ulna (52.9 mm), pisiform, carpometacarpus (27 mm), phalanx I-1 (10.9 mm), manual ungual I (5.4 mm), phalanx II-1 (12.1 mm), phalanx II-2 (11.5 mm), manual ungual II (4.2 mm), phalanx III-1 (6.7 mm)
Diagnosis- (after Wang et al., 2013) sternum with angular rostral margin (~90°), lateral (zyphoid) processes, and robust, distally expanded lateral trabeculae; radius with deep distal fossa; ratio of length of manus relative to humerus 1.1.
Comments- Wang et al. (2013b) entered this into O'Connor's matrix and found it to be a basal euornithine in large polytomy with taxa less derived than Ichthyornis but more derived than Patagopteryx. The flexor tuber on manual phalanx III-1 suggests Yumenornis is as close to Aves as Iteravis.
References- Wang, O'Connor, Li and You, 2013a. A new ornithuromorph bird from the Early Cretaceous Changma Basin of Gansu Province, Northwestern China. Journal of Vertebrate Paleontology. Program and Abstracts 2013, 234-235.
Wang, O'Connor, Li and You, 2013b. Previously unrecognized ornithuromorph bird diversity in the Early Cretaceous Changma Basin, Gansu Province, Northwestern China. PLoS ONE. 8(10), e77693.

Juehuaornis Wang, Wang and Hu, 2015
?= Changzuiornis Huang, Wang, Hu, Liu, Peteya and Clarke, 2016
= Dingavis O'Connor, Wang and Hu, 2016
J. zhangi Wang, Wang and Hu, 2015
?= Changzuiornis ahgmi Huang, Wang, Hu, Liu, Peteya and Clarke, 2016
= Dingavis longimaxilla O'Connor, Wang and Hu, 2016
Early Albian, Early Cretaceous
Sihedang, Jiufotang Formation, Liaoning, China
Holotype- (SJG 00001) skull (63.3 mm), mandible, cervical vertebrae, cervical ribs, about nine dorsal vertebrae, dorsal ribs, synsacrum, caudal vertebrae, pygostyle, scapulae (41 mm), coracoid, furcula, sternum, humeri (46.7, 45.5 mm), radii, ulnae (55.5 mm), scapholunare, carpometacarpi (31.1 mm), phalanx I-1 (11 mm), manual ungual I (3.4 mm), phalanges II-1 (15.5 mm), phalanges II-2 (12.2 mm), manual unguals II, phalanges III-1 (6.8 mm), phalanx III-2, ilium, pubes (~38.9 mm), ischium, femur (~33.3 mm), tibiotarsi (55.6 mm), fibula, metatarsal I, phalanges I-1, pedal ungual I, tarsometarsi (38.7 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, body feathers, remiges
Referred- (AGB5840; holotype of Changzuiornis ahgmi) (adult) skull (65 mm), scleral ring, mandibles, hyoids, basihyal, eleven or twelve cervical vertebrae (~7.1 mm) with fused ribs, about ten dorsal vertebrae, few dorsal ribs, gastralia, sacrum (~33 mm), several caudal vertebrae, pygostyle (9.1 mm), scapula (46.4 mm), coracoid (23.8 mm), furcula, humeri (50.4, 50.1 mm), radii (50.6, 48.6 mm), ulnae (52, 53.6 mm), scapholunares, pisiforms, carpometacarpi (30.1, 31.3 mm; mcI 5.4, 5.1 mm), phalanx I-1 (11.7 mm), manual ungual I (5.4 mm), phalanges II-1 (12.9, 11.6 mm), phalanges II-2 (14.4, 12.6 mm), partial manual ungual II (3.6 mm), fragmentary ilium (30.4 mm), pubes (34.3 mm), ischium (38.4 mm), incomplete femur (29.4 mm), tibiotarsi (53.7, 54 mm excluding cnemial crest), phalanx I-1 (7.2 mm), pedal ungual I, tarsometatarsi (36, 36.1 mm), phalanges II-1 (9.5, 8.7 mm), phalanges II-2 (one proximal; 10.7, 9.9 mm), pedal ungual II, phalanges III-1 (8.9, 7.1 mm), phalanges III-2 (8.4, 6.8 mm), phalanges III-3 (~5.9, 6.3 mm), pedal ungual III, phalanges IV-1 (7.7, 7.4 mm), phalanges IV-2 (7.2, 7.1 mm), phalanges IV-3 (5.4, 6 mm), phalanges IV-4 (5.4, 6.5 mm), pedal unguals IV, body feathers, remiges, ~five gastroliths (~30 mm) (Wang et al., 2015b; described by Huang et al., 2016)
(IVPP V20284; holotype of Dingavis longimaxilla) (adult) skull (58.6 mm), mandible, eight cervical vertebrae, dorsal fragments, partial dorsal ribs, gastralia, synsacrum (28.2 mm), four caudal vertebrae, pygostyle (7.8 mm), scapulae (38.4 mm), proximal coracoid, fragmentary sternum, humeri (48.9, ~51 mm), radii, ulnae (~44.9, ~52 mm), scapholunare, proximal carpal, carpometacarpi (30.4, 29.9 mm; mcI 4.1 mm), phalanges I-1 (12.4, 12.5 mm), manual unguals I (4.9, 5 mm), phalanges II-1 (14, 13.2 mm), phalanges II-2 (13.2, 13.2 mm), manual unguals II (3.9, 4 mm), phalanges III-1 (6.6, 7.9 mm), ilia, pubes (42.7 mm), ischia, femora (one partial; 36.1 mm) tibiotarsi (55.6, 55.4 mm), fibula, metatarsals I, phalanges I-1, pedal unguals I, tarsometatarsi (37.9, 40.6 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanges IV-4, pedal unguals IV, ~40 gastroliths (O'Connor, Wang and Hu, 2016)
Diagnosis- (after Wang et al., 2015a) anterior of mandible straight; teeth only present in maxilla and dentary.
(after O'Connor et al., 2016; for Dingavis) rostrum forms 63-65% of skull length; jugal process of lacrimal posterolaterally excavated; length of carpometacarpus + major digit exceeds humeral length by 25% (118-126% in Dingavis' type, ~135% in Juehuaornis' type, 118-~121% in Changzuiornis' type); short metacarpal I (13.7% of metacarpal II) (12-14% in Dingavis' type, ~14% in Juehuaornis' type, 16-18% in Changzuiornis' type); tarsometatarsus with small but sharp medial and lateral plantar crests, plantar surface of metatarsus not excavated; metatarsal II much shorter than metatarsal IV; metatarsal II and IV trochlea plantarly displaced; metatarsal II trochlea strongly angled craniomedially.
Other diagnoses- Wang et al. (2015a) listed a longer snout length (~70%) as diagnostic of Juehuaornis. They claim the premaxilla is hooked, but this isn't apparent from the photo. The Dingavis holotype has a disarticulated predentary which resembles a frigatebird-style hook at first glance, so this provides a possible explanation for the Juehuaornis holotype. Wang et al. also list forelimb and hindlimb similar in length as diagnostic, which is 104% in Juehuaornis and a similar 96-101% in Dingavis' type. However, Changzuiornis' type has a longer forelimb (111-112%).
O'Connor et al. (2016) claimed Dingavis lacks teeth, but the material is very poorly preserved, so that small teeth may not be visible (as in the Hongshanornis type).
Huang et al. (2016) distinguished Changzuiornis and Juehuaornis from Dingavis by their longer skulls (221% and 190% of femoral length vs. 162%), but these form a gradation that matches specimen size. Similarly, they distinguished Changzuiornis by its longer scapula (158% of femoral length vs. 123% in Juehuaornis and 101-107% in Dingavis), but this also matches specimen size. One difference noted by Huang et al. that doesn't match specimen size is the ratio between manual phalanges II-1 and II-2, which is 109-112% in Changzuiornis, but 79% in Juehuaornis and 94-100% in Dingavis.
Comments- While O'Connor et al. (2016) assigned Dingavis to the Yixian Formation, it was found in Sihedang, which is here viewed as belonging to the Jiufotang Formation (see Iteravis entry). Chen (DML 2016) proposed Dingavis is a junior synonym of Juehuaornis. As he noted, they have very similar proportions and each has the others' diagnostic characters when known, with the exceptions of the supposed hooked bill of Juehuaornis, and toothlessness of Dingavis as described above under 'Other diagnoses'. The only other significant difference observed by Chen is that Dingavis supposedly lacks manual phalanx III-2, but as he says, this is very small in Juehuaornis and so easily lost in the poorly preserved Dingavis holotype. Wang et al. (2015b) first noted another Jiufotang longirostrine euornithine which was formally described by Huang et al. (2016) as Changzuiornis. Huang et al. considered the possibility their new taxon was synonymous with the other Sihedang longirostrine birds, stating "while if new data shows that Xinghaiornis, Juehuaornis and Dingavis form a clade that constitutes the same genus, the genus name Juehuaornis would have priority for Dingavis longimaxilla and Changzuiornis ahgmi." The few differences listed are all proportional, and it's notable almost all proportional differences between the three holotypes covary with size, with the generally intermediate-sized Juehuaornis the usual intermediary proportion-wise too. This suggests the possibility of a growth series, which is provisionally accepted here.
The holotype of Juehuaornis was briefly described in Chinese and only illustrated as low resolution photos of part and counterpart. It has yet to be included in a phylogenetic analysis, but was classified by Wang et al. (2015a) as an ornuthuromorph. O'Connor et al. recovered Dingavis as more derived than Archaeorhynchus but less than hongshanornithids and songlingornithids plus avians using O'Connor's matrix. Huang et al. (2016) recovered Changzuiornis as more derived than hongshanornithids and songlingornithids, but less than Iteravis, Gansus and taxa closer to Aves, using a version of Clarke's matrix.
References- Wang, Clarke and Huang, 2015b. Ornithurine bird from the Early Cretaceous of China provide new evidence for the timing and pattern of the evolution of avian skull. Journal of Vertebrate Paleontology. Program and Abstracts 2015, 233.
Wang, Wang and Hu, 2015a. Discovery of a new ornithuromorph genus, Juehuaornis gen. nov. from Lower Cretaceous of western Liaoning, China. Global Geology. 34(1), 7-11.
Chen, DML 2016. https://web.archive.org/web/20160901192554/http://dml.cmnh.org/2016Jan/msg00050.html
Huang, Wang, Hu, Liu, Peteya and Clarke, 2016. A new ornithurine from the Early Cretaceous of China sheds light on the evolution of early ecological and cranial diversity in birds. PeerJ. 4:e1765.
O'Connor, Wang and Hu, 2016. A new ornithuromorph (Aves) with an elongate rostrum from the Jehol Biota, and the early evolution of rostralization in birds. Journal of Systematic Palaeontology. 14(11), 939-948.

Iteravis Zhou, O'Connor and Wang, 2014
I. zheni (Liu, Chiappe, Zhang, Bell, Meng, Ji and Wang, 2014) new combination
= Gansus zheni Liu, Chiappe, Zhang, Bell, Meng, Ji and Wang, 2014
= Iteravis huchzermeyeri Zhou, O'Connor and Wang, 2014
Early Albian, Early Cretaceous
Sihedang, Jiufotang Formation, Liaoning, China
Holotype- (BMNHC Ph 1342) (adult) skull (53.3 mm), mandibles, hyoid, eleven cervical vertebrae, few dorsal vertebrae, several dorsal ribs, gastralia, incomplete sacrum, few caudal vertebrae, pygostyle, scapulae (40.4 mm), coracoids (20.7, 20.7 mm), furcula, sternum, sternal ribs, humeri (54.6, 53.4 mm), radii (54.9, 54.3 mm), ulnae (56.1, 55.1 mm), scapholunares, pisiforms, carpometacarpi (27.1, 25.6 mm), phalanges I-1 (~11 mm), manual unguals I (~6 mm), phalanges II-1 (~10, ~12 mm), phalanges II-2 (~12, ~13 mm), partial manual ungual II, phalanges III-1 (~6, ~8 mm), ilia, pubes, ischia, femora (36.4 mm), tibiotarsi (64.4, 66.1 mm), proximal fibulae, metatarsals I, phalanges I-1 (8.4, 8.2 mm), pedal unguals I (3.9, 4.2 mm), tarsometatarsi (37.9, 38.1 mm), phalanges II-1 (15, 14.9 mm), phalanges II-2 (13.5, 14.4 mm), pedal unguals II (4.6, 5.1 mm), phalanges III-1 (15.5, 14.3 mm), phalanges III-2 (11, 11 mm), phalanges III-3 (10.2, 9.1 mm), pedal unguals III (4.1, 4.8 mm), phalanges IV-1, (10.6, 11 mm), phalanges IV-2 (9.1, 8.7 mm), phalanges IV-3 (8.5, 8.5 mm), phalanges IV-4 (8.2, 8.3 mm), pedal unguals IV (3.5, 3.5 mm), remiges, body feathers, gastroliths
Paratypes- (BMNHC Ph 1318) (adult) skull (45.4 mm), mandibles, hyoid, ten cervical vertebrae, few dorsal vertebrae, several dorsal ribs, incomplete sacrum, scapular fragments, coracoids (one incomplete; 22.9, 21.2 mm), furcula, incomplete sternum, sternal ribs, incomplete humeri (53.6, 52.3 mm), radii (one partial; 50.2 mm), ulnae (one partial; 54.1 mm), fragmented proximal carpals, partial carpometacarpi (21.6 mm), phalanges I-1, manual ungual I, phalanges II-1, phalanges II-2, manual ungual II, phalanges III-1, partial ilia, pubes, ischium, incomplete femora (34.5, 34.6 mm), tibiotarsi (63.8, 65.4 mm), fibulae, metatarsi I, phalanges I-1 (7.7, 7.5 mm), pedal unguals I (4.1, 4.6 mm), tarsometatarsi (36.9, 36.5 mm), phalanges II-1 (13.7, 12.9 mm), phalanges II-2 (12, 12.7 mm), pedal unguals II (4.6, 4.5 mm), phalanges III-1 (13.5, 13.8 mm), phalanges III-2 (10.4, 10.4 mm), phalanges III-3 (8.8, 8.7 mm), pedal unguals III (4.7, 4.2 mm), phalanges IV-1 (10.4, 9.8 mm), phalanges IV-2 (8.5, 8.3 mm), phalanges IV-3 (8, 8.3 mm), phalanges IV-4 (7.9, 7.1 mm), pedal unguals IV (3.7, 3.9 mm), remiges, gastroliths (Liu et al., 2014)
(BMNHC Ph 1394) complete specimen including sternum and gastroliths (Liu et al., 2014)
Referred- (IVPP V18958; holotype of Iteravis huchzermeyeri) (old subadult) skull (46 mm), sclerotic plates, mandibles, hyoid, ten cervical vertebrae fused with ribs, nine dorsal vertebrae, dorsal ribs, uncinate process, gastralia, synsacrum, five or six caudal vertebrae, chevrons, pygostyle (6.93 mm), scapulae (one incomplete; 35 mm), coracoids (21 mm), furcula, incomplete sternum, three sternal ribs, humeri (52 mm), radii, ulnae (53 mm), scapholunare, pisiform, carpometacarpi (mcI 4, mcII 22, mcIII 18 mm), phalanges I-1 (9.5 mm), manual ungual I (4 mm), phalanges II-1 (11.5 mm), phalanges II-2 (11 mm), manual ungual II (3 mm), phalanx III-1 (6 mm), fused pelves (pubis 41 mm), femora (35 mm), tibiotarsi (59 mm), fibula, metatarsals I, phalanx I-1 (8 mm), pedal ungual I (3 mm), tarsometatarsi (31.50 mm), phalanges II-1, phalanges II-2 (11.5 mm), pedal unguals II (4.5 mm), phalanges III-1 (12 mm), phalanges III-2 (10 mm), phalanges III-3 (8 mm), pedal ungual III (4 mm), phalanges IV-1 (10 mm), phalanges IV-2 (8 mm), phalanges IV-3 (8 mm), phalanges IV-4 (7 mm), pedal unguals IV (3.5 mm), bulbi retricium, skin, remiges, retrices, body feathers, six gastroliths (4-5 mm) (Zhou, O'Connor and Wang, 2014)
most of twenty specimens including tarsometatarsi (32-36 mm) (Zhou, O'Connor and Wang, 2014)
Diagnosis- (after Zhou et al., 2014) ischium with concave ventral margin and weak mid dorsal process (also in Piscivoravis, Yanornis and Gansus).
(modified after Liu et al., 2014) pedal digit IV subequal to 10% longer than III, excluding unguals (also in Schizooura and some Gansus); pedal unguals III and IV plesiomorphically lacking prominent pendant flexor tubercle of Gansus.
Other diagnoses- Zhou et al. (2014) listed a number of characters which are actually symplesiomorphic for Gansus-grade euornithines- elongate premaxilla; toothless premaxilla; rostrum 50% of skull length; ectethmoid bone lining anterior half of orbit; flexor tubercle on posterior margin of manual phalanx III-1; pubes with posteriorly expanded distal boot. They also listed "maxilla with numerous teeth", but only "several" teeth are claimed to be present and only a couple are visible, so this is plesiomorphic for euornithines too.
Liu et al. (2014) also diagnosed Gansus zheni using several characters compared to G. yumenensis which are problematic. The broader interclavicular angle (~45-~53 degrees, not 60 as Liu et al. state) is found in several other basal euornithines, and almost all basal euornithines have U-shaped furculae. Compared to Gansus yumenensis, zheni/Iteravis actually has a longer cnemial crest (8-15% of tibiotarsal length vs. 4%), a shorter manual digit II (excluding ungual, 86-102% of metacarpal II length vs. 81-83%; same ratio as several other basal euornithines), and overlapping pedal digit III / tarsometatarsal ratios (excluding ungual, 89-97% vs. 74-101%; same ratio as several other basal euornithines), contra Liu et al..
Comments- Zhou et al. (2014) believed the Sihedang locality which these specimens derive from to be in the Yixian Formation, whereas Liu et al. (2014) believed it to be in the overlying Jiufotang Formation. Zhou et al. cite undescribed turtles and a caudipterid as being found in the locality, though both are known from both formations (as Similicaudipteryx has been referred to Caudipteridae, though it is near certainly more basal). The pterosaurs Guidraco and Ikrandraco are also from Sihedang however, referred to the Jiufotang Formation in both descriptions. As Ikrandraco is also known from another Jiufotang locality (Lamadong), the Jiufotang Formation is favored here as the stratigraphic placement of Iteravis.
Zhou et al. (2014) found Iteravis to be more derived than hongshanornithids and songlingornithids, but outside hesperornithoids and Aves. Liu et al. (2014) found it to be sister to Gansus yumenensis, so they named it as a new species of that genus. The position used here, just basal to Gansus and more derived birds, is based on the partly corrected matrix of Liu et al. as described below and coincidentally matches the first most parsimonious tree found by Zhou et al. before they found more trees one step shorter.
Note the main skeletal figures in Liu et al. (2014; figures 1 and 2) have the specimen numbers switched, so figure 1 says its of BMNHC Ph 1342 but is actually of BMNHC Ph 1318, and the reverse is true of figure 2. Also, Zhou et al. claim they used the data matrix of O'Connor et al.'s 2011 redescription of Rapaxavis, but that paper has no phylogenetic analysis. It seems they actually used the matrix of O'Connor and Zelenkov's 2013 redescription of Ambiortus
Synonymization of Iteravis hutchzermeyeri and Gansis zheni- Mortimer (online, 2014) proposed these two species of basal euornithines from the same locality that were named within a month of each other are actually synonyms. Gansus zheni has all of Iteravis' diagnostic characters, including a toothless premaxilla and apparent maxillary alveoli that were not noticed by Liu et al. (2014). Similarly, Iteravis has all of Gansus zheni's supposed diagnostic characters as compared to Gansus yumenensis, excluding those which are actually absent in zheni (see above).
There are also several characters which differ in their descriptions. zheni is said to have a "small, rostrally tapered, and tear-shaped" external naris (mistakenly cited as the internal naris), but given the odd premaxillary shape in BMNHC Ph 1318, the premaxilla and maxilla are probably crushed in largely ventral view (note several possible alveoli in the maxilla and the deep bone under them which would be the palatal shelf), artificially shortening and tapering the anterior narial edge. Liu et al. state zheni's naris posteriorly overlaps the antorbital fenestra, which would barely be true in their interpretation, while the labeled nasal fragment in Iteravis suggests this isn't so in that taxon. However, the antorbital fenestral area in both specimens is a jumble of bone fragments and multicolored sediment reflecting the fragile nature of that region in birds and the separation of slabs which exposed it. Thus any edge of the fenestra is impossible to identify exactly. Liu et al. claim "Unlike other Jehol ornithuromorphs [including Iteravis] ... no pre-mandibular ossification is visible in any of the two studied specimens." This would be easily explainable by taphonomy as both skulls are rather poorly preserved and the element is small and loosely connected to the dentaries. Regardless, there are possible predentaries in each specimen- contacting the premaxillae just in front of the dentary in BMNHC Ph 1342 and attached to the left dentary tip projecting dorsally in BMNHC Ph 1318.
Liu et al. state zheni has "a broad ventral groove running along the entire exposed surface" of the synsacrum, while Zhou et al. state Iteravis has "a flat ventral surface". The latter seems true, but the 'groove' in zheni seems to be the taphonomic collapse of the hollow interior as seen in its tibiotarsi, humeri and ulnae. Zhou et al. states Iteravis lacks "the cranial hook present in Gansus", while it is clearly present in zheni's coracoids. Yet both coracoids are broken in this area in Iteravis, and the left shows a depression in the matrix which seems to indicate the hook's original presence. Liu et al. state zheni has a "prominent and triangular-shaped laterocranial process", which is absent in Iteravis. Yet this process is also absent in the illustrated zheni specimens BMNHC Ph 1318 and 1342. Liu et al. cites BMNHC Ph 1394 as having the process, but until this specimen is illustrated, it can be considered polymorphic at best to misinterpreted at worst. zheni is said to lack ossified uncinate processes, whereas Iteravis is reported to preserve "one probable uncinate process". All three specimens have ribcages which are only partly articulated and exposed though, so its easily possible uncinate processes are hidden if present in zheni, or that the one was misidentified in Iteravis. Liu et al. state zheni has a deltopectoral crest on the humerus "which extends more than one-third the total length of the bone", while Iteravis' is described as extending "the proximal one-third of the humerus", but the crest in the latter is almost entirely covered by other elements so cannot be measured. Iteravis' carpometacarpus is described as incompletely fused versus completely fused in zheni, but the specimen is slightly smaller than zheni specimens (humeri 97% of BMNHC Ph 1318, 95-97% of BMNHC Ph 1342) so could be expected to have less fusion. Liu et al. say zheni lacks an extensor process on metacarpal I, while Iteravis is said to have a small extensor process. Both taxa have the same morphology though, which is comparable to the extensor flange of basal paravians and not the extensor process of some euornithines.
The authors give very different lengths for Iteravis' and zheni's cnemial crests (10 vs. 25% of tibiotarsal length), though the real apparent values are 8% vs. 15%. The discrepancy largely seems due to zheni's tibiotarsi being preserved in anterior view, where the collapse of the element causes a median groove that exaggerates structures on either side such as the laterally placed cnemial crest. Iteravis' right tibiotarsus is in medial view, but the left element is partially covered by the sternum and has a taphonomic concavity that extends the apparent length of the cnemial crest. Iteravis' fibula is described as "just over half the length of the tibiotarsus", while zheni's is said to only extend "to nearly the midshaft of the tibia." In reality, all specimens have distal ends hidden by the tibiotarsus so cannot be exactly measured. Liu et al. state "the proximal phalanges of all pedal digits are longer than any of their respective distal phalanges" in zheni, while Zhou et al. say Iteravis has a slightly longer II-2 than II-1. Their own measurement table shows zheni is polymorphic for this though. Iteravis is reported to have a pedal digit IV shorter than III in contrast to zheni, but the ratio excluding unguals is 110% in Iteravis vs. 99-106% in zheni. So Iteravis actually has the longer digit IV, but there's more variation in zheni than difference between it and Iteravis.
Given the lack of difference between Iteravis and zheni, they are near certainly synonyms. Iteravis was published online October 29th vs. zheni on November 14th. Yet Zhou et al. didn't include a ZooBank registration. So the physical publication time is what counts, which is December 1. Thus zheni wins by 30 days.
Is zheni Gansus? Liu et al. referred zheni to Gansus based on several characters. Of these, the hooked omal projection on the coracoid's sternolateral process is polymorphic in Gansus yumenensis, and the intermembral index (humerus+ulna)/(femur+tibiotarsus) of 0.9-1.1 and pedal digit IV that is longer than digit III are polymorphic in zheni. The posteromedially curved posterolateral sternal process is more accurately understood as a distal expansion of the posterolateral process that is expanded medially but not much laterally. It is also present in Jiuquanornis, Hongshanornis, Jianchangornis, Yumenornis and Ambiortus. A metatarsal II which extends distally only as far as the base of IV's trochlea is a synapomorphy of birds more derived than songlingornithids. Proximal pedal phalanges which are longer than distal phalanges is true in almost every basal euornithine, with zheni and Gansus ironically being the only taxa with some discordant specimens (both in digit II). The supposed absence of a coracoid foramen is untrue in IVPP V18958, so the foramen may be hidden in the two BMNHC specimens or this may be polymorphic in zheni. An intermetacarpal space terminating distal to the distal end of metacarpal I is unreliable, as it varies with metacarpal I length as well as how the laminar metacarpal III is crushed in relation to metacarpal II. Some of these characters were miscoded by Liu et al., and changing these ten miscodings (with zheni conservatively coded as polymorphic for the coracoid foramen) led to zheni being basal to Gansus and birds closer to the crown. Checking which characters supported this, twenty-two additional miscodings were discovered. Correcting these left zheni in this position, supported only by its gastralia. Yet Gansus specimens may have taphonomically lost their gastralia (e.g. no crania are connected to any), so this isn't the greatest evidence. Enforcing zheni to be Gansus results in trees one step longer, so is basically as parsimonious. Thus neither position is well supported, and the new combination Iteravis zheni is used until good evidence for referring it to Gansus is presented.
References- Liu, Chiappe, Zhang, Bell, Meng, Ji and Wang, 2014. An advanced, new long-legged bird from the Early Cretaceous of the Jehol Group (northeastern China): Insights into the temporal divergence of modern birds. Zootaxa. 3884(3), 253-266.
Mortimer, online 2011. http://theropoddatabase.blogspot.com/2014/12/gansus-zheni-is-iteravis.html
Zhou, O'Connor and Wang, 2014. A new species from an ornithuromorph (Aves: Ornithothoraces) dominated locality of the Jehol Biota. Chinese Science Bulletin. 59(36), 5366-5378.
O'Connor, Wang, Zhou and Zhou, 2015. Osteohistology of the Lower Cretaceous Yixian Formation ornithuromorph (Aves) Iteravis huchzermeyeri. Palaeontologia Electronica. 18.2.35A, 1-11.
Bailleul, Li, O'Connor and Zhou, 2019. Origin of the avian predentary and evidence of a unique form of cranial kinesis in Cretaceous ornithuromorphs. Proceedings of the National Academy of Sciences. 116(49), 24696-24706.

Gansus Hou and Liu, 1984
G. yumenensis Hou and Liu, 1984
Late Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Holotype- (IVPP V6862) (~250 mm) distal tibiotarsus, phalanx I-1 (8.4 mm), pedal ungual I (4.1 mm), phalanx II-1 (10.1 mm), tarsometatarsus (31.6 mm), phalanx II-2 (11.5 mm), pedal ungual II (5 mm), phalanx III-1 (13 mm), phalanx III-2 (10.8 mm), phalanx III-3 (8 mm), pedal ungual III (5 mm), phalanx IV-1 (11.1 mm), phalanx IV-2 (8.6 mm), phalanx IV-3 (8.4 mm), phalanx IV-4 (7.5 mm), pedal ungual IV (4 mm)
Referred- ?(ANSP 23403) feather (Moyer et al., 2014)
(CAGS-IG-04-CM-001) tibiotarsi (one distal; 63.7 mm), fibula, metatarsal I, phalanges I-1 (8.1 mm), pedal unguals I, tarsometatarsi (36.3 mm), phalanges II-1 (13.9 mm), phalanges II-2 (11.9 mm), pedal unguals II (5.2 mm), phalanges III-1 (14.2 mm), phalanges III-2 (9.4 mm), phalanges III-3 (8.7 mm), pedal unguals III (4.8 mm), phalanges IV-1 (12 mm), phalanges IV-2 (9.7 mm), phalanges IV-3 (9.4 mm), phalanges IV-4 (~9.4 mm), pedal unguals IV (4.9 mm) (You et al., 2006)
(CAGS-IG-04-CM-002) three posterior cervical vertebrae, (dorsal series 37 mm) ten dorsal vertebrae, three dorsal ribs, synsacrum (26.6 mm), (caudal series 15.6 mm) six caudal vertebrae, pygostyle (5.9 mm), ilia (38.2 mm), pubes (~49.1 mm), ischia (23.7 mm), femora (30 mm), tibiotarsi (one incomplete; 65.8 mm), fibulae, phalanx I-1 (8.2 mm), pedal ungual I (4.2 mm), tarsometatarsus (You et al., 2006)
(CAGS-IG-04-CM-003) (160 g) few posterior cervical vertebrae, (dorsal series ~38 mm) ten dorsal vertebrae, dorsal ribs, synsacrum (26.9 mm), coracoids (21.7 mm), furcula, sternum (43.4 mm), sternal ribs, humeri (~48.4 mm), radii (one proximal), ulnae (one proximal; 52.8 mm), pisiform, carpometacarpus (25.2 mm), proximal phalanx I-1, phalanx II-1 (11 mm), phalanx II-2 (9.6 mm), phalanx III-1, ilia (34.6 mm), proximal pubes, proximal ischium, femur (31 mm), proximal tibiotarsus, proximal tarsometatarsus (You et al., 2006)
(CAGS-IG-04-CM-004) (160 g) three posterior cervical vertebrae, (dorsal series 33.3 mm) ten dorsal vertebrae, dorsal ribs, synsacrum (29.2 mm), scapulae (41.7 mm), coracoids (19.2 mm), furcula, anterior sternum, sternal ribs, humeri (48 mm), radii (46.8 mm), ulnae (48.8 mm), scapholunares, pisiform, carpometacarpi (23.4 mm), phalanges I-1 (9 mm), manual unguals I (3.6 mm), phalanges II-1 (9.8 mm), phalanges II-2 (9.1 mm), manual unguals II (3.4 mm), ilia (33.4 mm), proximal pubis, proximal ischium (You et al., 2006)
(CAGS-IG-04-CM-008) dorsal rib, distal femur, tibiotarsus (53.4 mm), metatarsals I (4.52, 4.4 mm), phalanges I-1 (8.2, 8.19 mm), pedal unguals I (3.51, 3.88 mm), tarsometatarsi (32.04, 31.55 mm), phalanges II-1 (13.74, 13.4 mm), phalanges II-2 (10.81, 11.19 mm), pedal unguals II (4.46, 3.94 mm), phalanges III-1 (13.82, 14.19 mm), phalanges III-2 (8.88, 9.01 mm), phalanges III-3 (7.73, 7.65 mm), pedal unguals III (4.46, 4.42 mm), phalanges IV-1 (11.23, 10.98 mm), phalanges IV-2 (8.34, 8.39 mm), phalanges IV-3 (7.42, 7.35 mm), phalanges IV-4 (7.29, 7.30 mm), pedal unguals IV (4.18, 4.56 mm), scales (You et al., 2006)
(CAGS-IG-04-CM-012) specimen including coracoid, furcula, sternum and humerus (O'Connor and Zelenkov, 2013)
(CAGS-IG-04-CM-018) tibiotarsus (61 mm), fibula (Wang et al., 2015)
(CAGS-IG-04-CM-031) partial tarsometatarsus (Wang et al., 2015)
(CAGS-IG-05-CM-014) dorsal ribs, humerus (47.8 mm), radii (one incomplete; 48.9 mm), ulnae (one incomplete; 51.1 mm), scapholunares, pisiform, carpometacarpi (23.7 mm), phalanx I-1 (9.6 mm), manual ungual I (~3.6 mm), phalanges II-1, phalanx II-2, manual ungual II (2.8 mm), phalanx III-1 (5.8 mm), femora (29.3 mm), tibiotarsi (63.7 mm), partial fibulae, metatarsals I, phalanges I-1 (7.3 mm), pedal unguals I (4.1 mm), tarsometatarsi (40 mm), phalanges II-1 (15.1 mm), phalanges II-2 (one partial; 12.9 mm), pedal unguals II (4.6 mm), phalanges III-1 (13.5 mm), phalanges III-2 (12.2 mm), phalanges III-3 (9 mm), pedal unguals III (4.6 mm), phalanges IV-1 (12 mm), phalanges IV-2 (9.7 mm), phalanges IV-3 (one partial; 8.7 mm), phalanx IV-4 (9.3 mm), pedal unguals IV (3.7 mm), feathers, gastroliths (Wang et al., 2015)
(CAGS-IG-06-CM-011) dorsal ribs, furcula, incomplete sternum, sternal ribs, gastroliths (Wang et al., 2015)
(CAGS-IG-07-CM-006) scapula, coracoid (~21.6 mm), incomplete humerus (49.7 mm), incomplete radius (52.8 mm), incomplete ulna (54.3 mm), scapholunare, pisiform, incomplete carpometacarpus, phalanx I-1, feathers (Wang et al., 2015)
(CAGS-IG-07-CM-009) eighth dorsal vertebra, ninth dorsal vertebra, tenth dorsal vertebra, dorsal rib, synsacrum, seven caudal vertebra, pygostyle, fused incomplete pelvis (ilium 37.9, ischium 24.2 mm), partial ilium (Wang et al., 2015)
(CAGS-IG-07-CM-011) several dorsal vertebrae, dorsal ribs, synsacrum, incomplete sternum, sternal ribs, ilium, pubes (47.7 mm), ischia (24.4 mm), femora (30.3 mm), tibiotarsi (61.5 mm), fibulae, metatarsals I, phalanges I-1 (8.3 mm), pedal unguals I (3.5 mm), tarsometatarsi (one incomplete; 37.9 mm), phalanges II-1 (12.5 mm), phalanges II-2 (12.4 mm), pedal unguals II (4.6 mm), phalanges III-1 (14.1 mm), phalanges III-2 (9.4 mm), phalanges III-3 (8.6 mm), pedal unguals III (3.1 mm), phalanges IV-1 (11 mm), phalanges IV-2 (8.9 mm), phalanges IV-3 (7.6 mm), phalanges IV-4 (8.6 mm), pedal unguals IV (3.4 mm), gastroliths (Wang et al., 2015)
(CAGS coll.) numerous specimens including about 60 partial to incomplete skeletons (Harris et al., 2009)
(IVPP V15074) distal tibiotarsus, pedal phalanx I-1 (~9.8 mm), tarsometatarsus (28 mm), phalanx II-1 (12.1 mm), phalanx II-2 (8.2 mm), pedal ungual II, phalanx III-1 (9.5 mm), phalanx III-2 (7.7 mm), phalanx III-3 (7 mm), phalanx IV-1, phalanx IV-2, phalanx IV-3, pedal ungual IV (Li et al., 2011)
(IVPP V15075) incomplete radius, ulnar fragment, scapholunare, pisiform, carpometacarpus, phalanx I-1, manual ungual I, incomplete phalanx II-1, phalanx II-2, manual ungual II (Li et al., 2011)
(IVPP V15076) incomplete furcula, sternum (39.1 mm), three sternal ribs, three partial sternal ribs (Li et al., 2011)
(IVPP V15077) distal femur, incomplete tibiotarsus, metatarsal I, pedal phalanx I-1 (7.4 mm), pedal ungual I, tarsometatarsus (38.9 mm), phalanx II-1 (14.3 mm), phalanx II-2 (13.3 mm), partial phalanx III-1, phalanx III-2, incomplete phalanx III-3, phalanx IV-1, phalanx IV-2, phalanx IV-3, incomplete phalanx IV-4, pedal scales (Li et al., 2011)
(IVPP V15079) scapular fragment, incomplete humerus, radius (50.4 mm), ulna (51.7 mm), scapholunare, carpometacarpus (mcII 24.3, mcIII 23.5 mm), phalanx I-1 (~8.3 mm), phalanx II-1 (10.3 mm), phalanx II-2 (9.9 mm), manual ungual II, phalanx III-1 (6.1 mm) (Li et al., 2011)
(IVPP V15080) femur (31.6 mm), tibiotarsus (56.2 mm), fibula, metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsus (30.1 mm), phalanx II-1 (13.8 mm), phalanx II-2 (12.3 mm), pedal ungual II, incomplete phalanx III-1, phalanx IV-1, partial phalanx IV-2 (Li et al., 2011)
(IVPP V15081) partial radius, partial ulna, scapholunare, pisiform, carpometacarpus (mcI 5.3, mcII 28.6, mcIII 26.9 mm), phalanx I-1 (12 mm), manual ungual I, phalanx II-1 (12.7 mm), phalanx II-2 (11.1 mm), manual ungual II, phalanx III-1 (Li et al., 2011)
(IVPP V15083) metatarsal I, pedal phalanx I-1 (6.6 mm), pedal ungual I, tarsometatarsus (29.1 mm), phalanx II-1 (11.5 mm), phalanx II-2 (10 mm), pedal ungual II, phalanx III-1 (12.2 mm), phalanx III-2 (8 mm), phalanx III-3 (6.2 mm), pedal ungual III, phalanx IV-1 (10.2 mm), phalanx IV-2 (7.9 mm), phalanx IV-3 (6.9 mm), phalanx IV-4 (7.1 mm), pedal ungual IV, skin impressions (Li et al., 2011)
(IVPP V15084) femur (~31.6 mm), tibiotarsus (42.2 mm), fibula, metatarsal I, phalanx I-1 (7.9 mm), pedal ungual I, tarsometatarsus (36.7 mm), phalanx II-1 (9.7 mm), phalanx II-2 (9.8 mm), pedal ungual II, phalanx III-1 (11.7 mm), phalanx III-2 (8.5 mm), phalanx III-3 (6.8 mm), pedal ungual III, phalanx IV-1 (9 mm), phalanx IV-2 (5.6 mm), phalanx IV-3 (5.2 mm), phalanx IV-4 (4.7 mm), pedal ungual IV (Li et al., 2011)
?(IVPP V26199) skull (37.56 mm), sclerotic ossicles, mandibles (31.46 mm), urohyal, hyoids (19.93 mm), atlas, axis, third cervical vertebra, feathers (O'Connor et al., 2021)
? two feathers (Barden et al., 2011)
Diagnosis- (after Wang et al., 2015) pygostyle narrow throughout length with dorsal spinous ridge; sternum with well-developed anteroolateral and postcostal processes; posterolateral sternal processes curved medially; sternum with pair of posterior fenestrae; coracoid with anteriorly hooked lateral process; tibiotarsus long, with two strongly proximally projected cnemial crests; position of metatarsal II trochlea high and plantarly displaced relative to metatarsal III trochlea; pedal digit IV longest; pedal unguals with pointed flexor tubercles.
Comments- The holotype was discovered in 1981 and described by Hou and Liu (1984), who believed birds were divided into land and water clades, with Archaeopteryx ancestral to the former and Gansus ancestral to the latter (except hesperornithines). Hou (1997) placed it sister to Ornithurae in his phylogram, and redescribed the taxon. Hope (2002) believed the specimen to be an ornithurine, but not an avian. Clarke (2002) coded the holotype for her matrix, finding it to be a carinate more derived than Ichthyornis, but less than Iaceornis and Aves. She noted the specimen was poorly preserved and "glued into the slab after being removed and repaired, obscuring almost all morphologies." You et al. (2005) coded the specimen for Chiappe's matrix and found it to be a euornithine outside Ornithurae. You et al. (2006) describe several additional far more complete specimens of this genus, which they place as an ornithurine sister to Carinatae. Ji et al. (2006) later described one of the new specimens (CAGS-IG-04-CM-008) in detail, noting it preserves webbed feet. Bailleul et al. (2019) figured mandibles in their supplementary information as an unpublished specimen of Gansus, but these were later described by O'Connor et al. (2021, 2022) as a new taxon Brevidentavis (originally "Brachydontornis"). Harris et al. (2009) give preliminary data on more new specimens which include cranial elements, but these ended up being described as Meemannavis (IVPP V26198) and Euornithes indet. (IVPP V26194-26196) by O'Connor et al.. The latter three specimens belong to at least two taxa (with IVPP V26196 being distinct in cervical proportions), but which of these (if either) are Gansus is unknown due to a lack of comparable material. However, O'Connor et al. did describe another skull discovered in 2004 or 2005 with anterior cervicals (IVPP V26199) that they referred to Gansus based on similarity to Iteravis.
References- Hou and Liu, 1984. A new fossil bird from Lower Cretaceous of Gansu and early evolution of birds. Scientia Sinica. 27, 1296-1302.
Hou, 1997. Mesozoic birds of China. Taiwan Provincial Feng Huang Ku Bird Park. Taiwan: Nan Tou. 228 pp.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Zhou and Hou, 2002. The discovery and study of Mesozoic birds in China. in Chiappe and Witmer, (eds.). Mesozoic Birds- Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London. 160-183.
You, O'Connor, Chiappe and Ji, 2005. A new fossil bird from the Early Cretaceous of Gansu Province, northwestern China. Historical Biology. 17, 7-14.
Harris, You and Lamanna, 2006. New specimens of the ornithuran bird Gansus yumenensis from the Xiagou Formation (Lower Cretaceous) of Gansu province, China. Journal of Vertebrate Paleontology. 26(3), 72A.
Ji, Ji, You, Lu and Yuan, 2006. Webbed foot of an Early Cretaceous ornithurine bird Gansus from China. Geological Bulletin of China. 25(11), 1295-1298.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.
Harris, Lamanna, Li and You, 2009. Avian cranial material and cranial cervical vertebrae from the Lower Cretaceous Xiagou Formation of Gansu Province, China. Journal of Vertebrate Paleontology. 29(3), 111A.
Barden, Wogelius, Edwards, Manning and van Dongen, 2011. Preservation in the feathers of the Early Cretaceous bird Gansus yumenensis. Journal of Vertebrate Paleontology. Program and Abstracts 2011, 66.
Li, Zhang, Zhou, Li, Liu and Wang, 2011. New material of Gansus and a discussion on its habit. Vertebrata PalAsiatica. 49(4), 435-445.
O'Connor and Zelenkov, 2013. The phylogenetic position of Ambiortus: Comparison with other Mesozoic birds from Asia. Paleontological Journal. 47(11), 1270-1281.
Moyer, Zheng, Johnson, Lamanna, Li, Lacovera and Schweitzer, 2014. Melanosomes or microbes: Testing an alternative hypothesis for the origin of microbodies in fossil feathers. Scientific Reports. 4, 4233.
Wang, O'Connor, Li and You, 2015. New information on postcranial skeleton of the Early Cretaceous Gansus yumenensis (Aves: Ornithuromorpha), Historical Biology. DOI: 10.1080/08912963.2015.1006217
Bailleul, Li, O'Connor and Zhou, 2019. Origin of the avian predentary and evidence of a unique form of cranial kinesis in Cretaceous ornithuromorphs. Proceedings of the National Academy of Sciences. 116(49), 24696-24706.
O'Connor, Lamanna, Harris, Hu, Bailleul, Wang and You, 2021. First avian skulls from the Lower Cretaceous Xiagou Formation, Gansu, China. The Society of Vertebrate Paleontology Virtual Meeting Conference Program, 81st Annual Meeting. 196.
O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2022 (online 2021). Avian skulls represent a diverse ornithuromorph fauna from the Lower Cretaceous Xiagou Formation, Gansu Province, China. Journal of Systematics and Evolution. 60(5), 1172-1198.

Ambiortus Kurochkin, 1982
A. dementjevi Kurochkin, 1982
Hauterivian-Barremian, Early Cretaceous
Andaikhudag (= Anda Khooduk) Formation, Mongolia
Holotype- (PIN 3790-271/272) (~270 mm) seven cervical vertebrae, three or four anterior dorsal vertebrae, dorsal rib fragments, incomplete scapula, incomplete coracoid, incomplete sternum, partial furcula, proximal humerus (~67 mm), incomplete radius, incomplete ulna, proximal carpal, incomplete carpometacarpus, phalanx II-1, phalanx II-2, manual ungual II, body feathers, remiges
Diagnosis- (after Kurochkin, 2000) transverse ligamental fossa proximal to bicipital crest.
(after O'Connor and Zelenkov, 2013) posterolateral sternal process wide; posterolateral sternal process curved medially; ventral edge of proximal end of humerus strongly developed and with distinct tubercle on its cranial surface; transverse groove short, fossa-like, and runs dorsoventrally; pneumotricipital fossa of humerus not developed; deltopectoral crest projected dorsally; bicipital crest distally ends abruptly.
Other diagnoses- Kurochkin (2000) included several additional characters in his diagnosis. Most basal euornithines (e.g. Patagopteryx, Apsaravis, basal Aves) share dorsoventrally compressed acromia. The acromia of Patagopteryx and Yixianornis are equally long, while that of Apsaravis is even longer. The scapular blades of most basal euornithines except Patagopteryx are equally slender. The longitudinal groove in the posterolateral scapular blade is also present in most basal euornithines (e.g. Patagopteryx, Archaeorhynchus, Apsaravis, Yixianornis). The procoracoid process is equally long and broad in Hongshanornis and songlingornithids. The absent capital groove is shared with Apsaravis. Several other basal euornithines have a fossa instead of a transverse ligamental groove, but that of Apsaravis, Gansus and Ichthyornis differ in being on the bicipital crest, not proximal to it. The proximal fusion of the carpometacarpus is symplesiomorphic for avialans, while the dorsoventrally compressed manual phalanx II-1 is seen in euornithines except Patagopteryx.
O'Connor and Zelenkov (2013) proposed other characters. The hooked acromion is shared with Apsaravis. The procoracoid process is similarly angled in e.g. songlingornithids.
Comments- The holotype was discovered in 1977 and described by Kurochkin (1982) as a carinate (which was equivalent to Ornithurae then as the few known fragments of taxa intermediate between Archaeopteryx and hesperornithines were not recognized as such). Cracraft (1986) was the first to include it in a phylogenetic analysis, which placed Ambiortus in an unresolved trichotomy with Ichthyornis and Aves (his Neognathae), though enantiornithines were also placed in this position because no other avialans were known and hesperornithines were placed too basally based on their flightlessness. Sanz and Buscalioni (1992) found Ambiortus to have an uncertain position compared to Ornithurae and Enantiornithes in their cladogram.
Ambiortus a palaeognath? Kurochkin referred it to Palaeognathae in 1985 based on several characters. The long pointed acromion is also found in songlingornithids and anatoids. The supposedly wide and short acrocoracohumeral ligament scar is equally long in other basal euornithines (e.g. Archaeorhynchus, Apsaravis, Yixianornis), and mediolaterally narrower as in Gansus. The longitudinal groove on the ventral acrocoracoid face is homologized to a pit in palaeognaths, but a similar depressed area is present in Archaeorhynchus and Yixianornis. In his 1995 paper, Kurochkin added a few supposed palaeognath characters. The bicipital crest was said to be absent, but is the "slightly pronounced cranial tubercle" he described in 1999. The deltopectoral crest begins just as proximally in other basal euornithines. The glenoid facet on the coracoid is displaced dorsally in Apsaravis and Ichthyornis as well. The short and wide acrocoracoid is symplesiomorphic for euornithines. The hypocleidium is also absent in Archaeorhynchus, Yanornis, Gansus and Ichthyornis. In 1999, Kurochkin added yet more supposed palaeognath characters in his description. The dorsoventrally flattened acromion is symplesiomorphic for euornithines (e.g. Patagopteryx, Apsaravis, Galliformes). A dorsal tubercle on the acromion is also present in Iaceornis and Anas. The well developed ventral tuber is also present in Archaeorhynchus, Yixianornis and Alamitornis. The "remarkable cranial tubercle" with an anterior pit is the bicipital crest, which also has such a pit in enantiornithines and Apsaravis. The strongly laterally projecting, posteriorly placed "caudal transverse processes" seem to be laterally flared postzygapophyseal processes instead, as seen in Ichthyornis.
Hope (2002) states several characters (capital groove; pneumotricipital fossa; ventral tuber; bicipital crest) are poorly developed in Ambiortus, Ichthyornis, palaeognaths and galliforms compared to most neognaths and enantiornithines. She attributes this either to convergence in the latter groups or placement of Ambiortus in Palaeognathae. Yet the first three characters are well developed in Lithornis and tinamiforms, while the bicipital crest is extremely reduced in neognaths in addition to tinamiforms. Given the distribution of characters in recently discovered basal euornithines, Ambiortus and Apsaravis lost their capital grooves independently of ratites, pneumotricipital fossae developed convergently in some enantiornithines and Aves, ventral tuber size is quite homoplasic, and a low bicipital crest is primitive for euornithines.
In conclusion, nearly all of the proposed palaeognath characters in Ambiortus are symplesiomorphic, with the exception of the dorsal acromion tubercle.
Ambiortus an ichthyornithine? Martin (1987) believed Ambiortus was the sister taxon to Apatornis (based on the Iaceornis holotype) within Ichthyornithiformes because of their long acromia, but those of Apsaravis, Yixianornis and Patagopteryx are also elongate, as are most enantiornithes'.
Chatterjee (1999) found Ambiortus to clade with Ichthyornithiformes in his analysis. This was based on the supposedly amphicoelous cervicals (actually heterocoelous in Ambiortus- Kurochkin, 1999) and absent bicipital crest (actually present in both Ambiortus and Ichthyornis).
Ambiortus a basal euornithine? Sereno and Rao (1992) found Ambiortus to be a euornithine outside of Ornithurae based on an unpublished phylogenetic analysis, but this cannot be evaluated.
Elzanowski (1995) placed Ambiortus in basal Euornithes (his Neornithes), excluded from Aves (his Neognathae) due to the dorsally projecting deltopectoral crest and lack of an extensor process on metacarpal I, and excluded from Carinatae (unnamed node in his cladogram, not equivalent to his Carinatae) based on the more laterally facing scapular glenoid and prominent acromion process. The deltopectoral crest is anteriorly projecting in patagopterygids, but otherwise seems to be an unambiguous avian character. As described and illustrated by Kurochkin (1999), Ambiortus actually has an extensor process, albeit a low one. Small acromia are also present in Archaeorhynchus and Hongshanornis but absent in the very derived Iaceornis, so show some homoplasy. The glenoid does seem less dorsally angled than carinates.
Chiappe (2001) placed Ambiortus closer to Aves than Patagopteryx based on the procoracoid process (also absent in Apsaravis) and proximally globe-shaped humeral head. It was excluded from Carinatae due to the absent extensor process (again miscoded, as it is actually present but low) and the presence of manual ungual II (miscoded as absent in Ichthyornis based on an Iaceornis element, but still valid to exclude Ambiortus from an Iaceornis+Aves clade). While placed between Hesperornithes and Ichthyornis on his cladogram, Chiappe later (2002) noted it could equally parsimoniously be placed as sister to Ornithurae.
Clarke (2002) first included Ambiortus in her unpublished thesis' matrix, finding it positioned above Patagopteryx, but in a polytomy with Apsaravis, Gansus, Hesperornithes, Ichthyornis, Limenavis and Iaceornis+Aves. It was first published in a version of Clarke's matrix by You et al. (2006), which presents Ambiortus as falling out more derived that Patagopteryx and Hongshanornis, but more basal than Apsaravis, songlingornithids, Gansus and ornithurines. The supplementary information indicates it also emerged as a songlingornithid in some trees. In the first position, Ambiortus was more derived than Patagopteryx and Hongshanornis based on the absent hypocleideum, proximally domed humeral head, extensor process on metacarpal I, and highly compressed manual phalanx II-1. It was less derived than Aves based on several characters- acrocoracoid process not hooked medially; pit on bicipital crest absent (miscoded in Ambiortus); extensor process on metacarpal I not projecting; thick metacarpal III (which cannot actually be coded, as only the fused base is preserved); phalanx II-2 longer than II-1 (miscoded in Ambiortus).
While several characters were miscoded by various authors, Ambiortus does seem excluded from Aves based on- scapular glenoid less dorsally angled; acrocoracoid not medially hooked; dorsally projecting deltopectoral crest; low extensor process on metacarpal I; manual ungual II present.
References- Kurochkin, 1982. Novyy otryad ptits iz nizhnego mela Mongolii. Doklandy Akademii Nauk SSSR. 262(2), 452-455.
Kurochkin, 1983. New order of birds from the Lower Cretaceous in Mongolia. Palaeontological Journal. 17, 215-218.
Kurochkin, 1985. Lower Cretaceous birds from Mongolia and their evolutionary significance. XVIII Congressus Internationalis Ornithologicus: Programme. 1, 191-199.
Kurochkin, 1985. A true carinate bird from Lower Cretaceous deposits in Mongolia and other evidence of Early Cretaceous birds in Asia. Cretaceous Research. 6, 271-278.
Cracraft, 1986. The origin and early diversification of birds. Paleobiology. 12, 383-399.
Martin, 1987. The beginning of the modern avian radiation. Documents des Laboratoires de Geologie de la Faculte des Sciences de Lyon. 99, 9-20.
Sanz and Buscalioni, 1992. A new bird from the Early Cretaceous of Las Hoas, Spain, and the early radiation of birds. Palaeontology. 35, 829-845.
Sereno and Rao, 1992. Early evolution of avian flight and perching: New evidence from Lower Cretaceous of China. Science. 255, 845-848.
Elzanowski, 1995. Cretaceous birds and avian phylogeny. Courier Forschungsinstitut Senckenberg. 181, 37-53.
Kurochkin, 1995. Synopsis of Mesozoic birds and early evolution of class Aves. Archaeopteryx. 13, 47-66.
Kurochkin, 1996. Morphological differentiation of palaeognathous and neognathous birds. Courier Forschungsinstitut Senckenberg. 181, 79-88.
Kurochkin, 1999. The relationships of the Early Cretaceous Ambiortus and Otogornis (Aves: Ambiortiformes). In Olson (ed.). Avian Paleontology at the Close of the 20th Century: Proceedings of the 4th International Meeting of the Society of Avian Paleontology and Evolution. Smithsonian Contributions to Paleobiology. 89, 275-284.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. In Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press. 533-559.
Chiappe, 2001. Phylogenetic relationships among basal birds. In Gauthier and Gall (eds). New perspectives on the origin and early evolution of birds: Proceedings of the international symposium in honor of John H. Ostrom. New Haven: Peabody Museum of Natural History. 125-139.
Chiappe, 2002. Basal bird phylogeny: Problems and solutions. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 448-472.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.
O'Connor and Zelenkov, 2013. The phylogenetic position of Ambiortus: Comparison with other Mesozoic birds from Asia. Paleontological Journal. 47(11), 1270-1281.

