Carinatae sensu Gauthier and de Queiroz, 2001
Definition- (keeled sternum homologous with Vultur gryphus)

Ornithothoraces Chiappe and Calvo, 1994
Definition- (Iberomesornis romerali + Passer domesticus) (Turner, Makovicky and Norell, 2012; modified from Chiappe, 1995)
Other Definitions- (Sinornis santensis + Passer domesticus) (Sereno, online 2005; modified from Sereno, 1998)
= Ornithopectae Chiappe, 1991
Definition- (Iberomesornis romerali + Passer domesticus) (modified from Chiappe, 1991)
= Euornithes sensu Sanz and Buscalioni, 1992
Definition- (Iberomesornis romerali + Passer domesticus) (modified)
= Ornithothoraces sensu Sereno, 1998
Definition- (Sinornis santensis + Passer domesticus) (modified)
= Ornithuromorpha sensu Chiappe, 2001
Definition- (Vorona berivotrensis + Patagopteryx deferrariisi + Passer domesticus) (modified)
Diagnosis- dentary teeth present (also in many non-avialans; absent in Alethoalaornis, Gobipteryx, "Gobipipus", Archaeorhynchus, Apsaravis and Aves); dentary not strongly forked posteriorly (also in many non-euavialans; absent in Dapingfangornis, "Gobipipus", Yixianornis + Songlingornis, Apsaravis and Palaeognathae); external mandiblar fenestra absent (also in Juravenator, Compsognathidae, Shenzhouraptor and Omnivoropterygidae; absent in Hebeiornis, Dapingfangornis, Yixianornis and many Aves); less than thirteen dorsal vertebrae (also in Harpymimus+Ornithomimus and Oviraptoriformes); scapulocoracoid mobily jointed (also in Rahonavis, Shenzhouraptor and Jixiangornis; absent in Ratites); distal end of posterodistal sternal process fused to sternum (absent in Liaoningornithidae, Cuspirostrisornis, Hesperornis and Ichthyornis); posterolateral sternal process extends posteriorly past median posterior edge of sternum (also in Yandangornis; absent in Jibeinia, Hebeiornis, Eoenantiornis and "Cathayornis" chabuensis); projected carina on sternum (also in Parvicursorinae; absent in Jibeinia, Longchengornis, Rapaxavis, Eoalulavis, Patagopteryx, Hesperornis and Ratites); interclavicular angle <68 degrees (also in Jixiangornis and Dalianraptor; absent in Hesperornis); capital groove developed on proximal humerus (also in Gallimimus, Neimongosaurus, Therizinosauridae, Mononykus, Deinonychus and Bambiraptor; absent in Elsornis, Apsaravis and Ambiortus); dorsal condyle of distal ulna developed as semilunate ridge (also in Heyuannia, Rahonavis, Anchiornis, Zhongjianornis and Confuciusornis zhengi; absent in Eocathayornis); less than four phalanges on manual digit III (also in Tyrannosauridae, Caudipteryx, Jinfengopteryx and Omnivoropterygidae); alula present (also somewhat developed in Microraptor).
References- 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, 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.

Aberratiodontuiformes Gong, Hou and Wang, 2004
Aberratiodontuidae Gong, Hou and Wang, 2004
Aberratiodontus Gong, Hou and Wang, 2004
A. wui Gong, Hou and Wang, 2004
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (LHV0001a/b) skull (58.7 mm), mandibles, hyoid, eleven cervical vertebrae (88 mm), dorsal vertebrae, dorsal ribs, sacrum, caudal vertebrae?, pygostyle (24.5 mm), scapula (53 mm), coracoid (31 mm), furcula, sternum (55 mm), sternal ribs?, humeri (69 mm), radii (70 mm), ulnae (71 mm), two carpals, partial digit I?, partial metacarpal II, phalanx II-1, phalanx II-2, manual ungual II, partial digit III?, ilium (46 mm), pubes (43 mm), ischium?, femur (55 mm), tibiotarsi (66.7 mm), fibula, metatarsal I, pedal phalanx I-1 (8.7 mm), pedal ungual I, metatarsal II, phalanx II-1 (12.6 mm), phalanx II-2 (10.2 mm), pedal ungual II, metatarsal III (33 mm), phalanx III-1 (13.4 mm), rest of digit III, metatarsal IV (31 mm), phalanx IV-1 (8.4 mm), phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV (5.9 mm), feathers
Diagnosis- anterior four maxillary teeth much smaller than premaxillary or posterior maxillary teeth; elongate postorbital region; about twenty-four dentary teeth; scapula dorsoventrally curved; scapular acromion process short; sternum elongate; broad posterolateral sternal process with weakly expanded distal ends; manus shorter than humerus; postacetabular process broad; pubic boot absent.
Comments- This may be an enantiornithine less derived than Protopteryx or a euornithine outside Ornithuromorpha. It has been suggested to be a songlingornithid (Cau and Arduini, 2008), and a possible/probable junior synonym of Yanornis (Zhou et al., 2008/O'Connor, 2009).
References- Gong, Hou and Wang, 2004. Enantiornithine bird with diapsidian skull and its dental development in the Early Cretaceous in Liaoning, China. Acta Geologica Sinica. 78(1), 1-7.
Cau and Arduini, 2008. Enantiophoenix electrophyla gen. et sp. nov. (Aves, Enantiornithes) from the Upper Cretaceous (Cenomanian) of Lebanon and its phylogenetic relationships. Atti Societa italiana di Scienze naturali e del Museo civico di Storia naturale in Milano. 149(II), 293-324.
Zhou, Clarke and Zhang, 2008. Insight into diversity, body size and morphological evolution from the largest Early Cretaceous enantiornithine bird. Journal of Anatomy. 212, 565-577.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD Thesis. University of Southern California. 586 pp.