Hongshanornithidae O'Connor, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009
Other definition- (Hongshanornis longicresta + Longicrusavis houi) (O'Connor, Gao and Chiappe, 2010)
Comments- O'Connor et al. (2009) propose Hongshanornithidae to include Hongshanornis and the at-the-time undescribed Longicrusavis. This is based on- dorsal dentary convex and dorsal surangular concave (also in Archaeorhynchus, many enantiornithines and probably Patagopteryx); posterolateral sternal processes not expanded much distally (probably symplesiomorphic as it is found in Archaeorhynchus, Gansus and basal enantiornithines); manus longer than humerus (probably symplesiomorphic as it is found in non-ornithothoracines, Protopteryx, Pengornis and Longipteryx); forelimb/hindlimb ratio (humerus+ulna / femur+tibia) <90% (also in Patagopteryx and hesperornithines). O'Connor et al. (2010) later described Longicrusavis and used the same matrix, also adding the manual formula of 2-3-2 to the diagnosis for Hongshanornithidae. Yet this is plesiomorphic, also being found in basal enantiornithines. Notably, Archaeorhynchus was not included in their matrix, Patagopteryx was coded as lacking the mandibular character even though the surangular is dorsally concave and the dentary missing, no enantiornithines with the mandibular character were included, Shanweiniao and Longipteryx were miscoded as having greatly expanded posterolateral sternal processes, and basal enantiornithines that have long manus and sternal processes with small expansions were not included.
References- O'Connor, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009. Phylogenetic support for a specialized clade of Cretaceous enantiornithine birds with information from a new species. Journal of Vertebrate Paleontology. 29(1), 188-204.
O'Connor, Gao and Chiappe, 2010. A new ornithuromorph (Aves: Ornithothoraces) bird from the Jehol Group indicative of higher-level diversity. Journal of Vertebrate Paleontology. 30(2), 311-321.

Archaeornithura Wang, Zheng, O'Connor, Lloyd, Wang, Wang, Zhang and Zhou, 2015a
A. meemannae Wang, Zheng, O'Connor, Lloyd, Wang, Wang, Zhang and Zhou, 2015a
Late Hauterivian, Early Cretaceous
Sichakou Sedimentary Member of the Huajiying Formation, Hebei, China
Holotype- (STM 7-145) fragmentary posterior skull, cervical vertebrae, dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, caudal vertebrae, pygostyle, partial scapula, coracoids (15.4 mm), furcula, partial sternum, humeri (25.9 mm), radii (23.9 mm), ulnae (25.8 mm), pisiform, carpometacarpi (13.1 mm), phalanges I-1 (6 mm), manual unguals I (3 mm), phalanges II-1 (6.6 mm), phalanges II-2 (7.6 mm), manual ungual II (2.4 mm), phalanges III-1 (3.3 mm), partial ilium, pubes, femora (23.8 mm), tibiotarsi (38 mm), fibulae, metatarsals I, phalanges I-1, pedal unguals I, tarsometatarsi (23 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, pedal claw sheaths, body feathers, remiges, retrices
Paratype- (STM 7-163) fragmentary posterior skull, ten cervical vertebrae, dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, synsacrum, six caudal vertebrae, pygostyle, coracoids (12.7 mm), furcula, partial sternum, sternal ribs, humeri (27.5 mm), radii (26 mm), ulnae (28.3 mm), scapholunare, carpometacarpi (13.8 mm), phalanges I-1 (7.6 mm), manual ungual I (3.9 mm), phalanges II-1 (6.8 mm), phalanges II-2 (7 mm), manual unguals II (3 mm), manual claw sheaths, pubes, ischia, femora, tibiotarsi (37.5 mm), fibulae, metatarsals I, phalanges I-1, pedal unguals I, tarsometatarsi, phalanges II-1, phalanges II-2, pedal ungual II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, pedal claw sheaths, body feathers, remiges
Diagnosis- (after Wang et al., 2015a) differs from Hongshanornis and Longicrusavis in- anterior margin of sternum strongly vaulted.
differs from from Hongshanornis and Parahongshanornis in- posteromedian sternal process well developed and squared.
differs from Hongshanornis, Parahongshanornis and Tianyuornis in- manual digit I extends further distally than metacarpal II.
differs from Hongshanornis, Longicrusavis and Tianyuornis in- manual phalanx II-2 longer than II-1; shorter femur relative to tarsometatarsus.
Comments- The type specimens were acquired from a dealer. Wang et al. (2015) added the taxon to a version of O'Connor's bird analysis and found it to be a hongshanornithid.
References- Wang, Zheng, O'Connor, Lloyd, Wang, Wang, Zhang and Zhou, 2015a. The oldest record of Ornithuromorpha from the Early Cretaceous of China. Nature Communications. 6:6987.
Wang, Zheng, O'Connor, Lloyd, Wang, Wang, Zhang and Zhou, 2015b. The oldest record of Ornithuromorpha with implications for evolutionary rate of Early Cretaceous birds. Journal of Vertebrate Paleontology. Program and Abstracts 2015, 233.

Tianyuornis Zheng, O'Connor, Wang, Zhang and Wang, 2014
T. cheni Zheng, O'Connor, Wang, Zhang and Wang, 2014
Late Barremian-Early Aptian, Early Cretaceous
Jianshangou Beds of Yixian Formation, Inner Mongolia, China
Holotype- (STM7-53) (subadult) skull (30 mm), mandibles, several cervical vertebrae, cervical ribs, several dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, synsacrum, caudal vertebrae, pygostyle (3.3 mm), scapula, coracoids (11, 11.5 mm), partial furcula, sternum (19 mm), sternal ribs, humeri (25.4 mm), radii (24.6 mm), ulnae (26.4 mm), scapholunare, pisiform, metacarpal I (2.7 mm), phalanges I-1 (6.6 mm), manual unguals I (2.9 mm), carpometacarpi (13.2 mm; II 13, III 10.7 mm), phalanges II-1 (6.9 mm), phalanges II-2 (7 mm), manual ungual II (~2.6 mm), phalanges III-1 (3.3 mm), phalanx III-2, incomplete ilium, partial pubes, femora (24.8 mm), tibiotarsi (39 mm), fibula, metatarsal I (3.5 mm), phalanges I-1 (4.1 mm), pedal unguals I (2.5 mm), tarsometatarsi (II 17.8, III 23.1, IV 18.5 mm), phalanges II-1 (6 mm), phalanges II-2 (5.1 mm), pedal unguals II (3.2 mm), phalanges III-1 (~7.5 mm), phalanx III-2 (~5.3 mm), phalanx III-3 (4.5 mm), pedal ungual III (4 mm), phalanx IV-1 (~3.8 mm), phalanx IV-2 (3.5 mm), phalanx IV-3 (3.3 mm), phalanx IV-4 (3 mm), pedal ungual IV (2.6 mm), remiges, retrices
Diagnosis- (after Zheng et al., 2014) toothed upper and lower jaws; premaxillary and maxillary teeth much larger than dentary teeth; anterior half of dentary straight; uncinate processes elongate, crossing two adjacent ribs; coracoid length/width ratio ~1.6; U-shaped furcula without hypocleideum; sternum with anterior margin angled ~96 degrees; posterolateral sternal process distally expanded.
Comments- Zheng et al. (2014) refer this new taxon to Hongshanornithidae without a phylogenetic analysis, but as I argue here, that family is mostly based on symplesiomorphies. Tianyuornis even lacks the supposed hongshanornithid character of posterolateral sternal processes not expanded much distally. Also note Hongshanornis has recently been shown to have both upper and lower teeth, so at least this character is not diagnostic of Tianyuornis. However, Wang et al. (2015) added it to O'Connor's bird analysis and found it to fall within Hongshanornithidae as the sister of Archaeornithura.
References- Zheng, O'Connor, Wang, Zhang and Wang, 2014. New information on Hongshanornithidae (Aves: Ornithuromorpha) from a new subadult specimen. Vertebrata PalAsiatica. 52(2), 217-232.
Wang, Zheng, O'Connor, Lloyd, Wang, Wang, Zhang and Zhou, 2015. The oldest record of Ornithuromorpha from the Early Cretaceous of China. Nature Communications. 6:6987.

Parahongshanornis Li, Wang and Hou, 2011
P. chaoyangensis Li, Wang and Hou, 2011
Early Albian, Early Cretaceous
Chaoyang, Jiufotang Formation, Liaoning, China
Holotype- (PMOL.AB00161) eight cervical vertebrae, dorsal ribs, synsacrum, incomplete scapula, coracoids (14.7 mm), furcula (~13 mm), sternum, sternal ribs, humeri (one partial; 29.4 mm), radii (one partial; 26.8 mm), ulnae (one partial; 28.4 mm), scapholunares, pisiforms, metacarpals I (3.4 mm), phalanges I-1 (6.7 mm), manual unguals I (2.7 mm), carpometacarpi (II 12.3, III 11.4 mm), phalanges II-1 (7.1 mm), phalanges II-2 (8 mm), manual unguals II (2.6 mm), phalanges III-1 (3.5 mm), phalanges III-2 (1.3 mm), ilia, pubes (24 mm), ischium, femora (24.8 mm), tibiotarsi (41.3 mm), fibulae (20.7 mm), metatarsals I (3.2 mm), phalanges I-1, pedal unguals I, tarsometatarsi (II 20.3, III 21.2, IV 20.2 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, body feathers
Diagnosis- (after Li et al., 2011) coracoid elongate (length/distal width 2.3) (also in Hongshanornis); furcula anteroposteriorly compressed proximally (also in Yanornis); deep groove along clavicular symphysis (also in Yanornis); fibula close to half tibiotarsal length (also in Longicrusavis).
Other diagnoses- Li et al. (2011) listed other characters in the diagnosis as well. A U-shaped furcula, elongate sternum, xiphoid sternal processes, short posteromedial sternal processes (which create two pairs of posterior excavations), distally expanded posterolateral sternal processes, anteriorly extensive sternal keel, subequally long metacarpals II and III, straight and slender manual phalanx II-2, opisthopubic pelvis and a pubic boot are primitive for euornithines. The forelimb is also short in Patagopteryx, Hongshanornis and Longicrusavis. Manual phalanx II-1 is also short in Yanornis and Gansus. The tibiotarsofemoral ratio is also high in Hongshanornis, Longicrusavis, Yanornis and Gansus. The tibiotarsus is also slender in Hongshanornis, Longicrusavis, Yixianornis and Gansus. The tarsometatarsus is shorter in Archaeorhynchus, Jianchangornis, Patagopteryx, Longicrusavis, Yanornis and Yixianornis.
Comments- Li et al. (2011) referred this taxon to Hongshanornithidae based on the U-shaped elongated furcula and short forelimb. The former is also true in Archaeorhynchus, Yanornis and Jianchangornis. The latter is also true in Patagopteryx. Wang et al. (2015) added it to O'Connor's bird analysis and found it to clade in Hongshanornithidae as sister to other members except Hongshanornis.
O'Connor et al. (2005) mention a new euornithine (as an ornithuromorph) in an SVP abstract, distinct from most in having a tibiotarsus longer than the humerus. While the authorship is the same as Longicrusavis from JVP five years later, the locality of near Chaoyang in the Jiufotang Formation matches Parahongshanornis instead (Longicrusavis was found near Lingyuan in the Yixian Formation). The reported forelimb/hindlimb ratio is also slightly closer to Parahongshanornis than Longicrusavis (79% versus 80% and 77%), but whether this is the holotype that was described by new authors six years later or another specimen is unknown.
References- O'Connor, Chiappe and Gao, 2005. A new fossil bird from the Lower Cretaceous Jiufotang Formation, Liaoning Province, northeastern China. Journal of Vertebrate Paleontology. 25(3), 97A.
Li, Wang and Hou, 2011. A new ornithurine bird (Hongshanornithidae) from the Jiufotang Formation of Chaoyang, Liaoning, China. Vertebrata PalAsiatica. 49(2), 195-200.
Wang, Zheng, O'Connor, Lloyd, Wang, Wang, Zhang and Zhou, 2015. The oldest record of Ornithuromorpha from the Early Cretaceous of China. Nature Communications. 6:6987.

Hongshanornis Zhou and Zhang, 2005
H. longicresta Zhou and Zhang, 2005
Late Barremian-Early Aptian, Early Cretaceous
Jianshangou Beds of Yixian Formation, Inner Mongolia, China
Holotype- (IVPP V14533) (88 g) skull, mandibles, hyoids, at least seven cervical vertebrae, dorsal vertebrae, dorsal ribs, uncinate processes(?), gastralia, sacrum, caudal vertebrae, pygostyle, scapulae, coracoid, furcula, sternum, humeri (26 mm), radii, ulnae (24 mm), scapholunare, pisiform(?), carpometacarpi (13 mm), phalanges I-1, manual unguals I, phalanges II-1, phalanges II-2, manual unguals II, phalanges III-1, phalanges III-2, ilia, pubes (24 mm), ischium, femora (22 mm), tibiotarsi (38 mm), fibula, metatarsal I, phalanges I-1, pedal unguals I, tarsometatarsus (22 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal ungual IV, body feathers, remiges, retrices
Referred- (DNHM D2945/6) skull (30.5 mm), mandible, hyoid, eight cervical vertebrae, nine dorsal vertebrae, dorsal ribs, four uncinate processes, synsacrum, scapulae, coracoids, furcula, incomplete sternum, six sternal ribs, humeri (24.6 mm), radii, ulna (24.5 mm), scapholunare, carpometacarpus (13 mm), phalanx I-1, manual ungual I, phalanx II-1, phalanx II-2, manual ungual II, phalanx III-1, phalanx III-2, manual claw sheaths, partial ilia, distal pubes, femora (22 mm), tibiotarsi (35.5 mm), fibulae, metatarsal I, phalanges I-1, pedal unguals I, tarsometatarsi (20.6 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, body feathers, remiges, retrices, gastroliths (O'Connor et al., 2010)
(STM coll.) over 24 specimens (Zheng et al., 2011)
Diagnosis- (from Zhou and Zhang, 2005) dentary ventrally curved (also in Archaeorhynchus); posterolateral sternal processes angled medially; hypocleidium present; forelimb/hindlimb (humerus+ulna / femur+tibiotarsus) ratio 83-85%.
Other diagnoses- Zhou and Zhang (2005) included additional characters in their diagnosis. A premaxilla with a slender and pointed anterior end is also present in Archaeorhynchus, Longicrusavis, songlingornithids and hesperornithines. Though they state both the premaxilla and maxilla are toothless, O'Connor et al. (2010) note alveoli are present in both. Similarly, contra Zhou and Zhang, Chiappe et al. (2014) find teeth in the dentary. A sternum with two pairs of posterior excavations is primitive for ornithothoracines. Chiappe et al. note the supposed tapering posterolateral process on the holotype's sternum is too poorly preserved to verify, and DNHM D2945/6 has either an expanded process or a fenestra. STM 35-3 shows expanded ends. A U-shaped furcula and laterally expanded manual phalanx II-1 are primitive for euornithines. Manual phalanx II-2 is also sinuously curved in Longicrusavis, Yixianornis and Gansus.
Comments- Note Wang et al. (2014) incorrectly call DNHM D2945/6 the paratype, but it is not as it was not mentioned in the original description.
Miscoded originally? You et al. (2006) changed numerous codings for Hongshanornis based on personal observation from Chiappe and O'Connor. These include making the following states uncertain- dentary teeth absent (untrue- Chiappe et al., 2014); amount of upper beak formed by premaxilla (yet the suture seems clear and DNHM D2945/6 also has a short ventral margin); length of dorsal premaxilla process (yet the tip of the process is clearly seen); length of dorsal maxilla process; anterior extent of splenial; amphicoely of cervical centra; length/width ratio of dorsal centra (DNHM D2945/6 shows they were elongate); presence of uncinate processes (present in DNHM D2945/6); number of free caudal vertebrae (yet the pygostyle's position indicates it must be small); epicleidial morphology (hidden by matrix- Nesbitt et al., 2009); presence of procoracoid process; presence of lateral coracoid process (it seems absent in the photo of the holotype, but is definitely present in DNHM D2945/6); length of acromion process (long in DNHM D2945/6); depth of sternal keel; orientation of deltopectoral crest (yet it seems obviously dorsally projected in the photo and in DNHM D2945/6); prominence of bicipital crest; development of semilunate dorsal condyle on ulna (present in DNHM D2945/6); presence of pisiform; fusion of carpometacarpus (completely fused in DNHM D2945/6); convexity of medial edge of metacarpal I (it seems convex in the photo, but is definitely concave in DNHM D2945/6); ginglymoidy of metacarpal I (seems flat in DNHM D2945/6); dorsal contact of ilia (at least unfused to sacral neural spines in DNHM D2945/6); orientation of postacetabular process; pubic orientation (the pubis is in anterior view, though O'Connor et al. state they are retroverted; definitely retroverted in DNHM D2945/6); cross sectional shape of pubis (transversely compressed in DNHM D2945/6); presence of ilioischiadic fenestra; presence of proximodorsal ischial process (though O'Connor et al. state one is absent); presence of obturator flange; tibiotarsal fusion (astragalocalcaneum fused to tibia but with visible suture posteriorly in DNHM D2945/6); comparative width of tibiotarsal condyles (lateral largest in DNHM D2945/6); tarsometatarsal fusion (yet it seems present in the photo and is complete in DNHM D2945/6); absence of metatarsal V (yet the holotype and DNHM D2945/6 are complete enough to make its absence probably not taphonomic); ginglymoidy of metatarsal II (present in DNHM D2945/6). Additionally, they added several codings- dentary symphysis dorsally concave; dorsal centra with deep lateral fossae (as in DNHM D2945/6); gastralia present (as noted by Zhou and Zhang); lateral coracoid margin not convex (as in DNHM D2945/6; Chiappe et al. suggest the holotype is too poorly preserved to code); scapula subequal or longer than humerus (shorter in DNHM D2945/6); intermetacarpal process absent or present as a scar (process present in DNHM D2945/6); pubic boot absent (as noted by Zhou and Zhang, though DNHM D2945/6 has a pubic boot). Unfortunately, the photo of the specimen is small and often makes independant confirmation of states impossible.
References- Zhou and Zhang, 2005. Discovery of an ornithurine bird and its implication for Early Cretaceous avian radiation. Proceedings of the National Academy of Sciences. 102(52), 18998-19002.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.
Nesbitt, Turner, Spaulding, Conrad and Norell, 2009. The theropod furcula. Journal of Morphology. 270, 856-879.
O’Connor, Gao and Chiappe, 2010. A new ornithuromorph (Aves: Ornithothoraces) bird from the Jehol Group indicative of higher-level diversity. Journal of Vertebrate Paleontology. 30(2), 311-321.
Li, Zhou and Clarke, 2011. A reevaluation of the relationships among basal ornithurine birds from China and new information on the anatomy of Hongshanornis longicresta. Journal of Vertebrate Paleontology. Program and Abstracts 2011, 144.
Zheng, Martin, Zhou, Burnham, Zhang and Miao, 2011. Fossil evidence of avian crops from the Early Cretaceous of China. Proceedings of the National Academy of Sciences of the United States of America. 108, 15904-15907.
Chiappe, Zhao, O'Connor, Gao, Wang, Habib, Marugan-Lobon, Meng and Cheng, 2014. A new specimen of the Early Cretaceous bird Hongshanornis longicresta: Insights into the aerodynamics and diet of a basal ornithuromorph. PeerJ. 2,e234.
Wang, Zheng, O'Connor, Lloyd, Wang, Wang, Zhang and Zhou, 2015. The oldest record of Ornithuromorpha from the Early Cretaceous of China. Nature Communications. 6:6987.

Khinganornis Wang, Cau, Kundrát, Chiappe, Ji, Wang, Li and Wu, 2020 online
K. hulunbuirensis Wang, Cau, Kundrát, Chiappe, Ji, Wang, Li and Wu, 2020 online
Early Aptian, Early Cretaceous
Pigeon Hill, Longjiang Formation, Inner Mongolia, China
Holotype- (SGM-AVE-2017001) (adult) skull (46 mm), sclerotic plates?, mandibles, nine cervical vertebrae, seven dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, first-seventh caudal vertebrae, scapulae (~43 mm), coracoids (27 mm), furcula, partial sternum, sternal ribs, humeri (52 mm), radii (48 mm), ulna (~49 mm), carpometacarpi (mcII 24, mcIII 24 mm), phalanges I-1 (12 mm), manual unguals I (5 mm), phalanx II-1 (12 mm), phalanx II-2 (12 mm), manual ungual II (5 mm), phalanx III-1 (8 mm), phalanx III-2, ilia, pubes (45 mm), ischia, femora (~37 mm), tibiotarsi (60 mm), fibula, metatarsals I (5 mm), phalanges I-1 (8 mm), pedal unguals I (5 mm), tarsometatarsi (31 mm; mtII 28 mm), phalanges II-1 (11 mm), phalanges II-2 (9 mm), pedal unguals II (6 mm), phalanges III-1 (12 mm), phalanges III-2 (9 mm), phalanges III-3 (8 mm), pedal unguals III (6 mm), phalanges IV-1 (8 mm), phalanges IV-2 (7 mm), phalanges IV-3 (6 mm), phalanges IV-4 (6 mm), pedal unguals IV (4 mm)
Diagnosis- (after Wang et al., 2020 online) premaxillary teeth present; dentary alveoli developed along the whole oral margin; low-crowned, blunt teeth with unconstricted crown-root transition; manual digit III-1 67% length of manual digit II-1; preacetabular process subequal in length to postacetabular process; postacetabular process slightly curved posteroventrally; pubic shaft straight along the proximal 67% of length and then curved posterodorsally; pubic boot expanded posterodorsally; metatarsals II and IV much narrower than metatarsal III at mid-shaft; pedal digit III most robust; pedal unguals II-IV ventrally straight.
Other diagnoses- Based on their figure 2, the proximal edge of the tarsometatarsus does not appear to be "sloped laterally" in the right pes, while the left pes is in side view.
Comments- Likely discovered in 2017 based on its specimen number. Wang et al. recovered this as sister to Iteravis+Changzuiornis, with this group in turn sister to Gansus plus ornithuromorphs, using a reduced subset of Cau's megamatrix.
Reference- Wang, Cau, Kundrát, Chiappe, Ji, Wang, Li and Wu, 2021 (2020 online). A new advanced ornithuromorph bird from Inner Mongolia documents the northernmost geographic distribution of the Jehol paleornithofauna in China. Historical Biology. 33(9), 1705-1717.

Longicrusavis O'Connor, Gao and Chiappe, 2010
L. houi O'Connor, Gao and Chiappe, 2010
Early Aptian, Early Cretaceous
Lingyuan, Dawangzhangzi Beds of Yixian Formation, Liaoning, China
Holotype- (PKUP V1069) (89 g) skull (30.7 mm), mandibles, hyoid, seven cervical vertebrae, two anterior dorsal vertebrae, two dorsal vertebrae, several dorsal vertebrae, dorsal ribs, synsacrum, incomplete scapulae (23.1 mm), coracoids (12.7 mm), incomplete furcula (~12.7 mm), partial sternum, humeri (26 mm), radii (24 mm), ulnae (25 mm), scapholunare, pisiforms, carpometacarpi (one incomplete; 13.1 mm, mcI ~2.7 mm, mcII 11.5 mm, mcIII 11.1 mm), phalanx I-1 (6.9 mm), manual ungual I (4.3 mm), phalanges II-1 (7 mm), phalanges II-2 (7.3 mm), manual unguals II (3.4 mm), phalanges III-1 (3.2 mm), phalanges III-2 (0.8 mm), incomplete ilium, incomplete pubes (~31 mm), ischia, femora (24.3 mm), tibiotarsi (37.6 mm), fibulae (~16.6 mm), metatarsal I (4 mm), phalanx I-1 (4.1 mm), pedal ungual I (3.3 mm), tarsometatarsi (one incomplete; 21.5 mm, mtII 19.2, mtIII 21 mm, mtIV 19.6 mm), phalanx II-1 (6.3 mm), phalanx II-2 (5.4 mm), pedal ungual II (3.3 mm), phalanx III-1 (6.8 mm), phalanx III-2 (5.7 mm), phalanx III-3 (5.1 mm), pedal ungual III, phalanx IV-1 (~4 mm), phalanx IV-2 (4.1 mm), phalanx IV-3 (3.7 mm), phalanx IV-4 (3.8 mm), pedal ungual IV (3 mm), body feathers, remiges
Diagnosis- (after O'Connor et al., 2010) robust beak (relative to Hongshanornis); posteromedial sternal process absent; dorsal supracondylar process present on distal humerus; lateral cnemial crest hooked; second and fourth metatarsals subequal in length.
Comments- This taxon is a hongshanornithid in O'Connor et al.'s (2009, 2010) trees, but this is problematic as noted in the comments under Hongshanornithidae.
References- O'Connor, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009. Phylogenetic support for a specialized clade of Cretaceous enantiornithine birds with information from a new species. Journal of Vertebrate Paleontology. 29(1), 188-204.
O’Connor, Gao and Chiappe, 2010. A new ornithuromorph (Aves: Ornithothoraces) bird from the Jehol Group indicative of higher-level diversity. Journal of Vertebrate Paleontology. 30(2), 311-321.

Mystiornithiformes Kurochkin, Zelenkov, Averianov and Leshchinskiy, 2011
= "Mystiornithiformes" Kurochkin, Zelenkov, Averianov and Leshchinskiy, 2010 online
Mystiornithidae Kurochkin, Zelenkov, Averianov and Leshchinskiy, 2011
= "Mystiornithidae" Kurochkin, Zelenkov, Averianov and Leshchinskiy, 2010 online
Mystiornis Kurochkin, Zelenkov, Averianov and Leshchinskiy, 2011
= "Mystiornis" Kurochkin, Zelenkov, Averianov and Leshchinskiy, 2010 online
M. cyrili Kurochkin, Zelenkov, Averianov and Leshchinskiy, 2011
= "Mystiornis cyrili" Kurochkin, Zelenkov, Averianov and Leshchinskiy, 2010 online
Barremian-Aptian, Early Cretaceous
Shestakovo Formation, Russia
Holotype- (PM TSU 16/5-45) tarsometatarsus (26.4 mm; II 21.4, III 26.1, IV 25.8 mm)
Diagnosis- (after Kurochkin et al., 2011) central proximal articular facet on tarsometatarsus; canal in lateral extensor sulcus opening in distal vascular foramen; metarsal II does not reach distal vascular foramen.
Other diagnoses- Kurochkin et al. (2011) listed numerous characters in their diagnosis of Mystiornithiformes, but among them, coplanar metatarsals and an absent proximodorsal fossa are primitive for theropods; dorsally ridged metatarsals are also present in avisaurids; distally fused metatarsals are also present in Avisaurus gloriae and Vorona.
Kurochkin et al also listed many supposedly diagnostic characters of Mystiornithidae and Mystiornis. Of these, metatarsal II is often the shortest of II-IV in theropods; trochlea often have acutely angled sagittal planes; dorsally concave metatarsal shafts, an anteriorly angled proximal surface of metatarsal II, extremely dorsoventrally flattened trochlea II and a ventrally flat metatarsal III are also present in avisaurids; the proximal surface of metatarsal II is not positioned more distally than those of III and IV, nor is the ventral surface of metatarsal III projected noticably compared to metatarsal II.
Comments- The holotype was discovered in 2000 and announced by Kurochkin et al. (2009). The description was first posted online in December 2010 before being officially published in March 2011. While Kurochkin et al. placed the taxon in its own order and family, it is not as distinctive as their paper would suggest. They included it in a version of O'Connor et al.'s (2009) matrix, which resulted in an basal avialan clade of Mystiornis, Avisaurus, Vorona and Mei. The other newly added taxon, Anchiornis, is in a polytomy with the aforementioned clade and avebrevicaudans. This suggests a systematic coding error by the authors for their added taxa, which I have not yet confirmed via examination. When Mystiornis, Avisaurus and Vorona are coded for that matrix, the latter two fall out in their normal positions (derived enantiornithine and basal euornithine), while Mystiornis is an ornithothoracine outside of Longipterygidae and Hongshanornis+Aves. Indeed, Cau's (2011, online) unpublished analysis places Mystiornis as an avisaurid enantiornithine.
References- Kurochkin, Averianov, Leshchinskiy and Zelenkov, 2009. A new bird from the Early Cretaceous of Western Siberia. Journal of Vertebrate Paleontology. 29(3), 130A-131A.
Cau, 2011 online. http://theropoda.blogspot.com/2011/05/lenigmatico-o-forse-no-mystiornis.html
Kurochkin, Zelenkov, Averianov and Leshchinskiy, 2011. A new taxon of birds (Aves) from the Early Cretaceous of Western Siberia, Russia. Journal of Systematic Palaeontology. 9(1), 109-117.

Bellulornis Wang, Zhou and Zhou, 2016b
= Bellulia Wang, Zhou and Zhou, 2016a (preoccupied Fibiger, 2008)
= "Bellulornis" IVPP, online 2016
B. rectusunguis (Wang, Zhou and Zhou, 2016a) Wang, Zhou and Zhou, 2016b
= Bellulia rectusunguis Wang, Zhou and Zhou, 2016a
= "Bellulornis" rectusunguis (Wang, Zhou and Zhou, 2016a) IVPP, online 2016
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V17970) two posterior cervical vertebrae, several dorsal vertebrae, six dorsal ribs, synsacrum, three caudal vertebrae, pygostyle (11.2 mm), two chevrons, scapulae (one incomplete; ~60.4 mm), coracoids (one incomplete; 29.7 mm), incomplete furcula, incomplete sternum two sternal ribs, humeri (one incomplete; 69.6 mm), radii (one partial; 74.3 mm), ulnae (78.2 mm), scapholunare, pisiforms, carpometacarpi (one incomplete; 39.3 mm, mcI 7.6 mm), phalanges I-1 (17 mm), manual unguals I (8.3 mm), phalanges II-1 (16.5 mm), phalanges II-2 (15.5 mm), manual unguals II (10.9 mm), phalanges III-1 (10.1 mm), pelvis, pubis (~49.5 mm), femora (one incomplete; 53 mm), incomplete tibiotarsi (66 mm), fibula, metatarsals I, pedal ungual I (3.8 mm), tarsometatarsi (34.9 mm), phalanx II-1 (11.3 mm), phalanges II-2 (8.3 mm), pedal unguals II (6.4 mm), phalanx III-1 (9.8 mm), phalanx III-2 (8.2 mm), phalanges III-3 (7.1 mm), pedal unguals III (7 mm), phalanx IV-1 (8.5 mm), phalanges IV-2 (5.5 mm), phalanges IV-3 (4.9 mm), phalanges IV-4 (4.5 mm), pedal unguals IV (5.2 mm), 12+ gastroliths (3.5-8.8 mm), remiges, retrices
Diagnosis- (after Wang et al., 2016a) large hypocleidium (also in Parahongshanornis and Schizoouridae); long posterolateral sternal processes with fan-shaped distal expansion (also in Archaeornithura and Jiuquanornis); 113 degree angle between sternal coracoidal sulci (also in Archaeornithura and Schizooura); intermembral index (humerus + ulna + carpometacarpus / femur + tibiotarsus + tarsometatarsus) 1.21; manual unguals nearly straight; proximal ends of ends of metatarsals II-IV coplanar (also in Schizooura and Jianchangornis); metatarsal IV robust; pedal ungual I reduced (also in Schizooura).
Other diagnoses- Wang et al. (2016a) included other characters in their diagnosis. The furcula only appears V-shaped due to the hypocleidium, but has medially curved arms.
Comments- The genus Bellulia is preoccupied by a micronoctuid moth (Fibiger, 2008), so the bird was renamed Bellulornis by Wang et al. (2016b). The latter name was first used in an IVPP press release, so was an nomen nudum for a time. Wang et al. (2016a) added the taxon to O'Connor's bird matrix and found it to be a euornithine sensu Sereno more derived than only Archaeorhynchus and Jianchangornis, in a clade with Schizooura.
References- Fibiger, 2008. Revision of the Micronoctuidae (Lepidoptera: Noctuoidea). Part 2, Taxonomy of the Belluliinae, Magninae and Parachrostiinae. Zootaxa. 1867, 1-136.
IVPP, online 2016. http://english.ivpp.cas.cn/rh/rp/201601/t20160111_158608.html
Wang, Zhou and Zhou, 2016a. A new basal ornithuromorph bird (Aves: Ornithothoraces) from the Early Cretaceous of China with implication for morphology of early Ornithuromorpha. Zoological Journal of the Linnean Society. 176(1), 207-223.
Wang, Zhou and Zhou, 2016b. Corrigendum. Renaming of Bellulia Wang, Zhou & Zhou, 2016. Zoological Journal of the Linnean Society. 177(3), 695.
Wang, O'Connor, Pan and Zhou, 2017. A bizarre Early Cretaceous enantiornithine bird with unique crural feathers and an ornithuromorph plough-shaped pygostyle. Nature Communications. 8:14141.

Xinghaiornis Wang, Chiappe, Teng and Ji, 2013
X. lini Wang, Chiappe, Teng and Ji, 2013
Barremian-Aptian, Early Cretaceous
Yixian Formation, Liaoning, China
Holotype- (XHPM 1121) skull (81 mm), mandible, cervical vertebrae, dorsal vertebrae, dorsal ribs, synsacrum, caudal vertebrae, scapulae (~62 mm), coracoid, furcula, sternum, humeri (~75 mm), radii, ulnae, carpometacarpus, phalanx II-1, phalanx II-2, manual ungual II, ilia, femora (~52 mm), tibiotarsi (~72 mm), fibula, metatarsal I, phalanx I-1, tarsometatarsi (~34 mm), pedal phalanges, pedal unguals, body feathers, remiges
Diagnosis- (after Wang et al., 2013) long and slim rostrum; toothless beak; dentary with elongated grooves; slender, Y-shaped furcula; large, robust deltopectoral crest; (humerus+radius)/(femur+tibiotarsus) ratio ~1.2; metatarsal I articulates close to midshaft of metatarsal II; trochlea of metatarsal I much more proximally located than trochlea II-IV.
Comments- Wang et al. (2013) believe this taxon may be close to the base of Ornithothoraces based on the combination of classic enantiornithine (long hypocleidium; metacarpal III extends distal to II) and euornithine (dome/ball-shaped humeral head; proximally placed pedal digit I; small, weakly curved pedal unguals) characters. Yet the description is so brief and the photo quality so poor that any meaningful analysis is impossible.
Reference- Wang, Chiappe, Teng and Ji, 2013. Xinghaiornis lini (Aves: Ornithothoraces) from the Early Cretaceous of Liaoning: An example of evolutionary mosaic in early birds. Acta Geologica Sinica. 87(3), 686-689.

Mengciusornis Wang, O'Connor, Zhou and Zhou, 2019 online
M. dentatus Wang, O'Connor, Zhou and Zhou, 2019 online
Early Albian, Early Cretaceous
Lamadong, Jiufotang Formation, Liaoning, China
Holotype- (IVPP V26275) skull (59.52 mm), mandibles, hyoid, several cervical vertebrae, several dorsal vertebrae, dorsal ribs, gastralia, synsacrum (27.31 mm), caudal vertebra, scapulae (~61.91 mm), coracoids (30.34 mm), incomplete furcula, humeri (65.90 mm), radii (61.00 mm), ulnae (64.85 mm), scapholunare, pisiform, carpometacarpi (32.19 mm; mcI 7.27 mm), phalanges I-1 (13.47 mm), manual ungual I (3.81 mm), phalanges II-1 (14.55 mm), phalanges II-2 (14.85 mm), manual ungual II, phalanx III-1 (6.70 mm), ilia, pubes (~51.31 mm), ischia, femora (47.57 mm), tibiotarsi (60.74 mm), fibula, metatarsals I, phalanges I-1 (4.9 mm), pedal unguals I (3.65 mm), tarsometatarsi (34.25 mm), phalanges II-1 (8.93 mm; one proximal), phalanx II-2 (6.81 mm), pedal ungual II (5.41 mm), phalanges III-1 (8.83 mm), phalanges III-2 (6.94 mm), phalanges III-3 (6.34 mm; one proximal), pedal unguals III (5.99 mm), phalanx IV-1 (5.98 mm), phalanges IV-2 (5.70 mm), phalanges IV-3 (4.19 mm), phalanges IV-4 (3.63 mm), pedal unguals IV (4.46 mm), remiges
Diagnosis- (after Wang et al., 2020) teeth only found in premaxillae; scapula over 90% of humeral length; scapula with ventrally hooked acromion; coracoid with small procoracoid process; coracoid lacking supracoracoidal nerve foramen; furcula with relatively elongate hypocleidium that measures approximately 31% length of ramus; elongate forelimb - (humerus/ulna) 120% the length of the hind limb (femur/tibiotarsus); ulna shorter than humerus.
Comments- Discovered prior to August 2019. The article describing Mengciusornis was published online on November 11 9019 but not published physically until 2020.
Wang et al. (2020) added it to O'Connor's avialan analysis to recover it as a basal euornithine sister to Schizooura, a clade they named Schizoouridae.
Reference- Wang, O'Connor, Zhou and Zhou, 2020 (online 2019). New toothed Early Cretaceous ornithuromorph bird reveals intraclade diversity in pattern of tooth loss. Journal of Systematic Palaeontology. 18(8), 631-645.

Changmaornis Wang, O'Connor, Li and You, 2013
C. houi Wang, O'Connor, Li and You, 2013
Late Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Holotype- (GSGM-08-CM-002) two dorsal vertebrae, dorsal rib, synsacrum, partial ilia, incomplete pubis, incomplete ischium, distal tibiotarsus, metatarsal I, phalanx I-1 (7.4 mm), pedal ungual I (3.9 mm), tarsometatarsus (36.9 mm), phalanx II-1 (10 mm), phalanx II-2 (9.9 mm), pedal ungual II (4.8 mm), phalanx III-1 (11.4 mm), phalanx III-2 (7.4 mm), phalanx III-3 (7.3 mm), pedal ungual III (4.2 mm), phalanx IV-1 (8.5 mm), phalanx IV-2 (6.3 mm), phalanx IV-3 (4.9 mm), phalanx IV-4 (4.9 mm), pedal ungual IV (3.6 mm)
Diagnosis- (after Wang et al., 2013) synsacrum composed of at least 11 sacral vertebrae with elongate distal transverse processes; ischium with dorsal process; distal half of the pubis compressed mediolaterally; metatarsal I J-shaped; distal margin of metatarsal II trochlea does not reach proximal margin of metatarsal III trochlea; pedal digit III longest in foot; ratio of pedal digit III to tibiotarsus 0.82; robust and blunt pedal unguals with poorly developed flexor tubercles.
Comments- Wang et al. entered this into O'Connor's matrix and found it to be a basal ornithomorph in large polytomy with taxa less derived than Ichthyornis but more derived than Patagopteryx.
Reference- Wang, O'Connor, Li and You, 2013. Previously unrecognized ornithuromorph bird diversity in the Early Cretaceous Changma Basin, Gansu Province, Northwestern China. PLoS ONE. 8(10), e77693.

Apsaraviformes Livezey and Zusi, 2007
Definition- (Apsaravis ukhaana <- Passer domesticus) (Martyniuk, 2012)
= "Apsaravidae" Livezey and Zusi, 2007
= Palintropiformes Longrich, Tokaryk and Field, 2011
Definition- (Palintropus retusus <- Hesperornis regalis, Ichthyornis dispar, Passer domesticus) (modified from Longrich et al., 2011)
= Apsaraves Zelenkov in Zelenkov and Kurochkin, 2015
= Apsaravidae Zelenkov in Zelenkov and Kurochkin, 2015
Comments- Livezey and Zusi (2007) named Apsaraviformes and "Apsaravidae" as monotypic and redundant taxa including only Apsaravis. "Apsaravidae" is a nomen nudum as it was only included in a table, without definition or diagnosis (ICZN Article 13.1.1). Martyniuk defined Apsaraviformes. Apsaraves was created by Zelenkov in a book chapter by Zelenkov and Kurochkin (2015) as a clade including Apsaraviformes which in turn included Apsaravis and Schizooura. He also named Apsaravidae, this time officially due to the inclusion of a diagnosis.
Longrich et al. (2011) erected Palintropiformes for Palintropus and Apsaravis, which they found formed a clade based on a version of Clarke's matrix.
References- Livezey and Zusi, 2007. Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy. II. Analysis and discussion. Zoological Journal of the Linnean Society. 149 (1), 1-95.
Longrich, Tokaryk and Field, 2011. Mass extinction of birds at the Cretaceous-Paleogene (K–Pg) boundary. Proceedings of the National Academy of Sciences. 108(37), 15253-15257.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Zelenkov and Kurochkin, 2015. Class Aves. In Kurochkin, Lopatin and Zelenkov (eds.). Fossil vertebrates of Russia and adjacent countries. Part 3. Fossil Reptiles and Birds. GEOS. 86-290.

Apsaravis Norell and Clarke, 2001
A. ukhaana Norell and Clarke, 2001
Late Campanian, Late Cretaceous
Ukhaa Tolgod, Djadokhta Formation, Mongolia
Holotype- (IGM 100/1017) (180 g) partial jugal, posterior skull, sclerotic ring, incomplete mandible, twelve cervical vertebrae, six dorsal vertebrae (4.5 mm), fragmentary dorsal ribs, synsacrum (28.6 mm), five caudal vertebrae (2.04 mm), partial pygostyle, scapulae (~52.5 mm), coracoids (29.25 mm), anterior sternum, humeri (48.43 mm), radii (43.11 mm), ulnae (45.69 mm), scapholunare, pisiform, incomplete carpometacarpi, phalanx II-1 (~9.62 mm), ilia (31.5 mm), pubes (one proximal; 30.14 mm), ischia (30.14 mm), proximal femora (~40.9 mm), distal tibiotarsi, tarsometatarsi (28.7 mm), phalanges II-1, phalanges II-2, pedal ungual II, phalanges III-1 (one proximal), phalanx III-2, phalanx III-3, pedal unguals III, phalanges IV-1, phalanges IV-2, phalanx IV-3, pedal ungual IV, several pedal phalanges, ossified tarsometatarsal tendon
Diagnosis- (after Norell and Clarke, 2001) dentary forked posteriorly (unknown in Ambiortus; also in Yixianornis+Songlingornis); strong tubercle on the proximal posterior surface of the humerus directly distal to the humeral head; distal humerus strongly flared and anteroposteriorly compressed (unknown in Ambiortus); humeral distal condyles strap-like (unknown in Ambiortus); dorsal condyle of humerus transversely oriented (unknown in Ambiortus); ventral condyle of humerus strongly projected distally (unknown in Ambiortus); enlarged lateral ridge on the femur (unknown in Ambiortus; also in hesperornithines); medial tibiotarsal condyle <60% the width of the lateral condyle (unknown in Ambiortus; also in Longicrusavis); tibiotarsal condyles do not slope towards center in distal view (unknown in Ambiortus; also in Longicrusavis); tibiotarsal intercondylar groove less than 30% as wide as distal condyles (unknown in Ambiortus); well-projected wings of the sulcus cartilaginis tibialis on the posterodistal tibiotarsus.
(after Clarke and Norell, 2002) laterally hooked acromion process (also in Yanornis); metatarsal II non-ginglymoid (unknown in Ambiortus; also in some hesperornithines and Yanornis).
Other diagnoses- Norell and Clarke (2001) also use the scapular blade which does not expand at midlength in their diagnosis, though Clarke and Norell (2002) later exclude it from their diagnosis and analysis, citing difficulty in defining it objectively. In any case, such a scapula is also present in songlingornithids and Hesperornis, making its presence in Patagopteryx, Ichthyornis and Ambiortus equally likely to be convergent as it is to be developed basally in Euornithes and lost by Apsaravis. Norell and Clarke note a supposedly apomorphic hypertrophied trochanteric crest on the femur, which is also described and photographed by Clarke and Norell. However, this structure is a posterolaterally projected crest distal to the femoral head, which is unlike trochanteric crests but like the lateral ridge of more basal maniraptorans which is derived from the trochanteric shelf. Whether the lateral ridge's size is apomorphic is uncertain, as hesperornithines have an even larger bulge and Patagopteryx and Gansus have small tubercles. Another less developed vertical ridge is present posterior to this, which could also be homologized to the trochanteric shelf. However, topologically, this would be equivalent to the posterior trochanter.
Clarke and Norell (2002) also add a fused dentary symphysis to their diagnosis, but that is optimized as a carinate character here.
Comments- The holotype was discovered in 1998 and described briefly in 2001 by Norell and Clarke, then in detail the next year (Clarke and Norell, 2002). It was originally placed as the sister taxon to Carinatae, but Clarke (2002) and Clarke and Norell (2002) found it to be the sister group of Ornithurae instead. This result has been found in further permutations of Clarke's matrix as well (e.g. You et al., 2006; O'Connor et al., 2009).
References- Clarke and Norell, 2001. Fossils and avian evolution. Nature. 414, 508.
Feduccia, 2001. Fossils and avian evolution. Nature. 414, 507-508.
Norell and Clarke, 2001. Fossil that fills a critical gap in avian evolution. Nature. 409, 181-184.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke and Norell, 2002. The morphology and phylogenetic position of Apsaravis ukhaana from the Late Cretaceous of Mongolia. American Museum Novitates. 3387, 1-46.
You, Lamanna, Harris, Chiappe, O'Connor, Ji, Lu, Yuan, Li, Zhang, Lacovara, Dodson and Ji, 2006. A nearly modern amphibious bird from the Early Cretaceous of Northwestern China. Science. 312, 1640-1643.
O'Conner, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009. Phylogenetic support for a specialized clade of Cretaceous enantiornithine birds with information from a new species. Journal of Vertebrate Paleontology. 29(1), 188-204.

Palintropus Brodkorb, 1970
Diagnosis- (after Longrich, 2009) acrocoracoid process massive and knob-like (also in Gansus and Ichthyornis); edge of humeral articular facet with a prominent lip in ventral view (also in Yixianornis); prominent scar inside supracoracoid sulcus (unknown in most non-avian euornithines).
Other diagnoses- Marsh (1892) first noted the absent procoracoid process as diagnostic, but this is shared with Apsaravis.
Here I interpret the very large, centrally and distally placed supracoracoid foramen noted as diagnostic by Hope (2002) as the proximal edge of a dorsal coracoid fossa as in Apsaravis. This same feature was described as "prominent dorsal groove in coracoid shaft" by Longrich (2009).
Longrich also included the supracoracoid foramen opening into a medial groove of the coracoid shaft, which is shared with Apsaravis.
Comments- Marsh (1892) originally included retusus in Cimolopteryx, as C. retusa. Shufeldt (1915) noted it was not referrable to Cimolopteryx and probably not even closely related, though he felt it was too fragmentary for further evaluation. Brodkorb (1963) first removed it to Apatornis, which he viewed as an ichthyornithine. He then (1970) placed it in a new genus Palintropus, which he believed was a cimolopterygid charadriiform.
Palintropus a galliform? Hope (2002) questionably referred this taxon to Galliformes. This was based on the reduced procoracoid process, coracoid facet for scapula placed entirely distal to glenoid. Several other characters were listed in Hope's Galliformes diagnosis as being reasons why she placed "specimens below" (consisting solely of Palintropus) in that order, but are eithjer undescribed (coracoid neck with stout and triangular cross section) or unknown (elongate coracoid shaft; narrow sternal end of coracoid; rudimentary lateral process) in that genus. She also noted the acrocoracoid was similar in size to galliforms (larger than tinamiforms, smaller than anseriforms and most neoavians), the absence of a pneumatic foramen is unlike tinamiforms, and the laterally positioned coracoid tubercle which merges with the glenoid is similar to galliforms. However, the procoracoid process is also absent in Patagopteryx and (as noted by Longrich, 2009) Apsaravis, while it is still present though reduced in basal galliforms like Paraortygoides, Paraortyx and Ameripodius. I also note Apsaravis has a coracoid facet placed distal to the glenoid. Lack of coracoid pneumatization is present in all non-avians (except perhaps Jixiangornis and Jianchangornis). The laterally positioned coracoid tubercle that merges with the glenoid is also found in galliforms, tinamiforms, Lithornis, Patagopteryx, Yixianornis, Jianchangornis, Ichthyornis and Ambiortus, so seems symplesiomorphic for Aves. Gansus and Ichthyornis also have moderate sized acrocoracoid processes.
Hope referred it questionably to the basal galliform family Quercymegapodiidae based on the large free lateral flange on the coracoid glenoid, further reduced procoracoid process (only with Quercymegapodius and not Ameripodius), and scar within the supracoracoid sulcus (only verified in Ameripodius). Also she correctly noticed the deep cup-like scapular facet is unlike crown galliforms. Apsaravis, Ichthyornis, Gansus, Yixianornis, Patagopteryx and Archaeorhynchus also have a large lateral flange on the coracoid glenoid. Almost all non-avian euornithines also have scapular cotyla which are deeper than those of crown galliforms. The texture of the supracoracoid sulcus is generally indeterminable in non-avian euornithines, even when they expose the sulcus as in Yixianornis. Hope, Mayr (2009) and Longrich all noted that it was unlike Tertiary Galliformes in having a supracoracoid foramen, and Longrich stated it differed further in lacking a strongly hooked acrocoracoid.
Thus Palintropus does not share any characters with galliforms not seen in Apsaravis except for the larger acrocoracoid (which is also seen in some non-avian euornithines). As Palintropus has some characters which exclude it from Galliformes, and the only character shared with a quercymegapodiid (the supracoracoid sulcus scar) is indeterminate in Apsaravis and most other non-avian euornithines, it is near certainly not a member of Quercymegapodiidae.
Palintropus related to Apsaravis? Longrich (2009) suggested Palintropus was related to Apsaravis based on the absent procoracoid process and medial supracoracoid groove. They also seem to share a deep dorsal fossa in the coracoid. While these characters are also shared with most enantiornithines, the scapulocoracoid articulation is unlike that clade. The referred dorsal and femur also lack enantiornithine synapomorphies (e.g. they have anteriorly placed parapophyses and no posterior trochanter). Longrich et al. (2011) included Palintropus in a version of Clarke's matrix where it claded with Apsaravis, but did not include basal galliforms that could test Hope's hypothesis.
References- Marsh, 1892. Notes on Mesozoic vertebrate fossils. American Journal of Science. 55, 171-175.
Shufeldt, 1915. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.
Brodkorb, 1970. The generic position of a Cretaceous bird. Quarterly Journal of the Florida Academy of Science. 32(3), 239-240.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Mayr, 2009. Paleogene Fossil Birds. Springer-Verlag, Heidelberg & New York. 262 pp.
Longrich, Tokaryk and Field, 2011. Mass extinction of birds at the Cretaceous-Paleogene (K–Pg) boundary. Proceedings of the National Academy of Sciences. 108(37), 15253-15257.
P. retusus (Marsh, 1892) Brodkorb, 1970
= Cimolopteryx retusa Marsh, 1892
= Apatornis retusus (Marsh, 1892) Brodkorb, 1963
Late Maastrichtian, Late Cretaceous
Lance Formation, Wyoming, US
Holotype- (YPM 513) proximal coracoid
Diagnosis- (after Longrich, 2009) smaller than both Campanian species; lacks kink in the ridge connecting the humeral articular facet and acrocoracoid; acrocoracoid process shorter and more expanded; humeral articular facet broader anteriorly than posteriorly; dorsal groove extends to level of scapular cotyle.
Comments- The holotype was discovered in 1980.
References- Marsh, 1892. Notes on Mesozoic vertebrate fossils. American Journal of Science. 55, 171-175.
Brodkorb, 1963. Birds from the Upper Cretaceous of Wyoming. in Sibley (ed.). Proceedings of the XIII International Ornithological Congress. 50-70.
Brodkorb, 1970. The generic position of a Cretaceous bird. Quarterly Journal of the Florida Academy of Science. 32(3), 239-240.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
P. sp. nov. (Hope, 2002)
Late Campanian, Late Cretaceous
Dinosaur Park Formation, Alberta, Canada
Material- (TMP 1986.036.0126) proximal coracoid (Hope, 2002)
?(TMP 1989.081.0012) dorsal vertebra (Longrich, 2009)
?(TMP 2001.012.0150) distal femur (Longrich, 2009)
Diagnosis- (after Longrich, 2009) over twice as large as P. retusus, a third larger than the other Campanian species; kink in the ridge connecting the humeral articular facet and acrocoracoid; acrocoracoid process shorter and more expanded; humeral articular facet broader anteriorly than posteriorly; dorsal groove extends to level of scapular cotyle.
Comments- Hope (2002) referred TMP 1986.036.0126 to a new species of Palintropus, along with TMP 1986.146.0011, 1988.116.0001 and five other TMP specimens. She noted some of these specimens were smaller, so might belong to another species, or that Palintropus may have been sexually dimorphic. Longrich referred TMP 1986.036.0126 to his Palintropus species A, along with a dorsal vertebra and femur based on their size.
References- Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
P. sp. nov. (Longrich, 2009)
Late Campanian, Late Cretaceous
Dinosaur Park Formation, Alberta, Canada
Material- (TMP 1983.036.0070) coracoid fragment (Longrich, 2009)
(TMP 1988.116.0001) proximal coracoid (Hope, 2002)
?(TMP 1989.050.0053) dorsal vertebra, partial synsacrum (Longrich, 2009)
(TMP 1992.053.0003) coracoid fragment (Longrich, 2009)
?(TMP 1996.012.0336) femur (Longrich, 2009)
(TMP 2005.012.0190) partial coracoid (Longrich, 2009)
Late Campanian, Late Cretaceous
Foremost Formation, Alberta, Canada
?(TMP 1986.146.0011) proximal scapula (Hope, 2002)
Diagnosis- (after Longrich, 2009) intermediate in size between other species; lacks kink in the ridge connecting the humeral articular facet and acrocoracoid; acrocoracoid process taller and less expanded; humeral articular facet strongly semicircular; dorsal groove does not extend to level of scapular cotyle.
Comments- Hope (2002) referred TMP 1986.146.0011 and 1988.116.0001 to the same undetermined Palintropus species as TMP 1986.036.0126, though she noted the latter might belong to a different species or sex. Longrich (2009) placed the former specimens in his new Palintropus species B, which he stated differed markedly in morphology from P. retusus or P. species A.
References- Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
P. sp. (Hope, 2002)
Late Campanian, Late Cretaceous
Belly River Group, Alberta, Canada
Material- (TMP coll.) three partial coracoids (Hope, 2002)
Comments- Hope (2002) referred five coracoids in the TMP collections to her new Palintropus species, two of which are probably TMP 1983.036.0070 and 1992.053.0003 that were later mentioned by Longrich (2009) and referred to his Palintropus species B. Whether the other three belong to P. species A or B is unknown.
References- Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.

unnamed possible apsaraviform (Longrich, 2009)
Late Campanian, Late Cretaceous
Upper Dinosaur Park Formation, Alberta, Canada
Material- (UALVP 47942; Ornithurine C) proximal coracoid
Diagnosis- (after Longrich, 2009) small size; subcircular scapular cotyle; procoracoid process absent.
Comments- Longrich (2009) assigned this to his Ornithurae sensu Gauthier and de Quieroz based on an anteriorly placed scapular facet, and noted "within the Ornithurae, absence of a procoracoid process is a derived feature shared with Palintropus and Apsaravis, suggesting that it may be related to either or both.. Agnolin (2010) suggested it was a cimolopterygid, but Mohr et al. (2021) correctly noted it lacks his proposed characters for the family- distally extensive procoracoid process; laterally angled glenoid; distally placed and enlarged supracoracoid foramen (unknown as the bone is broken proximal to the foramen).
References- Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Agnolin, 2010. An avian coracoid from the Upper Cretaceous of Patagonia, Argentina. Studia Geologica Salmanticensia. 46(2), 99-119.
Mohr, Acorn, Funston and Currie, 2021 (2020 online). An ornithurine bird coracoid from the Late Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences. 58(2), 134-140.

Ornithurae Haeckel, 1866
Official Definition- (Hesperornis regalis + Ichthyornis dispar + Vultur gryphus) (Benito, Chen, Wilson, Bhullar, Burnham and Field, 2022; Registration Number 554)
Other definitions- (Passer domesticus <- Archaeopteryx lithographica) (Sereno, online 2005; modified from Gauthier, 1986)
(Hesperornis regalis + Passer domesticus) (Turner, Makovicky and Norell, 2012; modified from Padian, Hutchinson and Holtz, 1999; modified from Chiappe, 1991)
(tail shorter than the femur and with an upturned and ploughshare-shaped compressed pygostyle in the adult, composed of less than six segments, and shorter than the less than eight free caudals homologous with Vultur gryphus) (Gauthier and de Queiroz, 2001)
(Hesperornis regalis + Ichthyornis dispar + Passer domesticus) (modified from Padian, 2004)
= Ornithurae sensu Chiappe, 1991
Definition- (Hesperornis regalis + Passer domesticus) (modified)
= Carinatae sensu Chiappe, 1995
Definition- (Ichthyornis dispar + Passer domesticus) (modified)
= Ornithurae sensu Padian, 2004
Definition- (Hesperornis regalis + Ichthyornis dispar + Passer domesticus) (modified)
References- Haeckel, 1866. Generelle Morphologie der Organismen: allgemeine Grundzüge der organischen Formen-Wissenschaft mechanisch begründet durch die von Charles Darwin reformierte Deskendenz-Theorie. G. Reimer. 574 pp.
Gauthier, 1986. Saurischian monophyly and the origin of birds. Memoirs of the Californian Academy of Sciences 8, 1-55.
Chiappe, 1991. Cretaceous avian remains from Patagonia shed new light on the early radiation of birds. Alcheringa. 15, 333-338.
Chiappe, 1995. The first 85 million years of avian evolution. Nature. 378, 349-355.
Padian, Hutchinson and Holtz, 1999. Phylogenetic definitions and nomenclature of the major taxonomic categories of the carnivorous Dinosauria (Theropoda). Journal of Vertebrate Paleontology. 19(1), 69-80.
Gauthier and de Quieroz, 2001. Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and the name "Aves." In Gauthier and Gall (eds.). New Perspectives on the Origin and Early Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom. Peabody Museum of Natural History. 7-41.
Padian, 2004. Basal Avialae. In Weishampel, Dodson and Osmolska (eds.). The Dinosauria Second Edition. University of California Press. 210-231.
Sereno, online 2005. Stem Archosauria - TaxonSearch. http://www.taxonsearch.org/dev/file_home.php [version 1.0, 2005 November 7]
Turner, Makovicky and Norell, 2012. A review of dromaeosaurid systematics and paravian phylogeny. Bulletin of the American Museum of Natural History. 371, 1-206.
Benito, Chen, Wilson, Bhullar, Burnham and Field, 2022. Forty new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds. PeerJ. 10:e13919.

Gargantuaviidae Buffetaut and Angst, 2019
Gargantuavis Buffetaut and Le Loeuff, 1998
G. philoinos Buffetaut and Le Loeuff, 1998
Early Maastrichtian, Late Cretaceous
Bellevue, Marnes de la Maurine Formation, Aude, France
Holotype- (MDE-CE-525) synsacrum (180 mm), partial ilia
Late Campanian-Early Maastrichtian, Late Cretaceous
Combebelle site, Villespassans, Herault, France
Paratype- ?(MDE-A08) (>10 year old adult; 147 kg) incomplete femur (~334 mm)
Late Campanian-Early Maastrichtian, Late Cretaceous
Montplo-Nord, Cruzy, Herault, France
Referred- (MC-MN 431) ilial fragment (Buffetaut and Angst, 2015; described by Buffetaut and Angst, 2016b)
?..?(MC-MN 478) mid cervical vertebra (Buffetaut, 2011a; described by Buffetaut and Angst, 2013)
?...(MC-MN 1165) synsacral fragment (Buffetaut and Angst, 2015; described by Buffetaut and Angst, 2016b)
?...(MC-MN 1335) (~57 kg) femur (235 mm) (Angst and Buffetaut, 2018; described by Buffetaut and Angst, 2019)
Late Campanian-Early Maastrichtian, Late Cretaceous
Bastide-Neuve, Fox Amphioux, Var, France
(BN 758) incomplete synsacrum, partial ilia (Buffetaut and Angst, 2015; described by Buffetaut, Angst, Mechin and Mechin-Salessy, 2015)
(BN 763) dorsal rib fragment, incomplete synsacrum, partial ilium, ?ilial fragment (Buffetaut and Angst, 2015; described by Buffetaut, Angst, Mechin and Mechin-Salessy, 2015)
(Mechin coll. 711) (75 kg) incomplete femur (Buffetaut, Angst, Mechin and Mechin-Salessy, 2019)
?(MDE-A07) partial synsacrum (Buffetaut, Angst, Mechin and Mechin-Salessy, 2015)
Late Campanian, Late Cretaceous
Laño, Sedano Formation, Spain
(MCNA 2583) partial synsacrum, ilial fragments (Buffetaut and Angst, 2015; described by Angst, Buffetaut, Corral and Pereda-Suberbiola, 2017)
Early Maastrichtian, Late Cretaceous
Nălaţ-Vad, Sinpetru Formation, Romania
(UBB V649) synsacrum (147 mm), incomplete ilia (Mayr, Codrea, Solomon, Bordeianu and Smith, 2020)
Diagnosis- (after Buffetaut and Le Loeuff, 1998) robust and short synsacrum; ten synsacral vertebrae; broad pelvis; acetabulum placed at level of third and fourth synsacral transverse processes; well-developed antitrochanter placed posterodorsally to large acetabulum; ilia do not contact dorsally.
(after Buffetaut and Angst, 2016a) heterocoelous cervical vertebra with remarkably narrow posterior articular surface; synsacrum markedly arched ventrally; pelvis extensively pneumatized; robust femur with trochanteric crest but no posterior trochanter.
(after Buffetaut and Angst, 2019) synsacrum and ilium extensively pneumatized; lateral femoral condyle is divided into two semicondyles; medial condye extends farther distally than lateral condyle.
Comments- Buffetaut et al. (1995) described a synsacral fragment of a large bird, which they left unnamed. Buffetaut and Le Loeuff (1998) later described the holotype partial pelvis and paratype femur from different localities as the new taxon Gargantuavis philoinos. They referred the femur because of its similar size and large trochanteric crest which could articulate with the holotype's antitrochanter, but this must be regarded as provisional. While they state the previously described synsacral fragment MDE-A07 is similar to the middle of MDE-CE-525, they do not refer it explicitly to the taxon. Buffetaut (2011a, b) first noted a referred completely heterocoelous cervical vertebra, which was described by Buffetaut and Angst (2013). A new femur MC-MN 1335 was described by Angst et al. (2019), which along with the cervical and sacral and ilial fragments (Buffetaut and Angst, 2016b) "come from the same sedimentary layer and were found a short distance from each other and may belong to a single individual." This femur is smaller and at first glance very different in shape from the paratype, but Angst et al. argue to paratype is extremely crushed and badly reconstructed. They stated that if the two are different taxa, MC-MN 1335 was more likely to be Gargantuavisas it was found in the same locality as other specimens. Buffetaut et al. (2019) describe a new femur Mechin coll. 711 from the same beds as three other synsacra which resembles MC-MN 1335, further supporting the referral of this morphotype to Gargantuavis. Mayr et al. (2020) describe a new partial pelvis found in 2003 in Romania as "Gen. et sp. indet. (cf. Elopteryx nopcsai Andrews, 1913)" although they also call it Gargantuavis multiple times in the paper. They state it is "only about 80% the size of the G. philoinos holotype, from which it furthermore differs in a more caudally positioned acetabulum, which is situated on the level of the fifth synsacral vertebra, whereas it is on the level of the fourth vertebra in G. philoinos" and thus "certainly represents a different species." While this may be true, Mesozoic theropod species show large varience in size and only the holotype and Bastide-Neuve pelvises can be shown to have anteriorly placed acetabula. If further discoveries show correlated characteristics in certain localities, it may prove more useful to separate Gargantuavis species.
Buffetaut and Le Loeuff (1998) placed Gargantuavis as a non-ornithurine euornithine, closer to Patagopteryx based on the broad pelvis but closer to ornithurines in sacral number. Despite the large number of basal euornithines described in the last two decades, Buffetaut's qualitative opinion has remained vague with Buffetaut and Angst (2019) stating only "Gargantuavis philoinos is certainly an ornithuromorph, and in all likelihood a basal ornithurine" while assigning it a monotypic family. Mayr (2009; based on Worthy, pers. comm.) suggested Gargantuavis was pterosaurian based on the anteriorly placed acetabulum and contemporaneous large azhdarchids, but Buffetaut and Le Loeuff (2011) demonstrated pterosaur femora are highly dissimilar and that that clade generally has posteriorly placed acetabula. Mayr et al. (2020) subsequently agreed "azhdarchid affinities of Gargantuavis are not well founded." Most recently, Mayr et al. (2020) suggested Gargantuavis was excluded from Ornithurae based on the unfused pelvis (iliopubic and ilioischial articulations in UBB V649) and from Pygostylia based on middle sacral vertebrae without transverse expansion. While sacral expansion has yet to be incorporated into phylogenetic analyses, a lack of pelvic fusion also seems to be present in Enaliornis (BGS 87431). Mayr et al. noted that the proximal femur Elopteryx "was of a similar size to UBB V649, and we consider it well possible that the new pelvis belongs to Elopteryx", but the latter taxon was recovered as a non-ornithothoracine avialan by Hartman et al. (2019) and certainly differs from both supposed Gargantuavis femora. They further argued the basal avialan Balaur was similar in a few features (ventrally arched sacrum, broad pelvis, large antitrochanter) although smaller with a fused pelvis. This led them to propose the hypothesis that "Elopteryx, Balaur, and Gargantuavis belong to a distinctive theropod clade, which was characteristic for the Late Cretaceous European archipelago or parts thereof." Gargantuavis has only been entered into a single published phylogenetic analysis, that of Hartman et al. (2019) which recovered it as a non-hesperornithoid hesperornithine (a clade which included Ichthyornis). This is unchanged after entering in the new data from MC-MN 1335 and UBB V649. Forcing it to be sister to Balaur takes 11 more steps, while forcing it to be sister to Patagopteryx only takes 1 more step. Restricting the OTU to sacral and ilial characters retains its position as a basal hesperornithine, and forcing it sister to Balaur takes 6 more steps while forcing it to be sister to Elopteryx takes 3 steps but the latter moves to Hesperornithes instead of Gargantuavis being more basal. Forcing all three genera to form an exclusive clade is 8 steps longer, with the phylogenetic position of Balaur winning out. Considering this data, Gargantuavis is here considered to be an euornithine not particularly close to Balaur, with the cervical and femora probably correctly referred considering their phylogenetic characters and stratigraphical proximity at Montplo-Nord. Elopteryx is more parsimoniously the femur of Balaur (1 step longer).
References- Buffetaut, Le Loeuff, Mechin and Mechin-Salessy, 1995. A large French Cretaceous bird. Nature. 377, 110.
Buffetaut and Le Loeuff, 1998. A new giant ground bird from the Upper Cretaceous of southern France. Journal of the Geological Society, London. 155(1), 1-4.
Buffetaut, 2002. Giant ground birds at the Cretaceous-Tertiary boundary: Extinction or Survival? In Koeberl and MacLeod (eds.). Catastrophic Events and Mass Extinctions: Inpacts and Beyond. Geological Society of America Special Paper. 356, 303-306.
Mayr, 2009. Paleogene Fossil Birds. Berlin: Springer. 262 pp.
Buffetaut, 2011a. Gargantuavis philoinos: Giant bird or giant pterosaur? 9th Annual Meeting of the European Association of Vertebrate Palaeontologists. 16-17.
Buffetaut, 2011b. Giant birds from the Late Cretaceous of southern France: An update. 8th Romanian Symposium of Paleontology, Abstract Book. 13-14.
Buffetaut and Le Loeuff, 2010. Gargantuavis philoinos: Giant bird or giant pterosaur? Annales de Paléontologie. 96(4), 135-141.
Buffetaut and Angst, 2013. New evidence of a giant bird from the Late Cretaceous of France. Geological Magazine. 150(1), 173-176.
Chinsamy, Buffetaut, Canoville and Angst, 2014. Insight into the growth dynamics and systematic affinities of the Late Cretaceous Gargantuavis from bone microstructure. Naturwissenschaften. 101(5), 447-452.
Buffetaut and Angst, 2015. Twenty years of Gargantuavis philoinos: A summing up on an enigmatic Late Cretaceous giant bird. SVPCA 2015, 24.
Buffetaut, Angst, Mechin and Mechin-Salessy, 2015. New remains of the giant bird Gargantuavis philoinos from the Late Cretaceous of Provence (south-eastern France). Palaeovertebrata. 39(2), e3.
Buffetaut and Angst, 2016a. The giant flightless bird Gargantuavis philoinos from the Late Cretaceous of southwestern Europe: A review. New Mexico Museum of Natural History and Science Bulletin. 71, 41-50.
Buffetaut and Angst, 2016b. Pelvic elements of the giant bird Gargantuavis from the Upper Cretaceous of Cruzy (southern France), with remarks on pneumatisation. Cretaceous
Research. 66, 171-176.
Angst, Buffetaut, Corral and Pereda-Suberbiola, 2017. First record of the Late Cretaceous giant bird Gargantuavis philoinos from the Iberian Peninsula. Annales de Paléontologie. 103(2), 135-139.
Angst and Buffetaut, 2018 (online 2017). Paleobiology of giant flightless birds. ISTE Press - Elsevier. 296 pp.
Buffetaut and Angst, 2019. A femur of the Late Cretaceous giant bird Gargantuavis from Cruzy (southern France) and its systematic implications. Palaeovertebrata. 42(1), e3.
Buffetaut, Angst, Mechin and Mechin-Salessy, 2019. A femur of the giant bird Gargantuavis from the Late Cretaceous of Var (south-eastern France). Carnets natures. 6, 47-52.
Buffetaut and Angst, 2020. Gargantuavis is an insular basal ornithurine: A comment on Mayr et al., 2020, 'A well-preserved pelvis from the Maastrichtian of Romania suggests that the enigmatic Gargantuavis is neither an ornithurine bird nor an insular endemic'. Cretaceous Research. 112, 104438.
Mayr, Codrea, Solomon, Bordeianu and Smith, 2020 (online 2019). A well-preserved pelvis from the Maastrichtian of Romania suggests that the enigmatic Gargantuavis is neither an ornithurine bird nor an insular endemic. Cretaceous Research. 106, 104271.
Mayr, Codrea, Solomon, Bordeianu and Smith, 2020. Reply to comments on "A well-preserved pelvis from the Maastrichtian of Romania suggests that the enigmatic Gargantuavis is neither an ornithurine bird nor an insular endemic". Cretaceous Research. 112, 104465.

Zhyraornithi Nessov, 1992
Zhyraornithidae Nesov, 1984
Zhyraornis Nesov, 1984
Diagnosis- (modified from Nesov, 1984) sacral centra four through eight extremely narrow ventrally (<30% of dorsal sacral width); well developed lateral fossa in second sacral centrum.
Other diagnoses- Of Nesov's (1984) other characters in his diagnosis- amphicoelous centra are symplesiomorphic for theropods; the sacrum's narrowness is similar to other basal carinates; the neural spine crest is continuous in most birds and is not tall in Z. logunovi; and the first sacral centrum has lateral fossae in Ichthyornis and Guildavis as well. Nessov's other characters are based on the questionably referred paratype dorsal (lateral central fossae in dorsal vertebrae) and scapula (curved and projected acromion).
Kurochkin (2000) included several additional characters in his diagnosis for the genus, but none are valid. Apatornis and many other Mesozoic birds have ventrally concave synsacra. The anterior articular surface is not particularily broad in Z. logunovi at least (width ~107% of height), comparable to the subcircular surfaces described for Ichthyornis and Guildavis. The slight anterior broadening is comparable to other basal carinates, as is the absence of a ventral groove. Ichthyornis can also only have one sacral with small transverse processes in front of those with large processes (in the holotype, but not YPM 1372). Finally, the largest transverse processes (on sacrals two and three) are also posteriorly directed in Ichthyornis.
Comments- Nesov (1984) first referred Zhyraornis to its own family within Ichthyornithiformes (in which he included Apatornis), due to the amphicoelous anterior articular surface and pleurocoels in the first two centra. While the latter seems to be based on incorrect homology with YPM 1372, Nesov was correct in his general idea. In 1992, he erected the suborder Zhyraornithi within Ichthyornithiformes, presumably to separate Zhyraornis further from Ichthyornis and Apatornis. Kurochkin (1995) suggested it was an enantiornithine, based on several characters and similarity to Gobipteryx (= Nanantius valifanovi of Kurochkin). Of the characters he lists, "flatness and general shape" are vague, but Zhyraornis has highly convex centra ventrally and the general sacral shape is almost identical to Apatornis. Contra Kurochkin, a ventral groove is absent in Zhyraornis, and pleurocoels are present anteriorly in Ichthyornis and Guildavis. In 1996, he elaborated his view, referring Zhyraornis to the Alexornithidae within Enantiornithes, again based on comparison to Gobipteryx. He referred it to Enantiornithes based on three characters. "General shortness" cannot be evaluated due to the missing posterior ends, but the taper of the sacrum and proportions of each vertebrae match Ichthyornis and Apatornis closely. The most anterior portion is said to have small, equisized transverse processes ventrally, but transverse processes two and three are much larger than the others, as in Apatornis and somewhat less in Ichthyornis (in the latter the third is largest, while the second is similar to the fourth). The wide neural canal is shared with all birds and most small maniraptoriforms. He referred it to Alexornithidae based on three characters. Dorsal curvature is also present in Apatornis and many other birds. Contra Kurochkin, the transverse processes are not equisized, being much larger in sacrals two and three, as noted above. Finally, he states only two or three costal processes are enlarged on the anterior synsacrum, but this is true in Apatornis, and is not necessarily true in Gobipteryx, as the anterior one or two sacrals are missing their lateral processes. Kurochkin later (2006) placed Zhyraornis in Euornithes (his Ornithurae) based on unstated characters. In both his phylogram and cladogram, it is placed between Confuciusornithidae (which Kurochkin viewed as basal euornithines unrelated to dinosaurs, while enantiornithines were theropods) and Carinatae. His cladogram specifies a placement more derived than Liaoningornis, yet they share no known elements, so the result would be impossible in an actual phylogenetic analysis. His phylogram indicates indicates he believed it branched around Patagopteryx, Kuszholia and Gargantuavis. O'Connor (2009) correctly criticized Kurochkin's (1995) characters and felt "a placement in Ornithuromorpha may be more fitting", noting that both Zhyraornis synsacra differed from enantiornithines. Yet she also declared the genus a nomen dubium without demonstrating its published diagnostic characters are present in any other taxon. Based on the diagnosis above, the taxon is valid.
Both species of Zhyraornis are similar in general morphology. The large lateral fossae on centra one and two are likely continuations of such fossae in the dorsal vertebrae, as seen in most Cretaceous avialans. Z. kashkarovi's sacrum includes at least seven vertebrae, indicating they belong to Avialae or perhaps Caenagnathoidea. Yet caenagnathoids with seven sacrals differ in having all sacral vertebrae pleurocoelous, except Avimimus which has apneumatic centra and a ventral median groove. Sapeornis' sacrum is dissimilar in that the posterior transverse processes are most robust and the anterior three are directed anteriorly. Confuciusornis differs in having broader centra with a ventral groove and robust posterior transverse processes, though the anterior centra are similar in having pleurocoels. Most enantiornithines differ in having much broader centra with ventral grooves where known, and robust posterior transverse processes. The Lecho Formation enantiornithine PVL-4041-4 is roughly similar, although the first centrum is narrower and the fifth and sixth are broader. Also, the second and third transverse processes angle anteriorly instead of posteriorly, while those of the fourth, sixth and seventh vertebrae are more prominent. Gansus' is much broader after sacral two, with transverse processes two and three directed perpendicular or anteriorly and those of five and six more prominent. It seems to be similar in having fossae on sacral centra one and two though. Hesperornithines and neornithines differ in having a heterocoelous anterior articulation, while hesperornithines also differ in being non-pneumatic. Ichthyornis' sacrum is extremely similar in centrum width, transverse process size and direction, though the third transverse process is broader ventrally and the fourth better developed. Importantly, they share a series of midsacral reduced transverse processes, which is a carinate sensu lato character. It is also similar in having pleurocoels on the first centrum, though seemingly not on the second. A complication is YPM 1372, which fused an extra dorsal to its sacrum, giving it two sacrals with pleurocoels. Yet the transverse process morphology in Zhyraornis suggests its first sacral is homologous to the second sacral in YPM 1372 and the first sacral in the Ichthyornis holotype. In Z. logunovi at least, the second transverse process is as robust as the third, unlike Ichthyornis. One major difference between Zhyraornis and Ichthyornis is that the centra of the former narrow drastically after the third centrum. Apatornis' is similar in being narrow and having a series of midsacrals with reduced transverse processes. The transverse process size and orientation are similar where known. Yet it differs from Zhyraornis in lacking a pleurocoel on sacral two (sacral one is not preserved), and apparently having less narrow centra ventrally, especially in the posterior centra (Nesov, 1984). Guildavis is similar in having narrow anterior centra without a ventral groove, and a pleurocoel on the first centrum. There may a be a pleurocoel in the second sacral as well, but if so it is smaller than Zhyraornis. Poor preservation presents further comparison. Which of these last three taxa Zhyraornis is more closely related to is unknown, as the total number of vertebrae, number of vertebrae with reduced transverse processes, and presence of parapophyses on the first vertebra are unknown. It is here assigned to Carinatae sensu Chiappe incertae sedis.
References- Nesov, 1984a. Pterozavry i ptitsy pozdnego mela Sredney Azii. Paleontologicheskii Zhurnal. 1, 47-57.
Nesov, 1984b. Upper Cretaceous pterosaurs and birds from central Asia. Paleontological Journal. 1, 38-49.
Nessov, 1992. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 1995. Synopsis of Mesozoic birds and early evolution of class Aves. Archaeopteryx. 13, 47-66.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
Kurochkin, 2006. Parallel evolution of theropod dinosaurs and birds. Entomological Review. 86(suppl. 1), S45-S58.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
Z. kashkarovi Nesov, 1984
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (TsNIGRI 42/11915) (~225 mm) anterior synsacrum (27 mm)
Diagnosis (after Nesov, 1984) neural spine crest on synsacrum tall.
(after Nessov, 1992) sacrum more concave ventrally than Z. logunovi or Apatornis; transverse processes in second and third sacrals with little projection in dorsal view; transverse processes of second and third sacrals extremely thin in ventral view.
(after Kurochkin, 2000) sacral centra four to eight <20% of dorsal width of sacrum.
Other diagnoses- Kurochkin (2000) listed a couple additional characters in his diagnosis. The slight anterior expansion of the first sacral centrum is indistinguishable from Guildavis. He notes the largest transverse processes (on sacrals two and three) are posteriorly angled (~55-60 degrees), but Ichthyornis shows this can be quite variable (~55-71 degrees in YPM 1372 and perhaps 86 degrees in the holotype), so this cannot be used to diagnose species. The sacrum does not appear more "extended" than in other basal carinates.
Comments- Zhyraornis kashkarovi was first used in Nessov and Borkin (1983) as a figure caption for the dorsal vertebra TsNIGRI 43/11915, which was later made a paratype of the species. As no description accompanied the name, it was a nomen nudum. It may belong to Zhyraornis, as it seems to be an ornithothoracine but not an enantiornithine, hesperornithine or avian. It is given its own entry here, however. Nesov made additional specimens paratypes of Z. kashkarovi as well. The proximal scapula TsNIGRI 44/11915 is here referred to Euornithes incertae sedis, while the humeral shaft TsNIGRI 45/11915 is referred to Maniraptora indet.. Isolated shafts of long bones (TsNIGRI 48/11915, 49/11915 and 50/11915) which were not described or illustrated are similarly referred to Maniraptora indet..
The tall neural spine is the only one of Nesov's (1984) original diagnostic characters for Z. kashkarovi that is still valid at the species level. The others are dealt with under the genus entry. Nessov (1992) in his diagnosis of the new species Z. logunovi noted numerous differences, a few of which are apomorphic and are noted above.
References- Nessov and Borkin, 1983. New records of bird bones from the Cretaceous of Mongolia and Soviet Middle Asia. USSR Academy of Sciences, Proceedings of the Zoological Institute. 116, 108-110 (in Russian).
Nesov, 1984a. Pterozavry i ptitsy pozdnego mela Sredney Azii. Paleontologicheskii Zhurnal. 1, 47-57.
Nesov, 1984b. Upper Cretaceous pterosaurs and birds from central Asia. Paleontological Journal. 1, 38-49.
Nessov, 1992. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
Z. logunovi Nessov, 1992
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (ZIN PO 4600) (~200 mm) anterior synsacrum (~24 mm)
Diagnosis- (after Nessov, 1992b) wider anterior articular surface than Z. kashkarovi; pleurocoel in first sacral vertebra larger than Z. kashkarovi.
Other diagnoses- Of Nessov's (1992b) other listed diagnostic characters, the narrow sacrum with prominent ventral ridge is also present in Z. kashkarovi. The second sacral transverse process angles to be perpendicular to the sacrum long axis distally, which is indeed unlike Z. kashkarovi (unless it is broken in the latter), but is similar to Ichthyornis. The third sacral's transverse processes angle posteriorly ~69-78 degrees, which is less than Z. kashkarovi (~55-60 degrees), but Ichthyornis shows this can be quite variable (~55-71 degrees in YPM 1372 and perhaps 86 degrees in the holotype), so this cannot be used to diagnose species. The low amount of ventral concavity seem to be primitive, as Apatornis is similar. The more ventrally placed second vertebra's pleurocoel may be diagnostic, but the pneumatic features are known to exhibit a high degree of variation between individuals and even between sides of the vertebra. The well developed anterior transverse processes (in dorsal view) and wide ventral struts supporting them are plesiomorphically similar to Ichthyornis and Apatornis, though indeed dissimilar to Z. kashkarovi. Nessov stated the upper ridge behind the contact of the second and third sacrals was wider and better developed than in Z. kashkarovi, but I don't see a difference. Most of the spinal nerve foramina are said to be more anteroposteriorly compressed, but this is not apparent in the poor photocopy available and has unknown variation.
Kurochkin (2000) listed two additional characters in his diagnosis. The abrupt anterior expansion of the first sacral centrum is similar to Ichthyornis. The sacrum is not "generally expanded and broadened" for a carinate, only in comparison to the derived condition in Z. kashkarovi.
Comments- This specimen was discovered in 1989 and mentioned as a new species of Zhyraornis (though unnamed) by Mourer-Chauvire (1989) and Nessov (1992a). Kurochkin (1996) considered Z. logunovi to probably belong to a separate genus than Z. kashkarovi based on the characters described by Nessov, but they seem more similar to each other than to other Mesozoic birds, with the narrow posterior centra and lateral fossae on sacral centrum two being derived characters not present in Ichthyornis or Apatornis. In contrast, O'Connor (2009) stated the holotypes "are not readily distinguishable; the differences suggested by the diagnosis provided by Kurochkin (2003) [actually 2000] cannot be confirmed from published figures." I disagree and find the characters cited in my diagnoses from Nessov's and Kurochkin's works to be readily visible in their figures.
References- Mourer-Chauvire, 1989. Society of Avian Paleontology and Evolution Information Newsletter. 3.
Nessov, 1992a. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. In Campbell (ed.). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.
Nessov, 1992b. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.

unnamed ornithurine (Longrich, 2009)
Late Campanian, Late Cretaceous
Oldman Formation, Alberta, Canada
Material- (TMP 1988.087.0027; Ornithurine D; Devil's Coulee bird) proximal coracoid
Diagnosis- (after Longrich, 2009) robust coracoid neck; robust rim of scapular cotyle; small, proximally placed nerve foramen with a slit-like ventral opening; relatively small size.
Comments- Longrich (2009) assigned this to his Ornithurae sensu Gauthier and de Quieroz based on an anteriorly placed scapular facet. Agnolin (2010) suggested it was a cimolopterygid, but Mohr et al. (2021) correctly noted it lacks his proposed characters for the family- distally extensive procoracoid process (presence of process "unclear" according to Longrich); distally placed and enlarged supracoracoid foramen; laterally angled glenoid.
References- Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Agnolin, 2010. An avian coracoid from the Upper Cretaceous of Patagonia, Argentina. Studia Geologica Salmanticensia. 46(2), 99-119.
Mohr, Acorn, Funston and Currie, 2021 (2020 online). An ornithurine bird coracoid from the Late Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences. 58(2), 134-140.

unnamed ornithurine (Longrich, 2006)
Late Campanian, Late Cretaceous
Upper Dinosaur Park Formation, Alberta, Canada
Material- (TMP 1998.068.0145) proximal carpometacarpus
Diagnosis- carpal fovea occupies entire proximal surface of metacarpal I; scar possibly for pisiform ligament present on dorsal surface of metacarpal II.
Comments- Longrich's phylogenetic analysis placed that taxon closer to Aves than Apsaravis, but further than Ichthyornis and Limenavis. Despite this phylogenetic position and apparent diving adaptations (thick-walled bones; distally placed extensor process), it is not especially similar to the only known hesperornithine carpometacarpal material (Pasquiaornis). The latter differs in Longrich's characters 3 ("Distal carpals, ventral ridge of carpal trochlea: radius of ventral ridge smaller than or subequal to radius of dorsal ridge (0)"), 8 ("Metacarpal I, concave proximal margin: absent (0)") and 15 ("Pisiform process, position on metacarpal II: ... cranially displaced towards base of metacarpal I (1)").
Reference- Longrich, 2006. An ornithurine bird from the Late Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences. 43, 1-7.

unnamed ornithurine (Bell and Everhart, 2011)
Late Cenomanian, late Cretaceous
Lincoln Limestone Member of the Greenhorn Limestone Formation, Kansas, US
Material- (FHSM VP-17459) proximal coracoid
Comments- Discovered in Summer 2004, Bell and Everhart (2011) described this as Ichthyornithes indet., but the character they based this on ("prominent, medially projecting acrocoracoid process") is also present in many avians such as 'cimolopterygids'.
Reference- Bell and Everhart, 2011. Remains of small ornithurine birds from a Late Cretaceous (Cenomanian) microsite in Russell County, north-central Kansas. Transactions of the Kansas Academy of Science. 114(1-2), 115-123.

Odontornithes Marsh, 1873
Definition- (Ichthyornis anceps, Hesperornis regalis <- Passer domesticus) (Martyniuk, 2012)
= Odontognathae Wetmore, 1930
= Ichthyornithes sensu Clarke, 2004
Definition- (Ichthyornis dispar <- Struthio camelus, Tinamus major, Vultur gryphus)
= Hesperornithes sensu Sereno, online 2005
Definition- (Hesperornis regalis <- Passer domesticus)
Comments- Marsh (1873) named the new subclass Odontornithes for Ichthyornis. He later (1875a, b) included Hesperornis in Odontornithes as well, though in a separate order. Wetmore (1930) named Odontognathae as a superorder containing Hesperornithiformes and Ichthyornithiformes.
References- Marsh, 1873. On a new sub-class of fossil birds (Odontornithes). American Journal of Science, 3rd series. 5, 161-162.
Marsh. 1875a. On the Odontornithes, or birds with teeth. American Journal of Science, Series 3. 10(59), 403-408.
Marsh, 1875b. Odontornithes, or birds with teeth. The American Naturalist. 9(12), 625-631.
Wetmore, 1930. A systematic classification for the birds of the world. Proceedings of the US National Museum. 76(24), 1-8.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Sereno, online 2005. Stem Archosauria - TaxonSearch. http://www.taxonsearch.org/dev/file_home.php [version 1.0, 2005 November 7]
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Horezmavis Nessov and Borkin, 1983
H. eocretacea Nessov and Borkin, 1983
Early Cenomanian, Late Cretaceous
Khodzhakul Formation, Uzbekistan
Holotype- (ZIN PO 3390) (~285 mm) proximal tarsometatarsus
Comments- Horezmavis was described as Aves (sensu lato) incertae sedis by Nessov and Borkin (1983), though Nessov later (1992) assigned it to Gruiformes based on resemblences to Ralli. Kurochkin (1995) considered it a gruiform based on several characters, but Hope (2002) found these to have a broader distribution within euornithines. The lateral position of the m. tibialis cranialis tubercle is shared with most euornithines; the intercotylar prominence is not as well developed as Aves; the presence of two proximal vascular foramina is present in carinates sensu Chiappe; a hypotarsus is present in Patagopteryx, Gansus and taxa as close to Aves as Changmaornis; and an elongate shaft is also found in such taxa as Gansus, Hollanda, basal hesperornithines and Apsaravis. Kurochkin (2000) later stated its position within Gruiformes was less certain, but did feel it was a neognath. The characters he cites are also present in more basal euornithines however. A completely fused tarsometatarsus is present in all euornithines while a infracotylar fossa is present in songlingornithids and more derived birds. Martin (1995) considered it an enantiornithine, but this is surely incorrect based on the distal metatarsal fusion, proximal metatarsal III which is displaced ventrally, intercotylar priminence, hypotarsus, presence of two proximal vascular foramina, centrally placed m. cranialis tibialis tubercle, and unreduced metatarsal IV. The character evidence thus suggests it is at least as derived as Ichthyornis, but further resolution depends on more detailed comparisons to basal Aves.
References- Nessov and Borkin, 1983. [New records of bird bones from Cretaceous of Mongolia and Middle Asia] Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 116, 108-110.
Nessov, 1992. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 1995. Synopsis of Mesozoic birds and early evolution of class Aves. Archaeopteryx. 13, 47-66.
Martin, 1995. The enantiornithines: terrestrial birds of the Cretaceous. Courier Forschungsinstitut Senckenberg. 181, 23–36.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin, eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.

Ichthyornithes Marsh, 1873b
Official Definition- (Ichthyornis dispar <- Hesperornis regalis, Vultur gryphus) (Benito, Chen, Wilson, Bhullar, Burnham and Field, 2022; Registration Number 555)
Other definition- (Ichthyornis dispar <- Struthio camelus, Tinamus major, Vultur gryphus) (Clarke, 2004)
= Ichthyornithidae Marsh, 1873a (emended Furbringer, 1888)
= Ichthyornithides Gill, 1874
= Odontotormae Marsh, 1875b
= Pteropappi Stejneger, 1885
= Ichthyornithiformes Furbringer, 1888
Definition- (Ichthyornis anceps <- Hesperornis regalis, Gansus yumenensis, Passer domesticus) (Martyniuk, 2012)
= Odontormae Steinmann and Doederlein, 1890
= Plegadornithidae Wetmore, 1962
= Angelinornithidae Kashin, 1972
Diagnosis- amphicoelous cervicals; acromion that does not extend anteriorly past the coracoid condyle; internal index process on manual phalanx II-1 (absent in Ichthyornis KUVP 2284- ontogenetic?).
Other diagnoses- Marsh (1873a, b) originally diagnosed Ichthyornidae, Ichthyornithes and Odontornithes based on their amphicoelous vertebrae (only the posterior dorsals were definitely amphicoelous in Apatornis, based on its sacrum), which are plesiomorphic.
Marsh diagnosed Ichthyornithes (1875a) then Odontormae (1875b) by their plesiomorphic presence of teeth placed in sockets (as in most archosaurs), a keeled sternum (as in most ornithothoracines) and "developed wings" (as in most birds).
Comments- Marsh (1873a) named Ichthyornidae to include Ichthyornis and Apatornis, which Furbringer (1888) emended to its proper form Ichthyornithidae. Marsh later (1873b) placed ichthyornithids in the new order Ichthyornithes, but in the 1875b publication, replaced Ichthyornithes with Odontotormae because he thought the previous name was preoccupied. As Clarke (2004) noted though, Marsh never mentioned which taxon supposedly preoccupied Ichthyornithes, and recent searches for homonyms have been unsuccessful. Furbringer created Ichthyornithiformes for a more inclusive group than Ichthyornithes (though with the same known contents), which became the name generally used until Clarke phylogenetically defined Ichthyornithes in her Ichthyornis monograph. Clarke (2002) incorrectly claimed Furbringer never named the taxon and that it was only mistakenly attributed to him by Brodkorb. Most recently Ichthyornithes was made official by Benito et al. (2022).
Wetmore (1962) named the Plegadornithidae for his new genus Plegadornis, which he placed in the Ciconiiformes close to threskiornithids. Kashin (1972) noted Plegadornis was preoccupied, so renamed it Angelinornis and suggested the family be named Angelinornithidae. Angelinornis was synonymized with Ichthyornis by Olson (1975), making Angelinornithidae a junior synonym of Ichthyornithidae. It should be noted Plegadornithidae should only be used for a family containing Plegadornis however.
Ex-ichthyornithines- Marsh (1873a) included Apatornis in Ichthyornithidae and later Ichthyornithes and Odontotormae, which has been followed by most authors (based largely on Iaceornis material after 1880) until Clarke (2004) found a lack of supportive characters. Nesov (1984) assigned his new taxon Zhyraornis to Ichthyornithiformes, which may be correct but has not been supported with any valid characters yet. Nessov (1986) described a partial synsacrum as Ichthyornis maltshevskyi, but this was placed in the new genus Lenesornis by Kurochkin (1996) and seems to be a more basal ornithothoracine, perhaps an enantiornithine. Martin (1987) assigned Ambiortus to the Ichthyornithiformes, but this has not been supported by phylogenetic analyses. Nessov (1990) described a dorsal vertebra as Ichthyornis minusculus, but this seems to be an enantiornithine (Kurochkin, 1996). Several specimens from the Bissekty Formation of Uzbekistan were assigned to Ichthyornithiformes by Nessov (1992a, b), but are here placed as Ornithothoraces incertae sedis (partial dentary ZIN PO 4608, and tooth ZIN PO 4610) or Euornithes incertae sedis (proximal coracoid ZIN PO 4605, and dorsal vertebra ZIN PO 4607). Bell and Everhart (2011) described coracoid FHSM VP-17459 as Ichthyornithes indet., but the character they based this on ("prominent, medially projecting acrocoracoid process") is also present in many avians such as 'cimolopterygids'.
References- Marsh, 1873a. Notice of a new species of Ichthyornis. American Journal of Science, 3rd series. 5, 74.
Marsh, 1873b. On a new sub-class of fossil birds (Odontornithes). American Journal of Science, 3rd series. 5, 161-162.
Gill, 1874. in Baird, Brewer and Ridgway. North American Birds. Volume 1.
Marsh. 1875a. On the Odontornithes, or birds with teeth. American Journal of Science, Series 3. 10(59), 403-408.
Marsh, 1875b. Odontornithes, or birds with teeth. The American Naturalist. 9(12), 625-631.
Stejneger, 1885. Birds. in Kingsley (ed). The Standard Natural History. Volume 4.
Furbringer, 1888. Untersuchungeb zur Morphologie und Systematik der Vogel. Amsterdam: Holkema, 1751 pp.
Steinmann and Doederlein, 1890. Elemente der Palaontologie.
Wetmore, 1962. Notes on fossil and subfossil birds. Smithsonian Miscellaneous Collections. 145, 1-17.
Kashin, 1972. New name for the genus Plegadornis. Ornitologiya. 10, 336-337.
Olson, 1975. Ichthyornis in the Cretaceous of Alabama. Wilson Bulletin. 87, 103-105.
Nesov, 1984a. Pterozavry i ptitsy pozdnego mela Sredney Azii. Paleontologicheskii Zhurnal. 1, 47-57.
Nesov, 1984b. Upper Cretaceous pterosaurs and birds from central Asia. Paleontological Journal. 1, 38-49.
Nessov, 1986. Pervaya nakhodka pozdnemelovoy ptitsyikhtiornisa v starom svete i nekotoryye drugiye kosti ptits iz mela i paleogena Sredney Axii [The first find of the Late Cretaceous bird, Ichthyornis, in the Old World, and some other bird bones from the Cretaceous and Paleogene of Middle Asia]. in Potapov (ed). Ekologicheskiye i faunisticheskiye issledovniya ptits. Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 147, 31-38.
Martin, 1987. The beginning of the modern avian radiation. Documents des Laboratoires de Geologie de la Faculte des Sciences de Lyon. 99, 9-20.
Nessov, 1990. Small Ichthyornis and other findings of the bird bones from the Bissekty Formation (Upper Cretaceous) of Central Kizylkum Desert. Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 21, 59-62.
Nessov, 1992a. Mesozoic and Paleogene birds of the USSR and their paleoenvironments. In Campbell (ed.). Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Science Series. 36, 465-478.
Nessov, 1992b. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Bell and Everhart, 2011. Remains of small ornithurine birds from a Late Cretaceous (Cenomanian) microsite in Russell County, north-central Kansas. Transactions of the Kansas Academy of Science. 114(1-2), 115-123.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Benito, Chen, Wilson, Bhullar, Burnham and Field, 2022. Forty new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds. PeerJ. 10:e13919.