Hollandiformes Zelenkov in Zelenkov and Kurochkin, 2015
Hollandidae Zelenkov in Zelenkov and Kurochkin, 2015
Comments- These monotypic groups were created by Zelenkov in a book chapter by Zelenkov and Kurochkin (2015) in Zelenkov's new parvclass Vorones that also included monotypic orders and families for Vorona, Mystiornis and Patagopteryx.
Reference- 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.
Hollanda Bell, Chiappe, Erickson, Suzuki, Watabe, Barsbold and Tsogtbaatar, 2010
= "Hollanda" Bell, Chiappe, Erickson, Suzuki, Watabe, Barsbold and Tsogtbaatar, 2009 online
H. luceria Bell, Chiappe, Erickson, Suzuki, Watabe, Barsbold and Tsogtbaatar, 2010
= "Hollanda luceria" Bell, Chiappe, Erickson, Suzuki, Watabe, Barsbold and Tsogtbaatar, 2009 online
Late Campanian, Late Cretaceous
Baruungoyot Formation, Mongolia
Holotype- (MPC-b100/202) distal tibiotarsus, tarsometatarsus, proximal phalanx II-1, phalanx III-1, phalanx III-2, proximal phalanx III-3
Paratypes- ....(MPC-b100/203) distal femur
....(MPC-b100/204) proximal tibiotarsus
....(MPC-b100/205) proximal tibiotarsus
....(MPC-b100/206) fibula
....(MPC-b100/207) fibula
Comments- The type material was discovered in 1997 and first announced by Bell et al. (2008) as "a new taxon of primitive ornithuromorph bird." Bell et al. (2010) later described and named the material Hollanda luceria, though their Table 1 lists it as Hollandornis birdus, clearly a typo. The authors recovered it as a basal ornithuromorph, either intermediate between Patagopteryx and songlingornithids or sister to Ornithurae. However, when included in a larger analysis with a greater variety of taxa, Hollanda emerges as a non-ornithuromorph ornithothoracine. Characters more primitive than ornithuromorphs include a lack of distal metatarsal fusion and proximal tarsometatarsal foramina absent, while characters shared with some enantiornithines include the posteriorly projected laterodistal femoral margin, and metatarsal IV reduced in width.
References- Bell, Chiappe, Suzuki and Watabe, 2008. Phylogenetic and morphometric analysis of a new ornithuromorph from the Barun Goyot Formation, southern Mongolia. Abstracts of the 7th International Meeting of the Society of Avian Paleontology and Evolution.1.
Bell, Chiappe, Erickson, Suzuki, Watabe, Barsbold and Tsogtbaatar, 2010. Description and ecologic analysis of Hollanda luceria, a Late Cretaceous bird from the Gobi Desert (Mongolia). Cretaceous Research. 31(1), 16-26.