Ichthyornis Marsh, 1872b
Definition- (the clade stemming from an ancestor that possessed amphicoelous cervical centra, an acromion that does not extend anteriorly past the coracoid condyle, a dorsal ulnar condyle where the posterior extent of the articular surface is equal to the width of the articular surface across its distal end, an oval scar on the posteroventral surface of the distal radius in the center of the ligamentous depression, and a large tubercle developed on the laterodistal surface of metacarpal II, homologous with those in Ichthyornis dispar; Ichthyornis dispar <- Struthio camelus, Tinamus major, Vultur gryphus) (Clarke, 2004)
= Colonosaurus Marsh, 1872c
= Plegadornis Wetmore, 1962 (preoccupied Brehm, 1855)
= Angelinornis Kashin, 1972
Not Ichthyornis- A number of other species have been referred to Ichthyornis in the past. Marsh (1873a) described Ichthyornis celer, but later referred it to its own genus Apatornis in 1873b. Marsh (1880) referred Graculavus lentus to Ichthyornis to form the new taxon Ichthyornis lentus, but this was placed in the new galliform genus Austinornis by Clarke (2002, 2004). Ichthyornis tener was named by Marsh (1880) and assigned to the new genus Guildavis by Clarke. Martin and Stewart (1982) described a dorsal vertebra from the Vermillion River Formation of Manitoba as Ichthyornis sp., but Clarke identified it as an enantiornithine. Zinsmeister (1985) reported tentative Ichthyornis material from the Lopez de Bertodano Formation of Antarctica, but Chatterjee (pers. comm. 12-6-2020) stated "It was misidentified in the field. These were some shark teeth." They are assigned to Odontaspidae here (Mortimer, online 2020). Nessov (1986) described a partial synsacrum as Ichthyornis maltshevskyi, but this was placed in the new genus Lenesornis by Kurochkin (1996) and seems to be a more basal ornithothoracine, perhaps an enantiornithine. Nessov (1990) described a dorsal vertebra as Ichthyornis minusculus, but this seems to be an enantiornithine (Kurochkin, 1996).
References- Brehm, 1855. Der vollständige Vogelfang. Weimar. 416 pp.
Marsh, 1872b. Notice of a new and remarkable fossil bird. American Journal of Science, 3rd series. 4, 344.
Marsh, 1872c. Notice of a new reptile from the Cretaceous. American Journal of Science, 3rd series. 4(23), 406.
Marsh, 1873a. Notice of a new species of Ichthyornis. American Journal of Science, 3rd series. 5, 74.
Marsh, 1873b. On a new sub-class of fossil birds (Odontornithes). American Journal of Science, 3rd series. 5, 161-162.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Wetmore, 1962. Notes on fossil and subfossil birds. Smithsonian Miscellaneous Collections. 145, 1-17.
Kashin, 1972. New name for the genus Plegadornis. Ornitologiya. 10, 336-337.
Olson, 1975. Ichthyornis in the Cretaceous of Alabama. Wilson Bulletin. 87, 103-105.
Martin and Stewart, 1982. An ichthyornithiform bird from the Campanian of Canada. Canadian Journal of Earth Sciences. 19, 324-327.
Zinsmeister, 1985. 1985 Seymour Island expedition. Antarctic Journal of U.S. 20, 41-42.
Nessov, 1986. Pervaya nakhodka pozdnemelovoy ptitsyikhtiornisa v starom svete i nekotoryye drugiye kosti ptits iz mela i paleogena Sredney Axii [The first find of the Late Cretaceous bird, Ichthyornis, in the Old World, and some other bird bones from the Cretaceous and Paleogene of Middle Asia]. in Potapov (ed). Ekologicheskiye i faunisticheskiye issledovniya ptits. Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 147, 31-38.
Nessov, 1990. Small Ichthyornis and other findings of the bird bones from the Bissekty Formation (Upper Cretaceous) of Central Kizylkum Desert. Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 21, 59-62.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, special issue. 50 pp.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Mortimer, 2020 online. https://theropoddatabase.blogspot.com/2020/12/antarctic-ichthyornis-solved.html
I. dispar Marsh, 1872b
Definition- (the species that includes YPM 1450) (Clarke, 2004)
?= Graculavus anceps Marsh, 1872a
= Colonosaurus mudgei Marsh, 1872c
?= Graculavus agilis Marsh, 1873b
= Ichthyornis victor Marsh, 1876
?= Ichthyornis agilis (Marsh, 1873) Marsh, 1880
?= Ichthyornis anceps (Marsh, 1872a) Marsh, 1880
?= Ichthyornis validus Marsh, 1880
= Plegadornis antecessor Wetmore, 1962
= Angelinornis antecessor (Wetmore, 1962) Kashin, 1972
= Ichthyornis antecessor (Wetmore, 1962) Olson, 1975
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US
Holotype- (YPM 1450; holotype of Colonosaurus mudgei) (~240 mm; adult) maxillary fragment, nasal fragment, lacrimal fragment, braincase, mandibles (87 mm), posterior cervical vertebra (5.5 mm), posterior cervical vertebra (6 mm), mid dorsal vertebra (5.8 mm), posterior dorsal vertebra (6 mm), several proximal dorsal ribs, synsacrum (26.2 mm), ossified tendons, distal coracoid, anterior sternum, incomplete humeri (58.4 mm), distal radius, ulnae (61.5 mm), distal carpometacarpus, femur (24.7 mm), distal femur, incomplete tibiotarsus (44.5 mm), fragments
Referred- (AMNH 30586) skeleton (AMNH online)
(BHI 6421) partial quadratojugal, quadrate, posterior mandibles, postcrania including manual phalanx II-1 (Field et al., 2018)
(FHSM VP-329) proximal scapula, incomplete coracoid, humerus (FHSM online)
(FHSM VP-2058) distal humerus (FHSM online)
(FHSM VP-2179) distal tarsometatarsus (FHSM online)
(FHSM VP-2180) incomplete radius, ulna (FHSM online)
(FHSM VP-2503; = SMM 2503; "SMM 13520" of Martin and Stewart, 1977) partial dentary, splenial, five cervical vertebrae, scapula, coracoids, partial furcula, sternum, humeri, radius, proximal ulnae, pisiform, carpometacarpus, phalanx II-1, phalanx II-2, femoral shaft, incomplete tibiotarsus (Martin and Stewart, 1977)
(FHSM VP-15573) distal humerus, limb fragment (FHSM online)
(FHSM VP-15574) proximal coracoid (FHSM online)
(FHSM VP-17317) incomplete coracoid (FHSM online)
(FHSM VP-18702) skull, mandibles (one anterior), partial skeleton including metacarpal II and manual phalanx II-1 (Field et al., 2018)
(KUVP 2294) humeral fragment (Chinsamy et al., 1998)
(KUVP 119673) jugal, quadrate, incomplete mandible, incomplete postcranial skeleton including coracoids and humerus (Burnham and Hines, 2005)
(NHMUK A905) partial postcranium including scapula, sternum and humerus (Harrison and Walker, 1973)
(RMDRC coll.) specimen including premaxillae, maxilla and postcrania (Maltese, 2017 online)
?(YPM 1208; holotype of Graculavus anceps) (~233 mm; adult) distal carpometacarpus (Marsh, 1872a)
(YPM 1209; holotype of Graculavus agilis) (size of YPM 1724; adult) proximal carpometacarpus (Marsh, 1873b)
?(YPM 1446) (adult) incomplete coracoid (Marsh, 1880)
(YPM 1447) (~292 mm; adult) humerus (71.1 mm) (Marsh, 1880)
(YPM 1452; holotype of Ichthyornis victor) (adult) proximal scapula, proximal coracoid, three humeral fragments (12.5 mm wide distally), ulna (lost) (Marsh, 1876)
(YPM 1453) (~288 mm; adult) ulna (73.8 mm) (Marsh, 1880)
(YPM 1454) (adult) ulna (Clarke, 2004)
(YPM 1456) (adult) distal tarsometatarsus (Marsh, 1880)
(YPM 1457) (adult) humerus (11 mm wide distally), radius, ulna (Marsh, 1880)
(YPM 1458) (adult) scapula, coracoid (Marsh, 1880)
(YPM 1459) (adult) premaxillary fragment (Marsh, 1880)
(YPM 1460) (adult) tooth, ulna (Clarke and Chiappe, 2001)
(YPM 1461) (adult) dorsal ribs, coracoid, partial sternum, humerus (Marsh, 1880)
(YPM 1462) (adult) ulna (Clarke and Chiappe, 2001)
(YPM 1463) (adult) manual phalanx II-1 (21 mm) (Marsh, 1880)
(YPM 1464) (adult) distal tarsometatarsus (Marsh, 1880)
(YPM 1718) (adult) scapula, coracoid (Marsh, 1880)
(YPM 1719) (adult) coracoid (Clarke, 2004)
(YPM 1720) (adult) humerus (Clarke, 2004)
(YPM 1721) (adult) humerus (Clarke, 2004)
(YPM 1722) (adult) humerus (Clarke, 2004)
(YPM 1723) (adult) tibiotarsus (57 mm) (Marsh, 1880)
(YPM 1724) (adult) carpometacarpus (39.5 mm) (Marsh, 1880)
(YPM 1725) (adult) humerus (Clarke, 2004)
(YPM 1726) (adult) manual phalanx II-1 (20.8 mm) (Marsh, 1880)
(YPM 1727) (adult) scapula, coracoid (Marsh, 1880)
(YPM 1728) (adult) posterior nasals, frontals, braincase (Clarke, 2004)
(YPM 1729) (adult) humerus (Clarke, 2004)
(YPM 1730) (~252 mm; adult) humerus (62.5 mm), carpometacarpus (31.5 mm) (Marsh, 1880)
(YPM 1731) (adult) ulna (Chiappe, 2002)
(YPM 1732) (adult) partial posterior dorsal vertebra, posterior dorsal vertebra, posterior dorsal vertebra, synsacrum, ossified tendons, first caudal vertebra (3.1 mm), second caudal vertebra (3.2 mm), third caudal vertebra (3.6 mm), fourth caudal vertebra (3.2 mm), fifth caudal vertebra (3.4 mm), anterior pygostyle, incomplete ilium, proximal pubis (26 mm), incomplete ischium, proximal femur, partial tibiotarsi (57 mm), pedal phalanx II-2 (9 mm) (Marsh, 1880)
(YPM 1733) (adult) atlas (2.7 mm), axis (7 mm), third cervical vertebra (6 mm), posterior cervical vertebra (6 mm), anterior dorsal vertebra (5.5 mm), anterior dorsal centrum, mid dorsal vertebra (6.7 mm), partial posterior dorsal vertebra, partial posterior dorsal centrum, posterior dorsal centrum, synsacrum, ossified tendons, scapula, incomplete coracoid, distal humerus, radius, partial ilium? (Marsh, 1880)
(YPM 1735) (adult) mandible (Marsh, 1880)
(YPM 1736) (adult) carpometacarpus (Chiappe, 2002)
(YPM 1737) (adult) humerus (Clarke, 2004)
(YPM 1738) (190-206 mm; adult) distal humerus (7.5 mm wide distally) (Marsh, 1880)
(YPM 1739) (adult) tarsometatarsus (58 mm) (Marsh, 1880)
?(YPM 1740; holotype of Ichthyornis validus) (~267 mm; subadult) ulna (68.5 mm) (Marsh, 1880)
(YPM 1741) (adult) scapula, coracoid, humerus, radius (71 mm) (Marsh, 1880)
(YPM 1742) (~294 mm; adult) humerus (71.5 mm) (Marsh, 1880)
(YPM 1743) (adult) coracoid (34 mm) (Marsh, 1880)
(YPM 1744) (adult) ulna (Clarke, 2004)
(YPM 1745) (adult) coracoid (32 mm) (Marsh, 1880)
(YPM 1746) (adult) coracoid (Clarke, 2004)
(YPM 1747) (adult) humerus (Clarke, 2004)
(YPM 1748) (adult) humerus (Clarke, 2004)
(YPM 1749) (adult) anterior mandible, partial humerus (Marsh, 1880)
(YPM 1750) (adult) humerus (Clarke, 2004)
(YPM 1751) (adult) carpometacarpus (Clarke, 2004)
(YPM 1752) (adult) carpometacarpus (Chiappe, 2002)
(YPM 1753) (adult) scapula (Chiappe, 2002)
(YPM 1754) (adult) distal tibiotarsus (Clarke, 2004)
(YPM 1755) (adult) furcular fragment, humerus (70.6 mm), radius, ulna, carpometacarpus (36.6 mm), manual phalanx II-1 (21.2 mm) (Marsh, 1880)
(YPM 1756) (~252 mm; adult) humerus (61.4 mm)
(YPM 1757) (adult) coracoid, humerus, ulna (Clarke, 2004)
(YPM 1758) (adult) radius, ulna (Chiappe, 2002)
(YPM 1759) (adult) manual phalanx I-1, phalanx II-1 (Marsh, 1880)
(YPM 1761) (>240 mm; adult) mandibular fragment (Elzanowski et al., 2001)
(YPM 1762) (adult) humerus (Clarke, 2004)
(YPM 1763) (adult) scapula, coracoid, humerus, radial fragment (Clarke, 2004)
(YPM 1764) (~269 mm; adult) partial humerus (10.5 mm wide distally), ulna (Olson, 1975)
(YPM 1765) (adult) coracoid (Chiappe, 2002)
(YPM 1766) (~240 mm; adult) coracoid (Marsh, 1880)
(YPM 1767) (adult) coracoid (Chiappe, 2002)
(YPM 1768) (adult) coracoid (Chiappe, 2002)
(YPM 1769) (adult) carpometacarpus (Clarke, 2004)
(YPM 1770) (adult) radius (Chiappe, 2002)
(YPM 1771) (adult) tarsometatarsus (Chiappe, 2002)
(YPM 1772) (adult) scapula (Chiappe, 2002)
(YPM 1773) (adult) endocast?, scapula, coracoid, humerus, radius, carpometacarpus (39.4 mm) (Chiappe, 2002)
(YPM 1774) (adult) coracoid (Clarke, 2004)
(YPM 1775) (adult) quadrates (one partial), anterior mandible, axis, anterior dorsal vertebra, partial pygostyle(?), humerus, radius, ulna, carpometacarpus, phalanx II-1, incomplete phalanges III-1, distal femur, distal tibiotarsus (Marsh, 1880)
(YPM 1776) (adult) coracoid (Chiappe, 2002)
(YPM 6264) (<240 mm; adult) posterior mandible (Gingerich, 1972)
(YPM 9685) (~300-317 mm; adult) humerus (Clarke, 2004)
(YPM 56577) (adult) scapula, coracoid (Clarke, 2004)
Early Turonian, Late Cretaceous
Kaskapau Formation, Alberta, Canada
(UA 18456) (~220 mm) humerus (53.5 mm) (Fox, 1984)
Campanian, Late Cretaceous
Pembina Member of the Vermillion River Formation, Manitoba, Canada
(CFDC B.80.05.14) femur (CFDC online)
Campanian, Late Cretaceous
Chico Formation, California, US
(UCMP 170785) partial humerus (Hilton et al., 1999)
Turonian, Cretaceous
Juan Lopez Member of Mancos Shale, New Mexico, US
(YPM 9148) (~238 mm) incomplete humerus (58 mm) (Lucas and Sullivan, 1982)
Early Coniacian, Late Cretaceous
Ector Chalk Formation of the Austin Group, Texas, US
(TMM 31051-24) (~262 mm) humerus (63.8 mm) (Parris and Echols, 1992)
(TMM 31051-25) (~257 mm) humerus (62.5 mm), partial ulna, partial radius, partial carpometacarpus (Parris and Echols, 1992)
Coniacian, Late Cretaceous
Gober Formation, Texas, US
(ET 4396) proximal carpometacarpus (Parris and Echols, 1992)
Campanian, Late Cretaceous
Pflugerville Formation, Texas, US
(TMM 42522-1) (~254 mm) distal humerus (10.1 mm wide distally) (Parris and Echols, 1992)
Late Coniacian-Early Campanian, Late Cretaceous
Upper Austin Group, Mexico
(MUZ-689) humerus (56 mm) (Porras-Muzquiz et al., 2014)
Early Campanian, Cretaceous
Mooreville Chalk, Alabama, US
(ALMNH 3316; = Red Mountain Museum coll.) premaxillae, partial maxillae, anterior mandible, vertebrae, pelvis, limb elements including manual phalanx II-1 (Lamb, 1997; described by Field et al., 2018)
(D2K coll.) material (Clarke, 2004)
(UAM PV93.2.133-1) tooth fragment (Dumont et al., 2016)
(UAM PV93.2.133-2) tooth fragment (Dumont et al., 2016)
(USNM 22820; holotype of Plegadornis antecessor) (~269 mm) distal humerus (10.5 mm wide distally) (Wetmore, 1962)
Late Cretaceous?
US?
(USNM 11641) radius (Chiappe, 1996)
Diagnosis- (after Clarke, 2004) anteromedial pneumatic foramen in quadrate; proximal caudal prezygopophyses clasp dorsal surface of preceding vertebra; pit-shaped fossa at distal tip of bicipital crest (also in Tianyuornis) dorsal ulnar condyle where the posterior extent of the articular surface is equal to the width of the articular surface across its distal end (unknown in other non-avian euornithines except Apsaravis); oval scar on the posteroventral surface of the distal radius in the center of the ligamentous depression; large tubercle developed on the laterodistal surface of metacarpal II.
Other diagnoses- Marsh (1872a) originally diagnosed Graculavus anceps as being larger than G. velox (which was not otherwise comparable, being based on a humerus; contra Clarke, 2004), and differing from the phalacrocoracid "Graculus violaceus" (now Phalacrocorax pelagicus) in several characters. These were- broader and flat articular surface for phalanx II-1; smaller and oval articular surface for phalanx III-1; larger distal tubercle between these surfaces. Obviously comparisons to cormorants are of little use, as Ichthyornis is not even a crown clade bird.
Marsh (1872b) suggested amphicoelous cervicals were diagnostic, but this is also present in NHMM/RD 271.
Marsh (1872c) distinguished Colonosaurus mudgei from mosasaurs in its lack of a conspicuous Meckelian groove, but this is common in derived birds.
Marsh (1873b) distinguished Graculavus agilis from G. anceps based on its smaller size, gracility and reduced carpal fossa. As Clarke (2004) noted, the first two differences do not seem to exist, while the third is unknown in the anceps holotype, since that only preserves the distal carpometacarpus.
Marsh (1876) distinguished Ichthyornis victor from I. dispar based on its larger size, but Clarke (2004) determined that there was a continuous variation in size of Ichthyornis specimens from the Smoky Hills Chalk and that no morphological differences between small and large specimens were apparent besides a few forelimb scars being more prominent on larger ones.
Marsh (1880) distinguished I. anceps from I. dispar based on a more slender mandible with more teeth, based on a referred specimen (YPM 1749) that cannot be compared to the anceps holotype. While Clarke (2004) thought it might be "slightly more delicate" than YPM 1450, she noted it contained the same number of teeth. Marsh distinguished I. victor from I. dispar based on the stouter and deeper mandible of YPM 1735, though Clarke notes its proportions cannot be determined as it is incomplete.
Harrison (1973) listed two humeral characters as diagnostic of Ichthyornis- dorsally projecting deltopectoral crest and small bicipital crest, but Clarke (2004) found these both to be plesiomorphic for birds.
Olson (1975) distinguished I. antecessor from supposed I. dispar specimen YPM 1764 based on several characters- more gracile humeral shaft; shallower and more distally positioned brachial fossa; ectepicondylar process more prominent; pit at base of ectepicondylar process shallower. Clarke (2004) noted the I. dispar holotype is slender as in the I. antecessor holotype and that the other differences were minor and vary in Smoky Hill Ichthyornis specimens.
Clarke (2004) suggested several diagnostic characters, at least two of which are now known in NHMM/RD 271- acromion that does not extend anteriorly past the coracoid condyle; internal index process on manual phalanx II-1.
Comments- While multiple species of Smoky Hill Chalk Ichthyornis were recognized early on, the lack of proper diagnoses made referral of remains to the species level uncertain through the 1900's. Elzanowski (1995), Clarke (1999, 2000), Clarke and Chiappe (2001) and Chiappe (2002) all noted the taxonomic mess and only provisionally referred elements not preserved in the holotype (or specimens which shared elements with the holotype) to the taxon, fearing multiple species were represented. Clarke (2002) examined all the specimens at the YPM for her thesis, removing some from Ichthyornis and synonymizing the others into one species, which she called Ichthyornis dispar. This study was published in 2004 in a slightly modified version that mostly differed in lacking several taxa in its phylogenetic analysis. Her taxonomy has been followed in the recent literature.
The holotype of Ichthyornis anceps (the distal carpometacarpus YPM 1208) was discovered in 1870 and described by Marsh (1872a) as Graculavus anceps. Marsh assigned it to Graculavus because he thought it resembled phalacrocoraciids, which he placed Graculavus velox near as well. Marsh (1880) later placed anceps in Ichthyornis without comment, also referring the mandible and partial humerus YPM 1749 to the species (though they are not comparable to the type). Shufeldt (1915) believed anceps was too fragmentary and distorted to diagnose or place precisely within Aves. However, Clarke (2004) noted it has Ichthyornis' apomorphic distal metacarpal tubercle and does not differ from the I. dispar holotype except in size. Clarke misinterpreted the ICZN in respect to Ichthyornis anceps vs. I. dispar when she sank the former into the latter though. Although I. anceps cannot be the type species of Ichthyornis, it can be a senior synonym of of I. dispar. Furthermore, according to the 1999 edition of the ICZN, I. anceps is not a nomen oblitum, as it was used as a valid species by Stewart (1990). While previously this website used I. anceps as a senior synonym of I. dispar, the recent recognition of Belgian NHMM/RD 271 as a distinct species of ichthyornithine complicates matters as it does not preserve a carpometacarpus. Thus anceps cannot be distinguished from it and should not be the holotype of Smoky Hill ichthyornithines. Similar issues arise for agilis and validus, as NHMM/RD 271 also lacks a preserved ulna, but further consideration is delayed pending redescription and naming of the Belgian taxon.
Marsh (1872b) briefly described Ichthyornis dispar as a partial bird postcranium and a week later (1872c) described Colonosaurus mudgei as reptilian mandibles similar to mosasaurs. However, these are based on the remains of one individual, as Marsh later (1873a) realized. Marsh described Ichthyornis dispar in more detail in 1873a, 1875a, 1875b and especially 1880. In the latter publication, Marsh also referred YPM 1718, 1723 and 1730 to I. dispar preseumbly based on size. Gregory (1952) believed the mandibular elements (including Colonosaurus) belonged to juvenile individuals of the mosasaur Clidastes, which was followed by several later authors. Gingerich (1972) described a posterior mandible as Ichthyornis cf. dispar, and agreed with Marsh, Russell (1967) and Walker (1967) that the toothed mandibles did belong to Ichthyornis. Olson (1975) referred YPM 1764 provisionally to I. dispar, pending a revision of Ichthyornis by Brodkorb which never appeared. Paris and Echols (1992) described a humerus and partial forelimb from the Ector Chalk Formation of Texas as I. dispar, though they are currently catalogued as I. victor in the TMM collections.
Marsh (1873b) named Graculavus agilis based on a proximal carpometacarpus (YPM 1209) found in 1872. The description was extremely brief and no type material was mentioned, though Marsh referred both Graculalvus anceps and G. agilis to the Natatores. Marsh (1880) later placed agilis in Ichthyornis without comment and referred the ulna YPM 1453 to the species (though it is not comparable to the type). Shufeldt (1915) believed the holotype was indeterminate and impossible to place precisely within Aves. Clarke (2004) found agilis was identical to other Smoky Hill Ichthyornis specimens, so synonymized it with I. dispar.
Ichthyornis victor was discovered in 1876 and described that year by Marsh as a new larger species of Ichthyornis. This was based on YPM 1452, which consists of three partial forelimb elements. Marsh (1880) described and referred numerous specimens to I. victor- YPM 1447, 1456, 1457, 1458, 1461, 1463, 1464, 1724, 1726, 1727, 1732, 1733, 1735, 1739, 1741, 1742, 1743, 1745 and 1775. While a partial coracoid was originally associated with YPM 1459, Clarke (2004) noted it articulates perfectly with a partial coracoid from YPM 1458, so was moved to that specimen. Hope (2002) illustrates these specimens as Ichthyornis sp., with the old coracoid number. Chinsamy et al. (1998) described the histology of KUVP 2294, a specimen they referred to I. victor. Clarke (1999) considered I. victor a chimera, because the mounted skeleton which was incorrectly labeled as the holotype actually contained elements from several Ichthyornis specimens (YPM 1447, 1453, 1461, 1724, 1728, 1732, 1733, 1739, 1741) as well as what would become the holotype of Iaceornis (which was previously noticed by Howard, 1955 and Elzanowski, 1995). Clarke (2004) noted YPM 1732 differs from the I. dispar holotype in having twelve sacral vertebrae, though the victor holotype is identical to dispar except in size. If the species really are distinct and diagnosed partially by size, I. anceps would be the valid name for the large species (with agilis, victor and validus as synonyms) while I. dispar would be the valid name for the small species.
Ichthyornis validus based on an ulna (YPM 1740) discovered in 1877 and not diagnosed by Marsh when he named it in 1880. Brodkorb (1967) claimed a radius was also known for YPM 1740, but this seems to be untrue. The partial coracoid YPM 1446 was referred to validus by Marsh (1880) without comment. Clarke (2004) noted it was more robust and larger than most other YPM specimens, the supracoracoid foramen did not lie in a groove, and that there is a unique groove extending from the supracoracoid foramen in the triossial canal. The holotype is the only subadult YPM specimen of Ichthyornis known, and is larger than some adult specimens such as the dispar holotype. Clarke synonymized it with I. dispar since it is morphologically identical.
Wetmore (1962) described a distal humerus (USNM 22820) as Plegadornis antecessor, which he thought was a ciconiiform close to threskiornithids. Kashin (1972) noted that Plegadornis was preoccupied by a genus named by Brehm in 1855, which in turn is a junior synonym of the threskiornithid genus Plegadis. Thus he renamed the genus Angelinornis. Olson (1975) synonymized Angelinornis with Ichthyornis but retained Ichthyornis antecessor as a valid species. Paris and Echols (1992) described a distal humerus (TMM 42522-1) from the Pflugerville Formation of Texas and proximal carpometacarpus (ET 4396) from the Gober Formation of Texas and referred them to Ichthyornis antecessor. The humerus was referred because it was thought to live at a later time than Smoky Hill Ichthyornis and compare better morphologically to the antecessor holotype, but the former is not necessarily true while Clarke notes it is equally similar to the I. dispar holotype. It is currently catalogued as I. sp. in the TMM collections. The carpometacarpus was only tentatively referred based on stratigraphy and supposed differences from Smoky Hill Ichthyornis material, but Clarke could not confirm these differences. As noted above, Clarke determined the supposedly distinct characters of antecessor fell within the range of individual variation for Smoky Hill Chalk Ichthyornis, so synonymized this species with I. dispar.
Martin and Stewart (1977) described the jaws of a skeleton found in 1970, which was found in 1970 and referred to Ichthyornis sp.. While they referred to this specimen as SMM 13520, though it is actually 2503. Clarke (2004) referred this specimen to I. dispar.
Lucas and Sullivan (1982) described a humerus (YPM 9148) from the Mancos Shale in New Mexico found in 1979 as Ichthyornis sp., but Clarke (2004) referred it to I. dispar.
KUVP 119673 was found in 1992 and was announced by Burnham and Hines (2005), but its fragmentary skull was described in detail by Fields et al. (2018). FHSM VP-18702 was found on August 17 2014 and its nearly complete skull was described by Field et al.. The latter study also redescribed and refigured all known Ichthyornis cranial elements, but the postcrania of the new specimens remain undescribed.
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Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.
Clarke, 2003. The morphology, taxonomy and systematic position of Ichthyornis; A case study of alpha taxonomic practice in a phylogenetic frame. Journal of Vertebrate Paleontology. 23(3), 41A.
Everhart, online 2003-2012. http://www.oceansofkansas.com/Ichthyornis.html
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Burnham and Hines, 2005. Transfer preparation of an Ichthyornis specimen from the Niobrara Formation. Journal of Vertebrate Paleontology. 25(3), 41A.
Porras-Muzquiz, Chatterjee and Lehman, 2014. The carinate bird Ichthyornis from the Upper Cretaceous of Mexico. Cretaceous Research. 51, 148-152.
Caggiano and Witmer, 2016. The anatomy of the nasal salt gland of extant birds and its relevance for inferring the behavior and habitat preferences of extinct birds and other archosaurs. Journal of Vertebrate Paleontology. Program and Abstracts, 108.
Dumont, Tafforeau, Bertin, Bhullar, Field, Schulp, Strilisky, Thivichon-Prince, Viriot and Louchart, 2016. Synchrotron imaging of dentition provides insights into the biology of Hesperornis and Ichthyornis, the "last" toothed birds. BMC Evolutionary Biology. 16:178.
Maltese, online 2017. The Accidental Ichthyornis. RMDRC paleo lab. 1-13-2017.
Field, Hanson, Burnham, Wilson, Super, Ehret, Ebersole and Bhullar, 2018. Complete Ichthyornis skull illuminates mosaic assembly of the avian head. Nature. 557, 96-100.
I. sp. (Cumbaa and Tokaryk, 1993)
Middle Cenomanian, Late Cretaceous
Carrot River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
Material- ?(RSM P2077.71) radius (Tokaryk et al., 1997)
Middle Cenomanian, Late Cretaceous
Bainbridge River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
(RSM P2626.9) humerus (Sanchez, 2010)
(RSM P2831.3) proximal humerus (Sanchez, 2010)
(RSM P2988.8) humerus (Sanchez, 2010)
?(RSM P2988.15) vertebra (Sanchez, 2010)
Comments- Cumbaa and Tokaryk (1993) mentioned two ichthyornithids from the Ashville Formation of Saskatchewan, which were later described by Tokaryk et al. (1997) as Ichthyornis species A (RSM P2077.11, P2077.67, P2077.112 and P2487.5), Ichthyornis species B (RSM P2077.111) and I. sp. indet. (RSM P2077.71). They referred the specimens to Ichthyornis based on the coracoid scapular facet being nearly parallel to the sternal end of the glenoid facet, which Clarke (2004) noted was found in Ichthyornis, but not apomorphic. Longrich (2009) suggested the Ashville coracoids did not resemble Ichthyornis, and were referrable to Pasquiaornis based on their dimorphism (P. hardiei vs. P? tankei), pachyostosis, and supposed lack of coracoids in the Pasquiaornis material. Sanchez (2010) confirms the coracoids are Pasquiaornis. The identity of RSM P2077.71 is unresolved.
Cumbaa et al. (2006) mention Ichthyornis-like bones from the Bainbridge River bed of the same member, which Sanchez specifies are two humeri and a questionably referred vertebra.
References- Cumbaa and Tokaryk, 1993. Early birds, crocodile tears, and fish tales: Cenomanian and Turonian marine vertebrates from Saskatchewan, Canada. Journal of Vertebrate Paleontology. 13(3), 31A-32A.
Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: The oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Cumbaa, Schröder-Adams, Day and Phillips, 2006. Cenomanian bonebed faunas from the northeastern margin, Western Interior Seaway. In Lucas and Sullivan (eds). Late Cretaceous Vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin. 35, 139-155.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Sanchez, 2010. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Masters thesis, Carleton University. 238 pp.
I? sp. (Hilton, Gohre, Embree and Stidham, 1999)
Campanian, Late Cretaceous
Chico Formation, California, US
Material- (UCMP 170785) incomplete humerus
Reference- Hilton, Gohre, Embree and Stidham, 1999. California's first fossil evidence of Cretaceous winged vertebrates. California Geology. 52(4), 4-10.
I? sp.
Maastrichtian, Late Cretaceous
Lance Formation, Wyoming, US
Material- (AMNH 110) sacrum (AMNH online)
I. sp.
Coniacian, Late Cretaceous
Fort Hays Member of the Niobrara Formation, Kansas, US
Material- (FHSM VP-5516) distal humerus (FHSM online)
I? sp.
Late Cenomanian, Late Cretaceous
Lincoln Member of the Greenhorn Limestone, Kansas, US
Material- ?(FHSM VP-17478) femur (FHSM online)
I? sp.
Late Cenomanian-Early Turonian, Late Cretaceous
Greenhorn Limestone, Kansas, US
Material- ?(FHSM VP-5517) long bone shaft (FHSM online)
Comments- FHSM VP-5517 is catalogued as Ichthyornis sp. at the FHSM, but is too fragmentary to identify past Coelurosauria indet..
I. sp. (Walker, 1967)
Early-Middle Turonian, Late Cretaceous
Pfeifer Shale Member of the Greenhorn Limestone or Fairport Chalk Member of the Carlile Shale, Kansas, US
Material- (FHSM VP-2139; = FSHM 11285; = SMM 2139) (~240 mm) proximal carpometacarpus (Walker, 1967)
Comments- Walker (1967) first noted this specimen as "“a fragmentary wing element of Ichthyornis", and it was later called FSHM 11285 by Martin and Stewart (1982). Clarke (2002, 2004) referred the carpometacarpus to Ichthyornis based on morphological similarity, and Shimada and Fernandes (2006) described and illustrated the specimen as Ichthyornis sp..
References- Walker, 1967. Revival of interest in the toothed birds of Kansas. Kansas Academy of Science, Transactions. 70(1), 60-66.
Martin and Stewart, 1982. An ichthyornithiform bird from the Campanian of Canada. Canadian Journal of Earth Sciences. 19, 324-327.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Fernandes and Shimada, 2005. A Turonian (Late Cretaceous) bird bone from Kansas. 6th Annual Kansas Academy of Science Paleontology Symposium, Abstracts.
Shimada and Fernandes, 2006. Ichthyornis sp. (Aves: Ichthyornithiformes) from the lower Turonian (Upper Cretaceous) of western Kansas. Transactions of the Kansas Academy of Science. 109(1/2), 21-26.
I. sp.
Cretaceous
Connecticut, US
Material- (FHSM VP-2210) partial skeleton (FHSM online)
I? sp.
Late Cretaceous?
US
Material- (AMNH 985) proximal scapula, proximal humerus (AMNH online)

Janavis Benito, Kuo, Widrig, Jagt and Field, 2022
J. finalidens Benito, Kuo, Widrig, Jagt and Field, 2022
Late Maastrichtian, Late Cretaceous
CBR-Romontbos Quarry 61H-45, Valkenburg Member of the Maastricht Formation, Belgium
Holotype- (NHMM/RD 271) (1.50 kg) pterygoid, tooth (4.90x2.80x1.23 mm), partial fourth cervical vertebra, fifth cervical vertebra, sixth cervical vertebra, seventh cervical vertebra, eighth cervical vertebra, partial ninth cervical vertebra, first dorsal vertebra, incomplete second dorsal vertebra, incomplete third dorsal vertebra, incomplete fourth dorsal vertebra, incomplete mid dorsal vertebra, partial mid dorsal vertebra, mid dorsal vertebral fragment, six partial dorsal ribs, scapula, humerus (134.88 mm), phalanx II-1, proximal femur, distal pedal phalanx
Diagnosis- (after Benito et al., 2022) large pneumatic openings in ventral wall of anterior dorsal central fossae; fenestrated ventrolateral tubercles on fourth dorsal vertebra; pneumatic dorsal ribs; complete absence of an acromion process on scapula; much larger size than Ichthyornis.
compared to Ichthyornis- medial side of the humeral head is flat instead of protruding proximally; ventral tubercle is more ovoid and dorsoventrally oriented; shorter deltopectoral crest (31 vs 37-42% of humeral length); dorsal and ventral rami which surround pneumotricipital fossa are be more distinct (taphonomic?); craniocaudally narrower manual phalanx II-1.
Comments- Discovered in 2000, Dyke et al. (2002) described this specimen as Ornithurae indet. based on the globular humeral head, and assigned it to Carinatae based on the prominent brachial fossa. Clarke (2004) considered it Avialae incertae sedis because free proximal tarsals are generally absent in adult euornithines, but the supposed tarsal was misidentified. Dumont et al. (2016) found it was "positively identifiable as either belonging to Ichthyornis sp., or to a closely related taxon within the Ichthyornithiformes" based on studies of the tooth.
Benito et al. (2020, 2022) CT scanned the specimen and recognized five cervical vertebrae, five more dorsal vertebrae, manual phalanx II-1, the rest of the scapula, proximal femur and a pedal phalanx in addition to what Dyke et al. reported. Benito et al (2022) report "the reported lower jaws, partial jugals and a possible quadrate all correspond to a portion of the thorax comprising two thoracic vertebrae and six associated ribs", the supposed proximal coracoid was reidentified as a pterygoid, "The reported partial right ulna instead corresponds to the caudal end of the right scapular blade", the proximal tarsal "most probably corresponds to a partial pedal phalanx" and "A reported tarsometatarsus also appears to be absent." The authors added NHMM/RD 271 to Clarke's and O'Connor's bird matrices and recovered it as an ichthyornithine.
References- Dyke, Chiappe, Dortangs, Jagt and Schulp, 2002. A new ornithurine bird from the Maastricht Formation of Belgium; Was there a bottleneck in avian diversity at the end of the Cretaceous? Journal of Vertebrate Paleontology. 22(3), 50A.
Dyke, Dortangs, Jagt, Mulder, Schulp and Chiappe, 2002. Europe’s last Mesozoic bird. Naturwissenshaften. 89, 408-411.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Dumont, Tafforeau, Bertin, Bhullar, Field, Schulp, Strilisky, Thivichon-Prince, Viriot and Louchart, 2016. Synchrotron imaging of dentition provides insights into the biology of Hesperornis and Ichthyornis, the "last" toothed birds. BMC Evolutionary Biology. 16:178.
Benito, Jagt and Field, 2020. Reinvestigating the 'Maastricht ichthyornithine' from the latest Cretaceous of Belgium. The Society of Vertebrate Paleontology 80th Annual Meeting, Conference Program. 73.
Benito, Kuo, Widrig, Jagt and Field, 2022. Cretaceous ornithurine supports a neognathous crown bird ancestor. Nature. 612, 100-105.

unnamed possible ichthyornithine (Zelenkov, Averianov and Kurochkin, 2017)
Middle Cenomanian, Late Cretaceous
Middle Member of Melovatka Formation, Russia
Material- (PIN 5554/1) distal tibiotarsus (6.1 mm trans)
Comments- Discovered in 1997, Zelenkov et al. (2017) assign this to ?Ichthyornithidae indet.. However while it is generally similar to Ichthyornis, the authors fail to describe any uniquely shared characters and their phylogenetic analysis (using O'Connor's avialan matrix) recovers it in a polytomy with other euornithines more derived than Archaeorhynchus and outside Songlingornithidae, Hongshanornithidae, Hesperornithes and Carinatae.
Reference- Zelenkov, Averianov and Kurochkin, 2017. An Ichthyornis-like bird from the earliest Late Cretaceous (Cenomanian) of European Russia. Cretaceous Research. 75, 94-100.

Hesperornithes Furbringer, 1888
Definition- (Hesperornis regalis <- Ichthyornis dispar, Passer domesticus) (suggested)
Other definition- (Hesperornis regalis <- Passer domesticus) (Sereno, online 2005; modified from Clarke, 2004)
= Odontolcae Marsh, 1875a
Definition- (Teeth set in grooves as in Hesperornis regalis) (Martyniuk, 2012)
= Odontognathes Marsh, 1880
= Dromaeopappi Stejneger, 1885
= Odontoholcae Stejneger, 1885
= Enaliornithes Furbringer, 1888
= Hesperornithomorphi Hay, 1930
Other diagnoses- Marsh (1875a, b) diagnosed his new taxon Odontolcae based on several characters. Teeth set in grooves are found in Hesperornis, Parahesperornis and Pasquiaornis, but are unknown in Enaliornis. All presacral vertebrae being heterocoeliys is not true in Pasquiaornis. The keelless sternum is present in Hesperornis and probably Fumicollis but still unknown for more basal genera, while the reduced forelimb is present at least as early as Pasquiaornis, but unknown in Enaliornis.
Comments- Marsh (1875a) named Odontolcae as an order including Hesperornis but not Ichthyornis. Martyniuk (2012) gave it an apomorphy-based definition, which could apply to all hesperornithines or only taxa as derived as Pasquiaornis given the lack of information for Enaliornis. Stejneger (1885) modified it to be the subclass Odontoholcae, and named the order Dromaeopappi.
Romer (1933) placed Eupterornis from the Paleocene of France in Baptornithidae, but is was reassigned to Gaviiformes by Brodkorb (1963). Brodkorb (1963) placed Neogaeornis in in Baptornithidae, but it was placed in Gaviiformes by Olson (1992) and has more recently been assigned to Vegaviidae by Agnolin et al. (2017). Nessov (1992) had identified KKM KP 4925/P131 as the incomplete humerus of a hesperornithine, but later (in Mourer-Chauvire, 1992) determined it was a mosasaur limb element. Longrich (2006) stated the dorsal vertebra TMP 1989.081.0012 from the Dinosaur Park Formation of Alberta was a possible hesperornithine, but later (2009) referred it to Palintropus sp.. Dyke et al. (2011) referred a supposed distal femur (MTCO 17637) from the Cornet bauxite of Romania to Hesperornithes (earlier listed as isolated bones similar to Enaliornis by Galton et al., 2009), but Agnolin and Varricchio (2012) believe it is more similar to an azhdarchid proximal radius.
References- Marsh, 1872. Preliminary description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. American Journal of Science, 3rd series. 3, 359-365.
Marsh. 1875a. On the Odontornithes, or birds with teeth. American Journal of Science, Series 3. 10(59), 403-408.
Marsh, 1875b. Odontornithes, or birds with teeth. The American Naturalist. 9(12), 625-631.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Stejneger, 1885. Birds. in Kingsley (ed). The Standard Natural History. Volume 4.
Furbringer, 1888. Untersuchungeb zur Morphologie und Systematik der Vogel. Amsterdam: Holkema. 1751 pp.
Shufeldt, 1890. On the affinities of Hesperornis. Nature. 43, 176.
Thompson, 1890. On the systematic position of Hesperornis. Studies from the Museum of Zoology. 1(10), 15 pp.
Anonymous, 1891. Professor Thompson on the systematic position of Hesperornis. Auk. 8(3), 304-305.
Helm, 1891. On the affinities of Hesperornis. Nature. 43, 368.
Marsh, 1897. The affinities of Hesperornis. Nature. 55, 534.
Hay, 1930. Second bibliography and catalogue of the fossil vertebrata of North America, Volume 2. Carnegie Institution of Washington Publication, 390, 1074 pp.
Romer, 1933. Vertebrate Paleontology. University of Chicago Press, Chicago.
Brodkorb, 1963. Catalogue of fossil birds. Part 1 (Archaeopterygiformes through Ardeiformes). Bulletin of the Florida State Museum, Biological Sciences. 7, 179-293.
Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6.
Nessov, 1992. Review of localities and remains of Mesozoic and Paleogene birds of the USSR and the description of new findings. Russkii Ornitologicheskii Zhurnal. 1(1), 7-50.
Olson, 1992. Neogaeornis wetzeli Lambrecht, a Cretaceous loon from Chile (Aves: Gaviidae). Journal of Vertebrate Paleontology. 12, 122-124.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Sereno, online 2005. Stem Archosauria - TaxonSearch. http://www.taxonsearch.org/dev/file_home.php [version 1.0, 2005 November 7]
Hinic-Frlog and Motani, 2006. Correlation of osteology and locomotion: Inferring swimming modes in extinct Ornithurae. Journal of Vertebrate Paleontology. 26(3), 76A.
Longrich, 2006. An ornithurine bird from the Late Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences. 43(1), 1-7.
Bell, Tseng and Chiappe, 2008. Diving mechanics of the extinct Hesperornithiformes: Comparison to modern diving birds. Journal of Vertebrate Paleontology. 28(3), 50A.
Galton, Dyke and Kurochkin, 2009. Re-analysis of Lower Cretaceous fossil birds from the UK reveals an unexpected diversity. Journal of Vertebrate Paleontology. 29(3), 102A.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Dyke, Benton, Posmosanu and Naish, 2011. Early Cretaceous (Berriasian) birds and pterosaurs from the Cornet bauxite mine, Romania. Palaeontology. 54(1), 79-95.
Wilson, 2011. The feeding ecology of Cretaceous and modern pursuit diving birds. Journal of Vertebrate Paleontology. Program and Abstracts 2011, 215.
Agnolin and Varricchio, 2012 . Systematic reinterpretation of Piksi barbarulna Varricchio, 2002 from the Two Medicine Formation (Upper Cretaceous) of Western USA (Montana) as a pterosaur rather than a bird. Geodiversitas. 34(4), 883-894.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Bell, 2013. Evolution & ecology of Mesozoic birds: A case study of the derived Hesperornithiformes and the use of morphometric data in quantifying avian paleoecology. PhD thesis. University of Southern California. 390 pp.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
Agnolín, Brissón Egli, Chatterjee, Garcia Marsà and Novas, 2017. Vegaviidae, a new clade of southern diving birds that survived the K/T boundary. The Science of Nature. 104(11), id.87.

Brevidentavis O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2022
= "Brachydontornis" O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2021 online
= "Brevidentavis" O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2021 online
B. zhangi O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2022
= "Brachydontornis zhangi" O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2021 online
= "Brevidentavis zhangi" O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2021 online
Late Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Material- (IVPP V26197) predentary, dentaries, basihyal or urohyal?, hyoids (12.3 mm), ?axis, ?third cervical vertebra (4.65 mm), ?fourth cervical vertebra (4.63 mm), ?fifth cervical vertebra, ?sixth cervical vertebra, ?seventh cervical vertebra, ?eighth cervical vertebra (6.06 mm), ?ninth cervical vertebra, two cervicodorsal vertebrae, two dorsal vertebrae, pellet (8.3x6.3 mm)
Diagnosis- (after O'Connor et al., 2022) predentary present; dentary teeth located in communal groove with interdental plates absent; teeth short, approximately equal in crown height and FABL; dentary teeth closely spaced, separated by a distance less than half their FABL.
Differs from other hesperornithines in- smaller size; dentary teeth shorter, straighter and blunter; shorter dentary tooth row with fewer teeth.
Comments- Discovered in 2004 or 2005, this was first mentioned and figured as an undescribed specimen of Gansus in the supplementary information of Bailleul et al. (2019). O'Connor et al. (2021) presented it at an SVP presentation as a new taxon "Brachydontornis zhangi", mentioned in the abstract as that specimen with "blunt, relatively low-crowned teeth placed in a communal groove". It was named and described by O'Connor et al. (2021 online) as "Brevidentavis zhangi", but the paper has no mention of ZooBank or an entry on the ZooBank webite. Thus according to ICZN Article 8.5.3 (an electronic work must "be registered in the Official Register of Zoological Nomenclature (ZooBank) (see Article 78.2.4) and contain evidence in the work itself that such registration has occurred"), "Brevidentavis zhangi" O'Connor et al., 2021 was a nomen nudum until September 2022. Interestingly, "Branchydontornis zhangi" was used in the graphical abstract, tables 1 and 2 and figure 9 of the Early View version of the paper. Creisler (DML 2021) revealed he had suggested both names (the other as "Brachyodontornis") and "The authors went with Brevidentavis as the formal name, but the earlier contemplated name apparently was not caught in editing."
O'Connor et al. (2021, 2022) added it to O'Connor's bird matrix and recovered it in a polytomy of hesperornithines. Note the trees in their figure are majority rule and implied weighting. Adding it to Hartman et al.'s maniraptoromorph analysis results in a sister group relationship with Parahesperornis, although other positions in Hesperornithidae are only one step longer, and other positions in Hesperornithes are two steps longer. O'Connor et al. (2022) say "Given the differences in dental and dentary morphology and the absence of any postcranial remains that could further support this placement, we do not consider Brevidentavis IVPP V26197 to be a hesperornithiform at this time", but while a relationship with the later and deeply nested Parahesperornis itself seems unlikely, the smaller basal hesperornithine Enaliornis is almost contemporaneous. Thus a hesperornithine identity may yet be plausible.
References- Bailleul, Li, O'Connor and Zhou, 2019. Origin of the avian predentary and evidence of a unique form of cranial kinesis in Cretaceous ornithuromorphs. Proceedings of the National Academy of Sciences. 116(49), 24696-24706.
O'Connor, Lamanna, Harris, Hu, Bailleul, Wang and You, 2021. First avian skulls from the Lower Cretaceous Xiagou Formation, Gansu, China. The Society of Vertebrate Paleontology Virtual Meeting Conference Program, 81st Annual Meeting. 196.
O'Connor, Stidham, Harris, Lamanna, Bailleul, Hu, Wang and You, 2022 (online 2021). Avian skulls represent a diverse ornithuromorph fauna from the Lower Cretaceous Xiagou Formation, Gansu Province, China. Journal of Systematics and Evolution. 60(5), 1172-1198.

unnamed hesperornithine (Longrich, 2009)
Late Campanian, Late Cretaceous
Upper Dinosaur Park Formation, Alberta, Canada
Material- (TMP 1986.112.0006; Ornithurine A) proximal coracoid
Diagnosis- (after Longrich, 2009) large size; humeral articular facet placed anterolaterally with respect to scapular cotyle; shallow scapular cotyle; coracoid shaft massive and posteriorly bowed.
Comments- Longrich (2009) suggested the shallow scapular cotyle, massive shaft, and dorsally bowed shaft were similar to coracoids from the Ashville Formation of Saskatchewan which were originally referred to Ichthyornis spp., but which proved to be Pasquiaornis. Agnolin (2010) suggested it was a cimolopterygid, but Mohr et al. (2021) correctly noted it lacks his proposed characters for the family- distally extensive procoracoid process; distally placed and enlarged supracoracoid foramen; laterally angled glenoid.
References- Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Agnolin, 2010. An avian coracoid from the Upper Cretaceous of Patagonia, Argentina. Studia Geologica Salmanticensia. 46(2), 99-119.
Mohr, Acorn, Funston and Currie, 2021 (2020 online). An ornithurine bird coracoid from the Late Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences. 58(2), 134-140.

undescribed Hesperornithes (Sanchez, 2010)
Middle Cenomanian, Late Cretaceous
Bainbridge River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
Material- (RSM P2626.17) vertebra
(RSM P2626.28) carpometacarpus (50.6 mm)
(RSM P2626.38) distal tarsometatarsus
(RSM P2831.17) proximal radius
(RSM P2987.9) distal tibiotarsus
(RSM P2987.19) synsacrum
?(RSM P2997.37) cranial or pelvic element
(RSM P2997.39) distal tibiotarsus
(RSM P2997.49) distal tibiotarsus
(RSM P2997.57) synsacrum
(RSM P2997.61) proximal dorsal rib
Comments- These are listed as hesperornithiform by Sanchez (2010), so may be Pasquiaornis or his unnamed hesperornithoid. RSM P2997.37 is listed as "unknown skull piece, may be part of pelvis."
Reference- Sanchez, 2010. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Masters thesis, Carleton University. 238 pp.

Hesperornithes indet. (Hanks and Shimada, 2002)
Middle-Late Turonian, Late Cretaceous
Carlile Shale, South Dakota, US
Material- (SMM P2001.12.10) (~900 mm) partial tibiotarsus
Comments- Hanks and Shimada (2002) first mentioned in an abstract that "the surface of one of the bird bones (possibly the distal 1/3 of a tibiotarsus of a hesperornithiform) has multiple tooth marks (with clear serration grooves) of the Late Cretaceous shark, Squalicorax sp.". It was later described in detail by Hanks and Shimada (2020).
References- Hanks and Shimada, 2002. Vertebrate fossils, including non-avian dinosaur remains and the first shark-bitten bird bone from a Late Cretaceous (Turonian) marine deposit of northeastern South Dakota. Journal of Vertebrate Paleontology. 22(3), 62A.
Shimada and Hanks, 2020. Shark-bitten hesperornithiform bird bone from a Turonian (Upper Cretaceous) marine deposit of northeastern South Dakota, U.S.A.. Transactions of the Kansas Academy of Science. 123(3-4), 414-418.

undescribed Hesperornithes (Kirkland et al., 1997)
Late Albian, Early Cretaceous
Mussentuchit Member of the Cedar Mountain Formation, Utah, US
Material- many teeth
Comments- Kirkland et al. (1997) listed Hesperornithiformes indet., while Cifelli et al. (1999) noted two Avialae dental morphs, one referrable to Hesperornithiformes. They described the latter specimens as having bulbous bases and rare serrations.
References- Kirkland, Britt, Burge, Carpenter, Cifelli, DeCourten, Eaton, Hasiotis and Lawton, 1997. Lower to Middle Cretaceous dinosaur faunas of the Central Colorado Plateau: a key to understanding 35 million years of tectonics, sedimentology, evolution, and biogeography. Brigham Young University Geology Studies. 42, 69-103.
Cifelli, Nydam, Gardner, Weil, Eaton, Kirkland, Madsen, 1999. Medial Cretaceous vertebrates from the Cedar Mountain Formation, Emery County, Utah: the Mussentuchit Local Fauna. in Gillette (ed.). Vertebrate Paleontology in Utah. Utah Geological Survey, Miscellaneous Publication. 99-1, 219-242.

undescribed hesperornithine (Mourer-Chauvire, 1991)
Maastrichtian, Late Cretaceous
Zhuravlovskaya Svita (not Eginsaiskaya Svita), Kazakhstan
Material- (ZIN PO coll.) tibiotarsal shaft, distal tibiotarsi (Nessov in Chauvire-Mourer, 1991)
Comments- Nessov (in Mourer-Chauvire, 1991) first mentioned two hesperornithine tibiotarsi from this locality, which may be this material. Nessov (in Mourer-Chavire, 1992) mentioned small hesperornithine material slightly larger than Baptornis advenus and referred to Baptornithidae, but not Baptornis itself because "of the peculiar structure of the fossa on the tibiotarsus, related to the side of the foramen interosseum proximale, and because the crista fibularis is not so strongly turned behind as in Baptornis, and much weaker." Nessov and Yarkov (1993) reported these as Baptornithidae indet., and Nessov (1997) commented on small hesperornithine material, some of which he thought was possibly referrable to Baptornis. Panteleev et al. (2004) thought this was possibly based on juvenile specimens of Asiahesperornis, while Dyke et al. (2006) thought it "probably pertains to a smaller hesperornithiform taxon, an area for future work." As the traditional Baptornithidae is paraphyletic and there is no evidence the Zhuravlovskaya tibiotarsi are more closely related to Baptornis than to Hesperornis, they are here placed as Hesperornithes incertae sedis.
References- Mourer-Chauvire, 1991. Society of Avian Paleontology and Evolution Information Newsletter. 5.
Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6.
Nessov and Yarkov, 1993. [Hesperornithes in Russia] Russkii Ornitolocheskii Zhurnal. 2(1), 37-54.
Nessov, 1997. Cretaceous non-marine vertebrates of Northern Eurasia. St. Petersburg State University, St-Petersburg. 218 pp.
Panteleev, Popov and Averianov, 2004. New record of Hesperornis rossicus (Aves, Hesperornithiformes) in the Campanian of Saratov Province, Russia. Paleontological Research. 8(2), 115-122.
Dyke, Malakhov and Chiappe, 2006. A re-analysis of the marine bird Asiahesperornis from northern Kazakhstan. Cretaceous Research. 27(6), 947-953.

unnamed Hesperornithes (Kurochkin, 1988)
Late Campanian-Early Maastrichtian, Late Cretaceous
Gurilin Tsav, Nemegt Formation, Mongolia
Material- cervical vertebra (Kurochkin, 1995)
Late Campanian-Early Maastrichtian, Late Cretaceous
Tsaagan Khushu, Nemegt Formation, Mongolia
(IGM 100/1311) distal tibiotarsus (12.1 mm wide) (Clarke and Norell, 2004)
distal tibiotarsus (11.7 mm wide) (Kurochkin, 1988)
partial mandible (Kurochkin, 2000)
Comments- Kurochkin (1988) identified a distal tibiotarsus as Baptornis sp., and later (1995, 2000) as closer to Parahesperornis. Clarke and Norell (2004) described a similar specimen and referred both to nonavian ornithurines (sensu Gauthier and de Queiroz), though they did note characters were shared with Baptornis while Kurochkin's Parahesperornis-like characters were disputed. They were skeptical of referring isolated Cretaceous diving euornithine specimens to Hesperornithines, though no reasons were given for removing any of it from that clade, and it seems most parsimonious to assume a single clade of Mesozoic taxa with hesperornithine-like limbs until shown otherwise. The elements are more similar to Enaliornis? seeleyi than Baptornis in the anteriorly rounded lateral condyle in distal view, though the anterior intercondylar sulcus is narrower as in Baptornis. The medial projection of the medial condyle is intermediate between the two taxa, while the extensor groove extends less distally than in both.
Kurochkin (2000) mentioned "two further remains (a cervical vertebra and the portion of a mandible) representing small hesperornithiforms were collected by the JRMPE in the Nemegt Beds of Guriliin Tsav and Tsagaan Khushuu" which were "somewhat different" from other hesperornithines. The order of localities matches the order of materials as shown by Kurochkin (1995) who mentioned a "Gurileen Tsav (vertebra)." He referred these to "Hesperornithiformes fam. nov." along with the then unnamed holotype of Brodavis mongoliensis from Bugin Tsav though he did not list any diagnostic characters.
References- Kurochkin, 1988. [Cretaceous birds of Mongolia and their significance for study of the phylogeny of class Aves.] Trudy Sovmestnoi Sovetsko-Mongolskoi Paleontologicheskoi Ekspeditsii. 34, 33-42.
Kurochkin, 1995. The assemblage of the Cretaceous birds in Asia. In Sun and Wang (eds.). Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota, Short Papers. 203-208.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Clarke and Norell, 2004. New avialan remains and a review of the known avifauna from the Late Cretaceous Nemegt Formation of Mongolia. American Museum Novitates. 3447. 12 pp.

unnamed hesperornithine (Tanaka, Kobayashi, Ikuno, Ikeda and Saegusa, 2020)
Early Maastrichtian, Late Cretaceous
Kita-ama Formation, Hyogo, Japan
Material- (MNHAH D1-048531) (juvenile) (tibiotarsus 153.43 mm) tibia, incomplete astragalocalcaneum
Comments- This was discovered in August 2004 and considered by Tanaka et al. (2020) to be a non-hesperornithid hesperornithine.
Reference- Tanaka, Kobayashi, Ikuno, Ikeda and Saegusa, 2020. Marine hesperornithiform (Avialae: Ornithuromorpha) from the Maastrichtian of Japan: Implications for the paleoecological diversity of the earliest diving birds in the end of the Cretaceous. Cretaceous Research. 113, 104492.

unnamed hesperornithine (Agnolin and Martinelli, 2009)
Campanian-Maastrichtian, Late Cretaceous
Los Alamitos Formation, Río Negro, Argentina
Material- (MACN PV RN 1114) distal tibia
Reference- Agnolin and Martinelli, 2009. Fossil birds from the Late Cretaceous Los Alamitos Formation, Río Negro province, Argentina. Journal of South American Earth Sciences. 27, 42-49.

undescribed Hesperornithes (Mourer-Chauvire, 1992)
Early Cretaceous
Antarctica
Comments- Mourer-Chauvire (1992) reported that after October 1992 "Hou will be busy studying Early Cretaceous Hesperornithiformes from the Antarctic", though these have yet to be described.
Reference- Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6, 7.

Hesperornithiformes Sharpe, 1899
Definition- (Hesperornis regalis + Enaliornis barretti) (Martyniuk, 2012)
References- Sharpe, 1899. A hand-list of the genera and species of birds. Vol. I. London. British Museum (Natural History).
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Pasquiaornis Tokaryk, Cumbaa and Storer, 1997
Other diagnoses- Tokaryk et al. (1997) used the less laterally projected trochanteric crest and less mediolaterally expanded proximal femur to distinguish Pasquiaornis from Baptornis, but this is primitive and also found in Enaliornis and Ichthyornis. The intercotylar prominence is anteriorly positioned and overhangs the shaft in Hesperornis and Parahesperornis as well. The trochlea of metatarsal II is posterior to and close to the base of trochlea III in all hesperornithines.
Comments- Both of these species were only briefly described and illustrated by Tokaryk et al. (1997), and not compared to the similar Enaliornis. This leaves them without a valid published diagnosis, nor are any characters known which could group them together to the exclusion of more derived hesperornithines. To the contrary, the larger size and metatarsal IV trochlear neck which is placed dorsal to that on trochlea III are characters which P? tankei shares with Baptornis and hesperornithids to the exclusion of P. hardiei. However, officially removing tankei from Pasquiaornis should not be done until the material of both hardiei and tankei is examined in detail, including the Bainbridge River specimens. Bell and Chiappe (2016) found both species to score identically in their matrix, and emerge basal to Enaliornis, but noted most material was unavailable for study. More recently Tanaka et al. (2018) gained access to the Bainbridge River material and recovered Pasquiaornis (scored as a single OTU) closer to hesperornithoids than Enaliornis (also a single OTU) based on three unambiguous characters, which also matches stratigraphically. Sanchez (2010) has described the Bainbridge River material in his thesis.
References- Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Sanchez, 2010. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Masters thesis, Carleton University. 238 pp.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
Tanaka, Kobayashi, Kurihara, Fiorillo and Kano, 2018 (online 2017). The oldest Asian hesperornithiform from the Upper Cretaceous of Japan, and the phylogenetic reassessment of Hesperornithiformes. Journal of Systematic Palaeontology. 16(8), 689-709.
P. hardiei Tokaryk, Cumbaa and Storer, 1997
Middle Cenomanian, Late Cretaceous
Carrot River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
Holotype- (RSM P2077.117) tarsometatarsus (54 mm)
Paratype- (RSM P2077.60) femur (47.5 mm)
Referred- (RSM P2077.11) partial coracoid (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.62) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.67) partial coracoid (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.110) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.111) partial coracoid (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.112) partial coracoid (Tokaryk, Cumbaa and Storer, 1997)
?(RSM P2077.125) (juvenile) distal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2409.1) proximal femur (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2409.9) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2409.11) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2409.49) distal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
?(RSM P2487.3) distal humerus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2487.7) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
Middle Cenomanian, Late Cretaceous
Bainbridge River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
(RSM P2526.4) partial dentary
(RSM P2626.18) anterior synsacrum
(RSM P2626.20; mislabeled in Appendix I of Sanchez, 2010 as RSM P2626.2) distal tibiotarsus
(RSM P2626.31) distal tarsometatarsus
(RSM P2626.33) distal tarsometatarsus
(RSM P2626.35) distal femur
(RSM P2626.37) distal femur
(RSM P2626.40) distal tibiotarsus
(RSM P2626.41) proximal fibula
(RSM P2830.1) proximal tarsometatarsus
(RSM P2830.2) distal tarsometatarsus
(RSM P2830.4) proximal tibiotarsus
(RSM P2831.1) proximal femur
(RSM P2831.6) anterior dentary
(RSM P2831.7) partial dorsal vertebra (10.0 mm)
(RSM P2831.8) ~twelfth-thirteenth cervical vertebra (14.8 mm)
(RSM P2831.12) partial synsacrum
(RSM P2831.15) pedal phalanx (17 mm)
(RSM P2831.16) pedal phalanx (14.4 mm)
(RSM P2831.18) partial angular
(RSM P2831.21) splenial
(RSM P2831.23) tooth
(RSM P2831.54) distal coracoid
(RSM P2957.6) distal tarsometatarsus
(RSM P2957.12) frontal
(RSM P2957.13) distal tibiotarsus
(RSM P2957.14) distal tibiotarsus
(RSM P2957.29) partial pelvis
(RSM P2985.2) dorsal vertebra (12.0 mm)
(RSM P2985.5) pedal phalanx (18.8 mm)
(RSM P2985.6) distal tarsometatarsus
(RSM P2985.8) proximal scapula
(RSM P2985.9) partial splenial
(RSM P2987.1) tarsometatarsus (56.5 mm)
(RSM P2987.21) proximal scapula
(RSM P2987.26) proximal radius
(RSM P2988.1) proximal femur
(RSM P2988.3) distal tarsometatarsus
(RSM P2988.17) partial pelvis
(RSM P2988.19) angular
(RSM P2988.21) proximal fibula
(RSM P2988.27) splenial
(RSM P2989.2) proximal tarsometatarsus
(RSM P2989.3) distal tarsometatarsus
(RSM P2989.4) distal tarsometatarsus
(RSM P2989.6) distal tarsometatarsus
(RSM P2989.8) proximal tarsometatarsus
(RSM P2989.9) proximal tarsometatarsus
(RSM P2989.15) distal humerus
?(RSM P2989.19) posterior mandible
(RSM P2989.25; mislabeled in Plate XV of Sanchez, 2010 as RSM P2985.25) anterior synsacrum
(RSM P2989.37) angular
(RSM P2989.39) pelvis
(RSM P2989.40) pedal phalanx
(RSM P2995.3) proximal ulna
(RSM P2995.7) proximal tibiotarsus
(RSM P2997.4) femur (50.7 mm)
(RSM P2997.9) distal femur
(RSM P2997.10) femur (49.9 mm)
(RSM P2997.12) femur (48.2 mm)
(RSM P2997.14) distal femur
(RSM P2997.15) tarsometatarsus (51.9 mm)
(RSM P2997.16) proximal tarsometatarsus
(RSM P2997.18) tarsometatarsus (60.8 mm)
(RSM P2997.19) proximal tarsometatarsus
(RSM P2997.20) distal tarsometatarsus
(RSM P2997.22) proximal tarsometatarsus
(RSM P2997.27) proximal ulna
(RSM P2997.28) proximal ulna
(RSM P2997.29) distal ulna
(RSM P2997.36) frontal
(RSM P2997.40) distal tibiotarsus
(RSM P2997.41) distal tibiotarsus
(RSM P2997.42) distal tibiotarsus
(RSM P2997.46) proximal tibiotarsus
(RSM P2997.47) distal tibiotarsus
(RSM P2997.48) distal tibiotarsus
(RSM P2997.62) partial pelvis
(RSM P2997.63) pelvic fragment
(RSM P2997.69) pedal phalanx (20.1 mm)
(RSM P2997.74) incomplete radius (58.3 mm)
(RSM P2997.75) incomplete radius
(RSM P2997.76) angular
(RSM P2997.79) proximal femur
(RSM P2997.81) proximal tarsometatarsus
(RSM P2997.83) proximal tarsometatarsus
(RSM P3015.1) proximal femur
(RSM P3015.2) proximal femur
(RSM P3015.3) proximal femur
(RSM P3015.10) proximal radius
(RSM P3015.14) distal pedal phalanx
(RSM P3015.18) distal tarsometatarsus
Diagnosis- (after Tokaryk et al., 1997) smaller than P? tankei.
Other diagnoses- Tokaryk et al. (1997) say the medial tarsometatarsal cotyle is "deflected toward shaft", but those of most hesperornithines are angled somewhat as well. The neck of trochlea III being higher anteriorly than that of trochlea IV is primitive, being present in Enaliornis barretti and E? seeleyi as well. The "distal rim" of the femoral head is said to be perpendicular to the shaft, but this does not appear to be true for either the rim of the articular surface or the medial or ventral edges of the head.
Comments- Excavated in 1992 and 1993, this was first noted as a new species of baptornithid by Cumbaa and Tokaryk (1993) before being described by Tokaryk et al. (1997). Tokaryk et al. (1997) reported that in 1994 and 1995 numerous bird fossils similar to Pasquiaornis were discovered at the Bainbridge River Bonebed. Cumbaa et al. (2006) states hundreds of bird specimens are known, mostly hesperornithine, and illustrates four teeth. Sanchez et al. (2009) note both P. hardiei and P? tankei are represented in this material, which was described by Sanchez (2010). Type A teeth of Sanchez (2010) are here assigned to P. hardiei because they are larger. Sanchez lists RSMP2989.19 as "small, may be Ichthyornis."
Cumbaa and Tokaryk mentioned two ichthyornithids from the Ashville Formation of Saskatchewan, which were later described by Tokaryk et al. (1997) as Ichthyornis species A (RSM P2077.11, P2077.67, P2077.112 and P2487.5), Ichthyornis species B (RSM P2077.111) and I. sp. indet. (RSM P2077.71). They referred the specimens to Ichthyornis based on the coracoid scapular facet being nearly parallel to the sternal end of the glenoid facet, which Clarke (2004) noted was found in Ichthyornis, but not apomorphic. Tokaryk et al. distinguished species A from species B by its gracility and round (vs. angular) scapular facet. Longrich (2009) suggested the Ashville coracoids did not resemble Ichthyornis, and were referrable to Pasquiaornis based on their dimorphism (P. hardiei vs. P? tankei), pachyostosis, and supposed lack of coracoids in the Pasquiaornis material. Sanchez (2010) confirms the coracoids are Pasquiaornis, and Ichthyornis species A is here placed in P. hardiei.
References- Cumbaa and Tokaryk, 1993. Early birds, crocodile tears, and fish tales: Cenomanian and Turonian marine vertebrates from Saskatchewan, Canada. Journal of Vertebrate Paleontology. 13(3), 31A-32A.
Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Cumbaa, Schröder-Adams, Day and Phillips, 2006. Cenomanian bonebed faunas from the northeastern margin, Western Interior Seaway. In Lucas and Sullivan (eds). Late Cretaceous Vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin. 35, 139-155.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Sanchez, Cumbaa and Schroder-Adams, 2009. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Journal of Vertebrate Paleontology. 29(3), 175A.
Sanchez, 2010. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Masters thesis, Carleton University. 238 pp.
Tanaka, Takasaki and Tokaryk, 2021. Osteological histology of the Cretaceous seabird Pasquiaornis (Avialae, Hesperornithiformes): Implications for the flight ability of the basal hesperornithiforms. 2021 Northeast Natural History Conference Poster Abstracts. 51.
P? tankei Tokaryk, Cumbaa and Storer, 1997
Middle Cenomanian, Late Cretaceous
Carrot River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
Holotype- (RSM P2077.63) incomplete tarsometatarsus (85.6 mm)
Paratype- (RSM P2077.108) femur (64.76 mm)
Referred- (RSM P2077.10) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.72) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.79) distal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.107) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.109) femur (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.113) partial coracoid (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.116) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.118) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.119) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.120) quadrate, distal tibiotarsus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.123) partial pelvic element (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.124) partial pelvic element (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2077.127) partial pelvic element (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2409.2) proximal tarsometatarsus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2409.3) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2467.2) distal femur (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2467.3) distal femur (Tokaryk, Cumbaa and Storer, 1997)
?(RSM P2467.8) distal humerus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2487.2) femur (Tokaryk, Cumbaa and Storer, 1997)
?(RSM P2487.4) distal humerus (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2487.5) partial coracoid (Tokaryk, Cumbaa and Storer, 1997)
(RSM P2487.8) proximal tibiotarsus (Tokaryk, Cumbaa and Storer, 1997)
Middle Cenomanian, Late Cretaceous
Bainbridge River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
(RSM P2526.2) proximal radius
(RSM P2526.3) proximal radius
(RSM P2626.6) partial pelvis
(RSM P2626.10; mislabeled in Appendix I of Sanchez, 2010 as RSM P2626.1) partial coracoid
(RSM P2626.11) distal coracoid
(RSM P2626.12) frontal
(RSM P2626.15) ~fourth-sixth cervical vertebra (25.7 mm)
(RSM P2626.16) ~fourth-sixth cervical vertebra (23.9 mm)
(RSM P2626.19) pedal phalanx III-2 (24.4 mm)
(RSM P2626.27) partial pelvis
(RSM P2626.29) pelvis
(RSM P2626.30) coracoid (42.8 mm)
(RSM P2626.31) pedal phalanx (22.5 mm)
(RSM P2626.34) distal femur
(RSM P2626.36) proximal femur
(RSM P2626.39) dorsal vertebra (17.8 mm)
(RSM P2626.42) surangular, prearticular
(RSM P2830.3) proximal scapula
(RSM P2831.2) proximal humerus
(RSM P2831.4) proximal carpometacarpus
(RSM P2831.5) dentary
(RSM P2831.9) partial ~fifth-eighth cervical vertebra (18.9 mm)
(RSM P2831.10) partial dorsal vertebra (14.7 mm)
(RSM P2831.11) dorsal vertebra (16.7 mm)
(RSM P2831.20) proximal radius
(RSM P2831.22) tooth
(RSM P2831.24) tooth
(RSM P2831.25) tooth
(RSM P2831.26) tooth
(RSM P2831.27) tooth
(RSM P2831.28) tooth
(RSM P2831.30) tooth
(RSM P2831.31) tooth
(RSM P2831.32) tooth
(RSM P2831.33) tooth
(RSM P2831.34) tooth
(RSM P2831.35) tooth
(RSM P2831.36) tooth
(RSM P2831.37) tooth
(RSM P2831.38) tooth
(RSM P2831.39) tooth
(RSM P2831.40) tooth
(RSM P2831.41) tooth
(RSM P2831.42) tooth
(RSM P2831.43) tooth
(RSM P2831.44) tooth
(RSM P2831.46) tooth
(RSM P2831.47) tooth
(RSM P2831.52) distal quadrate
(RSM P2831.53) pelvis
(RSM P2831.55) incomplete frontal
(RSM P2831.56) proximal scapula
(RSM P2831.57) proximal radius
(RSM P2957.2) coracoid (46.6 mm)
(RSM P2957.5) proximal femur
(RSM P2957.7) proximal humerus
(RSM P2957.9) proximal coracoid
(RSM P2957.10) proximal coracoid
(RSM P2957.15) dorsal vertebra (17.4 mm)
(RSM P2957.16) partial cervical vertebra
(RSM P2957.17) cervical vertebra (11.4 mm)
(RSM P2957.19) proximal scapula
(RSM P2957.21) distal tibiotarsus
(RSM P2957.22) proximal tibiotarsus
(RSM P2957.23) mandible
(RSM P2957.24) distal humerus
(RSM P2957.25) distal humerus
(RSM P2957.26) distal humerus
(RSM P2957.27) tarsometatarsus (81.3 mm)
(RSM P2985.1) dorsal vertebra
(RSM P2985.3) dorsal vertebra (16.0 mm)
(RSM P2985.4) dorsal vertebra
(RSM P2985.7) proximal coracoid
(RSM P2985.10) anterior dentary
(RSM P2986.2) angular
(RSM P2987.2) distal humerus
(RSM P2987.3) distal humerus
(RSM P2987.4) proximal humerus
(RSM P2987.5) proximal coracoid
(RSM P2987.6) distal coracoid
(RSM P2987.7) proximal coracoid
(RSM P2987.8) proximal carpometacarpus
(RSM P2987.10) proximal tibiotarsus
(RSM P2987.13) cervical vertebra (19.5 mm)
(RSM P2987.14) cervical vertebra (17.8 mm)
(RSM P2987.15) cervical vertebra (21.6 mm)
(RSM P2987.16) cervical vertebra (20.0 mm)
(RSM P2987.17) ~fourth-thirteenth cervical vertebra (18.5 mm)
(RSM P2987.18) partial dorsal vertebra (16.9 mm)
(RSM P2987.20) partial anterior synsacrum
(RSM P2987.24) pedal phalanx (25.1 mm)
(RSM P2987.25) proximal radius
(RSM P2988.2) distal femur
(RSM P2988.5) proximal humerus
(RSM P2988.6) proximal humerus
(RSM P2988.7) proximal humerus
(RSM P2988.9) coracoid (50.68 mm)
(RSM P2988.10) surangular
(RSM P2988.11) anterior dentary
(RSM P2988.12) first dorsal or last cervical vertebra (15.0 mm)
(RSM P2988.13) ~fourteenth-fifteenth cervical vertebra
(RSM P2988.14) ~fourteenth-fifteenth cervical vertebra (17.8 mm)
(RSM P2988.16) synsacrum
(RSM P2988.18) proximal radius
(RSM P2988.20) distal femur
(RSM P2988.22) maxilla
(RSM P2988.23) proximal pedal phalanx
(RSM P2988.24) distal pedal phalanx
(RSM P2988.25) distal quadrate
(RSM P2988.26) proximal radius
(RSM P2989.1) incomplete femur (68.4 mm)
(RSM P2989.10) distal humerus
(RSM P2989.11) proximal humerus
(RSM P2989.12) proximal humerus
(RSM P2989.13) proximal humerus
(RSM P2989.14) proximal humerus
(RSM P2989.16) distal ulna
(RSM P2989.17) proximal ulna
(RSM P2989.18) proximal carpometacarpus
(RSM P2989.20) frontal
(RSM P2989.21) posterior mandible
(RSM P2989.22) dorsal vertebra (15.9 mm)
(RSM P2989.23) dorsal vertebra (15.5 mm)
(RSM P2989.24) ~third-fourth cervical vertebra (16.2 mm)
(RSM P2989.27) pedal phalanx (18.7 mm)
(RSM P2989.28) pedal phalanx (21.4 mm)
(RSM P2989.29) proximal pedal phalanx
(RSM P2989.30) proximal radius
(RSM P2989.34) distal carpometacarpus
(RSM P2989.35) proximal fibula
(RSM P2989.36) angular
(RSM P2989.38) frontal
(RSM P2989.41) incomplete pedal phalanx
(RSM P2989.193) splenial
(RSM P2989.194) splenial
(RSM P2995.1) humerus (102.8 mm)
(RSM P2995.4) frontal
(RSM P2995.5) partial maxilla
(RSM P2995.8) (juvenile?) proximal pedal phalanx
(RSM P2995.9) proximal fibula
(RSM P2997.2) femur (65.1 mm)
(RSM P2997.3) incomplete femur (66.0 mm)
(RSM P2997.5) distal femur
(RSM P2997.6) femur (60.2 mm)
(RSM P2997.7) incomplete femur (57.6 mm)
(RSM P2997.8) incomplete femur
(RSM P2997.11) incomplete femur
(RSM P2997.13) femur
(RSM P2997.21) proximal tarsometatarsus
(RSM P2997.23) distal tarsometatarsus
(RSM P2997.24) distal humerus
(RSM P2997.25) distal humerus
(RSM P2997.30) distal ulna
(RSM P2997.31) proximal coracoid
(RSM P2997.32) proximal carpometacarpus
(RSM P2997.33) proximal carpometacarpus
(RSM P2997.34) proximal carpometacarpus
(RSM P2997.35) surangular, articular
(RSM P2997.38) frontal
(RSM P2997.43) proximal tibiotarsus
(RSM P2997.44) proximal tibiotarsus
(RSM P2997.45) partial tibiotarsus
(RSM P2997.50) ~third-sixth dorsal vertebra (17.0 mm)
(RSM P2997.51) dorsal vertebra (17.4 mm)
(RSM P2997.52) cervical vertebra
(RSM P2997.53) cervical vertebra
(RSM P2997.54) ~tenth-thirteenth cervical vertebra (17.3 mm)
(RSM P2997.55) ~fourth-sixth cervical vertebra
(RSM P2997.56) anterior synsacrum
(RSM P2997.58) scapula (47.0 mm)
(RSM P2997.59) proximal scapula
(RSM P2997.60) proximal scapula
(RSM P2997.64) pelvic fragment
(RSM P2997.65) pedal phalanx III-2 (24.1 mm)
(RSM P2997.66) pedal phalanx III-2 (24.4 mm)
(RSM P2997.67) pedal phalanx II-1 (22.8 mm)
(RSM P2997.68) pedal phalanx II or IV-1 (24.8 mm)
(RSM P2997.70) proximal pedal phalanx
(RSM P2997.71) proximal pedal phalanx (36 mm)
(RSM P2997.72) (juvenile?) pedal phalanx II-1
(RSM P2997.73) pedal phalanx II-1
(RSM P2997.77) proximal femur
(RSM P2997.78) distal carpometacarpus
(RSM P2997.80) proximal fibula
(RSM P2997.82) proximal scapula
(RSM P2997.84) caudal vertebra
(RSM P2997.85) incomplete frontal
(RSM P3015.4) proximal tarsometatarsus
(RSM P3015.5) distal ulna
(RSM P3015.6) ~fourth-sixth cervical vertebra
(RSM P3015.7) ~third-fourth cervical vertebra (14.3 mm)
(RSM P3015.8) proximal scapula
(RSM P3015.9) pedal phalanx III or IV-1 (31.8 mm)
(RSM P3015.11) proximal carpometacarpus
(RSM P3015.12) partial femur
(RSM P3015.15) distal pedal phalanx
(RSM P3015.16) proximal scapula
(RSM P3015.17) proximal scapula
(RSM P3015.19) incomplete tarsometatarsus
(RSM P3015.20) partial cervical vertebra
Diagnosis- (after Tokaryk et al., 1997) larger than P. hardiei.
Other diagnoses- Tokaryk et al. (1997) also state the "distal rim" of the femoral head is slanted toward the shaft, but the meaning of this is uncertain. The medial tarsometatarsal cotyle is said to be level in medial view, which is unlike Hesperornis and Parahesperornis, but similar to Gansus and Enaliornis? seeleyi, so may be plesiomorphic. The neck of trochlea III being lower anteriorly than that of trochlea IV is present in Enaliornis? sedgwicki, Parahesperornis and Hesperornis as well.
Comments- Excavated in 1992 and 1993, this was first noted as a new species of baptornithid by Cumbaa and Tokaryk (1993) before being described by Tokaryk et al. (1997). As noted in the Pasquiaornis comments, tankei may not belong to that genus and may be more closely related to Baptornis and hesperornithids.
Tokaryk et al. (1997) reported that in 1994 and 1995 numerous bird fossils similar to Pasquiaornis were discovered at the Bainbridge River Bonebed. Cumbaa et al. (2006) states hundreds of bird specimens are known, mostly hesperornithine, and illustrates four teeth. Sanchez et al. (2009) note both P. hardiei and P? tankei are represented in this material, which was described by Sanchez (2010). Type B teeth of Sanchez (2010) are here assigned to P. tankei because they are smaller.
Cumbaa and Tokaryk mentioned two ichthyornithids from the Carrot River beds of the Ashville Formation of Saskatchewan, which were later described by Tokaryk et al. (1997) as Ichthyornis species A (RSM P2077.11, P2077.67, P2077.112 and P2487.5), Ichthyornis species B (RSM P2077.111) and I. sp. indet. (RSM P2077.71). They referred the specimens to Ichthyornis based on the coracoid scapular facet being nearly parallel to the sternal end of the glenoid facet, which Clarke (2004) noted was found in Ichthyornis, but not apomorphic. Tokaryk et al. distinguished species A from species B by its gracility and round (vs. angular) scapular facet. Longrich (2009) suggested the Ashville coracoids did not resemble Ichthyornis, and were referrable to Pasquiaornis based on their dimorphism (P. hardiei vs. P? tankei), pachyostosis, and supposed lack of coracoids in the Pasquiaornis material. Sanchez (2010) confirms the coracoids are Pasquiaornis, and Ichthyornis species B is here placed in P? tankei.
References- Cumbaa and Tokaryk, 1993. Early birds, crocodile tears, and fish tales: Cenomanian and Turonian marine vertebrates from Saskatchewan, Canada. Journal of Vertebrate Paleontology. 13(3), 31A-32A.
Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. Ph.D. dissertation, Yale University, New Haven, CT. 532 pp.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Cumbaa, Schröder-Adams, Day and Phillips, 2006. Cenomanian bonebed faunas from the northeastern margin, Western Interior Seaway. In Lucas and Sullivan (eds). Late Cretaceous Vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin. 35, 139-155.
Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.
Sanchez, Cumbaa and Schroder-Adams, 2009. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Journal of Vertebrate Paleontology. 29(3), 175A.
Sanchez, 2010. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Masters thesis, Carleton University. 238 pp.
Tanaka, Takasaki and Tokaryk, 2021. Osteological histology of the Cretaceous seabird Pasquiaornis (Avialae, Hesperornithiformes): Implications for the flight ability of the basal hesperornithiforms. 2021 Northeast Natural History Conference Poster Abstracts. 51.
P. sp. nov. (Sanchez, 2010)
Middle Cenomanian, Late Cretaceous
Bainbridge River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
Material- (RSM P2989.5) distal tarsometatarsus
(RSM P2989.7) incomplete tarsometatarsus (56.9 mm)
(RSM P2997.17) proximal tarsometatarsus
Comments- Sanchez et al. (2009) noted "the fauna from the Pasquia Hills bonebed includes a possible new species of Pasquiaornis." This material is referred to Pasquiaornis sp. A by Sanchez (2010).
References- Sanchez, Cumbaa and Schroder-Adams, 2009. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Journal of Vertebrate Paleontology. 29(3), 175A.
Sanchez, 2010. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Masters thesis, Carleton University. 238 pp.
P. spp. (Sanchez, 2010)
Middle Cenomanian, Late Cretaceous
Bainbridge River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
Material- ?(RSM P2831.14) pedal ungual
(RSM P2831.29) tooth
(RSM P2831.45) tooth
(RSM P2831.48) tooth
(RSM P2831.49) tooth
(RSM P2831.50) tooth
(RSM P2831.51) tooth
(RSM P2989.189) tooth
(RSM P2989.190) tooth
(RSM P2989.191) tooth
(RSM P2989.192) tooth
(RSM coll.) over sixty teeth
Comments- This material is referred to Pasquiaornis by Sanchez (2010), but not to a particular species.
References- Sanchez, 2010. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Masters thesis, Carleton University. 238 pp.

Chupkaornis Tanaka, Kobayashi, Kurihara, Fiorillo and Kano, 2017 online
C. keraorum Tanaka, Kobayashi, Kurihara, Fiorillo and Kano, 2017 online
Coniacian-Santonian, Late Cretaceous
Kashima Formation of the Yezo Group, Japan
Holotype- (MCM.A.773) incomplete ~thirteenth cervical vertebra, partial fourteenth cervical vertebra, incomplete sixteenth cervical neural arch, incomplete seventeenth cervical vertebra, incomplete third dorsal vertebra, incomplete fourth dorsal vertebra (20.00 mm), distal femora, partial fibula
Diagnosis- (after Tanaka et al., 2018) slender base of hypapophysis on fourth dorsal vertebra (unknown in other non-hesperornithid hesperornithines); finger-like projected tibiofibular crest of femur.
Other diagnoses- Tanaka et al. (2018) list an emarginated lateral fossa on dorsal centra with pronounced and sharply defined ventral edge, but this is plesiomorphic being found in Pasquiaornis and most earlier euornithines. The laterally expanded fibular condyle of femur is stated to be present in all hesperornithiforms. The completely heterocoelous articular surface in dorsal vertebrae 3-4 at least (as defined by the authors) is a synapomorphy shared with hesperornithoids.
Comments- Discovered in 1996. Tanaka et al. (2014) found this specimen to be more derived than Enaliornis and Pasquiaornis, but outside Hesperornithoidea. The same was true in Tanaka et al. (2018), based on a reduced version of Bell and Chiappe's hesperornithione analysis.
References- Tanaka, Kobayashi, Kano and Kurihara, 2012. The first record of a hesperornithiform from Japan. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 183.
Tanaka, Kobayashi, Kurihara, Kano and Fiorillo, 2014. Phylogenetic position of a new hesperornithiform from the Upper Cretaceous of Hokkaido, Japan. Journal of Vertebrate Paleontology. Program and Abstracts 2014, 239.
Tanaka, Kobayashi, Kurihara, Fiorillo and Kano, 2018 (online 2017). The oldest Asian hesperornithiform from the Upper Cretaceous of Japan, and the phylogenetic reassessment of Hesperornithiformes. Journal of Systematic Palaeontology. 16(8), 689-709.

Hesperornithoidea Marsh, 1872 vide Shufeldt, 1903
Definition- (Baptornis advenus + Hesperornis regalis) (Martyniuk, 2012)
Diagnosis- (proposed) quadratojugal buttress on quadrate (absent in Hesperornis regalis; unknown in more basal hesperornithines); articular surfaces of dorsal vertebrae broad and trapezoidal; pygostyle less than two caudal vertebrae in length (unknown in more basal hesperornithines); medial area of coracoid depressed where supracoracoid foramen is (also in Apsaravis; unknown in more basal hesperornithines); sternum lacks keel (unknown in more basal hesperornithines); deltopectoral crest reduced in height (also in Patagopteryx and Aves; unknown in more basal hesperornithines); bicipital crest lacks fossae (also in Songlingornithidae and Patagopteryx; unknown in more basal hesperornithines); brachial fossa on humerus poorly developed (also in Apsaravis); humerus reduced to have indistinct distal condyles; femur very robust; tarsometatarsus less than five times longer than broad; intercotylar prominence well developed (also in Ichthyornis and Aves).
Comments- Shufeldt (1903) named Hesperornithoidea to contain both Enaliornithidae and Hesperornithidae. A clade to the exclusion of Enaliornis was proposed by Martin (1984) based on heterocoelous dorsal centra, but the amphicoelous presacrals referred to Enaliornis are now thought to belong to another taxon (Galton and Martin, 2002b). Bell and Chiappe (2016) recovered this clade to the exclusion of Enaliornis and Pasquiaornis in their phylogenetic analysis but left it unnamed.
References- Shufeldt, 1903. On the classification of certain groups of birds. The American Naturalist. 37, 33-64.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Galton and Martin, 2002b. Postcranial anatomy and systematics of Enaliornis Seeley, 1876, a footpropelled diving bird (Aves: Ornithurae: Hesperornithiformes) from the Early Cretaceous of England. Revue de Paleobiologie. 21(2), 489-538.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.

Hesperornis? macdonaldi Martin and Lim, 2002
Middle Campanian, Late Cretaceous
Sharon Springs Member of the Pierre Shale Group, South Dakota, US
Holotype- (LACM 9728) femur (44.7 mm)
Referred- (LACM 9727) femur (Bell and Chiappe, 2020)
Early Campanian, Late Cretaceous
Gammon Ferruginous Member of the Pierre Shale Group, Manitoba, Canada
(CFDC B.2012.01.13) femur (44.4 mm) (Aotsuka and Sato, 2016)
(CFDC B.2012.02.13) femur (52.5 mm) (Aotsuka and Sato, 2016)
Mid Campanian, Late Cretaceous
Pembina Member of the Pierre Shale Group, Manitoba, Canada
(CFDC B.80.08.16) femur (49.4 mm) (Aotsuka and Sato, 2016)
Mid Campanian, Late Cretaceous
Millwood Member of the Pierre Shale Group, Manitoba, Canada
(CFDC B.81.03.16) femur (48.2 mm) (Aotsuka and Sato, 2016)
(CFDC B.2006.01.05) femur (Aotsuka and Sato, 2016)
Diagnosis- (after Martin and Lim, 2002) small size, with tarsometatarsal length estimated at <60 mm (also in Pasquiaornis hardiei).
Other diagnoses- Martin and Lim (2002) also diagnosed this species based on the deeply concave lateral femoral margin, which is also present in Hesperornis regalis.
Comments- Bryant first mentions the holotype as one of "several femora including some very small (and presumably very young) ones collected by myself and others working with a Los Angeles County Museum field party in 1964", though it was undescribed at the time. Martin and Lim (2002) believe the holotype is an adult due to its well formed articular surfaces, but Bell and Chiappe (2016) stated the small size "may be due to the immature ages of the specimen, which is difficult to determine due to the poor preservation of the elements and in the absence of histological data." Aotsuka and Sato (2016) referred femora to macdonaldi from Manitoba based on their size.
This species was described in Hesperornis by Martin and Lim. However it has an uncertain placement, as the femora of hesperornithids besides Brodavis? varneri and Hesperornis regalis are still undescribed, and mostly unpreserved. The extreme robusticity is shared with H. regalis, but seemingly not H. bazhanovi or Parahesperornis. The strong anteroposterior compression of the shaft is also shared with H. regalis but not B? varneri or H. crassipes. However, the medial condyle is not distally projected, unlike B? varneri and H. regalis. The small size is unlike Hesperornithidae. Bell and Chiappe found macdonaldi to code identically to taxa placed in Hesperornis here.
References- Bryant, 1983. Hesperornis in Alaska. Paleobios. 40, 1-8.
Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds.). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution. 165-174.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
Aotsuka and Sato, 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, southern Manitoba, Canada. Cretaceous Research. 63, 154-169.
Bell and Chiappe, 2020. Anatomy of Parahesperornis: Evolutionary mosaicism in the Cretaceous Hesperornithiformes (Aves). Life. 10(5), 62.

Judinornis Nessov and Borkin, 1983
J. nogontsavensis Nessov and Borkin, 1983
Late Campanian-Early Maastrichtian, Late Cretaceous
Nogon Tsav, Nemegt Formation, Mongolia
Holotype- (ZIN PO 3389) incomplete last dorsal vertebra (14.1 mm)
Diagnosis- (proposed) highly elongate dorsal vertebrae (~2.5 longer than posteriorly high).
Other diagnoses- Kurochkin (2000) listed dorsal central articular surfaces transversely expanded, ventral surface of dorsal centrum transversely narrow in middle and expanded posteriorly, and prezygapophyses with little transverse separation in his diagnosis, but then correctly noted these are general hesperornithine characters in the comments section. In addition, he listed the trapezoidal dorsal central articular surfaces in his diagnosis, but these are found in other hesperornithines as well.
Comments- Nessov and Borkin (1983) originally referred Judinornis to the Charadriiformes, but it was reassigned to the Baptornithidae without evidence by Nessov (1986). Kurochkin (2001) listed characters shared with Baptornis, but these are plesiomorphic as noted in the Baptornithidae comments. The holotype is indeed extremely similar to Baptornis, though no synapomorphies seem evident. The low central articular surfaces with projecting ventrolateral corners indicate it is more derived than Enaliornis. Several characters are more similar to Baptornis and Parascaniornis than to Hesperornis- the prezygapophysis is elongate and well separated from the centrum in lateral view; ventral centrum surface is transversely constricted; the transverse processes extend further anteriorly.
References- Nessov and Borkin, 1983. [New records of bird bones from Cretaceous of Mongolia and Middle Asia] Trudy Zoologicheskogo Instituta Akademii Nauk SSSR. 116, 108-110.
Nessov, 1986. The first record of the Late Cretaceous bird Ichthyornis in the Old World and some other bird bones from the Cretaceous and Paleogene of Soviet Middle Asia. Proc. Zool. Inst. USSR Acad. Sci.. 147, 31-38.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. In Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.

Parascaniornis Lambrecht, 1933
P. stensioei Lambrecht, 1933
Early Campanian, Late Cretaceous
Bellemnellocamax mamillatus zone, Ivo Klack, Sweden
Holotype- (MGUH 1908.214) posterior dorsal vertebra (15 mm)
Referred- ?(RM PZ R1261) distal tarsometatarsus (Rees and Lindgren, 2005)
Comments- The holotype was discovered in 1908 and described by Lambrecht (1933) as a "scaniornithid" (Scaniornis is a Paleocene bird variously allied with ciconiiforms or phoenicopteriforms). Lambrecht originally spelled the species stensiöi, which must be corrected to stensioei according to ICZN Article 32.5.2.1- "in a name published before 1985 and based upon a German word, the umlaut sign is deleted from a vowel and the letter "e" is to be inserted after that vowel." Howard (1950) believed Parascaniornis was a phoenicopteriform, but it was reidentified as a hesperornithine by Nessov (in Mourer-Chauvire, 1990) and Nessov and Prizemlin (1991). Rees and Lindgren (2005) reexamined this vertebra and found it to be identical to Baptornis advenus and RSM P2306.2 of the Judith River Group, except for the more horizontally directed prezygapophyses. They viewed it as indeterminate within Baptornis and called it Baptornis sp., but as Ford (online, 1995) notes, you cannot sink a named species into "sp.". Instead, it would be named Baptornis stensioei, though this combination is not yet published. However, Rees and Lindgren did not list any derived characters that could be used to place stensioei in Baptornis, nor even any shared primitive characters. The low central articular surfaces with projecting ventrolateral corners indicate it is more derived than Enaliornis. In elongation, Parascansiornis is similar to Baptornis, more elongate than Hesperornis, but less than Judinornis. The prezygapophysis is elongate and well separated from the centrum in lateral view, as in Baptornis and Judinornis, but unlike Hesperornis. The ventral surface is transversely constricted and the transverse processes extend further anteriorly as in Baptornis and especially Judinornis, but less than Hesperornis. As Parascaniornis is roughly equally similar to Baptornis and Judinornis, and shares to obvious apomorphies with either, it is here retained in its own genus.
References- Lambrecht, 1933. Handbuch der Paläornithologie. Berlin, Gebrüder Borntraeger. 1024 pp.
Howard, 1950. Fossil evidence of avian evolution. Ibis. 92, 1-21.
Mourer-Chauvire, 1990. Society of Avian Paleontology and Evolution Information Newsletter. 4.
Nessov and Prizemlin, 1991. A large advanced flightless marine bird of the order Hesperornithiformes of the Late Senonian of Turgai Strait - the first finding of the group in the USSR. USSR Academy of Sciences, Proceedings of the Zoological Institute. 239, 85-107. [In Russian].
Nessov, 1992. [Flightless birds of meridional Late Cretaceous sea straits of North America, Scandinavia, Russia and Kazakhstan as indicators of features of oceanic circulation.] Byulleten Moskovskogo Obshchestva Ispytatelet Prirody Otdel Geologicheskii. 67, 78-83.
Rees and Lindgren, 1999. Early Campanian hesperornithiform birds from the Kristianstad Basin, southern Sweden. in Hoch and Brantsen (eds). Secondary adaptation to life in water. Abstracts. University of Copenhagen, Copenhagen. 53.
Ford, online 2005. http://www.dinohunter.info/html/articles2005.htm
Rees and Lindgren, 2005. Aquatic birds from the Upper Cretaceous (Lower Campanian) of Sweden and the biology and distribution of hesperornithiforms. Palaeontology. 48(6), 1321-1329.

undescribed hesperornithoid (Sanchez, Cumbaa and Schroder-Adams, 2009)
Middle Cenomanian, Late Cretaceous
Bainbridge River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
Material- (RSM P2626.43) partial humerus (Sanchez, 2010)
(RSM P2986.1) humerus (74.0 mm) (Sanchez, 2010)
?(RSM P2997.26) dorsal rib or humerus (Sanchez, 2010)
(RSM P3015.13) distal humerus (Sanchez, 2010)
Comments- Sanchez et al. (2009) note that among the 250 bird bones from the Bainbridge River Bonebed (most of which are Pasquiaornis), some are from a "possible new hesperornithiform genus." Sanchez's (2010) thesis reveal these to consist of humeri more reduced than Pasquiaornis. His appendix one lists RSM P2997.26 as "reduced wing or rib."
References- Sanchez, Cumbaa and Schroder-Adams, 2009. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Journal of Vertebrate Paleontology. 29(3), 175A.
Sanchez, 2010. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Masters thesis, Carleton University. 238 pp.

Hesperornithoidea indet. (Tokaryk and Harington, 1992)
Late Campanian, Late Cretaceous
Judith River Group, Saskatchewan, Canada
Material- (RSM P2306.2) fourth dorsal vertebra (21.2 mm)
Comments- This specimen was discovered in 1975-1976 and was described as Baptornis sp. by Tokaryk and Harington (1992). Of the characters used to refer this to Baptornis, the heterocoely of dorsal four is present in all hesperornithines. The narrower and lower posterior central articular surface (compared to centrum length) is plesiomorphic, being present in Enaliornis and Judinornis as well, while the lower anterior central articular surface and small parapophysis are also present in Judinornis. The centrally placed hypapophysis is also present in Hesperornis. However, as the centrum is trapezoidal, it is probably more derived than Enaliornis.
Reference- Tokaryk and Harington, 1992. Baptornis sp. (Aves: Hesperornithiformes) from the Judith River Formation (Campanian) of Saskatchewan, Canada. Journal of Paleontology. 66(6), 1010-1012.

Hesperornithoidea indet. (Aotsuka and Sato, 2016)
Early Campanian, Late Cretaceous
Gammon Ferruginous Member of the Pierre Shale Group, Manitoba, Canada
Material- (CFDC B.2010.03.13) vertebra (Aotsuka and Sato, 2016)
(CFDC B.2010.05.03) pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.2011.01.13) vertebra (Aotsuka and Sato, 2016)
(CFDC B.2011.04.13) vertebra (Aotsuka and Sato, 2016)
(CFDC B.2011.06.13) vertebra (Aotsuka and Sato, 2016)
Mid Campanian, Late Cretaceous
Pembina Member of the Pierre Shale Group, Manitoba, Canada
(CFDC B.00.33.03) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.00.38.00) fibula (Aotsuka and Sato, 2016)
(CFDC B.00.39.00) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.00.41.00) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.00.44.00) pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.00.45.00) vertebra (Aotsuka and Sato, 2016)
(CFDC B.00.48.00) vertebra (Aotsuka and Sato, 2016)
(CFDC B.00.49.00) vertebra (Aotsuka and Sato, 2016)
(CFDC B.00.50.00; lost) vertebra (Aotsuka and Sato, 2016)
(CFDC B.00.52.00) vertebra (Aotsuka and Sato, 2016)
(CFDC B.00.53.00) vertebra (Aotsuka and Sato, 2016)
(CFDC B.04.01.15) vertebra (Aotsuka and Sato, 2016)
(CFDC B.04.01.23) three vertebrae (Aotsuka and Sato, 2016)
(CFDC B.04.02.23) vertebra (Aotsuka and Sato, 2016)
(CFDC B.06.01.03) three dorsal vertebrae (Aotsuka and Sato, 2016)
(CFDC B.06.01.15) vertebra (Aotsuka and Sato, 2016)
(CFDC B.06.02.03) vertebra (Aotsuka and Sato, 2016)
(CFDC B.08.01-2.15) vertebra (Aotsuka and Sato, 2016)
(CFDC B.08.01.22) four vertebrae (Aotsuka and Sato, 2016)
(CFDC B.08.03.23) vertebra (Aotsuka and Sato, 2016)
(CFDC B.76.02.06) vertebra (Aotsuka and Sato, 2016)
(CFDC B.77.00.07) three vertebrae (Aotsuka and Sato, 2016)
(CFDC B.77.01.07) vertebra, pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.78.03.07) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.79.01.12) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.79.04.13) vertebra (Aotsuka and Sato, 2016)
(CFDC B.79.06.13) pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.79.07.13) tibiotarsus, fibula (Aotsuka and Sato, 2016)
(CFDC B.80.02.15) fibula, pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.81.05.16) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.81.06.16) vertebra (Aotsuka and Sato, 2016)
(CFDC B.81.09.16) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.82.02.05) pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.82.07.17; lost) vertebra (Aotsuka and Sato, 2016)
(CFDC B.82.08-2.17) pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.82.12.17) pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.82.13.17) two pedal phalanges (Aotsuka and Sato, 2016)
(CFDC B.82.14.17) pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.82.16.17; lost) vertebra (Aotsuka and Sato, 2016)
(CFDC B.83.05.18) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.84.01.17) vertebra (Aotsuka and Sato, 2016)
(CFDC B.84.02.03) vertebra, tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.85.02.03) vertebra (Aotsuka and Sato, 2016)
(CFDC B.85.02.05) vertebra (Aotsuka and Sato, 2016)
(FMNH PA287) pedal phalanx (Aotsuka and Sato, 2016)
(ROM coll; lost) seven vertebrae (Aotsuka and Sato, 2016)
Mid Campanian, Late Cretaceous
Millwood Member of the Pierre Shale Group, Manitoba, Canada
(CFDC B.04.02.15) tbiotarsus (Aotsuka and Sato, 2016)
(CFDC B.05.02.15) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.05.02.23) patella, pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.05.04.15) vertebra, pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.06.01-2.05) seven vertebrae, pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.06.02.15) three vertebrae (Aotsuka and Sato, 2016)
(CFDC B.06.02.23) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.06.03.23) vertebra (Aotsuka and Sato, 2016)
(CFDC B.07.01.23) dorsal vertebra (Aotsuka and Sato, 2016)
(CFDC B.07.05.23) vertebra (Aotsuka and Sato, 2016)
(CFDC B.08.01.23) dorsal vertebra (Aotsuka and Sato, 2016)
(CFDC B.08.02.23) vertebra (Aotsuka and Sato, 2016)
(CFDC B.08.04.23) pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.2010.02.15) pedal phalanx (Aotsuka and Sato, 2016)
(CFDC B.2010.02.23) two pedal phalanges (Aotsuka and Sato, 2016)
Comments- Aotsuka and Sato (2016) state tibiotarsi CFDC.B.00.33.00, B.06.02.23, B.78.03.07, B.79.07.13, B.81.05.16 and B.81.09.16 resemble Baptornis in size and gracility, while the vertebrae CFDC.B.05.02.15 [typo, as that specimen is listed as a tibiotarsus], B.06.01.03, B.07.01.23, and B.08.01.23 also resemble Baptornis in size. They note that these elements are unknown in small Hesperornis species however. At least some of the phalanges are said to resemble Hesperornis more than Baptornis in size and crescent-peg articulations, the latter of which are also known in Parahesperornis but unpreserved in Brodavis and Fumicollis (these would thus be hesperornithids but are not assigned to the family here because exactly which phalanges have the character is unreported).
Reference- Aotsuka and Sato, 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, southern Manitoba, Canada. Cretaceous Research. 63, 154-169.

Baptornithidae American Ornithologist Union, 1910
Definition- (Baptornis advenus ~ Hesperornis regalis) (Martyniuk, 2012)
Other diagnoses- Martin and Tate (1976) included several characters in their diagnosis for Baptornithidae, in which they included Baptornis and Neogaeornis (now thought to be a gaviiform). The character "fully heterocoelous vertebrae" was supposed to distinguish them from Enaliornis, but the amphicoelous presacral vertebrae assigned to that taxon are now thought to belong to another bird. The angled uncinate processes and elongate pygostyle are unknown for any putative baptornithid except B. advenus, so are made an apomorphy of that species here. The highly compressed pygostyle and uncompressed patella of Baptornis advenus are unlike Hesperornis, but unknown in other basal euornithines, so are provisionally made apomorphies of that species. The unfused chevrons ("intercentral bones"), slender coracoid, elongate preacetabular process, metatarsal II trochlea which is less rotated ventromedially, open groove between metatarsal trochlea III and IV, and comparatively small metatarsal trochlea IV are primitive characters.
Tokaryk et al. (1997) use some of the previous characters and the slender femora to place Pasquiaornis in the Baptornithidae, but this is also primitive.
Kurochkin (2000) noted three characters he thought united Baptornis with Judinornis in the Baptornithidae. Of these, a pneumatic pit between the transverse process and prezygapophysis on dorsal vertebrae is probably plesiomorphic, being present in Ichthyornis as well. A ventrally flat centrum is only found in the last dorsal of Baptornis advenus, as more anterior vertebrae are similar to Hesperornis in having prominent hyapophyses. Yet the last dorsal of Enaliornis also lacks hyapophyses, as do the last few dorsals of Ichthyornis and Gansus, so this is a plesiomorphy. Some presacrals of Baptornis advenus and Brodavis? varneri resemble Judinornis in having a central pit on their articular surfaces. While these seem to be absent in the two preserved presacrals of Enaliornis, they are likely to be remnants of the amphicoelous condition in more basal euornithines like Ichthyornis, Gansus and Yixianornis.
Martin and Cordes-Person (2007) note other characters supposedly diagnostic of baptornithids. A smooth femoral patellar groove, subcircular femoral shaft, and unreduced metatarsal II trochlea are plesiomorphic. The cervical vertebrae of Brodavis? varneri are said to be like those of B. advenus in being more elongate than Hesperornis (and Parahesperornis), but this does not seem to be true based on the photograph.
Everhart and Bell (2009) diagnosed a Baptornithidae including Baptornis, Pasquiaornis and FHSM VP-6318. The rounded intercotylar prominence is a plesiomorphy compared to Hesperornis, while the intermediate height between Enaliornis and Hesperornis cannot be used as a synapomorphy to exclude both of those taxa from a baptornithid clade. Similarly, the indentations which partially constrict the distal vascular foramen between metatarsals III and IV are an intermediate state between the unconstricted Enaliornis and the distally closed foramen in Hesperornis, and are also seen in Parahesperornis. The infracotylar fossa and anteriorly tilted cotyla are present in hesperornithids as well. Contra Everhart and Bell, Enaliornis barretti and E? seeleyi also have the groove on trochlea III deeper than that on trochlea IV.
Comments- Baptornithidae has been a paraphyletic taxon for hesperornithines which are more basal than Parahesperornis, but there is currently no evidence any other species was more closely related to Baptornis than to Hesperornis. Taxa which have been assigned to Baptornithidae in the past include Eupterornis (Romer, 1933), Neogaeornis (Brodkorb, 1963), Judinornis (Nessov, 1986) and Pasquiaornis (Tokaryk et al., 1997). The former two are now thought to be gaviiforms (Brodkorb, 1963 and Olson, 1992 respectively), while the latter two are Baptornis-grade hesperornithines.
References- American Ornithologist Union, 1910. Checklist of North American birds. Third edition. American Ornithologist’s Union, New York. 430 pp.
Romer, 1933. Vertebrate Paleontology. University of Chicago Press, Chicago.
Brodkorb, 1963. Catalogue of fossil birds. Part 1 (Archaeopterygiformes through Ardeiformes). Bull. Florida State Mus., Bioi. Sci.. 7, 179-293.
Martin and Tate, 1976. The skeleton of Baptornis advenus (Aves: Hesperornithiformes). In Olson (ed.). Collected Papers in Avian Phylogeny Honoring the 90th Birthday of Alaxander Wetmore. Smithsonian Contributions to Paleobiology. 27, 35-66.
Nessov, 1986. The first record of the Late Cretaceous bird Ichthyornis in the Old World and some other bird bones from the Cretaceous and Paleogene of Soviet Middle Asia. Proc. Zool. Inst. USSR Acad. Sci.. 147, 31-38.
Olson, 1992. Neogaeornis wetzeli Lambrecht, a Cretaceous loon from Chile (Aves: Gaviidae). Journal of Vertebrate Paleontology. 12, 122-124.
Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Martin and Cordes-Person, 2007. A new species of the diving bird Baptornis (Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper Cretaceous) of southwestern South Dakota. The Geological Society of America, Special Paper. 427, 227-237.
Everhart and Bell, 2009. A hesperornithiform limb bone from the basal Greenhorn Formation (Late Cretaceous; Middle Cenomanian) of north central Kansas. Journal of Vertebrate Paleontology. 29(3), 952-956.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Baptornis Marsh, 1877
Diagnosis- as for B. advenus.
Other diagnoses- Martin and Tate (1976) used the size as a diagnostic character of Baptornis, but it is similar to Pasquiaornis tankei. The greatly reduced forelimb is present in hesperornithids as well, while the retention of the radius and ulna are plesiomorphies also present in Pasquiaornis. Martin and Tate also distinguished Baptornis from Neogaeornis by having a less compressed tarsometatarsus, but this is true of all hesperornithines.
Tokaryk and Harington (1992) include a few dorsal characters in their diagnosis. The heterocoely of dorsal four is present in all hesperornithines. The narrower and lower posterior central articular surface (compared to centrum length) is plesiomorphic, being present in Enaliornis and Judinornis as well, while the lower anterior central articular surface and small parapophysis are also present in Judinornis. The centrally placed hypapophysis is also present in Hesperornis.
Martin and Cordes-Person (2007) list several synapomorphies of Baptornis advenus and "B." varneri. As noted under Baptornithidae, the cervical vertebrae of varneri do not appear to be more elongate than those of Hesperornis, contra the text. The absence of "vertebrarterial canals" (= transverse foramina) in Baptornis seems implausible, as all theropods have diapophyseal and parapophyseal articulations with their cervical ribs, and may refer to an absence of fused cervical ribs instead. This is affected by ontogeny, and was not stated to be certainly absent in B. advenus by Martin and Tate in any case. Heterocoelous dorsal vertebrae and medial femoral condyles which are smaller than the lateral condyle are present in all hesperornithines. Pits in the posterior central articular surfaces of presacral centra, a subcircular femoral cross section, a smooth patellar groove and subequally sized tarsometatarsal trochlea are primitive characters.
Comments- Several other taxa have been referred to Baptornis in the past. Kurochkin (1988) referred a distal tibiotarsus from the Nemegt Formation of Mongolia to Baptornis sp., but this is here shown to resemble Enaliornis? seeleyi as well and thus referred to Hesperornithes incertae sedis. Tokaryk and Harington (1992) described a dorsal vertebra from the Judith River Group of Asakatchewan as Baptornis sp., but the characters they used were symplesiomorphic and the specimen is here referred to the Baptornis + Hesperornis clade as a nomen dubium. Nessov (1997) thought some small hesperornithine material from the Zhuralovskaya Svita of Kazakhstan could be referrable to Baptornis, but this undescribed material is here referred to Hesperornithes incertae sedis. Rees and Lindgren (2005) placed Parascaniornis stensioei in Baptornis as B. sp., which as noted in its description here was not based on any synapomorphies. More recently, a specimen was described as the new species Baptornis varneri by Martin and Cordes-Person (2007), but this is based on a mix of symplesiomorphies and synapomorphies of more inclusive clades as noted above. The species is here placed as a basal hesperornithid and has been provisionally reassigned to Brodavis. A distal femur from the Pierre Shale group of Manitoba was initially identified as Baptornis advenus by Aotsuka et al. (2012), but Aotsuka and Sato (2016) later described it as Brodavis sp..
References- Marsh, 1877. Characters of the Odontornithes, with notice of a new allied genus. American Journal of Science. 14, 85-87.
Martin and Tate, 1976. The skeleton of Baptornis advenus (Aves: Hesperornithiformes). in Olson (ed). Collected papers in avian phylogeny honoring the 90th birthday of Alaxander Wetmore. Smithsonian Contributions to Paleobiology. 27, 35-66.
Kurochkin, 1988. [Cretaceous birds of Mongolia and their significance for study of the phylogeny of class Aves.] Trudy Sovmestnoi Sovetsko-Mongolskoi Paleontologicheskoi Ekspeditsii. 34, 33-42.
Tokaryk and Harington, 1992. Baptornis sp. (Aves: Hesperornithiformes) from the Judith River Formation (Campanian) of Saskatchewan, Canada. Journal of Paleontology. 66(6), 1010-1012.
Nessov, 1997. Cretaceous non-marine vertebrates of Northern Eurasia. St. Petersburg State University, St-Petersburg. 218 pp.
Rees and Lindgren, 2005. Aquatic birds from the Upper Cretaceous (Lower Campanian) of Sweden and the biology and distribution of hesperornithiforms. Palaeontology. 48(6), 1321-1329.
Martin and Cordes-Person, 2007. A new species of the diving bird Baptornis (Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper Cretaceous) of southwestern South Dakota. The Geological Society of America, Special Paper. 427, 227-237.
Aotsuka, Hatcher, Janzic and Sato, 2012. Diversity of the Hesperornithiformes (Aves) from the Upper Cretaceous Pierre Shale in Southern Manitoba, Canada. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 57.
Aotsuka and Sato, 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, southern Manitoba, Canada. Cretaceous Research. 63, 154-169.
B. advenus Marsh, 1877
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US
Lectotype- (YPM 1465) distal tarsometatarsus
Paralectotype- ?(YPM 5768; = YPM 1465 in part) (juvenile) proximal tarsometatarsus
Referred- (AMNH 5101) premaxillary fragment, frontal fragment (lost), ventral quadrate (lost), atlantal intercentrum, axis, fourteen cervical vertebrae, six dorsal vertebrae, dorsal rib fragments, synsacrum, four proximal caudal vertebrae, mid caudal vertebra, partial pelvis, distal tibiotarsus, tarsometatarsi (89.9 mm), partial phalanx (Martin and Tate, 1976)
(FMNH 395) posterior mandible, sixth dorsal vertebra (18.7 mm), dorsal rib fragments, synsacrum, five mid caudal vertebrae, pygostyle, pelvic fragments, femora (72 mm), tibiotarsi (194.76 mm), fibula, metatarsal I (14 mm), phalanx I-1 (22 mm), tarsometatarsus (83 mm), phalanx II-2 (31.7 mm), phalanx III-1 (23.73 mm), phalanx III-3 (20.5 mm), phalanx IV-1 (36.55 mm), phalanx IV-2 (25 mm), phalanx IV-3 (23 mm), phalanx IV-4 (23 mm), six pedal phalanges, two pedal unguals (Martin and Tate, 1976)
?(Fick Fossil Museum coll.) premaxillary fragment(?), femur, proximal tibiotarsus, tibiotarsal shaft, distal tibiotarsus, proximal fibula, two tarsometatarsi, three incomplete tarsometatarsi, eleven fragments (Martin and Tate, 1976)
(KUVP 2290) six cervical vertebrae, three dorsal vertebrae, dorsal rib fragments, partial synsacrum, proximal scapula, incomplete coracoid (52.93 mm), incomplete humerus (~118 mm), radius (20.5 mm), ulna (21.6 mm), anterior ilium, femora (74.90 mm), patella (20.51 mm), partial tibiotarsi, proximal fibulae, partial tarsometatarsus (~83 mm) (Lucas, 1903)
(KUVP 16112) (juvenile) premaxilla (lost), eighth cervical vertebra, thirteenth cervical vertebra, fourteenth cervical vertebra, three partial cervical vertebrae, second dorsal vertebra (~20 mm), third dorsal vertebra (21 mm), fourth dorsal vertebra (~22 mm), fifth dorsal vertebra (22 mm), dorsal rib fragments, synsacral fragment, partial pelvis, proximal femora, distal femur, tibial shaft, distal tibiae, incomplete metatarsi, phalanx III-1 (29.5 mm), proximal phalanx, distal phalanx (Walker, 1967)
?(YPM 1467) femur, tibiotarsus (~125 mm) (Marsh, 1880)
Diagnosis- (after Marsh, 1880) prominent medial tibial crest.
(after Lucas, 1903) cervical vertebrae highly elongate; procoracoid process absent.
(proposed) uncinate processes angled dorsally at base; pygostyle longer than four vertebrae; highly transversely compressed pygostyle; pubis and ischium appressed; patella transversely wider than deep; proximolateral fossa for fibula on tibiotarsus narrow and deep; intertrochlear grooves on tarsometatarsus not extending proximal to trochlea II.
Other diagnoses- Marsh (1877) mentions only plesiomorphies- metatarsal trochlea III and IV subequal in width and length.
Marsh (1880) later mentions the slender femur, which is also plesiomorphic.
Lucas (1903) lists several features which differ from Hesperornis, but most are plesiomorphic- short sacrum; elongate coracoid; radius and ulna present; femur not projected transversely; high cnemial crest.
The extreme transverse slenderness of the tarsometatarsus noted by Shufeldt (1915) is also present in Pasquiaornis hardiei.
Martin and Cordes-Person (2007) listed several characters for B. advenus, most of which are plesiomorphic and also present in Brodavis? varneri- heterocoelous dorsal vertebrae; subcircular femoral cross section; smooth patellar groove in femur; tarsometatarsus with proximal cap; metatarsal II trochlea which is less rotated ventromedially. The lack of crescent and peg articulations on pedal digit IV phalanges is also primitive, though unpreserved in B? varneri and other non-hesperornithid hesperornithines. The femoral medial condyle is actually larger than in B? varneri (as in Pasquiaornis), not smaller as in Enaliornis and Hesperornis. The distal tibiotarsus being angled anteriorly is plesiomorphic as well, being shared with Parahesperornis.
Comments- The lectotype and paralectotype were discovered in 1876 and described by Marsh in 1877, though Shufeldt (1915) and Martin and Tate (1976) confirmed they were from different individuals, as YPM 1465 is adult and YPM 5768 is juvenile. They designated YPM 1465 the lectotype. The large humerus reported by Walker (1967) for KUVP 16112 is a tibial shaft. Elzanowski et al. (2001) state that there is no quadrate catalogued under AMNH 5101, nor could any record of it be found there. They furthermore believe that the quadrate was too small to be derived from the specimen and question its referral to Baptornis, though they do believe it is an "odontognath." Bell and Chiappe (2020) stated "very small fragments of the quadrate and frontal of Baptornis (AMNH 5101) were previously reported, however no such elements are included with the specimen today. ... Likewise, a fragment of the bill was reported with Baptornis specimen KUVP 16112, however the specimen did not include material identifiable as such when consulted for this study." Martin and Tate (1976) noted they examined specimens at the Fick Fossil Museum, which are not described further, but are photographed on Oceans of Kansas (Everhart, online 2005). Chiappe (1996) listed KUVP 2295 as a Baptornis specimen, but probably meant KUVP 2290. Bell and Chiappe (2016) found most referred specimens coded identically or near identically to each other, but did not mention YPM 1467, YPM 5768 or the Fick Fossil Museum specimen. UNSM 20030 was described by Martin and Tate (1976) as a specimen of B. advenus, but Bell and Chiappe found it was actually a more derived taxon sister to Parahesperornis+Hesperornis and described it later (Bell and Chiappe, 2015) as Fumicollis hoffmani.
References- Marsh, 1877. Characters of the Odontornithes, with notice of a new allied genus. American Journal of Science. 14, 85-87.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Lucas, 1903. Notes on the osteology and relationships of the fossil birds of the genera Hesperornis, Hargeria, Baptornis, and Diatryma. Proceedings of the United States National Museum. 26, 545-556.
Brown, 1911. Notes on the restorations of the Cretaceous birds Hesperornis and Baptornis. Annals of the New York Academy of Sciences. 20, 401.
Shufeldt, 1915. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.
Walker, 1967. Revival of interest in the toothed birds of Kansas. Transactions of the Kansas Academy of Sciences. 70(1), 60-66.
Martin and Tate, 1969. New information on Baptornis advenus. Proceedings of the Nebraska Academy of Sciences (79th Annual Meeting). 49-50.
Martin and Tate, 1976. The skeleton of Baptornis advenus (Aves: Hesperornithiformes). in Olson (ed). Collected papers in avian phylogeny honoring the 90th birthday of Alaxander Wetmore. Smithsonian Contributions to Paleobiology. 27, 35-66.
Martin and Bonner, 1977. An immature specimen of Baptornis advenus from the Cretaceous of Kansas. The Auk. 94, 787-789.
Witmer, 1990. The craniofacial air sac system of Mesozoic birds (Aves). Zoological Journal of the Linnaean Society of London. 100, 327-378.
Chiappe, 1996. Late Cretaceous birds of Southern South America: Anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. In Arratia (ed.). Contributions of Southern South America to Vertebrate Paleontology. Münchner Geowissenschaftliche Abhandlungen (A). 30, 203-244.
Elzanowski, Paul and Stidham, 2001. An avian quadrate from the Late Cretaceous Lance Formation of Wyoming. Journal of Vertebrate Paleontology. 20(4), 712-719.
Everhart, online 2005. http://www.oceansofkansas.com/Birds/fickhesp.jpg
Martin and Cordes-Person, 2007. A new species of the diving bird Baptornis (Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper Cretaceous) of southwestern South Dakota. The Geological Society of America, Special Paper. 427, 227-237.
Everhart, online 2008-2017. http://www.oceansofkansas.com/Baptornis.html
Bell and Chiappe, 2015. Identification of a new hesperornithiform from the Cretaceous Niobrara Chalk and implications for ecologic diversity among early diving birds. PLoS ONE. 10(11), e0141690.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
Bell and Chiappe, 2020. Anatomy of Parahesperornis: Evolutionary mosaicism in the Cretaceous Hesperornithiformes (Aves). Life. 10(5), 62.

unnamed baptornithid (Martin, 1983)
Middle Cenomanian, Late Cretaceous
Basal Lincoln Limestone Member of the Greenhorn Limestone, Kansas, US
Material- (FHSM VP-6318) proximal and distal tarsometatarsus (16.7 mm wide proximally)
Comments- This was discovered in 1979 and mentioned by Martin (1983) and Tokaryk et al. (1997). Though the description was listed on the Oceans of Kansas website as set to appear in volume 28(4) of JVP (Everhart, online 2008), it was not published until volume 29(3). Everhart and Bell (2009) refer this specimen to Baptornithidae based on several problematic characters (see Baptornithidae other diagnoses). Bell and Chiappe (2016) found it to code identically to Baptornis advenus in their analysis.
References- Martin, 1983. The origin and early radiation of birds. in Bush and Clark (eds.). Perspectives in Ornithology. Cambridge University Press, Cambridge. 291-338.
Tokaryk, Cumbaa and Storer, 1997. Early Late Cretaceous birds from Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal of Vertebrate Paleontology. 17(1), 172-176.
Everhart, online 2008. https://web.archive.org/web/20081101143014/http://www.oceansofkansas.com/Hesperornis.html
Everhart and Bell, 2009. A hesperornithiform limb bone from the basal Greenhorn Formation (Late Cretaceous; Middle Cenomanian) of north central Kansas. Journal of Vertebrate Paleontology. 29(3), 952-956.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.

Hesperornithidae Marsh, 1876
= Hesperornidae Marsh, 1872
= Asiahesperornithinae Nessov and Prizemlin, 1991
Definition- (Hesperornis regalis <- Baptornis advenus) (Clarke, 2004)
Other definitions- (Parahesperornis alexi + Hesperornis regalis) (Bell and Chiappe, 2020)
Diagnosis- (proposed) proximal tibiotarsal shaft gradually expanded anteroposteriorly; elongate fibular crest on tibiotarsus (~59% of tibiotarsal length); large size (tarsometatarsus >20 mm in proximal transverse width).
Comments- Marsh (1872) originally called this family Hesperornidae, but this had to be corrected to Hesperornithidae as there is no genus 'Hesperorna'. Nessov and Prizemlin's (1991) taxon Asiahesperornithinae is redundant as Asiahesperornis seems to be nested within Hesperornis itself.
References- Marsh, 1872. Preliminary description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. American Journal of Science, 3rd series. 3, 359-365.
Marsh, 1876. Notice of new Odontornithes. The American Journal of Science and Arts. 11, 509-511.
Nessov and Prizemlin, 1991. A large advanced flightless marine bird of the order Hesperornithiformes of the Late Senonian of Turgai Strait - the first finding of the group in the USSR. USSR Academy of Sciences, Proceedings of the Zoological Institute. 239, 85-107 (in Russian).
Bogdanovich, 2003. Morphologic aspect of phylogeny of Hesperornithidae (Ornithurae, Aves). Vestnik zoologii. 37(6), 65-71.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286: 1-179.
Wilson and Chin, 2008. Bone histology of hesperornithiforms (Aves) from Late Cretaceous greenhouse high-latitude environments. Journal of Vertebrate Paleontology. 28(3), 160A-161A.
Bell and Chiappe, 2020. Anatomy of Parahesperornis: Evolutionary mosaicism in the Cretaceous Hesperornithiformes (Aves). Life. 10(5), 62.

Brodavidae Martin, Kurochkin and Tokaryk, 2012
Definition- (Brodavis americanus <- Hesperornis regalis) (Martyniuk, 2012)
References- Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.

Potamornis Elzanowski, Paul and Stidham, 2001
P. skutchi Elzanowski, Paul and Stidham, 2001
Late Maastrichtian, Late Cretaceous
Lance Formation, Wyoming, US
Holotype- (UCMP 73103) quadrate (18 mm)
Referred- ?(AMNH 22002; Lancian Ornithurine D) proximal coracoid (Longrich, Tokaryk and Field, 2011)
?(University of Nebraska coll.) tarsometatarsus (Elzanowski, Paul and Stidham, 2001)
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, Montana, US
Referred- ?(UCMP 117605) tarsometatarsus (Elzanowski, Paul and Stidham, 2001)
?(UCMP 13355; Lancian Hesperornithiform A) tarsometatarsus (Longrich, Tokaryk and Field, 2011)
?(UCMP 159207) distal tarsometatarsus (UCMP online)
?(UCMP 159208) femur (UCMP online)
?(UCMP 174715) tibiotarsus (UCMP online)
?(UCMP 174718) dorsal vertebra (UCMP online)
?(UCMP 187203) tarsometatarsus (UCMP online)
?(UCMP 187205) vertebra (UCMP online)
?(UCMP 187206) vertebra (UCMP online)
?(UCMP 187207; Lancian Ornithurine D) proximal coracoid (Longrich, Tokaryk and Field, 2011)
Diagnosis- (after Elzanowski et al., 2001) distinct medial depression for m. protractor pterygoidei et quadrati dorsal to orbital process.
(after Longrich et al., 2011) (for Lancian Ornithurine D) shallowly concave, subtriangular scapular facet; short, deep, and weakly hooked acrocoracoid process; coracoid shaft mediolaterally compressed and bowed dorsally; procoracoid hooked ventrally around the triosseal canal; glenoid lateral to scapular cotyle.
(for Lancian Hesperornithiform A) short, broad metatarsus; metatarsal IV subequal in length to metatarsal III; dorsal flange of metatarsal IV does not extend the full length of the metatarsus; distal metatarsus not twisted relative to proximal metatarsus; large and proximally located depression for reception of metatarsal I.
Other diagnoses- Elzanowski et al. (2001) list the strongly asymmetrical quadrate head, with the beak-shaped medial part overhanging the otic process as an apomorphy, but note it is also present in most palaeognaths, Psophia, Cariama and Opisthocomus. Similarly, they list the presence of a quadratojugal buttress as diagnostic, but then state it is also present in Baptornis and Parahesperornis. A pit on the medial part of the quadrate head and small orbital process are also present in Ichthyornis, so are possibly plesiomorphies. Elzanowski et al. state the low angle between the lateral and medial condyles is diagnostic, as those of Baptornis and hesperornithids are higher, but that of Ichthyornis is even lower, making it a probable plesiomorphy. The smooth connection between medial and "posterior" condyles is plesiomorphic (Clarke, 2004), while contra Elzanowski et al., the lateral condyle is separated from the posterior articular surface by a groove.
Comments- Elzanowski et al. (2001) do not describe the tentatively referred paratype tarsometatarsi, merely stating they are the right size to belong to Potamornis. The UCMP specimens are identified as Potamornis in the UCMP collections, but cannot be compared to the holotype. UCMP 159208, 187205 and 187206 are from the Danian (Paleocene), so were presumably reworked. The coracoids were called Lancian Ornithurine D by Longrich et al. (2011), who recovered it sister to Ichthyornis using Clarke's bird matrix. He suggested it "appears to be closely related to Judithian Ornithurine A" and that "both morphotypes closely resemble coracoids described from the Carrot River Formation of Saskatchewan", which have since been referred to Pasquiaornis. Coracoid RSM P2992.1 is tentatively referred to Brodavis sp. nov. here while AMNH 22002 may be Potamornis based on provenence and UCMP 187207 could be Potamornis or Brodavis? baileyi. Indeed, it's probable Potamornis and Brodavis refer to the same concept, and the Hell Creek material listed here might all be better referred to Brodavis? baileyi. Then again, Lancian Ornithurine D coracoids seem to be from a smaller species than Lancian Hesperornithiform A tarsometatarsi (B? baileyi-sized), and two distinctly sized species are present in the Frenchman Formation. Which size class the Potamornis type quadrate falls into is unknown and none of the tarsometatarsi listed as Potamornis here have been described or figured so cannot be compared to Brodavis species.
While the lack of pneumaticity and quadratojugal buttress suggests Potamornis is a hesperornithine, the lack of and elongate orbital process excludes it from the Parahesperornis + Hesperornis clade.
References- Elzanowski, Paul and Stidham, 2001. An avian quadrate from the Late Cretaceous Lance Formation of Wyoming. Journal of Vertebrate Paleontology. 20(4), 712-719.
Clarke, 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History. 286, 1-179.
Longrich, Tokaryk and Field, 2011. Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary. Proceedings of the National Academy of Sciences. 108(37), 15253-15257.

Brodavis Martin, Kurochkin and Tokaryk, 2012
Comments- Nessov (1992) first commented on the possibility of small volant hesperornithines based on small elements in North American museums from the Late Campanian and Maastrichtian of the US and Canada. No details were given, but Martin et al. (2012) eventually described these tarsometatarsi including one from the Nemegt Formation previously described by Kurochkin (2000) as species of the new genus Brodavis. Further study will be necessary to determine whether the diagnosis provided by Martin et al. includes synapomorphic characters, or merely symplesiomorphies, and thus whether B? baileyi, B? varneri and B? mongoliensis are properly referred to this genus. Bell and Chiappe (2016) did find baileyi and varneri to group together in their phylogenetic analysis, but did not test the type species B. americanus or mongoliensis. It's likely material assigned to Potamornis belongs here as well, which may move the clade stemward of Baptornis.
References- Nessov, 1992. [Flightless birds of meridional Late Cretaceous sea straits of North America, Scandinavia, Russia and Kazakhstan as indicators of features of oceanic circulation.] Byulleten Moskovskogo Obshchestva Ispytatelet Prirody Otdel Geologicheskii. 67, 78-83.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
B. americanus Martin, Kurochkin and Tokaryk, 2012
Late Maastrichtian, Late Cretaceous
Frenchman Formation, Saskatchewan, Canada
Holotype- (RSM P2315.1; Lancian Hesperornithiform A) incomplete tarsometatarsus (~34 mm)
Referred- ?(RSM MB.AV.705; Lancian Hesperornithiform A) tarsometatarsus (Longrich, Tokaryk and Field, 2011)
Diagnosis- (after Martin et al., 2012) facet for metatarsal one placed below the middle of tarsometatarsus; metatarsal shaft broader and more robust than in B. baileyi but is smaller and less robust than B? varneri; trochlea for digit IV swollen proximally, being slightly broader than the trochlea for digit III, with broad and flat anterodistal surface.
Comments- Longrich et al. (2011) described three tarsometatarsi as Lancian Hesperornithiform A, noting similarity to what would be named Brodavis? mongoliensis the following year. One (RSM P2315.1) was described as Brodavis americanus by Martin et al. (2012), and another (RSM MB.AV.705) is tentatively assigned to B. americanus here based on provenance and size. Note Longrich et al. also propose a second smaller species Lancian Hesperornithiform B from the same formation.
References- Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
Longrich, Tokaryk and Field, 2011. Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary. Proceedings of the National Academy of Sciences. 108(37), 15253-15257.
B? baileyi Martin, Kurochkin and Tokaryk, 2012
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, South Dakota, US
Holotype- (USNM 50665) incomplete tarsometatarsus
Diagnosis- (after Martin et al., 2012) shaft of the tarsometatarsus more slender than in B. americanus with trochlea for digit IV less expanded at base; trochlea for digit II more elevated proximally at base and placed more behind trochlea for digit III; outer anterior ridge of shaft extending more distally; proximal nutrient foramina reduced practically to absence.
Comments- Note some of the Hell Creek Potamornis material may belong to this species, particularly similarly-sized tarsometatarsus UCMP 13355.
Reference- Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
B? varneri (Martin and Cordes-Person, 2007) Martin, Kurochkin and Tokaryk, 2012
= Baptornis varneri Martin and Cordes-Person, 2007
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, South Dakota, US
Holotype- (SDSM 68430) (adult) anterior (~3-6) cervical vertebra, mid (~7-10) cervical vertebra, fourteenth cervical vertebra, fifteenth cervical vertebra, sixteenth cervical vertebra, seventeenth cervical vertebra, posterior cervical or anterior dorsal vertebrae, first dorsal vertebra, two dorsal ribs, posterior synsacrum, posterior ilia, pubes, ischia, partial femora, tibiotarsus (206.47 mm), fibula, tarsometatarsus (96.13 mm)
Diagnosis- (after Martin and Cordes-Person, 2007) tarsometatarsus more robust than other hesperornithines.
Other diagnoses- Martin and Cordes-Person (2007) list elongate cervical vertebrae as a character of this species, but they are shorter than in B. advenus. The capitulum and tuberculum of the illustrated dorsal rib are similarly placed to B. advenus, not necessarily more separated as stated by the authors, especially when one considers that only two proximal rib portions are photographed for B. advenus. The indistinct antitrochanter is a plesiomorphy shared with Enaliornis barretti, while the open acetabulum is also a plesiomorphy shared with taxa such as Ichthyornis and Apsaravis. The well separated pubis and ischium is a plesiomorphy found in Enaliornis, Parahesperornis and Hesperornis. The proximolateral ischial fossa is said to be more shallow than in B. advenus and Hesperornis, but does not seem so in the photo. A broad popliteal fossa is primitive, being present in Enaliornis, Hesperornis and Pasquiaornis? tankei (but perhaps not P. hardiei), whereas the fossa does not appear smoother in varneri than in other hesperornithines. A shallow popliteal fossa is also present in Enaliornis, while a wide intercondylar fossa is also present in Enaliornis and Hesperornis. The prominent medial femoral condyle is also present in Enaliornis? sedgwicki, and the lateral condyle does not appear more "high and distinct" than in B. advenus. The anteroposteriorly expanded proximal tibiotarsus and elongate fibular crest (~59% of tibiotarsal length) are shared with Hesperornis. The straightness of the fibular crest might refer to the fact it doesn't seem to curve distally onto the anterior shaft as in B. advenus, but polarity is difficult to establish. Enaliornis shares the shallow proximolateral fossa for the fibula, making the opposite state a possible apomorphy of B. advenus. Contra Martin and Cordes-Person, the distal tibiotarsus does not curve medially more than in B. advenus. Proximal foramina are present in Parahesperornis and Hesperornis as well (and Pasquiaornis? tankei), as noted in the description of FHSM VP-17312, making the reported absence in B. advenus probably due to incomplete preparation. Elongate intertrochlear grooves are also found in Enaliornis, Pasquiaornis, Parahesperornis and Hesperornis, making their absence an apomorphy of B. advenus. The tarsometatarsi of all hesperornithines are waisted transversely just proximal to trochlea II as in varneri.
Comments- This specimen was discovered in 1991 and first published in an abstract by Martin and Varner (1992), to be formally described and named by Martin and Cordes-Person (2007). While most published references refer the species to Baptornis, this is based on a mix of symplesiomorphies and synapomorphies of more inclusive clades as noted in the Baptornis other diagnoses section. In contrast, there is some support for placing this species as the basalmost hesperornithid, as seen in the Hesperornithidae diagnosis above. Martin et al. (2012) included it in their new genus Brodavis based on "overall shape of the tarsometatarsus" and the symplesiomorphic small metatarsal IV trochlea compared to Hesperornis. As this is vague and problematic reasoning and the authors themselves state it "should probably have its own generic designation", this assignment is provisional. However, Bell and Chiappe (2016) did recover a phylogeny similar to my unpublished one where varneri is a basal hesperornithid, and found Brodavis? baileyi to be its sister group. The Brodavis type species B. americanus was not included though, making it still uncertain whether varneri should be referred to that genus.
References- Martin and Varner, 1992. The highest stratigraphic occurrence of the fossil bird Baptornis. Proceedings of the South Dakota Academy of Science. 71, 167 (abstract).
Person and Martin, 2004. A new species of the diving bird Baptornis (Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper Cretaceous) of southwestern South Dakota. Geological Society of America Abstracts with Programs. 36(4), 80.
Martin and Cordes-Person, 2007. A new species of the diving bird Baptornis (Ornithurae: Hesperornithiformes) from the lower Pierre Shale Group (Upper Cretaceous) of southwestern South Dakota. The Geological Society of America, Special Paper. 427, 227-237.
Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
B? mongoliensis Martin, Kurochkin and Tokaryk, 2012
Late Campanian-Early Maastrichtian, Late Cretaceous
Bugin Tsav, Nemegt Formation, Mongolia
Holotype- (PIN 4491-8) incomplete tarsometatarsus (Kurochkin, 2000)
Diagnosis- (after Martin et al., 2012) external cotyla in proximal head of the tarsometatarsus expands anteroposteriorly, with anterior and posterior parts inclined distally; proximal nutrient foramina are well developed; metatarsal facet for digit I placed almost in the middle of the tarsometatarsus; metatarsal shaft slender; transverse section in the middle of shaft close to quadrangular.
Comments- The holotype was discovered in 1987. Kurochkin (2000) described it and mentioned a small mandible and cervical vertebra which were "somewhat different" from other hesperornithines. He referred these to "Hesperornithiformes fam. nov." though he did not list any diagnostic characters. Kurochkin also related these to small hesperornithine remains from the Zhuralovskaya Svita (Mourer-Chauvire, 1992), which are presently undescribed and generally referred to Baptornithidae. The mandible and vertebral may be the same taxon as B. mongoliensis and IGM 100/1311, which are of similar size and also have thinner bone walls than Baptornis or Hesperornis.
References- Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Martin, Kurochkin and Tokaryk, 2012. A new evolutionary lineage of diving birds from the Late Cretaceous of North America and Asia. Palaeoworld. 21(1), 59-63.
B. sp. nov. (Longrich, Tokaryk and Field, 2011)
Late Maastrichtian, Late Cretaceous
Frenchman Formation, Saskatchewan, Canada
Material- (RSM P2604.1; Lancian Hesperornithiform B) (adult) partial tarsometatarsus (Longrich, Tokaryk and Field, 2011)
(RSM P2992.1; Lancian Ornithurine D) proximal coracoid
Comments- Longrich et al. (2011) propose Lancian Hesperornitiform B for a tarsometatarsus "identical to" but much smaller than what was later named Brodavis americanus. The coracoids RSM P2992.1 was called Lancian Ornithurine D by Longrich et al. (2011), who recovered it sister to Ichthyornis using Clarke's bird matrix. He suggested it "appears to be closely related to Judithian Ornithurine A" and that "both morphotypes closely resemble coracoids described from the Carrot River Formation of Saskatchewan", which have since been referred to Pasquiaornis. As its estimated mass is closer to Lancian Hesperornithiform B, it is referred to that species here.
Reference- Longrich, Tokaryk and Field, 2011. Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary. Proceedings of the National Academy of Sciences. 108(37), 15253-15257.
B? sp. (Aotsuka, Hatcher, Janzic and Sato, 2012)}
Mid Campanian, Late Cretaceous
Pembina Member of the Pierre Shale Group, Manitoba, Canada
Material- (CFDC B.08.01.15) distal femur
Comments- Initially identified as Baptornis advenus by Aotsuka et al. (2012), Aotsuka and Sato (2016) later described this specimen as Brodavis sp.. As only B. varneri includes femoral material, it cannot be compared to other species, though B. varneri matches in size and stratigraphy.
References- Aotsuka, Hatcher, Janzic and Sato, 2012. Diversity of the Hesperornithiformes (Aves) from the Upper Cretaceous Pierre Shale in Southern Manitoba, Canada. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 57.
Aotsuka and Sato, 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, southern Manitoba, Canada. Cretaceous Research. 63, 154-169.
B? sp. ( Tanaka, Takasaki, Chiba, Hayashi, Brink, Buuvei and Tsogtbaatar, 2021)
Early Maastrichtian, Late Cretaceous
White Beds of Khermeen Tsav, Nemegt Formation, Mongolia
Material- distal tarsometatarsus
Comments- Tanaka et al. (2021) report this tarsometatarsus "shows the following features unique to non-hesperornithid hesperornithiforms: (1) the proximally positioned distal edge of metatarsal trochlea II which does not reach the base of metatarsal trochlea IV; (2) metatarsal trochleae III and IV which distally extend to a similar level; and (3) the equally mediolaterally wide metatarsal trochleae III and IV. Additionally, the broad and flat anterodistal surface of the tarsometatarsus suggests this specimen can be tentatively assigned to Brodavis sp." It notably differs from B. americanus in having thinner bone walls (relative cortical bone thickness 66.7% vs. 84.9%). While they did not compare it to B. mongoliensis from the same formation, only a middle fourth of the shaft from above the distal vascular foramen to the hallucial facet are preserved in both, with metatarsal II's trochlea broken off in B. mongoliensis. That being said, both are more slender than B. americanus but the Khermeen Tsav specimen is about 50% larger so may be a different species.
Reference- Tanaka, Takasaki, Chiba, Hayashi, Brink, Buuvei and Tsogtbaatar, 2021. A hesperornithiform from the Upper Cretaceous Nemegt Formation in the Gobi Desert of southwest Mongolia: Implications for paleonecology of island hesperornithiforms. The Society of Vertebrate Paleontology Virtual Meeting Conference Program, 81st Annual Meeting. 248-249.

unnamed clade (Fumicollis hoffmani + Hesperornis regalis)
Diagnosis- (proposed) deep proximodorsal metatarsal III fossa.

Fumicollis Bell and Chiappe, 2015
F. hoffmani Bell and Chiappe, 2015
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US
Holotype- (UNSM 20030) sixteenth cervical vertebra (16.9 mm), seventeenth cervical vertebra (15.3 mm), first dorsal vertebra (16.7 mm), incomplete second dorsal vertebra (16.5 mm), incomplete third dorsal vertebra (15.9 mm), incomplete fourth dorsal vertebra (16.7 mm), partial fifth dorsal vertebra, sixth dorsal vertebra (14 mm), four dorsal ribs, six uncinate processes, five mid caudal vertebrae (lost?), incomplete pygostyle, partial coracoid (lost?), partial sternum (lost?), four sternal ribs (lost?), incomplete humerus (lost?), pelves (one incomplete, one partial; ilium ~198.04 mm), femur (71.8 mm), patella (21.11 mm), tibiotarsi (one partial; 193.82 mm), fibula, tarsometatarsus (83.72 mm), phalanx II-1 (37.4 mm), phalanges III-1 (37.77 mm), phalanges III-2 (25.8 mm), phalanx III-3 (24.4 mm), pedal skin impression, cololites
Diagnosis- (after Bell and Chiappe, 2015) presacral vertebrae with expanded hypapophyses; elongate pelvis with reduced acetabulum (acetabulum/pelvis ratio 9.6%); moderately expanded trochanteric crest (transverse extent nearly half of midshaft width); expanded lateral femoral condyle (transverse extent of condyle over 75% of midshaft width; tibiotarsus with triangular cnemial expansion; medial cnemial crest extended to midshaft; patella pyramidal with flattened posterior face; patella perforated for ambiens tendon; fibula with posteriorly expanded proximal end; slightly depressed, saddle-shaped articular surface of fibula; tarsometatarsus with shingled metatarsals; distinct dorsal ridge of tarsometatarsus formed by entire length of metatarsal IV; tarsometatarsus with reduced and plantarly displaced trochlea II; enlarged medial trochlear ridge of metatarsal IV; phalanx III-1 narrow mediolaterally; greatly expanded, curved medial face of distal pedal phalanx III-1.
Comments- UNSM 20030 was discovered in 1936, but not described until 1976 by Martin and Tate. Bell and Chiappe (2016, online 2015) found it was actually a more derived taxon sister to Parahesperornis+Hesperornis and described it as a new genus and species later that year (2015). Bell and Chiappe did not mention the free caudals, pectoral elements or humerus described by Martin and Tate, and reidentified the six pedal phalanges. Bell (pers. comm., 2016) stated she didn't know "if the material has been lost or was incorrectly attributed to 20030", but that it wasn't catalogued with that number when she examined it. The cololites include a jaw of the fish Enchodus cf. parvus.
References- Martin and Tate, 1976. The skeleton of Baptornis advenus (Aves: Hesperornithiformes). in Olson (ed). Collected papers in avian phylogeny honoring the 90th birthday of Alaxander Wetmore. Smithsonian Contributions to Paleobiology. 27, 35-66.
Bell and Chiappe, 2015. Identification of a new hesperornithiform from the Cretaceous Niobrara Chalk and implications for ecologic diversity among early diving birds. PLoS ONE. 10(11), e0141690.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.

Hesperornithidae sensu Bell and Chiappe, 2020
Definition- (Parahesperornis alexi + Hesperornis regalis)
Diagnosis- (proposed) elongate orbital process on quadrate (unknown in Brodavis and Fumicollis); coracoid tubercle distal to glenoid (unknown in Brodavis); humerus extremely slender (unknown in Brodavis); short preacetabular process; metatarsal IV trochlea >140% as wide as trochlea III; crescent and peg articulations between phalanges in pedal digit IV (unknown in Brodavis and Fumicollis).
Comments- This clade correlates to the Hesperornithidae of Martin (1984), which he supported with the cresecent and peg articulations in pedal digit IV.
References- Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Bell and Chiappe, 2020. Anatomy of Parahesperornis: Evolutionary mosaicism in the Cretaceous Hesperornithiformes (Aves). Life. 10(5), 62.

Hesperornithidae indet. (Aotsuka and Sato, 2016)
Mid Campanian, Late Cretaceous
Pembina Member of the Pierre Shale Group, Manitoba, Canada
Material- (CFDC B.00.43.00) ilium (Aotsuka and Sato, 2016)
(CFDC B.00.57.00; lost) synsacrum (Aotsuka and Sato, 2016)
(CFDC B.07.04.23) two vertebrae, patella (Aotsuka and Sato, 2016)
(CFDC B.09.02.13) ilium (Aotsuka and Sato, 2016)
(CFDC B.80.09.16) ilium (Aotsuka and Sato, 2016)
(CFDC B.82.04.03) ilium (Aotsuka and Sato, 2016)
(CFDC B.2010.01.03) ilium (Aotsuka and Sato, 2016)
(FMNH PA290; in part) nine vertebrae, ilium (Aotsuka and Sato, 2016)
(ROMM coll.; lost) synsacrum (Aotsuka and Sato, 2016)
Comments- Aotsuka and Sato (2016) referred these to Hesperornithidae indet., which in their taxonomy excludes Brodavis. It presumably also excludes Fumicollis, as the latter genus has a patella similar to Baptornis and a pelvis that was the basis of Baptornis' anatomy until Fumicollis was excluded from the genus.
Reference- Aotsuka and Sato, 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, southern Manitoba, Canada. Cretaceous Research. 63, 154-169.

Parahesperornis Martin, 1984
= "Parahesperornis" Martin, 1983
P. alexi Martin, 1984
= "Parahesperornis alexi" Martin, 1983
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US
Holotype- (KUVP 2287) (subadult) incomplete skull, mandibles (208 mm), axis, third cervical vertebra, fourth cervical vertebra, fifth cervical vertebra, sixth cervical vertebra, seventh cervical vertebra, eighth cervical vertebra, ninth cervical vertebra, tenth cervical vertebra, eleventh cervical vertebra, twelfth cervical vertebra, thirteenth cervical vertebra, fourteenth cervical vertebra, fifteenth cervical vertebra, sixteenth cervical vertebra, seventeenth cervical vertebra, first dorsal vertebra, second dorsal vertebra, third dorsal vertebra, fourth dorsal vertebra, fifth dorsal vertebra, sixth dorsal vertebra, several dorsal rib fragments, several uncinate processes, synsacrum, four caudal vertebrae, incomplete coracoid, partial sternum, sternal ribs(?), partial humeri, pelves (ilium ~237.63 mm), femora (68.8 mm), patellae (44.61 mm; one incomplete), tibiotarsi (212.97 mm), fibula (130.71 mm), tarsometatarsi (100.73 mm), phalanges I-1, pedal ungual I, phalanges II-1, phalanges II-2, pedal unguals II, phalanges III-1 (31.14 mm), phalanx III-2, phalanx III-3, pedal unguals III, phalanges IV-1 (29.17 mm), phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, feathers(?), pedal scales (Williston, 1896)
Paratype- partial tarsometatarsus (Wetmore, unpublished MS)
Referred- (FHSM VP-17312) tarsometatarsus (99.93 mm) (Bell and Everhart, 2009)
(KUVP 24090) posterior mandible (lost?), incomplete fourth cervical vertebra, incomplete fifth cervical vertebra, incomplete ~sixth/seventh cervical vertebra, cervical vertebra, eleventh cervical vertebra, twelfth cervical vertebra, thirteenth cervical vertebra, fourteenth cervical vertebra, fifteenth cervical vertebra, sixteenth cervical vertebra, seventeenth cervical vertebra, first dorsal vertebra, second dorsal vertebra, third dorsal vertebra, fourth dorsal vertebra, fifth dorsal vertebra, sixth dorsal vertebra, partial dorsal ribs, uncinate processes, sacrum, four caudal vertebrae, pygostyle, coracoid (55.38 mm), sternum, pelves (ilium 246.6 mm), femora (74.53 mm), patellae (56.54 mm), tibiotarsi (230.94 mm), fibulae (Witmer, 1990)
(RMDRC coll.) pelvis (Anthony, pers. comm., 2009)
Diagnosis- (after Bell and Chiappe, 2020) premaxillae short (width across the premaxillae at the nares is approximately 35% the pre-nares length); lacrimal elongate with long ventral process that terminates in a flattened face; frontals flattened and very wide (width roughly 75% the length of the frontals); interfrontal suture forms deep groove; arched frontoparietal suture; reduced pneumaticity of the braincase; deep notch separating the zygomatic process and paraoccipital process; prominent paraoccipital processes; narrow and deep basisphenoid recess; suture between basioccipital and basisphenoid on basal tubera; small occipital condyle; posteromedial depression present on quadrate; lateral crest of quadrate restricted to lateral margin; pterygoid triangular with flattened faces; articulation of the angular with dentary along a broad surface; surangulars convex laterally; expanded retroarticular process of the articular; anterior cervical vertebrae elongate while posterior cervical vertebrae become more compact; triangular coracoid with elongate neck; flat sternum with five costal processes; humerus reduced with only poorly defined condyles; elongate pelvis with reduced, circular acetabulum (acetabulum diameter approximately 10% ilium length); head of femur extends proximally past trochanter; femur slightly waisted, with expanded trochanter and fibular condyle; lateral condyle of femur extends only slightly distally past medial condyle; elongate, triangular patella (distal mediolateral width approximately 50% of the proximodistal length); tibiotarsus with triangular cnemial expansion; medial face of fibula with triangular depression; tarsometatarsus with shingled metatarsals, proximal articular surface rhombic in proximal view; rounded intercotylar eminence of tarsometatarsus; trochlea IV extending slightly further distally than trochlea III; phalanges of pedal digit IV robust, with unevenly sized cotylae.
Other diagnoses- Lucas (1903) distinguished his Hargeria gracilis (based on the holotype of Parahesperornis) from Hesperornis regalis with two plesiomorphies- lacrimal ventral process slender; femur more elongate and less proximally expanded. Contra Lucas, the nasal processes do not appear shorter than H. regalis. While the orbital quadrate process is much longer than H. regalis specimen YPM 1206 as illustrated by Marsh, it is not much longer than the actual specimen of YPM 1206 or KUVP 71012, making this difference invalid.
Martin (1984) stated Parahesperornis' skull was mesokinetic (has a flexible frontoparietal joint), but this was later disproven by Buhler et al. (1988). Two of the characters listed by Martin are plesiomorphies compared to Hesperornis regalis- coracoid elongate; tarsometatarsal trochlea IV smaller and less projected distally. Contra Martin, the anterior lacrimal process is less extended anteriorly than in Hesperornis. Crescent and peg articulations on pedal digit IV are shared with Hesperornis. The tibiotarsus is said to be less compressed than Hesperornis, but without knowing the plane of depression this is vague.
Comments- The holotype was discovered in 1894 and referred to Hesperornis gracilis by Williston (1896, 1898). Lucas (1903) described it as an example of Hesperornis gracilis, using it to separate the species as Hargeria gracilis. However, the ICZN dictates Hargeria must stay associated with its type species regardless of what specimen its description was based on. The mandible was illustrated by Gregory (1951, 1952) as Hesperornis gracilis and Swinton (1975) as H. regalis, while a tooth was illustrated by Martin et al. (1980) as "a hesperornithid." Gregory (1951) argued the differences between regalis and KUVP 2287 were insufficient for generic separation, partially caused by inaccuracies in Marsh's illustrations. In 1952, he argued the quadrate was not disimilar when compared to the actual material instead of Marsh's illustration and that femoral differences could be caused by crushing. Gingerich (1973) described the skull and stated gracilis only differs from regalis in being slightly smaller, while in 1976 he deferred identification of KUVP 2287 to the species. Martin (1983) proposed the new taxon Parahesperornis alexi for KUVP 2287, but as Neas and Jenkinson (1986) note, it is not a proper description as it lacks a diagnosis (ICZN Article 13.1.1). The name is thus a nomen nudum until Martin's (1984) official description. While Martin (1984) stated he had a full description in preparation, one didn't appear until Bell and Chiappe (2020). Some cranial morphologies were described by Buhler et al. (1988) and Witmer (1990). Both Witmer and Elzanowski (1991) have noted various unfused cranial sutures suggest it was not an adult but Bell and Chiappe say "compound bone development is consistent with that of a fully-grown individual." Williston described a patch of material associated with pedal scales as feathers, but Bell and Chiappe find "it is not possible to confirm his interpretation."
Martin (1984) mentions a partial tarsometatarsus of Parahesperornis which was going to be described by Wetmore, but the paper was never completed.
KUVP 24090 was discovered in 1981. Witmer (1990) says it includes a "fragment of the articular region of the right lower jaw", but this is not mentioned by Bell and Chiappe in their description.
Bell and Everhart (2009) described tarsometatarsus FHSM VP-17312 as Parahesperornis sp., which is slightly more elongate with a smaller trochlea III (about half the size of IV). It was referred to P. alexi by Bell and Chiappe (2020). As it was discovered in the early 1990s, this cannot be the specimen Martin mentioned.
References- Williston, 1896. On the dermal covering of Hesperornis. Kansas University Quarterly. 5(1), 53-54.
Williston, 1898. Birds. The University Geological Survey of Kansas, Part 2. 4, 43-53.
Lucas, 1903. Notes on the osteology and relationships of the fossil birds of the genera Hesperornis, Hargeria, Baptornis, and Diatryma. Proceedings of the United States National Museum. 26, 545-556.
Gregory, 1951. Convergent evolution: The jaws of Hesperornis and the mosasaurs. Evolution. 5, 345-354.
Gregory, 1952. The jaws of the Cretaceous toothed birds Ichthyornis and Hesperornis. Condor. 54(2), 73-88.
Gingerich, 1973. Skull of Hesperornis and early evolution of birds. Nature. 243, 70-73.
Swinton, 1975. Fossil Birds. 3rd Ed. British Museum (Natural History), London. 1-81.
Gingerich, 1976. Evolutionary significance of the Mesozoic toothed birds. Smithsonian Contributions to Paleobiology. 27, 23-34.
Martin, Stewart and Whetstone, 1980. The origin of birds: structure of the tarsus and teeth. The Auk. 97, 86-93.
Martin, 1983. The origin and early radiation of birds. in Bush and Clark (eds). Perspectives in Ornithology. Cambridge University Press, Cambridge. 291-338.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Neas and Jenkinson, 1986. Type and figured specimens of fossil vertebrates in the collection of the University of Kansas Museum of Natural History, Part III. Fossil birds. Miscellaneous Publication 78, Museum of Natural History, University of Kansas, Lawrence. 1-14.
Bühler, Martin and Witmer, 1988. Cranial kinesis in the Late Cretaceous birds Hesperornis and Parahesperornis. The Auk. 105, 111-122.
Witmer, 1990. The craniofacial air sac system of Mesozoic birds (Aves). Zoological Journal of the Linnaean Society of London. 100, 327-378.
Elzanowski, 1991. New observations on the skull of Hesperornis with reconstructions of the bony palate and otic region. Postilla. 207, 20 pp.
Martin and Stewart, 1999. Implantation and replacement of bird teeth. Smithsonian Contributions to Paleobiology. 89, 295-300.
Bell and Everhart, 2009. A new specimen of Parahesperornis (Aves: Hesperornithiformes) from the Smoky Hill Chalk (Early Campanian) of Western Kansas. Transactions of the Kansas Academy of Science. 112(1/2), 7-14.
Bell and Chiappe, 2020. Anatomy of Parahesperornis: Evolutionary mosaicism in the Cretaceous Hesperornithiformes (Aves). Life. 10(5), 62.

Hesperornis? mengeli Martin and Lim, 2002
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, Manitoba, Canada
Holotype- (CFDC B.78.01.08; = BO 780108) tarsometatarsus (85.6 mm)
Other diagnoses- Martin and Lim (2002) diagnosed this based on its small size, which is probably primitive and still larger than Hesperornis? macdonaldi. The more slender shaft is also plesiomorphic. Trochlea III is not smaller compared to IV than in Hesperornis crassipes and H. rossicus. Trochlea II is more hidden behind III in H. crassipes, H. rossicus and H. bazhanovi.
Comments- This was described as a species of Hesperornis, but its true position is more uncertain. The slender tarsometatarsus is more primitive than the Baptornis + Hesperornis clade, while the small size is unlike hesperornithids. However, the deep proximodorsal metatarsal III fossa and enlarged metatarsal IV trochlea are shared with the Parahesperornis + Hesperornis clade. The distally projecting metatarsal IV is like Hesperornis, but the rounded intercotylar process is not. The slender tarsometatarsus and medial cotyla which is not transversely compressed suggests it is not part of the large Hesperornis clade. It is here tentatively assigned to the Parahesperornis + Hesperornis clade, where it may be an extremely basal species of Hesperornis. Bell and Chiappe (2016) found it to group with other Hesperornis species in their analysis. They also noted the specimen number of the holotype is BO 780108, not BO 780106 as reported by Martin and Lim.
References- Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds.). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution. 165-174.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
Bell and Chiappe, 2020. Anatomy of Parahesperornis: Evolutionary mosaicism in the Cretaceous Hesperornithiformes (Aves). Life. 10(5), 62.

Canadaga Hou, 1999
C. arctica Hou, 1999
Middle Maastrichtian, Late Cretaceous
Bylot Island, Nunavut, Canada
Holotype- (NMC 41050) incomplete fifteenth cervical vertebra, sixteenth cervical vertebra (28 mm), partial seventeenth cervical vertebra
Paratypes- ?(NMC 41053) (juvenile) femoral shaft
?(NMC 41054) (juvenile) femoral shaft
?(NMC 41064) (juvenile) last synsacral vertebra (29 mm)
Coniacian, Late Cretaceous
Kanguk Formation, Nunavut, Canada
Referred- (NUVF 284) sixteenth cervical vertebra (26.3 mm), seventeenth cervical vertebra (25.5 mm), incomplete first dorsal vertebra (26.7 mm), rib fragments (Wilson et al., 2009; described in Wilson et al., 2011)
Diagnosis- (after Hou, 1999) posterior cervical centrum expanded transversely to be wider than interzygapophyseal width; lateral fossa occupies entire posterior cervical centrum; large hypapophysis, extending from anterior rim to middle of centrum; angle between posterior cervical postzygapophyses much less than 90 degrees; short posterior cervical neural spines; well developed anterior ligament fossa on posterior cervical vertebrae.
(after Wilson et al., 2009) fovea between the parapophysis and centrum with a deep cavity below the transverse process.
Comments- Hou studied the type remains in 1991 and described them in 1999 as a new taxon of hesperornithid- Canadaga arctica. While the diagnosis does distinguish Canadaga from Baptornis advenus and Hesperornis regalis, the remains of other hesperornithines are either not comparable or not described/illustrated well enough to compare. The size (estimated tarsometatarsal length of 212 mm) is greater than other hesperornithids, which suggests it may be referrable to the subgroup of large Hesperornis species. However, no other characters are presently known which could resolve where Canadaga belongs within Hesperornithes.
References- Hou, 1999. New hesperornithid (Aves) from the Canadian Arctic. Vertebrata PalAsiatica. 37(7), 228-233.
Wilson, Chin, Dyke and Cumbaa, 2009. A high-latitude hesperornithiform (Aves) from Devon Island: Paleobiogeography and size distribution of North American hesperornithiforms. Journal of Vertebrate Paleontology. 29(3), 202A.
Wilson, Chin, Cumbaa and Dyke, 2011. A high latitude hesperornithiform (Aves) from Devon Island: Palaeobiogeography and size distribution of North American hesperornithiforms. Journal of Systematic Palaeontology. 9(1), 9-23.
Wilson. 2012. Paleobiology of hesperornithiforms (Aves) from the Campanian Western Interior Seaway of North America, with analyses of extant penguin bone histology. PhD thesis, University of Colorado. 150 pp.

Hesperornis Marsh, 1872a
= Lestornis Marsh, 1876
= Coniornis Marsh, 1893
= Hargeria Lucas, 1903
= Asiahesperornis Nessov and Prizemlin, 1991
Diagnosis- (proposed) hypertrophied ilial antitrochanter (also in Baptornis advenus); acetabulum partially closed (also in Baptornis advenus); pointed intercotylar process on tarsometatarsus (absent in Hesperornis crassipes); metatarsal IV extends distally far beyond III (also in Enaliornis? seeleyi).
Comments- While numerous species and specimens have been referred to Hesperornis, several have been given their own genera. Most of the literature synonymizes Lestornis, Coniornis and Hargeria with Hesperornis, but retains Asiahesperornis as a separate genus. Yet no reasons for excluding the latter taxon from Hesperornis have been given, and it clades within Hesperornis when included in a phylogenetic analysis (Bell and Chiappe, 2016; Mortimer, unpublished). Bell and Chiappe found all of these taxa to code identically in their matrix and suggested the current named species diversity is unsupported, though they did not create any new formal taxonomy. Hesperornis mengeli and H. macdonaldi were named by Martin and Lim (2002), but are here provisionally removed from the genus though Bell and Chiappe found the first to only differ from other Hesperornis by one character and the latter to code identically to other Hesperornis.
References- Marsh, 1872a. Discovery of a remarkable fossil bird. American Journal of Science, Series 3. 3(13), 56-57.
Marsh, 1876. Notice of new Odontornithes. The American Journal of Science and Arts. 11, 509-511.
Marsh, 1893. A new Cretaceous bird allied to Hesperornis. American Journal of Science. 45, 81-82.
Lucas, 1903. Notes on the osteology and relationships of the fossil birds of the genera Hesperornis, Hargeria, Baptornis, and Diatryma. Proceedings of the United States National Museum. 26, 545-556.
Nessov and Prizemlin, 1991. A large advanced flightless marine bird of the order Hesperornithiformes of the Late Senonian of Turgai Strait - the first finding of the group in the USSR. USSR Academy of Sciences, Proceedings of the Zoological Institute. 239, 85-107 (in Russian).
Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds.). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution. 165-174.
Wilson, 2012. The effects of climate and behavior on avian bone microstructure: A comparative osteohistology study of hesperornithiforms from the Late Cretaceous Western Interior Seaway. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 195.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
H. bairdi Martin and Lim, 2002
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, South Dakota, US
Holotype- (YPM PU 17208A) synsacrum, incomplete ilium, proximal pubis, proximal ischium, tarsometatarsus (102.4 mm)
Other diagnoses- Martin and Lim (2002) diagnosed this based on Hesperornis characters (more enlarged and distally placed trochlea IV than Parahesperornis) and its primitively small size (which is still larger than H? mengeli and H? macdonaldi).
Comments- This taxon seems to be the most basal species of Hesperornis, which explains its similarity to Parahesperornis. Bell and Chiappe (2016) found it to group with Hesperornis in their analysis, differing from other species in a single character.
Reference- Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds.). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution. 165-174.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
unnamed clade (Hesperornis regalis <- Hesperornis bairdi)
Diagnosis- (proposed) large size (proximal tarsometatarsal width over 25 mm); coracoid short proximodistally (unknown in H. bairdi); clavicles unfused (unknown in other hesperornithines); interclavicular angle >70 degrees (unknown in other hesperornithines); distal tibiotarsus not angled anteriorly (unknown in H. bairdi); tarsometatarsus robust (less than 4.5 times longer than proximally wide (also in Brodavis? varneri); medial tarsometatarsal cotyla transversely compressed (also in Enaliornis? seeleyi).
Comments- This large Hesperornis clade may also include Canadaga, based on its size.
H. altus (Marsh, 1893) Shufeldt, 1915b
= Coniornis altus Marsh, 1893
Campanian, Late Cretaceous
Claggett Shale or Judith River Formation, Montana, US
Holotype- (YPM 515) (adult) distal tibiotarsus
Campanian-Maastrichtian, Late Cretaceous
Pierre Shale Group, South Dakota, US
Referred- ?(YPM PU 17208C) posterior dorsal vertebra, synsacrum, ilium, femur (YPM online)
?(YPM PU 17208D) tibiotarsus, metatarsal I, tarsometatarsus, seven pedal phalanges including III-1 (39.2 mm) (YPM online)
?(YPM PU 18589) cranial material, cervical vertebrae, dorsal vertebrae, clavicle, sternal fragments, femur (81.9 mm), patellae, tibiotarsus (Wilson, Chin and Cumbaa, 2016)
Diagnosis- indeterminate relative to H. regalis.
Comments- This specimen was discovered in 1892 and described by Marsh (1893) as a new taxon of hesperornithine, which he named Coniornis altus. This was based on two characters- lateral condyle projects distally further than medial condyle; medial condyle does not extend medially past shaft. Shufeldt (1915a) believed Marsh only separated Coniornis from Hesperornis on stratigraphic grounds, though he did not officially place altus in Hesperornis. Shufeldt (1915b) compared the element to Hesperornis regalis and found them similar enough to place in the same genus, or even the same species. He noted "where the condylar crests are more prominent in Hesperornis, they have been broken off in Marsh's Coniornis altus." He thus synonymized Coniornis with Hesperornis, which was followed by Martin (1984) due to the compressed distal end. Indeed, comparing the holotype to H. regalis, the two characters described by Marsh could be eliminated by rotating the distal end of altus' tibiotarsus so that the condyles are vertical instead of medially tilted. There is an obvious plaster filled area just proximal to the condyles where misalignment could have taken place. Once this is corrected for, the tibiotarsi are extremely similar. YPM 515 seems to have a more anteriorly projected lateral condyle, but this would again be solved by rotating the distal area. The lack of a medial epicondyle on YPM 515 could be due to damage.
Shufeldt (1915a) described Hesperornis montana from a dorsal vertebra found in the Claggett Shale of Montana and considered the possibility YPM 515 was from the same beds (as the area was not well segregated when it was collected), but felt it more likely that the size difference indicated there were two species present. They are here kept separate as many formations have more than one hesperornithid species, and there is no overlapping material.
The referred material from the Pierre Shale Group may be H. bairdi, H. chowi, H? macdonaldi or H? mengeli based on stratigraphy. Martin et al. (2016) describe a pathology on YPM PU 17208D (as Hesperornis sp. YPM PU 17208), noting it "is smaller than the common Hesperornis regalis of the Niobrara Chalk, but it differs from the slender limbed, contemporary H. chowi by having a broader tarsometatarsus with a more enlarged outer trochlea."
References- Marsh, 1893. A new Cretaceous bird allied to Hesperornis. American Journal of Science. 45, 81-82.
Shufeldt, 1915a. The fossil remains of a species of Hesperornis found in Montana. The Auk. 32(3), 290-284.
Shufeldt, 1915b. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Martin, Rothschild and Burnham, 2016. Hesperornis escapes plesiosaur attack. Cretaceous Research. 63, 23-27.
Wilson, Chin and Cumbaa, 2016. A new hesperornithiform (Aves) specimen from the Late Cretaceous Canadian High Arctic with comments on high-latitude hesperornithiform diet. Canadian Journal of Earth Sciences. 53(12), 1476-1483.
H. montanus Schufeldt, 1915a
Early Campanian, Late Cretaceous
Claggett Shale, Montana, US
Holotype- (USNM 8199) sixth dorsal vertebra (Shufeldt, 1915a)
Diagnosis- (after Shufeldt, 1915a) lateral fossae extremely shallow in dorsal centra.
Comments- Shufeldt (1915) reported on a dorsal vertebra discovered in 1914, which he sent to Lull for examination. Lull determined it most closely matched the last dorsal vertebra of Hesperornis, differing only in minor ways, most of which also varied between different spcimens of that genus. He concluded it was referrable to Hesperornis, and only perhaps a new species due to stratigraphy. Shufeldt noted it may have been found in the same beds as Coniornis altus but thought it was too small to derive from the same species, so named it Hesperornis montana. However, the ICZN dictates it must be emmended to montanus, as Hesperornis is masculine.
Marsh (1893) earlier described Coniornis altus from what may be the same beds and while Shufeldt considered the possibility of synonymy (as have later authors), he felt it more likely that the size difference indicated there were two species present. They are here kept separate as many formations have more than one hesperornithid species, and there is no overlapping material.
References- Marsh, 1893. A new Cretaceous bird allied to Hesperornis. American Journal of Science. 45, 81-82.
Shufeldt, 1915a. The fossil remains of a species of Hesperornis found in Montana. The Auk. 32(3), 290-284.
H. gracilis Marsh, 1876
= Hargeria gracilis (Marsh, 1976) Lucas, 1903
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US
Holotype- (YPM 1473) incomplete tarsometatarsus (~130 mm), two pedal phalanges
Referred- (YPM 1478) dorsal vertebrae, partial femur, partial tibiotarsus, tarsometatarsi (one partial; 138 mm), phalanx III-1 (34.87 mm), phalanx IV-1 (41 mm) (Marsh, 1880)
(YPM 1679) cervical vertebrae, dorsal vertebrae, rib fragments, partial synsacrum, pelvis, femora (84.06 mm), patella (~88.24 mm), tibiotarsi, fibula, tarsometatarsi (126.44 mm), phalanx IV-1 (40.32 mm), two pedal phalanges (Marsh, 1880)
(YPM 55000) vertebrae, synsacrum, femora, tibiotarsi, tarsometatarsi and pedal phalanges including III-1 (35.9 mm) (Bell, Irwin and Davis, 2015)
Other diagnoses- Marsh (1876) diagnosed H. gracilis as being smaller and more slender than H. regalis, but these are plesiomorphies.
Comments- Martin (1984) incorrectly listed the holotype as YPM 1478 in his figure 1, which is a specimen listed in two tables as H. gracilis by Marsh (1880). The holotype was discovered in 1876 and briefly described by Marsh that year, but it was not illustrated until Martin (1984). Williston (1896, 1898) referred KUVP 2287 to Hesperornis gracilis, but it was later made the holotype of Parahesperornis alexi by Martin (1984). Lucas (1903) also believed KUVP 2287 was referrable to gracilis and used it as the basis for transferring that species to his new genus Hargeria. However, the ICZN dictates Hargeria must stay associated with its type species regardless of what specimen its description was based on. Lang (1973) placed a species of leptocheliid tanaidacean Leptochelia rapax Harger, 1879 into the new genus Hargeria. Thus the crustacean Hargeria is preoccupied by the bird Hargeria, contra Bell and Everhart (2009). Martin (1984) synonymized Hargeria with Hesperornis, but retained gracilis as a distinct species. The taxon needs to be described in detail to determine how it compares to other Hesperornis species.
YPM 1679 was referred to H. gracilis by Marsh (1880), but only listed as Hesperornis sp. by Chiappe (2002) and the YPM catalog. YMP 55000 is listed as Hesperornis gracilis in the YMP catalog, but as Hesperornis sp. by Bell, Irwin and Davis (2015).
References- Marsh, 1876. Notice of new Odontornithes. The American Journal of Science and Arts. 11, 509-511.
Harger, 1879. Notes on New England Isopoda. Proceedings of the United States National Museum. 79, 157-165.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Lucas, 1903. Notes on the osteology and relationships of the fossil birds of the genera Hesperornis, Hargeria, Baptornis, and Diatryma. Proceedings of the United States National Museum. 26, 545-556.
Lang, 1973. Taxonomische und phylogenetische Untersuchungen uber die Tanaidaceen (Crustacea). 8. Die Gattungen Leptochelia Dana, Heterotanais G.O. Sars und Nototanais Richardson. Dazu einige Bemerkungen uber die Monokonophora und ein Nachtrag. Zoologica Scripta. 2, 197-229.
Martin, Stewart and Whetstone, 1980. The origin of birds: structure of the tarsus and teeth. The Auk. 97, 86-93.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Chiappe, 2002. Basal bird phylogeny: Problems and solutions. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 448-472.
Bell and Everhart, 2009. A new specimen of Parahesperornis (Aves: Hesperornithiformes) from the Smoky Hill Chalk (Early Campanian) of Western Kansas. Transactions of the Kansas Academy of Science. 112(1/2), 7-14.
Bell, Irwin and Davis, 2015. Hesperornithiform birds from the Late Cretaceous (Campanian) of Arkansas, USA. Transactions of the Kansas Academy of Science. 118(3/4), 219-229.
H. chowi Martin and Lim, 2002
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, South Dakota, US
Holotype- (YPM PU 17208) tarsometatarsus (137.2 mm)
Mid Campanian, Late Cretaceous
Pembina Member of the Pierre Shale Group, Manitoba, Canada
Referred- (CFDC B.00.27.00) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.79.05.13) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.82.08.17) (2 individuals) two tarsometatarsi (Aotsuka and Sato, 2016)
(CFDC B.83.02.18) tarsometarsi (Aotsuka and Sato, 2016)
Mid Campanian, Late Cretaceous
Millwood Member of the Pierre Shale Group, Manitoba, Canada
(CFDC B.05.01.15) two tarsometatarsi (Aotsuka and Sato, 2016)
(CFDC B.05.01.23) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.07.02.23) tarsometatarsus (Aotsuka and Sato, 2016)
Diagnosis- (after Martin and Lim, 2002) medial anterior metatarsal ridge blends into median groove distally.
Other diagnoses- Martin and Lim (2002) diagnosed Hesperornis chowi with several characters that differ from H. regalis. However, the more elongate tarsometatarsus and slender lateral anterior metatarsal ridge are plesiomorphic, while the fourth trochlea is not more enlarged compared to trochlea III. A short medial anterior metatarsal ridge is also present in Hesperornis mengeli and H. bazhanovi.
Comments- Martin and Lim (2002) also believed remains described by Russell (1967) as H. regalis from the Northwest Territories might be H. chowi, but these are from a different formation.
References- Russell, 1967. Cretaceous vertebrates from the Anderson River, N.W.T. Canadian Journal of Earth Sciences. 4, 21-38.
Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds.). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution. 165-174.
Aotsuka and Sato, 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, southern Manitoba, Canada. Cretaceous Research. 63, 154-169.
H. lumgairi Aotsuka and Sato, 2016
Mid Campanian, Late Cretaceous
Pembina Member of the Pierre Shale Group, Manitoba, Canada
Holotype- (CFDC B.78.02.07; Hesperornis sp. A) (adult) incomplete tarsometatarsus
Late Campanian, Late Cretaceous
Foremost Formation, Alberta, Canada
Paratype- (UA 9716) incomplete tarsometatarsus (147 mm)
Diagnosis- (after Aotsuka and Sato, 2016) lateral tarsometatarsus cotyle only one third of medial cotyle [size?]; smooth and rounded posterior surface of tarsometarasus shaft, giving D-shaped outline in proximal view; indistinct triangular surface on posterior side of proximal tarsometatarsus.
Comments- The holotype was discovered in 1978, noted in Nicholls' (1988) thesis and Aotsuka et al.'s (2012) thesis as Hesperornis sp. A, and described as a new species by Aotsuka and Sato (2016).
UA 9716 was discovered in 1972 and described by Fox (1974) as Hesperornis cf. regalis. He noted it was more similar to regalis than to crassipes in being slender and lacking the metatarsal II tuberosity of crassipes, though it is slightly larger. However, the lack of a rugosity is plesiomorphic and the width / length ratio (4.47) resembles H. gracilis (4.45) more than H. regalis (4.00-4.13). Nessov and Yarkov (1993) thought it possibly belonged to "another more advanced species", and indeed it was referred to Aotsuka and Sato's new species H. lumgairi by those authors.
References- Fox, 1974. A Middle Campanian, nonmarine occurrence of the Cretaceous toothed bird Hesperornis Marsh. Canadian Journal of Earth Sciences. 11(9), 1335-1338.
Nicholls, 1988. Marine vertebrates of the Pembina Member of the Pierre Shale (Campanian, Upper Cretaceous) of Manitoba and their significance to the biogeography of the Western Interior Seaway. PhD Thesis. University of Calgary. 317 pp.
Nessov and Yarkov, 1993. [Hesperornithes in Russia] Russkii Ornitolocheskii Zhurnal. 2(1), 37-54.
Aotsuka, Hatcher, Janzic and Sato, 2012. Diversity of the Hesperornithiformes (Aves) from the Upper Cretaceous Pierre Shale in Southern Manitoba, Canada. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 57.
Aotsuka and Sato, 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, southern Manitoba, Canada. Cretaceous Research. 63, 154-169.
H. regalis Marsh, 1872a
Late Santonian-Early Campanian, Late Cretaceous
Spinaptychus sternbergi and Hesperornis Zones of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US
Holotype- (YPM 1200) third cervical vertebra (22.5 mm), sixth cervical vertebra (29 mm), fourth dorsal vertebra (24 mm), fifth dorsal vertebra (24 mm), dorsal ribs, third caudal vertebra (12 mm), fourth caudal vertebra (12 mm), fifth caudal vertebra (13 mm), sixth caudal vertebra (13.5 mm), seventh caudal vertebra (13 mm), eighth caudal vertebra (15.2 mm), ninth caudal vertebra (16 mm), pygostyle (25 mm), partial pelvis, femora (99.2, 99.1 mm), patellae (108.54 mm), tibiotarsi (321.11 mm), fibulae (240 mm), tarsometatarsi (136.4, 135.9 mm), phalanx III-1 (40.24 mm), phalanx III-2 (30 mm), proximal phalanx III-3, phalanx IV-1 (44.22 mm), phalanx IV-2 (39.5 mm), phalanx IV-3 (40 mm), proximal phalanx IV-4
Referred- (AMNH 2181) femur, patella, tibiotarsus, fibula (Bell and Chiappe, 2020)
(AMNH 5100) sixteen cervical vertebrae, six dorsal vertebrae, synsacrum, four caudal vertebrae, scapulae, ilia, pubes, ischia, femora, patellae, tibiotarsi, fibulae, phalanx I-1, pedal ungual I, tarsometatarsi, phalanges II-1, phalanges II-2, phalanx III-1, phalanx III-2, phalanx III-3, pedal ungual III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal ungual IV (Sternberg, 1917)
(FMNH PA206) (Chiappe, 1996)
(FMNH PA316) (Chiappe, 1996)
(FHSM VP-186) fifth dorsal vertebra, sixth dorsal vertebra, synsacrum, incomplete ilium, proximal pubis (Everhart, 2011))
(FHSM VP-2069) cervical vertebrae, dorsal vertebrae, dorsal ribs, synsacrum, caudal vertebrae, scapula, coracoids (53.88 mm), incomplete sternum, sternal ribs, humerus, ilium, pubis, ischium, femora (93.87 mm), patella, tibiotarsi, fibula, tarsometatarsi, proximal phalanx II-1, phalanx III-1, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4 (Everhart, 2011)
(FHSM VP-2293) seven dorsal vertebrae, two proximal dorsal ribs, scapula, humerus, partial femur, patella, partial tibiotarsus (Bell and Chiappe, 2020)
(HMN MB Av 106.1) incomplete tibiotarsus (Zinoviev, 2011)
....(HMN MB Av 106.3) incomplete femur (Zinoviev, 2011)
....(HMN MB Av 106.8) proximal fibula (Zinoviev, 2011)
(HMN MB Av 106.2) tarsometatarsus (Zinoviev, 2011)
(HMN MB Av 106.10) patella (Zinoviev, 2011)
(KUVP 2289) axial material, femoral fragment (Chinsamy, Martin and Dodson, 1998)
(KUVP 71012) skull, mandibles, axis, cervical vertebrae, tarsometatarsus (128 mm), eleven pedal phalanges (Martin, 1987; Witmer and Martin, 1987)
(KUVP 123108) distal femoral fragment (Chinsamy, Martin and Dodson, 1998)
(LACM 128317) maxilla (Witmer, 1990)
(UNSM 1212) fifteen presacral vertebrae, three dorsal ribs, uncinate processes, pubis, femur, patella, tarsometatarsus, phalanx III-1 (Everhart, 2011))
(USNM 53) three vertebrae (USNM online)
(USNM 54) three vertebrae (USNM online)
(USNM 55) two vertebrae (USNM online)
(USNM 77) pelvis (USNM online)
(USNM 78) sternum (USNM online)
(USNM 4978) anterior skull, partial mandibles, eight cervical vertebrae, six dorsal vertebrae, dorsal ribs, partial uncinate process, synsacrum, caudal vertebrae, scapula, coracoid, clavicle, sternum, sternal ribs, ilium, pubis, ischium, femora, tibiotarsi, tarsometatarsi, pedal phalanges (Lucas, 1903)
(USNM 6622) premaxilla (Bell and Chiappe, 2020)
(USNM 7276) partial mandible (USNM online)
(USNM 7277) partial mandible (USNM online)
(USNM 11640) vertebra, pelvis (USNM online)
(USNM 13580) cranial material, dorsal vertebrae, dorsal rib, synsacrum, femur, patella, tibiotarsus, fibula, tarsometatarsus (Bryant, 1983)
(USNM 13581) femur, partial tibiotarsus, proximal tarsometatarsus, phalanx (USNM online)
(USNM 13882) dorsal vertebra (USNM online)
(YPM 903) posterior mandible (Shufeldt, 1915b)
(YPM 1201) (adult) partial femur (Marsh, 1872b)
(YPM 1202) partial femur (Marsh, 1872b)
(YPM 1203) pedal phalanx III-1 (37.9 mm) (Marsh, 1872b)
(YPM 1204) (Marsh, 1872b)
(YPM 1205) distal tibiotarsus (Marsh, 1875)
(YPM 1206) skull (257 mm), mandible (257 mm), teeth, third cervical vertebra (24 mm), fourth cervical vertebra (26 mm), fifth cervical vertebra (28 mm), sixth cervical vertebra (31 mm), seventh cervical vertebra (32 mm), eighth cervical vertebra (33 mm), ninth cervical vertebra (32.5 mm), tenth cervical vertebra (32 mm), three cervicals ribs (37, 83 mm), fourth dorsal vertebra, sixth dorsal vertebra (25.5 mm), six dorsal ribs (145, 172, 190, 209 mm), six uncinate processes (25, 54, 52, 55, 50, 30 mm), synsacrum (320 mm- first sacral 21 mm), first caudal vertebra (19 mm), second caudal vertebra (15 mm), scapula, coracoid (54 mm), clavicle (78 mm), sternum (~200 mm), five incomplete sternal ribs (110 mm), humerus (152 mm), ilium (380 mm), pubis (330 mm), ischium (260 mm), femur (96 mm), tarsometatarsus (132 mm), proximal phalanx II-1, phalanx IV-1 (42.5 mm), phalanx IV-2 (40 mm), phalanx IV-3 (41 mm) (Marsh, 1875)
(YPM 1207) quadrate, occiput, axis (29 mm), third cervical vertebra (22 mm), fourth cervical vertebra (24 mm), fifth cervical vertebra (28 mm), sixth cervical vertebra (30 mm), seventh cervical vertebra (32 mm), eighth cervical vertebra (33 mm), ninth cervical vertebra (31 mm), tenth cervical vertebra (30 mm), eleventh cervical vertebra (29 mm), twelfth cervical vertebra (24 mm), thirteenth cervical vertebra (25 mm), fourteenth cervical vertebra (23 mm), fifteenth cervical vertebra (22 mm), sixteenth cervical vertebra (18 mm), seventeenth cervical vertebra (20 mm), first dorsal vertebra (22 mm), second dorsal vertebra (24 mm), third dorsal vertebra (24.5 mm), fourth dorsal vertebra (25 mm), fifth dorsal vertebra (24.5 mm), sixth dorsal vertebra (24 mm), partial synsacrum, coracoid (55 mm), partial clavicle, pelvis, femora (98.5, 101 mm), patellae (98 mm), partial tibiotarsi, partial fibulae, tarsometatarsi (one partial; 136 mm), two pedal phalanges (Marsh, 1880)
(YPM 1470) synsacrum, caudal vertebra (YPM online)
(YPM 1471) limb bone fragments (YPM online)
(YPM 1472) femoral fragments (Marsh, 1880)
(YPM 1476) fourteenth cervical vertebra (24 mm), fifteenth cervical vertebra (22 mm), sixteenth cervical vertebra (18 mm), seventeenth cervical vertebra (22 mm), first dorsal vertebra (25 mm), second dorsal vertebra (26.5 mm), third dorsal vertebra (26 mm), fourth dorsal vertebra (26 mm), fifth dorsal vertebra (26 mm), synsacrum, scapula (135 mm), partial sternum, incomplete pelvis (ilium ~307.47 mm), femur (105 mm), patella (100 mm), tibiotarsi (335, 325 mm), proximal fibula, metatarsal I (20 mm), distal phalanx I-1, pedal ungual I (14 mm), tarsometatarsi (136 mm), phalanx II-1 (42 mm), phalanx II-2 (41 mm), pedal ungual II (15 mm), phalanx III-1 (38.7 mm) (Marsh, 1880)
(YPM 1477) fourteenth cervical vertebra (24 mm), fifteenth cervical vertebra (22 mm), sixteenth cervical vertebra (19 mm), seventeenth cervical vertebra (20 mm), first dorsal vertebra (22 mm), second dorsal vertebra (24 mm), fourth dorsal vertebra (25 mm), fifth dorsal vertebra (26 mm), sixth dorsal vertebra (25 mm), seventh dorsal vertebra (22 mm), rib fragments, synsacrum, partial coracoid, femora (97 mm), patella (103 mm), tibiotarsi, proximal fibulae (Marsh, 1880)
(YPM 1491) (adult) femoral fragments, tibiotrarsus, tarsometatarsus (Chiappe, 1996)
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, South Dakota, US
(SDSM 25005) incomplete femur, tibiotarsus (315 mm), incomplete fibula (Martin and Varner, 1992)
Early Campanian, Late Cretaceous
Gammon Ferruginous Member of the Pierre Shale Group, Manitoba, Canada
(CFDC B.09.03.13) tarsometatarsus (109.4 mm) (Aotsuka and Sato, 2016)
Mid Campanian, Late Cretaceous
Pembina Member of the Pierre Shale Group, Manitoba, Canada
(CFDC B.00.01.00) femur (90.8 mm) (Aotsuka and Sato, 2016)
(CFDC B.00.01.09) ten vertebrae, femora, tibiotarsus, tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.00.03.00) femur (93.8 mm) (Aotsuka and Sato, 2016)
(CFDC B.00.18.00) tarsometatarsus (Nicholls, 1988)
(CFDC B.00.20.00) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.00.22.00) tarsometatarsus (Nicholls, 1988)
(CFDC B.00.23.00; lost) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.00.24.00) tarsometatarsus (Nicholls, 1988)
(CFDC B.00.25.00) tarsometatarsus (Nicholls, 1988)
(CFDC B.00.55.00) femur (87.4 mm) (Aotsuka and Sato, 2016)
(CFDC B.03.01.05) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.03.06.18) femur, tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.05.03.23) tibiotarsus, tarsometatarsus (118.5 mm) (Aotsuka and Sato, 2016)
(CFDC B.07.01.04) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.07.03.23) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.75.01.06) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.75.03.06) four vertebrae, tarsometatarsi (one fragmentary) (Nicholls, 1988)
(CFDC B.77.04.07) three vertebrae, femur, tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.77.05.07) femur (93 mm) (Aotsuka and Sato, 2016)
(CFDC B.78.03.08) patella, tibiotarsus, tarsometatarsus (Nicholls, 1988)
(CFDC B.82.15.17) tarsometatarsus (Nicholls, 1988)
(CFDC B.83.03.18) tarsometatarsus (Nicholls, 1988)
(CFDC B.83.04.18) fragmentary tarsometatarsus (Nicholls, 1988)
(CFDC B.84.04.18) tibiotarsi, tarsometatarsus (128.9 mm) (Nicholls, 1988)
(CFDC B.2010.01.04) femur (96.2 mm) (Aotsuka and Sato, 2016)
(CFDC B.2010.01.09) vertebra, femur (93.3 mm) , patella, tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.2012.01.04) femur (93 mm) (Aotsuka and Sato, 2016)
(FMNH PA218) five vertebrae, tarsometatarsi (105.9, 106.1 mm) (Bardack, 1968)
(FMNH PA288) tarsometatarsus (113.4 mm) (Aotsuka and Sato, 2016)
(MM V-137) femur (Aotsuka and Sato, 2016)
(MM V-247A) femur (87.1 mm) (Aotsuka and Sato, 2016)
(MM coll.; lost) two tarsometatarsi (Aotsuka and Sato, 2016)
(ROM coll.; lost) vertebra, tarsometatarsus (Aotsuka and Sato, 2016)
Diagnosis- (after Marsh, 1875a, b) seventh through tenth caudal vertebrae with extremely long and flattened transverse processes (unknown in other hesperornithids); pygostyle extremely broad and flattened (unknown in other hesperornithids).
(after Marsh, 1876) four sternal rib articulations; deep posterolateral excavations in sternum.
(after Marsh, 1877) radius, ulna and manus absent (unknown in other hesperornithids).
(after Lucas, 1903) fourteen sacral vertebrae (unknown in other hesperornithids; also in Aves).
(after Witmer, 1990) medial pneumatic lacrimal fossa small and shallow (unknown in other Hesperornis); articular lacks pneumaticity (unknown in other Hesperornis; also in Patagopteryx).
(proposed) scapular expanded distally (unknown in other hesperornithines; also in Songlingornis); humerus longer than scapula (unknown in other hesperornithines; also in Gansus and Yanornis);
Other diagnoses- Marsh's (1872a) original paper only described a few characters, which are either more broadly distributed among hesperornithines (short femur, elongate tibiotarsus) or incorrect (unfused metatarsals).
Marsh's (1872b) later description mentions several features as being distinctive, but these are either primitive (trochanteric crest less expanded anteroposteriorly than in grebes; supratendinal groove absent; hypotarsal grooves absent) or found in other hesperornithines (femur with compressed cross section; metatarsal IV longest; trochlea IV enlarged; pedal digit IV with crescent and peg articulations between phalanges).
Marsh (1875a, b) mentions several characters as being distinctive, though the described proximal caudal morphology (short centra, moderate sized transverse processes and tall neural spines) is primitive. The partially closed acetabulum is present in some other hesperornithines as well.
In 1877, Marsh noted Hesperornis was also distinctive for having dentary teeth placed in grooves (also in Parahesperornis), a sternum without a keel (probably also in Baptornis), and a hindlimb with diving adaptations (too vague, and found in other hesperornithines in any case).
Lucas (1903a) noted the femur was articulated so that it projected transversely, which is also now known to be true in Parahesperornis.
Comments- The holotype was discovered in 1871, though another specimen (YPM 1205) was discovered in 1870 but not recognized as such until Marsh (1875a, b). Marsh (1872a) gave a very brief commentary on the holotype, to be followed by a more detailed description in 1872b. Marsh (1875a, b) added details from a more complete specimen with a skull (YPM 1206). Marsh (1880) monographed the taxon, using the holotype, YPM 1206, 1207, 1476 and 1477. He misidentified the predentary as a basihyal (Martin and Naples, 2008). Palatal elements have been controversial- a structure was identified by Marsh (1880) as a vomer, Gingerich (1973, 1976) as a palatine, and Elzanowski (1991) as an anterior pterygoid. Another element was identified as a palatine by Marsh, a vomer by Gingerich, and a composite maxilla and palatine fragment by Elzanowski. Witmer and Martin (1987) identified elements as a paired vomer which Elzanowski identified as palatines. Bock (1969) questioned whether Hesperornis was really toothed, but their presence in its jaws is unambiguous. Although the YPM lists YPM 1201-1204 as paratypes, Marsh 1872a only mentions one specimen in his initial description. These are probably the four specimens mentioned in Marsh 1872b. Note Gregory (1951) incorrectly called YPM 1206 the type.
While Hesperornis specimens have generally been thought to be limited to the Early Campanian Hesperornis Zone of the Smoky Hill Chalk, Everhart (2011) showed that the holotype and several other specimens (FSHM 186, 349 and 2069, UNSM 1212, USNM 13581, and YPM 1202-1204) are actually from the earlier Spinaptychus sternbergi Zone. As it is unclear from the literature and online databases which specimens (if any) are actually from the Hesperornis Zone, they are not distinguished in this material list. It's also possible that other bird material listed on this site as being from the Hesperornis Zone is actually from the Spinaptychus sternbergi Zone.
Several specimens from other formations have been referred to Hesperornis regalis. Russell (1967) mentioned many specimens from the Smoking Hills Formation of the Northwest Territories. Bardack (1968) referred several specimens from Manitoba to H. regalis (FMNH PA216-219, MM V-532). Witmer (1990) noted differences in some Manitoban material, but Aotsuka and Sato (2016) referred FMNH PA218 to H. regalis, and FMNH PA216-217 and MM V-532 to H. sp.. Fox (1974) referred a tarsometatarsus from the Foremost Formation of Alberta to Hesperornis cf. regalis, though this seems untrue based on its proportions.
References- Marsh, 1872a. Discovery of a remarkable fossil bird. American Journal of Science, Series 3. 3(13), 56-57.
Marsh, 1872b. Preliminary description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. American Journal of Science, 3rd series. 3(17), 359-365.
Marsh, 1873. Fossil birds from the Cretaceous of North America. American Journal of Science, Series 3. 5(27), 229-231.
Marsh. 1875a. On the Odontornithes, or birds with teeth. American Journal of Science, Series 3. 10(59), 403-408.
Marsh, 1875b. Odontornithes, or birds with teeth. The American Naturalist. 9(12), 625-631.
Marsh, 1876. Notice of new Odontornithes. The American Journal of Science and Arts. 11, 509-511.
Marsh, 1877. Characters of the Odontornithes, with notice of a new allied genus. American Journal of Science. 14, 85-87.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Noack, 1880. Die Bedeutung des Hesperornis regalis für die Descendanzteorie. Jahresber. Ver. Naturwiss. Braunschweig. 1, 89-96.
Marsh, 1883. Birds with teeth. 3rd Annual Report of the Secretary of the Interior. 3, 43-88.
Thompson, 1890. On the systematic position of Hesperornis. Studies from the Museum of Zoology. 1(10), 15 pp.
Lucas, 1903a. A skeleton of Hesperornis. Smithsonian Miscellaneous Collections. 45, 95.
Lucas, 1903b. Notes on the osteology and relationships of the fossil birds of the genera Hesperornis, Hargeria, Baptornis, and Diatryma. Proceedings of the United States National Museum. 26, 545-556.
Brown, 1911. Notes on the restorations of the Cretaceous birds Hesperornis and Baptornis. Annals of the New York Academy of Sciences. 20, 401.
Shufeldt, 1915a. The fossil remains of a species of Hesperornis found in Montana. The Auk. 32(3), 290-284.
Shufeldt, 1915b. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.
Shufeldt, 1915c. On a restoration of the base of the cranium of Hesperornis regalis. Bulletins of American Paleontology. 5, 73-85.
Sternberg, 1917. Hunting Dinosaurs in the Badlands of the Red Deer River, Alberta, Canada. Published by the author, San Diego, California. 261 pp.
Stolpe, 1935. Colymbus, Hesperornis, Podiceps: ein Vergleich ihrer hinteren Extremität. Journal of Ornithology. 83(1), 115-128.
Lane, 1947. A survey of the fossil vertebrates of Kansas, Part IV, The Birds. Kansas Academy of Science, Transactions. 49(4), 390-400.
Edinger, 1951. The brains of the Odontognathae. Evolution. 5(1), 6-24.
Gregory, 1951. Convergent evolution: The jaws of Hesperornis and the mosasaurs. Evolution. 5, 345-354.
Gregory, 1952. The jaws of the Cretaceous toothed birds Ichthyornis and Hesperornis. Condor. 54(2), 73-88.
Martin and Tate, 1966. A bird with teeth. Museum Notes, University of Nebraska State Museum. 29, 1-2.
Russell, 1967. Cretaceous vertebrates from the Anderson River, N.W.T. Canadian Journal of Earth Sciences. 4, 21-38.
Walker, 1967. Revival of interest in the toothed birds of Kansas. Kansas Academy of Science, Transactions. 70(1), 60-66.
Bardack, 1968. Fossil vertebrates from the marine Cretaceous of Manitoba. Canadian Journal of Earth Sciences. 5, 145-153.
Bock, 1969. The origin and radiation of birds. Ann. New York Acad. Sci. 167, 147-155.
Gingerich, 1973. Skull of Hesperornis and early evolution of birds. Nature. 243, 70-73.
Fox, 1974. A Middle Campanian, nonmarine occurrence of the Cretaceous toothed bird Hesperornis Marsh. Canadian Journal of Earth Sciences. 11(9), 1335-1338.
Gingerich, 1976. Evolutionary significance of the Mesozoic toothed birds. Smithsonian Contributions to Paleobiology. 27, 23-34.
Martin, 1980. Foot-propelled diving birds of the Mesozoic. Acta XVII Congress of International Ornithology. 1237-1242.
Martin, Stewart and Whetstone, 1980. The origin of birds: structure of the tarsus and teeth. The Auk. 97, 86-93.
Bryant, 1983. Hesperornis in Alaska. Paleobios. 40, 1-8.
Martin, 1983. The origin and early radiation of birds. in Bush and Clark (eds). Perspectives in Ornithology. Cambridge University Press, Cambridge. 291-338.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Buhler, 1987. On the mobility of the upper jaw and the segments of the braincase in the Mesozoic birds. in Mourer-Chauvire (ed). L'évolution des oiseaux d'après le témoignage des fossiles. Docum. Lab. Geol. Fac. Sci. Lyon. 99, 41-48.
Martin, 1987. The beginning of the modern avian radiation. in Mourer-Chauvire (ed). L'évolution des oiseaux d'après le témoignage des fossiles. Docum. Lab. Geol. Fac. Sci. Lyon. 99, 9-19.
Witmer and Martin, 1987. The primitive features of the avian palate, with special reference to Mesozoic birds. in Mourer-Chauvire (ed). L'évolution des oiseaux d'après le témoignage des fossiles. Docum. Lab. Geol. Fac. Sci. Lyon. 99, 21-40.
Bühler, Martin and Witmer, 1988. Cranial kinesis in the Late Cretaceous birds Hesperornis and Parahesperornis. The Auk. 105, 111-122.
Nicholls, 1988. Marine vertebrates of the Pembina Member of the Pierre Shale (Campanian, Upper Cretaceous) of Manitoba and their significance to the biogeography of the Western Interior Seaway. PhD Thesis. University of Calgary. 317 pp.
Witmer, 1990. The craniofacial air sac system of Mesozoic birds (Aves). Zoological Journal of the Linnaean Society of London. 100, 327-378.
Elzanowski, 1991. New observations on the skull of Hesperornis with reconstructions of the bony palate and otic region. Postilla. 207, 20 pp.
Martin and Varner, 1992. The occurence of Hesperornis in the Late Cretaceous Niobrara Formation of South Dakota. Proceedings of the South Dakota Academy of Science. 71, 95-97.
Chiappe, 1996. Late Cretaceous birds of Southern South America: Anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. In Arratia (ed.). Contributions of Southern South America to Vertebrate Paleontology. Münchner Geowissenschaftliche Abhandlungen (A). 30, 203-244.
Chinsamy, Martin and Dodson, 1998. Bone microstructure of the diving Hesperornis and the volant Ichthyornis from the Niobrara Chalk of western Kansas. Cretaceous Research. 19(2), 225-233.
Everhart, 2000-2014. http://www.oceansofkansas.com/Hesperornis.html
Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds.). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution. 165-174.
Naples and Martin, 2004. Mandibular kinesis in Hesperornis. Sixth International Meeting of the Society of Avian Paleontology and Evolution, Abstracts. 46.
Reynaud, 2005. Functional morphology of the hindlimbs of Hesperornis regalis: A comparison with modern diving birds. Geological Society of America Abstracts with Programs. 37(7), 133.
Reynaud, 2006. Hindlimb and pelvis proportions of Hesperornis regalis: A comparison with extant diving birds. Journal of Vertebrate Paleontology. 26(3), 115A.
Martin and Naples, 2008. Mandibular kinesis in Hesperornis. Oryctos. 7, 61-65.
Zinoviev, 2009. Notes on hindlimb myology and syndesmology of Hesperornis regalis (Aves: Hesperornithiformes). Journal of Vertebrate Paleontology. 29(3), 207A.
Everhart, 2011. Rediscovery of the Hesperornis regalis Marsh 1871 holotype locality indicates an earlier stratigraphic occurrence. Transactions of the Kansas Academy of Science. 114(1-2), 59-68.
Zinoviev, 2011. Notes on the hindlimb myology and syndesmology of the Mesozoic toothed bird Hesperornis regalis (Aves: Hesperornithiformes). Journal of Systematic Palaeontology. 9(1), 65-84.
Wilson and Chin, 2014. Comparative osteohistology of Hesperornis with reference to pygoscelid penguins: The effects of climate and behaviour on avian bone microstructure. Royal Society Open Science. 1(3), 140245.
Zinoviev, 2015. Comparative anatomy of the intertarsal joint in extant and fossil birds: Inferences for the locomotion of Hesperornis regalis (Hesperornithiformes) and Emeus crassus (Dinornithiformes). Journal of Ornithology. 156(supp 1), 317-323.
Aotsuka and Sato, 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, southern Manitoba, Canada. Cretaceous Research. 63, 154-169.
Caggiano and Witmer, 2016. The anatomy of the nasal salt gland of extant birds and its relevance for inferring the behavior and habitat preferences of extinct birds and other archosaurs. Journal of Vertebrate Paleontology. Program and Abstracts, 108.
Dumont, Tafforeau, Bertin, Bhullar, Field, Schulp, Strilisky, Thivichon-Prince, Viriot and Louchart, 2016. Synchrotron imaging of dentition provides insights into the biology of Hesperornis and Ichthyornis, the "last" toothed birds. BMC Evolutionary Biology. 16:178.
Wilson, Chin and Cumbaa, 2016. A new hesperornithiform (Aves) specimen from the Late Cretaceous Canadian High Arctic with comments on high-latitude hesperornithiform diet. Canadian Journal of Earth Sciences. 53(12), 1476-1483.
unnamed clade (Hesperornis bazhanovi + Hesperornis crassipes + Hesperornis rossicus)
Diagnosis (proposed) metatarsal II trochlea almost completely hidden in anterior view (also in Pasquiaornis and Enaliornis? sedgwicki).
H. crassipes (Marsh, 1876) Marsh, 1880
= Lestornis crassipes Marsh, 1876
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US
Holotype- (YPM 1474) partial skeleton including dentary fragment, anterior angular, teeth, atlantal centrum, fourth cervical vertebra (24 mm), coracoid, clavicle (~80 mm), sternum (196 mm), partial femur (103 mm), patella (109 mm), tarsometatarsi (135 mm), phalanx II-1 (40.5 mm), phalanx III-1 (39 mm), phalanx IV-1 (42 mm), phalanx IV-2 (38 mm)
Referred- ?(AMNH 5102) incomplete tarsometatarsus (Nessov and Yarkov, 1993)
Diagnosis- (after Marsh, 1876) shallow posterolateral excavation in sternum; large proximolateral rugosity on metatarsal II.
(proposed) coracoid articulations on sternum widely separated (unknown in other Hesperornis; also in Patagopteryx).
Other diagnoses- Marsh (1876) also noted the sternum had five rib articulations as opposed to H. regalis' four, but this is primitive as Baptornis and Ichthyornis also have five. The less excavated posterolateral sternal margin has uncertain polarity, as Ichthyornis' is also shallow, whereas Gansus' is very deep.
Contra Marsh (1880), the tarsometatarsus does not appear more robust than in H. regalis.
Comments- Discovered in 1876, the specimen described that year by Marsh as a new genus of hesperornithid. Marsh (1880) placed it in Hesperornis without comment, provided illustrations and further measurements. The angular is illustrated by Gregory (1952). The species was accepted as valid by Martin (1984), but it desperately needs to be redescribed. The tarsometatarsus as illustrated by Marsh is quite distinct in shape from other Hesperornis, but the taxon clades within Hesperornis when included in phylogenetic analyses (Mortimer, unpublished; Bell and Chiappe, 2016).
References- Marsh, 1876. Notice of new Odontornithes. The American Journal of Science and Arts. 11, 509-511.
Marsh, 1880. Odontornithes: a monograph on the extinct toothed birds of North America. United States Geological Exploration of the 40th Parallel. Washington, DC: U.S. Government Printing Office. 201 pp.
Shufeldt, 1915a. The fossil remains of a species of Hesperornis found in Montana. The Auk. 32(3), 290-284.
Gregory, 1952. The jaws of the Cretaceous toothed birds Ichthyornis and Hesperornis. Condor. 54(2), 73-88.
Martin, 1984. A new hesperornithid and the relationships of the Mesozoic birds. Kansas Academy of Science, Transactions. 87, 141-150.
Nessov and Yarkov, 1993. [Hesperornithes in Russia] Russkii Ornitolocheskii Zhurnal. 2(1), 37-54.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
H. rossicus Nessov and Yarkov, 1993
Early Campanian, Late Cretaceous
Bellemnellocamax mamillatus zone, Rychkovo, Volgograd, Russia
Holotype- (VRM 26306/2) proximal tarsometatarsus (~173 mm)
Paratypes- (VRM 26306/2a) partial sixteenth cervical vertebra
(VRM 26306/26) pedal phalanx IV-3
(VRM 26306/3) distal tarsometatarsus
(VRM coll.) dorsal vertebral fragment
Referred- (ZIN PO 5099) (subadult) proximal tarsometatarsal fragment (Nessov and Yarkov, 1993)
? posterior dorsal vertebra, proximal tarsometatarsus (Yarkov and Nessov, 2000)
Early Campanian, Late Cretaceous
Bellemnellocamax mamillatus zone, Ivo Klack, Sweden
Paratype- (RM PZ R398) proximal tarsometatarsus
Referred- ?(LO 9067t) distal tibiotarsus (Mourer-Chauvire, 1992)
(SGU 3442 Ve01) proximal tarsometatarsus (Rees and Lindgren, 2005)
?(SGU 3442 Ve02) fifth dorsal vertebra (32 mm) (Rees and Lindgren, 2005)
Early Campanian, Late Cretaceous
Rybushka Formation, Saratov, Russia
(ZIN PO 5463) distal tarsometatarsus (~167 mm) (Panteleev, Popov and Averianov, 2004)
(ZIN PO 5464) (subadult) incomplete tarsometatarsus (158.8 mm) (Panteleev, Popov and Averianov, 2004)
Late Campanian, Late Cretaceous
Bereslavka, Vologograd, Russia
distal tarsometatarsal fragment (Yarkov and Nessov, 2000)
Mid Campanian, Late Cretaceous
Millwood Member of the Pierre Shale Group, Manitoba, Canada
?(CFDC B.2010.01.23) proximal tarsometatarsus (Aotsuka et al., 2012; described by Aotsuka and Sato, 2016)
Diagnosis- (after Nessov and Yarkov, 1993) adult size with tarsometarsus over 150 mm long (also in Canadaga).
(after Kurochkin, 2000) proximal end of tarsometatarsus over 160% wider than deep.
(after Panteleev et al., 2004) tarsometatarsal trochlea IV over 250% as wide as trochlea III in anterior view.
Other diagnoses- Kurochkin (2000) listed several diagnostic characters. The proximal tarsometatarsal articular surface is not more diagonally oriented than in H. crassipes or H. bairdi. The lateral edge of the lateral cotyla does not extend proximally past the intercotylar eminance, contra Kurochkin. He states the medial cotyla is located more distally than the lateral cotyla, which may be the same character as Rees and Lindgren's (2005) "cotyla medialis slopes distally in regard to the nearly horizontal plane formed by the cotyla lateralis." However, it seems Rees and Lindgren mistook their proximal metatarsus SGU 3442 Ve01 as a left element when it is in fact from the right side. Perhaps Kurochkin made the same mistake with the holotype, as the lateral condyle is more distally placed in all specimens, which is typical of hesperornithids.
Panteleev et al. (2004) noted the inner toes were reduced, and while it seems trochlea IV was indeed enlarged compared to III, the size of II is uncertain due to damage. The absence of a ginglymoid trochlea II and III is shared with Hesperornis mengeli, while trochlea II is equally hidden behind metatarsal III in H. bazhanovi and crassipes.
Rees and Limdgren (2005) listed a few additional diagnostic characters. They state the cotyla have less curvature, but this seems untrue of lateral cotyla at least, while the concavity of H. bazhanovi's medial cotyla does not seem very different. The intercotylar eminence does not seem more pointed than Hesperornis bazhanovi, H. chowi or H. bairdi.
Comments- This species was originally named H. rossica, but must be emended to rossicus as Hesperornis is masculine (Kurochkin, 2000). The holotype was first reported by Nessov (in Mourer-Chauvire, 1991) as "an advanced hesperornithiform." The two vertebral fragments and pedal phalanx were referred to H. rossicus by Nessov and Yarkov (1993), though Kurochkin and Rees and Lindgren (2005) felt this was problematic due to the presence of ZIN PO 5099. ZIN PO 5099 was originally referred to Hesperornis sp. by Nessov and Yarkov (1993), but determined to be a young specimen of H. rossicus by Panteleev et al. (2004). Thus only H. rossicus is known from that locality, which makes the referral of the vertebrae and phalanx more probable. Yarkov and Nessov (2000) referred a tarsometatarsal fragment reworked to Paleocene deposits at Bereslavka to Hesperornithidae indet., but Panteleev et al. (2004) referred it to H. rossicus. Yarkov and Nessov also described a proximal tarsometatarsus and dorsal vertebra as Hesperornis sp., which is tentatively referred to H. rossicus here, as it is from the same locality. Rees and Lindgren (1999, 2005) described a dorsal vertebra and partial tibiotarsus as Hesperornis sp., but these are here provisionally referred to H. rossicus due to the presence of only one known hesperornithid at that locality and their large size. LO 9067t had been previously mentioned as a possible large hesperornithine by Nessov (in Mourer-Chauvire, 1992).
References- Mourer-Chauvire, 1991. Society of Avian Paleontology and Evolution Information Newsletter. 5.
Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6.
Nessov, 1992. [Flightless birds of meridional Late Cretaceous sea straits of North America, Scandinavia, Russia and Kazakhstan as indicators of features of oceanic circulation.] Byulleten Moskovskogo Obshchestva Ispytatelet Prirody Otdel Geologicheskii. 67, 78-83.
Nessov and Yarkov, 1993. [Hesperornithes in Russia] Russkii Ornitolocheskii Zhurnal. 2(1), 37-54.
Rees and Lindgren, 1999. Early Campanian hesperornithiform birds from the Kristianstad Basin, southern Sweden. in Hoch and Brantsen (eds). Secondary adaptation to life in water. Abstracts. University of Copenhagen, Copenhagen. 53.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Yarkov and Nessov, 2000. New remains of hesperornithiform birds Hesperornithiformes from the Volgograd Reigion. Russkii Ornitolocheskii Zhurnal, Ekspress Vypusk. 94, 3-12. [in Russian]
Panteleev, Popov and Averianov, 2004. New record of Hesperornis rossicus (Aves, Hesperornithiformes) in the Campanian of Saratov Province, Russia. Paleontological Research. 8(2), 115-122.
Rees and Lindgren, 2005. Aquatic birds from the Upper Cretaceous (Lower Campanian) of Sweden and the biology and distribution of hesperornithiforms. Palaeontology. 48(6), 1321-1329.
Aotsuka, Hatcher, Janzic and Sato, 2012. Diversity of the Hesperornithiformes (Aves) from the Upper Cretaceous Pierre Shale in southern Manitoba, Canada. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 57.
Aotsuka and Sato, 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, southern Manitoba, Canada. Cretaceous Research. 63, 154-169.
H. bazhanovi (Nessov and Prizemlin, 1991) new combination
= Asiahesperornis bazhanovi Nessov and Prizemlin, 1991
Maastrichtian, Late Cretaceous
Zhuravlovskaya Svita (not Eginsaiskaya Svita), Kazakhstan
Holotype- (IZASK 5/287/86a) incomplete tarsometatarsus (~122 mm)
Paratypes- (IZASK 5/287/86) dorsal vertebra
(IZASK 5/287/86b) partial tarsometatarsus
(IZASK 5/287/86B) distal tibiotarsus
(IZASK 5/293/87) dorsal vertebra
Referred- (IZASK 1/KM 97) proximal tarsometatarsus (~120-125 mm) (Malakhov and Ustinov, 1998)
(IZASK 2/KM 97) cervical vertebra (Malakhov and Ustinov, 1998)
(IZASK 3/KM 97) partial tarsometatarsus (~80-90 mm) (Malakhov and Ustinov, 1998)
(IZASK 5/KM 97) distal femur (~60-70 mm) (Malakhov and Ustinov, 1998)
(IZASK 22/KM 97) tooth (Malakhov and Ustinov, 1998)
(IZASK 218/B-2003) partial tibiotarsus (Dyke et al., 2006)
(IZASK 220/B-2003) partial tarsometatarsus (Dyke et al., 2006)
? two distal tibiotarsi, proximal tarsometatarsus (Nessov in Mourer-Chauvire, 1992)
Diagnosis- (after Nessov and Prizemlin, 1991) (?) medial tibiotarsal condyle markedly compressed transversely; (?) anterior intercondylar groove deep; (?) scar for the attachment of the first metatarsal is very small, located proximally on the shaft.
(proposed) round fossa around distal vascular foramen between metatarsals III and IV.
Other diagnoses- Kurochkin (2000) listed the characters from Nessov and Prizemlin's (1991) diagnosis (which has not been translated from Russian) which he considered were not generalized hesperornithine characters. The gracility and parallel sides of the tarsometatarsus are plesiomorphies compared to Hesperornis regalis. The sharp posterolateral tarsometatarsal crest is also present in Hesperornis bairdi, while a sharp posteromedial crest is present in H. bairdi, H? mengeli and Parahesperornis. A deep proximodorsal metatarsal III fossa is also present in Hesperornis and Parahesperornis, while those of H. regalis and H. chowi are equally narrow. The high dorsolateral crest by this feature is not easily observable in the figures, so cannot be compared to other taxa. Hesperornis chowi and Parahesperornis also have an expanded fossa distally between metatarsals III and IV, though they are not as round as in Asiahesperornis. Trochlea IV is larger compared to III in Hesperornis crassipes, H? mengeli and H. rossicus than in bazhanovi. The remaining characters listed above aren't possible to see in the published figures, making comparison to other taxa and thus their diagnostic status uncertain. However, compressed medial tibiotarsal condyles and deep intercondylar grooves are present in most derived hesperornithines.
Dyke et al. (2006) listed a couple additional features in their diagnosis. Hesperornis and Parahesperornis also have prominent medial and lateral grooves on the dorsal tarsometatarsus between the metatarsals. Hesperornis regalis and H. bairdi both have well developed grooves on the posterior surface of their third trochlea.
Comments- The type material was first reported by Prizemlin and Nessov (in Mourer-Chauvire, 1990) as "a large hesperornithiform bird of a new genus, and maybe a new family." Nessov and Prizemlin (1991) later described it as the new genus Asiahesperornis, which they placed in a new subfamily Asiahesperornithinae. Yet comparisons suggest the species is more similar to Hesperornis regalis than some other species assigned to that genus such as H. gracilis, H. bairdi and H? mengeli, where is is resolved in phylogenetic analyses (Mortimer, unpublished; Bell and Chiappe, 2016). Thus it is placed within Hesperornis here, in a combination not seen in the literature.
The stratigraphy of the Kushmurun Quarry where Asiahesperornis is found has been controversial, with Dyke et al. (2006) assigning it to the Zhuravlovskaya Svita, not the Eginsaiskaya Svita as found in Nessov in Mourer-Chauvire (1992) and Kurochkin (2000). IZASK 5/287/86 was originally misidentified as a cervical vertebra by Nessov and Prizemlin (1991), but reidentified by Kurochkin (2000). This material is only provisionally referred to a single taxon of hesperornithine, based on size. Nessov and Yarkov (1993) later illustrated IZASK 5/293/87 and 5/287/86B as merely "hesperornithiforms" and provisionally assigned IZASK 5/287/86b to another species, but Dyke et al. found no reason to doubt their assignment to Asiahesperornis. Bell and Chiappe (2020) stated dentary IZASK 4/KM 97 "shows clear alveoli for the teeth. As this is not the case among other hesperornithiforms, and the Asiahesperornis material consists entirely of unassociated elements, it is unlikely this specimen belongs to a hesperornithiform bird" and reassigned it to Aves incertae sedis.
References- Mourer-Chauvire, 1990. Society of Avian Paleontology and Evolution Information Newsletter. 4.
Nessov and Prizemlin, 1991. A large advanced flightless marine bird of the order Hesperornithiformes of the Late Senonian of Turgai Strait - the first finding of the group in the USSR. USSR Academy of Sciences, Proceedings of the Zoological Institute. 239, 85-107 (in Russian).
Mourer-Chauvire, 1992. Society of Avian Paleontology and Evolution Information Newsletter. 6.
Nessov and Yarkov, 1993. [Hesperornithes in Russia] Russkii Ornitolocheskii Zhurnal. 2(1), 37-54.
Malakhov and Ustinov, 1998. New findings of Upper Cretaceous toothed birds (Aves; Hesperornithiformes) in northern Kazakhstan. Kazakh State University Yearbook, Biological Series. 1998, 162-167 (in Russian).
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. 533-559.
Dyke, Malakhov and Chiappe, 2006. The hesperornithiform bird Asiahesperornis from Kushmurun, Northern Kazakhstan. Journal of Vertebrate Paleontology. 26(3), 57A-58A.
Dyke, Malakhov and Chiappe, 2006. A re-analysis of the marine bird Asiahesperornis from northern Kazakhstan. Cretaceous Research. 27(6), 947-953.
Bell and Chiappe, 2016 (online 2015). A species-level phylogeny of the Cretaceous Hesperornithiformes (Aves: Ornithuromorpha): Implications for body size evolution amongst the earliest diving birds. Journal of Systematic Palaeontology. 14(3), 239-251.
Bell and Chiappe, 2020. Anatomy of Parahesperornis: Evolutionary mosaicism in the Cretaceous Hesperornithiformes (Aves). Life. 10(5), 62.
H? sp. (Bryant, 1983)
Coniacian-Campanian, Late Cretaceous
Ignek Formation, Alaska, US
Material- (UCMP 103841) (subadult) partial third dorsal vertebra, partial fourth dorsal vertebra, partial fifth dorsal vertebra
Comments- This specimen was discovered in 1962 and described by Bryant (1983) as Hesperornis sp.. He found no differences between it and H. regalis specimen USNM 13580, and thought differences from the H. regalis holotype were due to age. However, other hesperornithines are difficult to compare, so the generic assignment should be provisional.
Reference- Bryant, 1983. Hesperornis in Alaska. Paleobios. 40, 1-8.
H. sp. (Hills, Nicholls, Núñez-Betelu and McIntyre, 1999)
Early-Middle Campanian, Late Cretaceous
Kanguk Formation, Nunavut, Canada
Material- ?(CMN 40824) (Wilson and Chin, 2014)
(NUVF 286) (subadult) four teeth (5.0-6.2 mm), vertebral fragments, rib fragments, ilia (one partial, one fragmentary), femora (91.8, 94.5 mm), tibiotarsal fragments, few elements (uncollected) (Wilson, 2012; Wilson, Chin and Cumbaa, 2016)
(TMP 1997.004.0001) distal tarsometatarsus (Hills, Nicholls, Núñez-Betelu and McIntyre, 1999)
Comments- CMN 40824 was found in June 1988 and was listed by Wilson and Chin (2014) as one of the "Arctic specimens identified as hesperornithiforms in museum collections", but is currently identified as indet. in the collection so is probably one of the specimens which "could not be confidently attributed to Hesperornis or even Aviale."
TMP 1997.004.0001 was found in July 1992 and was referred to Hesperornis sp. by Hills et al. (1999).
NUVF 286 was found in 2003, initially described in Wilson's (2012) thesis. The latter states "a few associated bones below the specimen could not be collected because they were frozen in permafrost." The thesis was later published as Wilson and Chin (2014) for the histology and Wilson et al. (2016) for the anatomy, where it is referred to cf. Hesperornis sp.. This is due to the uncertain status of Canadaga and controversial synonymy of Hesperornis species, but they do say it is more robust than Parahesperornis.
References- Hills, Nicholls, Núñez-Betelu and McIntyre, 1999. Hesperornis (Aves) from Ellesmere Island and palynological correlation of known Canadian localities. Canadian Journal of Earth Sciences. 36(9), 1583-1588.
Wilson. 2012. Paleobiology of hesperornithiforms (Aves) from the Campanian Western Interior Seaway of North America, with analyses of extant penguin bone histology. PhD thesis, University of Colorado. 150 pp.
Wilson and Chin, 2014. Comparative osteohistology of Hesperornis with reference to pygoscelid penguins: The effects of climate and behaviour on avian bone microstructure. Royal Society Open Science. 1(3), 140245.
Wilson, Chin and Cumbaa, 2016. A new hesperornithiform (Aves) specimen from the Late Cretaceous Canadian High Arctic with comments on high-latitude hesperornithiform diet. Canadian Journal of Earth Sciences. 53(12), 1476-1483.
H. cf. regalis (Russell, 1967)
Early Campanian, Late Cretaceous
Smoking Hills Formation, Northwest Territories, Canada
Material- (CMN 10431) (adult) tarsometatarsal fragment
(CMN 10432) (subadult) ?tibiotarsal fragment, tarsometatarsus
(CMN 10433) (subadult) tarsometatarsus
(CMN 10434A) (adult) first sacral vertebra (22.0 mm), fragmentary tibiotarsi
(CMN 10434B) (subadult) third dorsal vertebra (22.0 mm), fourth dorsal vertebra (22.0 mm), fifth dorsal vertebra (21.5 mm), dorsal vertebra, sacral fragments, pelvic fragments, femora, tibiotarsus, tarsometatarsus
(CMN 10437) (subadult) tarsometatarsal fragments
(CMN 10441) (adult) sternal fragments, sternal ribs, femur (48.0 mm trans dist), tibiotarsal shaft
(CMN 10442) (subadult) tarsometatarsal fragment
(CMN 10446) (adult) fifth dorsal vertebra (~32 mm)
(CMN 10551) (juvenile) preacetabular process
Comments- Russell (1967) referred remains found in 1965 to Hesperornis regalis as "their morphology in no way distinguishes them from corresponding elements of Hesperornis regalis", but according to Martin and Lim these may H. chowi instead. However, the "brown beds" of the Anderson River are not from the same formation as H. chowi.
References- Russell, 1967. Cretaceous vertebrates from the Anderson River, N.W.T. Canadian Journal of Earth Sciences. 4(1), 21-38.
Martin and Lim, 2002. New information on the hesperornithiform radiation. In Zhou and Zhang (eds.). Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution. 165-174.
H. sp. (Hills, Nicholls, Núñez-Betelu and McIntyre, 1999)
Late Campanian-Early Maastrichtian, Late Cretaceous
Mason River Formation, Northwest Territories, Canada
Reference- Hills, Nicholls, Núñez-Betelu and McIntyre, 1999. Hesperornis (Aves) from Ellesmere Island and palynological correlation of known Canadian localities. Canadian Journal of Earth Sciences. 36(9), 1583-1588.
H? sp. (Wilson, 2012)
Late Cretaceous
Horton River, Northwest Terrotories, Canada
Material- (CMN 11409) element
(CMN 11421) element
(CMN 11441) element
Late Cretaceous
Eglinton Island, Northwest Terrotories, Canada
(CMN 40730) element
Late Cretaceous
Devon Island, Nunavut, Canada
(CMN 51580) element
(CMN 51585) element
Comments- These were collected in 1966 (CMN 11409, 11421, 11441), 1972 (CMN 40730), July 20 1998 (CMN 51580) and July 25 1998 (CMN 51585), and are in the CMN catalog as Hesperornis sp. (CMN 11421, 11441, 40730, 51580) or cf. Hesperornis (CMN 11409, 51585). Wilson (2012; published as Wilson and Chin, 2014) stated that for these (and CMN 40824 from the Kanguk Formation) "microbial alteration obscured the microstructure of three of these bones, and the other five specimens could not be confidently attributed to Hesperornis or even Aviale." They are among the specimens Wilson et al. (2016) are referring to when they state "undescribed specimens attributed to hesperornithiforms have also been collected from Eglinton Island and Horton River (Northwest Territories), and are housed at the CMN."
References- Wilson. 2012. Paleobiology of hesperornithiforms (Aves) from the Campanian Western Interior Seaway of North America, with analyses of extant penguin bone histology. PhD thesis, University of Colorado. 150 pp.
Wilson and Chin, 2014. Comparative osteohistology of Hesperornis with reference to pygoscelid penguins: The effects of climate and behaviour on avian bone microstructure. Royal Society Open Science. 1(3), 140245.
Wilson, Chin and Cumbaa, 2016. A new hesperornithiform (Aves) specimen from the Late Cretaceous Canadian High Arctic with comments on high-latitude hesperornithiform diet. Canadian Journal of Earth Sciences. 53(12), 1476-1483.
H. sp.
Late Campanian, Late Cretaceous
Foremost Formation, Alberta, Canada
Material- (UCMP 108074) tarsometatarsus (UCMP online)
H. sp. (Bardack, 1968)
Turonian-Santonian, Late Cretaceous
Boyne Member of the Vermillion River Formation, Manitoba, Canada
Material- (FMNH 219) braincase fragment, posterior mandible, seven incomplete dorsal vertebrae, femora, partial tibiotarsus, tarsometatarsus
Comments- These were collected in 1965 and referred to H. regalis by Bardack (1968). Witmer (1990) notes the postcranium is slightly more gracile and that differences exist in middle ear morphology, making that assignment uncertain. This is especially true with the recent description of other species similar to H. regalis, such as H. chowi.
References- Bardack, 1968. Fossil vertebrates from the marine Cretaceous of Manitoba. Canadian Journal of Earth Sciences. 5, 145-153.
Witmer, 1990. The craniofacial air sac system of Mesozoic birds (Aves). Zoological Journal of the Linnaean Society of London. 100, 327-378.
H. sp. nov. (Tanaka, Kobayashi, Kurihara, Kano and Fiorillo, 2014)
Early Campanian, Late Cretaceous
Gammon Ferruginous Member of Pierre Shale Group, Manitoba, Canada
Material- (V-2487) (adult) distal femur, patella, tibiotarsi, proximal tarsometatarsus, distal tarsometatarsus, several pedal phalanges
Diagnosis- (after Tanaka et al., 2015) medially positioned foramen for M. ambiens on patella; flat femur with strong lateral orientation of fibular trochlea.
Comments- Tanaka et al. (2014) referred to an unnamed hesperornithid from Manitoba with the specimen number V-2487 that emerged in Hesperornis as here used, which was later detailed by Tanaka et al. (2015) but has yet to be formally described.
References- Tanaka, Kobayashi, Kurihara, Kano and Fiorillo, 2014. Phylogenetic position of a new hesperornithiform from the Upper Cretaceous of Hokkaido, Japan. Journal of Vertebrate Paleontology. Program and Abstracts 2014, 239.
Tanaka, Tokaryk and Kobayashi, 2015. A new small hesperornithiform from the Upper Cretaceous Pierre Shale of Manitoba. Journal of Vertebrate Paleontology. Program and Abstracts 2015, 223.
H. sp. (Bardack, 1968)
Early Campanian, Late Cretaceous
Gammon Ferruginous Member of the Pierre Shale Group, Manitoba, Canada
Material- (CFDC B.2010.02.13) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.2011.02.13) femur (Aotsuka and Sato, 2016)
(CFDC B.2011.03.13) (2 individuals) two tarsometatarsi (Aotsuka and Sato, 2016)
(CFDC B.2011.05.13) tarsometatarsus (Aotsuka and Sato, 2016)
Mid Campanian, Late Cretaceous
Pembina Member of the Pierre Shale Group, Manitoba, Canada
(CFDC B.00.02.00; lost) femur (Aotsuka and Sato, 2016)
(CFDC B.00.02.15-1) vertebra, tibiotarsus, tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.00.04.00) femur (Aotsuka and Sato, 2016)
(CFDC B.00.04.03) femur (Aotsuka and Sato, 2016)
(CFDC B.00.06.00) femur (Aotsuka and Sato, 2016)
(CFDC B.00.07.00; lost) femur (Aotsuka and Sato, 2016)
(CFDC B.00.08.00) femur (Aotsuka and Sato, 2016)
(CFDC B.00.09.00) femur (Aotsuka and Sato, 2016)
(CFDC B.00.10.05) femur (Aotsuka and Sato, 2016)
(CFDC B.00.11.05) femur (Aotsuka and Sato, 2016)
(CFDC B.00.13.00) femur (Aotsuka and Sato, 2016)
(CFDC B.00.12.05) femur (Aotsuka and Sato, 2016)
(CFDC B.00.14.00) femur (Aotsuka and Sato, 2016)
(CFDC B.00.15.00) femur (Aotsuka and Sato, 2016)
(CFDC B.00.16.00) femur (Aotsuka and Sato, 2016)
(CFDC B.00.19.00) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.00.21.00) femur (Aotsuka and Sato, 2016)
(CFDC B.00.26.00) femur, tarsometarsus (Aotsuka and Sato, 2016)
(CFDC B.00.28.00) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.00.29.00) femur (Aotsuka and Sato, 2016)
(CFDC B.00.30.00) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.00.31.00) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.00.32.00) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.00.34.00) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.00.36.00) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.00.42.00) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.00.56.00; lost) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.00.59.05; lost) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.00.61.05; lost) femur (Aotsuka and Sato, 2016)
(CFDC B.01.01.15) femur (Aotsuka and Sato, 2016)
(CFDC B.01.04.13) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.02.01.21) fibula, tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.03.01.24) femur (Aotsuka and Sato, 2016)
(CFDC B.03.03.05) femur (Aotsuka and Sato, 2016)
(CFDC B.06.03.03) femur (Aotsuka and Sato, 2016)
(CFDC B.06.04.23) femur (Aotsuka and Sato, 2016)
(CFDC B.07.02.15) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.09.01.30) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.72.01.01) femur (Aotsuka and Sato, 2016)
(CFDC B.73.02.05) vertebra, tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.76.03.06) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.76.04.06) femur (Aotsuka and Sato, 2016)
(CFDC B.77.01.06) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.77.02.09; lost) synsacrum, femur, tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.78.01.07) fragmentary femur (Aotsuka and Sato, 2016)
(CFDC B.79.02.12) femur (Aotsuka and Sato, 2016)
(CFDC B.79.03.13) (?)tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.79.08.13) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.80.00.14) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.80.01.15) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.80.03.15) femur (Aotsuka and Sato, 2016)
(CFDC B.80.04.14) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.80.06.14) femur (Aotsuka and Sato, 2016)
(CFDC B.80.07.14) femur (Aotsuka and Sato, 2016)
(CFDC B.80.10.16; lost) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.80.11.16) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.80.12.16) tibiotarsi (Aotsuka and Sato, 2016)
(CFDC B.81.01.16) tibiotarsi (Aotsuka and Sato, 2016)
(CFDC B.81.02.16) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.81.04.16) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.81.07.16) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.81.10.16) femora (Aotsuka and Sato, 2016)
(CFDC B.82.01.17) vertebra, ilium, tibiotarsi, tarsometatarsi (Aotsuka and Sato, 2016)
(CFDC B.82.03.17) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.82.06.03) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.82.10.17) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.82.11.17; lost) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.83.02-2.18) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.84.02.18) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.84.03.18) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.84.05.18) femur (Aotsuka and Sato, 2016)
(CFDC B.85.01.03) femur (Aotsuka and Sato, 2016)
(CFDC B.2010.04.13) femur (Aotsuka and Sato, 2016)
(CFDC B.2011.01.03) tibiotarsus (Aotsuka and Sato, 2016)
(FMNH PA216) femur, tibiotarsus (Bardack, 1968)
(FMNH PA217; lost) femur, tibiotarsus (Bardack, 1968)
(FMNH PA286) distal femur (Aotsuka and Sato, 2016)
(FMNH PA289) tibiotarsus (Aotsuka and Sato, 2016)
(FMNH PA291) vertebral fragment, femur (Aotsuka and Sato, 2016)
(FMNH PA292) tibiotarsus (Aotsuka and Sato, 2016)
(MM P-532; lost) femur (Bardack, 1968)
(MM V-247B) femur (Aotsuka and Sato, 2016)
(MM V-395) femur (Aotsuka and Sato, 2016)
(MM V-606A) femur (Aotsuka and Sato, 2016)
(MM V-606B) femur (Aotsuka and Sato, 2016)
(MM V-607) femur (Aotsuka and Sato, 2016)
(MM V-608) femur (Aotsuka and Sato, 2016)
(MM V-1629) vertebra, femur (Aotsuka and Sato, 2016)
(MM coll.; lost) seven tibiotarsi (Aotsuka and Sato, 2016)
(ROM coll.) six femora, four tibiotarsi (Aotsuka and Sato, 2016)
Mid Campanian, Late Cretaceous
Millwood Member of the Pierre Shale Group, Manitoba, Canada
(CFDC B.02.02.05) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.06.03.15) tibiotarsus (Aotsuka and Sato, 2016)
(CFDC B.08.05.23) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.81.03.16) femur (Aotsuka and Sato, 2016)
(CFDC B.2010.01.15) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.2010.01.30) tarsometatarsus (Aotsuka and Sato, 2016)
(CFDC B.2010.03.23) femur (Aotsuka and Sato, 2016)
(CFDC B.2011.01.23) femur (Aotsuka and Sato, 2016)
(CFDC B.2011.02.23) tarsometatarsus (Aotsuka and Sato, 2016)
Comments- Several specimens were referred to H. regalis by Bardack (1968). Nicholls and Russell (1990) stated 170 specimens of Hesperornis were known from the Pembina Member, which presumably included those listed above whose CFDC catalog numbers indicate they were catalogued before this (the number after the B). These were detailed by Aotsuka and Sato (2016), who assigned most to Hesperornis sp..
References- Bardack, 1968. Fossil vertebrates from the marine Cretaceous of Manitoba. Canadian Journal of Earth Sciences. 5, 145-153.
Nicholls and Russell, 1990. Paleobiogeography of the Cretaceous Western Interior Seaway of North America: The vertebrate evidence. Palaeogeography, Palaeoclimatology, Palaeoecology. 79, 149-169.
Aotsuka and Sato, 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous Pierre Shale, southern Manitoba, Canada. Cretaceous Research. 63, 154-169.
H. sp. (Macdonald, 1951)
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, South Dakota, US
Material- partial skeletons
Comments- Nicholls and Russell (1990) listed sixty-five specimens of Hesperornis from this formation, though some are probably the types of H. bairdi, H. chowi, H. macdonaldi or H. mengeli.
Reference- Macdonald, 1951. The fossil Vertebrata of South Dakota. in Guidebook, Fifth Field Conference, Society of Vertebrate Paleontology. 63-74.
Nicholls and Russell, 1990. Paleobiogeography of the Cretaceous Western Interior Seaway of North America: the vertebrate evidence. Palaeogeography, Palaeoclimatology, Palaeoecology. 79, 149-169.
H. sp. (Tokaryk, 1999)
Campanian-Maastrichtian, Late Cretaceous
Pierre Shale Group, Saskatchewan, Canada
Material- (Tokaryk, 1999)
Campanian-Maastrichtian, Late Cretaceous
Pierre Shale Group, South Dakota, US
Material- (UCMP 113168) femur, tibiotarsus, pedal phalanges (UCMP online)
(UCMP 113169) tarsometatarsus (UCMP online)
(UCMP 113170) vertebrae (UCMP online)
(UCMP 123257) vertebral fragments, patella, pedal phalanges (UCMP online)
(UCMP 123258) femur (UCMP online)
(UCMP 123259) incomplete skeleton (UCMP online)
(USNM 244158) femur (USNM online)
(USNM 244159) proximal tibiotarsus, distal tibiotarsus (USNM online)
(USNM 244160) femur (USNM online)
(USNM 244161) tarsometatarsus (USNM online)
(USNM 244163) femur (USNM online)
(YPM PU 17193) femur (88 mm), patella, tibiotarsus, fibula (200.2 mm) (Wilson, Chin and Cumbaa, 2016)
Comments- These may be H. bairdi, H. chowi, H? macdonaldi or H? mengeli based on stratigraphy.
References- Tokaryk, 1999. The toothed bird Hesperornis sp. (Hesperornithiformes) from the Pierre Shale (Late Cretaceous) of Saskatchewan. The Canadian Field-Naturalist. 113(4), 670-672.
Wilson, Chin and Cumbaa, 2016. A new hesperornithiform (Aves) specimen from the Late Cretaceous Canadian High Arctic with comments on high-latitude hesperornithiform diet. Canadian Journal of Earth Sciences. 53(12), 1476-1483.
H? sp. (Hilton, 2003)
Campanian, Late Cretaceous
Chico Formation, California, US
Material- (SC-VBHE1) pedal phalanx
Reference- Hilton, 2003. Dinosaurs and Other Mesozoic Reptiles of California. University of California Press. 312 pp.
H. sp. (UCMP online)
Late Cammpanian, Late Cretaceous
Judith River Formation, Montana, US
Material- (UCMP 128365) proximal tarsometatarsus (UCMP online)
(UCMP 128366) distal tarsometatarsus (UCMP online)
H? sp. (Hutchinson, 2001)
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, Montana, US
Material- (MOR 971) tarsometatarsus (MOR online)
(MOR 975) distal tarsometatarsus (MOR online)
(UCMP 130124) proximal femur (Hutchinson, 2001)
(UCMP 131164) femur (Hutchinson, 2001)
Comments- The UCMP specimens are referred to cf. Hesperornis by Hutchinson (2001), while the MOR specimens are referred to Hesperornis in the museum's collection. The stratigraphic position suggests comparison to Potamornis, though without a description any identification must remain uncertain.
Reference- Hutchinson, 2001. The evolution of femoral osteology and soft tissues on the line to extant birds (Neornithes). Zoological Journal of the Linnaean Society. 131, 169-197.
H. sp. (Case, 1978)
Late Campanian, Late Cretaceous
Teapot Sandstone Member of the Mesaverde Formation, Wyoming, US
Material- (YPM PU 22390) partial tarsometatarsus (Case, 1978)
(YPM PU 22406) sternal fragment, three femora, fragments (Case, 1978)
(YPM PU 22407) distal tibiotarsal fragment (Case, 1978)
(YPM PU 22408) distal tibiotarsal fragment (Case, 1978)
(YPM PU 22437) three vertebrae, synsacrum, two phalanges (Case, 1978)
(YPM PU 22438) distal metatarsal IV (Case, 1978)
(YPM PU 22443) vertebrae, limb elements including tibiotarsus (Houde, 1987)
(YPM PU 22948) frontal (YPM online)
(YPM PU 22949) articular (YPM online)
Comments- Houde (1987) reported on the histology of YPM PU 22443, calling it Hesperornis sp..
References- Case, 1978. News from members; Eastern region; Jersey City. Society of Vertebrate Paleontology. News Bulletin. 114, 16-17.
Houde, 1987. Histological evidence for the systematic position of Hesperornis (Odontornithes: Hesperornithiformes). The Auk. 104(1), 125-129.
H. sp. (Martin and Tate, 1967)
Middle Campanian, Late Cretaceous
Sharon Springs Formation of the Pierre Shale Group, Nebraska, US
Material- partial skeleton
Comments- This was discovered in 1966, and may be H. bairdi, H. chowi, H? macdonaldi or H? mengeli based on stratigraphy.
Reference- Martin and Tate, 1967. A Hesperornis from the Pierre Shale. Nebraska Academy of Science Proceedings. 77th Annual Meeting. 40.
H. sp. (Shufeldt, 1915a)
Early Campanian, Late Cretaceous
Hesperornis Zone of the Smoky Hill Chalk Member of the Niobrara Formation, Kansas, US
Material- (FSHM 349) specimen including pedal phalanx III-1 (37.2 mm) (Everhart, 2011)
(USNM 244239) tarsometatarsus (USNM online)
(YPM 1475) (YPM online)
(YPM 1479) vertrbral fragments, sacral fragments (Chiappe, 2002)
(YPM 1480) proximal tibiotarsus, phalanx (Chiappe, 2002)
(YPM 1481) sacrum, femur, tibiotarsus, tarsometatarsus (Chiappe, 2002)
(YPM 1482) tibiotarsal fragment (YPM online)
(YPM 1483) vertebral fragments, synsacral fragments (YPM online)
(YPM 1484) synsacral fragments (YPM online)
(YPM 1485) vertebral fragment (YPM online)
(YPM 1486) proximal tarsometatarsal fragments (YPM online)
(YPM 1487) vertebral fragments, synsacral fragments (YPM online)
(YPM 1488) fragments (YPM online)
(YPM 1489) (adult) femur, tibiotarsus, fragments (Chiappe, 2002)
(YPM 1490) vertebral fragments, synsacrum (YPM online)
(YPM 1492) vertebral fragments (YPM online)
(YPM 1493) fragmentary synsacrum (YPM online)
(YPM 1494) fragments (YPM online)
(YPM 1495) vertebral fragment (YPM online)
(YPM 1496) synsacral fragment (YPM online)
(YPM 1497) skull, cervical vertebra(e), rib (YPM online)
(YPM 1498) phalanx (YPM online)
(YPM 1499) cervical vertebrae, dorsal vertebrae, femora, patellae, tibiotarsus, fibulae, tarsometatarsus, pedal phalanx III-1 (39.1 mm) (Shufeldt, 1915a)
Comments- Shufeldt (1915a) quoted Lull as saying YPM 1499 is either H. regalis or H. sp. indet., and is more similar to H. montanus than to H. regalis specimens YPM 1206, 1474 and 1477 in size, general appearence and the shallowness of its lateral central fossae. These specimens are listed by Chiappe (2002) and the YPM collections as being Hesperornis sp., and may be H. regalis, H. gracilis, H. crassipes or even Parahesperornis based on their locality.
References- Shufeldt, 1915a. The fossil remains of a species of Hesperornis found in Montana. The Auk. 32(3), 290-284.
Chiappe, 2002. Basal bird phylogeny: Problems and solutions. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 448-472.
Everheart, 2011. Rediscovery of the Hesperornis regalis Marsh 1871 holotype locality indicates an earlier stratigraphic occurrence. Transactions of the Kansas Academy of Science. 114(1-2), 59-68.
Wilson and Chin, 2014. Comparative osteohistology of Hesperornis with reference to pygoscelid penguins: The effects of climate and behaviour on avian bone microstructure. Royal Society Open Science. 1(3), 140245.
H. sp. (Davis and Harris, 1997)
Middle-Late Campanian, Late Cretaceous
Ozan Formation, Arkansas, US
Material- (SAU 203) tibiotarsal fragment (Bell, Irwin and Davis, 2015)
(SAU 204) incomplete tarsometatarsus (~158 mm) (Davis and Harris, 1997)
pedal phalanx III-? (Bell, Irwin and Davis, 2015)
References- Davis and Harris, 1997. Discovery of fossil Cretaceous bird in southwest Arkansas. Journal of the Arkansas Academy of Science. 51, 197-198.
Bell, Irwin and Davis, 2015. Hesperornithiform birds from the Late Cretaceous (Campanian) of Arkansas, USA. Transactions of the Kansas Academy of Science. 118(3/4), 219-229.
H. sp. (Bell, Irwin and Davis, 2015)
Late Campanian, Late Cretaceous
Marlbrook Marl Formation, Arkansas, US
Material- pedal phalanx III-1 (45.5 mm) (Bell, Irwin and Davis, 2015)
Reference- (FHSM VP-17988) Bell, Irwin and Davis, 2015. Hesperornithiform birds from the Late Cretaceous (Campanian) of Arkansas, USA. Transactions of the Kansas Academy of Science. 118(3/4), 219-229.
H. sp. (Bell, Irwin and Davis, 2015)
Late Cretaceous
US
Material- (NHMUK A-720) partial pelvis (Bell and Chiappe, 2020)
(KUVP 2280) dorsal vertebra (Bell and Chiappe, 2020)
(SDSM 551) material including pedal phalanx III-1 (38 mm) (Bell, Irwin and Davis, 2015)
(SDSM 5312) cervical vertebrae, dorsal vertebrae, synsacrum, incomplete pelvis, femur, patella, tibiotarsus, tarsometatarsus, phalanx III- 1 (42.3 mm), three pedal phalanges (Bell, Irwin and Davis, 2015)
(SDSM 5860) pelvis (Bell and Chiappe, 2020)
(UNSM 4-19-5-36) third dorsal vertebra, pelvic material (Bell and Chiappe, 2020)
(UNSM 10148) cranial material (Bell and Chiappe, 2020)
References- Bell, Irwin and Davis, 2015. Hesperornithiform birds from the Late Cretaceous (Campanian) of Arkansas, USA. Transactions of the Kansas Academy of Science. 118(3/4), 219-229.
Bell and Chiappe, 2020. Anatomy of Parahesperornis: Evolutionary mosaicism in the Cretaceous Hesperornithiformes (Aves). Life. 10(5), 62.
H. sp. nov. aff. regalis. (Kurochkin, 2004)
Early Campanian, Late Cretaceous
Rybushka Formation, Saratov, Russia
Material- (PIN 5027/5) proximal tarsometatarsus (40.6 mm trans) (Kurochkin, 2004; described in Zelenkov, Panteleyev and Yarkov, 2017)
(ZIN PO 6610) distal tarsometatarsus (Zelenkov, Panteleyev and Yarkov, 2017)
(ZIN PO 6611) distal tibiotarsus (35.1 mm trans) (Zelenkov, Panteleyev and Yarkov, 2017)
Early Campanian, Late Cretaceous
Bellemnellocamax mamillatus zone, Rychkovo, Volgograd, Russia
(PIN 5027/6) proximal tarsometatarsus (Zelenkov, Panteleyev and Yarkov, 2017)
Comments- Kurochkin (2004) stated PIN 5027/5 differs from the contemporary H. rossicus "by inverse ratio of the articular cotylas and some other characters", and that it also differs from H. regalis, H. crassipes, H. gracilis and H. bairdi, so is a new species. Zelenkov and Kurochkin (2015) referred it to H. rossicus without comment, but Zelenkov et al. (2017) listed several differences from H. rossicus that resembled H. regalis instead. They stated "the only essential difference of the specimen described here from H. regalis is the absence in proximal view of a distinct incisure in the dorsal margin of the bone medial to the eminentia intercotylaris (this incisure is also absent in H. rossicus, H. mengeli, H. lumgairi, and Asiahesperornis bazhanovi)." Zelenkov et al. list several characters distinguishing distal tarsometatarsus ZIN PO 6610 from H. regalis. These two specimens plus tibiotarsus ZIN PO 6611 and tarsometatarsus PIN 5027/6 are called Hesperornis sp. 1 by Zelenkov et al..
References- Kurochkin, 2004. New fossil birds from the Cretaceous of Russia. Sixth International Meeting of the Society of Avian Paleontology and Evolution, Abstracts. 35-36.
Zelenkov and Kurochkin, 2015. Class Aves. In Kurochkin, Lopatin and Zelenkov (eds.). Fossil vertebrates of Russia and adjacent countries. Part 3. Fossil Reptiles and Birds. GEOS. 86-290.
Zelenkov, Panteleyev and Yarkov, 2017. New finds of hesperornithids in the European Russia, with comments on the systematics of Eurasian Hesperornithidae. Paleontological Journal. 51(5), 547-555.
H. sp. nov. aff. rossicus. (Zelenkov, Panteleyev and Yarkov, 2017)
Early Campanian, Late Cretaceous
Rybushka Formation, Saratov, Russia
Material- (ZIN PO 6609) distal tarsometatarsus
Comments- Zelenkov et al. (2017) stated this can be "distinguished from specimen ZIN, no. PO 6610 by the considerably smaller size" and "the very poorly developed fovea lig. collateralis on the lateral surface of trochlea metatarsi IV." They believe the "specimen likely belongs to a separate Hesperornis species" and that the "narrow trochlea metatarsi IV with a deep and narrow sulcus suggests that this form is close to H. rossicus rather than to H. regalis." Zelenkov et al. call this Hesperornis sp. 2.
Reference- Zelenkov, Panteleyev and Yarkov, 2017. New finds of hesperornithids in the European Russia, with comments on the systematics of Eurasian Hesperornithidae. Paleontological Journal. 51(5), 547-555.
H. sp. nov. aff. bazhanovi (Zelenkov, Panteleyev and Yarkov, 2017)
Late Campanian, Late Cretaceous
Bereslavka, Vologograd, Russia
Material- (PIN 5555/1) proximal tarsometatarsus (~34.8 mm trans)
(PIN 5555/2) proximal tarsometatarsus
(PIN 5555/3) distal tarsometatarsus
Comments- Zelenkov et al. (2017) state "in specimen PIN, no. 5555/2, the sulcus on the dorsal surface of the bone is considerably more strongly developed than in other specimens; this is typical for the genus Asiahesperornis (Dyke et al., 2006). This suggests that Hesperornis from Bereslavka is closer to A. bazhanovi, which is also similar is absolute size. However, specimen PIN, no. 5555/1 differs from A. bazhanovi in the strongly oblique dorsomedial margin of the cotyla medialis, which does not project dorsally. The morphological distinctions of the Bereslavka form from A. bazhanovi suggest that it belongs to a separate taxon." They call this Asiahesperornis sp..
Reference- Zelenkov, Panteleyev and Yarkov, 2017. New finds of hesperornithids in the European Russia, with comments on the systematics of Eurasian Hesperornithidae. Paleontological Journal. 51(5), 547-555.
H? sp. (Yarkov and Nessov, 2000)
Late Campanian, Late Cretaceous
Bereslavka, Vologograd, Russia
Material- mid dorsal centrum, posterior dorsal centrum, pedal phalanx IV-?
Comments- Yarkov and Nessov (2000) referred two dorsal centra and a pedal phalanx to Hesperornithidae indet.
Reference- Yarkov and Nessov, 2000. New remains of hesperornithiform birds Hesperornithiformes from the Volgograd Reigion. Russkii Ornitolocheskii Zhurnal, Ekspress Vypusk. 94, 3-12. [in Russian]

Carinatae Merrem, 1813
Definition- (Passer domesticus <- Hesperornis regalis) (modified from Cracraft, 1986)
Other definitions- (Ichthyornis dispar + Passer domesticus) (Sereno, online 2005; modified from Chiappe, 1995)
(keeled sternum homologous with Vultur gryphus) (Gauthier and de Queiroz, 2001)
References- Cracraft, 1986. The origin and early diversification of birds. Paleobiology. 12, 383-399.
Chiappe, 1995. The first 85 million years of avian evolution. Nature. 378, 349-355.
Gauthier and de Quieroz, 2001. Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and the name "Aves." In Gauthier and Gall (eds.). New Perspectives on the Origin and Early Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom. Peabody Museum of Natural History. 7-41.
Sereno, online 2005. Stem Archosauria - TaxonSearch. http://www.taxonsearch.org/dev/file_home.php [version 1.0, 2005 November 7]