Kaririavis Carvalho, Agnolín, Rozadilla, Novas, Ferreira Gomes Andrade and Xavier-Neto, 2021 online
K. mater Carvalho, Agnolín, Rozadilla, Novas, Ferreira Gomes Andrade and Xavier-Neto, 2021 online
Aptian, Early Cretaceous
Pedra Branca Mine, Crato Formation, Brazil
Holotype- (UFRJ-DG 116 Av) incomplete tarsometatarsus (mtII 17.5, mtIII 19.6, mtIV 18.3 mm), phalanx II-1, phalanx II-2, pedal ungual II (6.6 mm), phalanx III-1, phalanx III-2, phalanx III-3, phalanx IV-1, distal phalanx IV-2, fragments, pedal claw sheath, ten contour feathers
Diagnosis- (after Carvalho et al., 2022) metatarsal fusion restricted to proximal end; very shallow proximal intercotylar eminence; proximal end of metatarsal II not expanded and overlapped plantarly by metatarsal III; shaft of metatarsal II thinner than metatarsal IV; hypotarsus distally extended and forming mediolaterally thick crest that extends distally beyond mid-length of metatarsal III; trochlea of metatarsal III with prominent lateral condyle; distal metatarsal III with small lateral flange defining vascular opening with metatarsal IV; distally open vascular foramen between metatarsals III and IV; proportionally large pedal ungual II, 1/3 of tarsometatarsal length.
Comments- The holotype was discovered on February 25 2019 (Carvalho, pers. comm. 3-7-2022). The description was published online on November 11 2021 but not placed into volume 41(4) until 2022 despite volume 41(4) being catalogued as 2021.
Carvalho et al. (2022) added this to O'Connor's bird analysis and stated it emerged in a large ornithuromorph polytomy with Piscivoravis, Yanornis, Yixianornis, Songlingornis, Iteravis, Gansus, hongshanornithids, Apsaravis, Ichthyornis, hesperornithines and neognaths in a reported 15 MPTs of 1247 steps. Oddly, their supplementary info shows "the 15 Most Parsimonious Trees (MPTs) resulted in present phylogenetic analysis", but in all of these Kaririavis is the sister taxon to Ichthyornis. Running the matrix actually results in 1104 shorter trees of 1246 steps where Kaririavis can go anywhere in Ornithothoraces except Hesperornithes+Aves and Schizoouridae sensu Wang et al., including trees where it is an enantiornithine. However, Carvalho et al. claim that "35 characters [were] treated as ordered" when their included NEXUS file leaves all characters unordered by default, and when those characters (identified from the Mengciusornis analysis this was taken from) are ordered, 720 MPTs of 1274 steps are found where Kaririavis is the basalmost euornithine in each one. When added to Hartman et al.'s maniraptoromorph analysis, Kaririavis can equally easily fall out as an enantiornithine or a neognath, and with a single extra step can be sister to all other euornithines with a plantarily displaced third metatarsal. Because of this it is placed as Ornithothoraces incertae sedis here.
Reference- Carvalho, Agnolín, Rozadilla, Novas, Ferreira Gomes Andrade and Xavier-Neto, 2022 (as 2021; 2021 online). A new ornithuromorph bird from the Lower Cretaceous of South America. Journal of Vertebrate Paleontology. 41(4), e1988623.

Lectavis Chiappe, 1993
L. bretincola Chiappe, 1993
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Holotype- (PVL-4021) (~575 mm) tibiotarsus (156 mm), incomplete tarsometatarsus
Diagnosis- (after Chiappe, 1993) tibiotarsus transversely wider than deep in proximal view; distal tibiotarsal condyles strongly projected anteriorly; slender tarsometatarsus (also in Hollanda and Neuquenornis); m. tibialis cranialis tubercle on metatarsal II circular; proximoplantar surface of metatarsal II forming prominent, thick edge (also in Hollanda); hypotarsus present and mostly developed on metatarsal II.
(proposed) plantar surface of tarsometatarsus excavated (also in Confuciusornis and Hollanda); m. tibialis cranialis tubercle on metatarsal II proximally placed (distance from proximal edge of tubercle to proximal edge of tarsometatarsus <60% transverse width of proximal tarsometatarsus).
Comments- Lectavis was originally identified as an enantiornithine (Walker, 1981; Chiappe, 1991) and was labeled Type-B by Chiappe (1992) before being named and described in 1993. It was illustrated in more detail by Chiappe and Walker (2002). Chiappe (1992) included Lectavis in a small phylogenetic analysis where it emerged as a non-avisaurid enantiornithine. Yet the three characters which placed it in Enantiornithes are now known in more basal taxa as well- plantar surface of tarsometatarsus excavated (Confuciusornis, Patagopteryx); m. tibialis cranialis tubercle on metatarsal II (Confuciusornis, Longicrusavis and many other euornithines); metatarsal IV reduced in width (Zhongjianornis). Kurochkin (1996) included Lectavis in his Alexornithiformes incertae sedis based on its enlarged medial tibiotarsal condyle, m. tibialis cranialis tubercle on metatarsal II, and tarsometatarsal trochlea which differ in size. Yet Kurochkin's taxonomic scheme is flawed, as his euornithiforms Boluochia, Sinornis and Concornis have enlarged medial condyles as well, none of his euornithiforms are known to lack the metatarsal II tubercle, and his euornithiforms Iberomesornis, Boluochia, Sinornis and Concornis have enlarged metatarsal II trochlea. In Hartman et al.'s (2019) maniraptoromorph analysis, it falls out sister to Hollanda within Enantiornithes, which it is likely from since all other bird remains at El Brete belong to that clade. Walker et al. (2007) incorrectly (mistakenly) assigned the holotype to Avisaurus, while Walker and Dyke (2009) indicate size and associations indicate it is probably a junior synonym of Enantiornis.
References- Walker, 1981. New subclass of birds from the Cretaceous of South America. Nature. 292, 51-53.
Chiappe, 1991. Cretaceous birds of Latin-America. Cretaceous Research. 12, 55-63.
Chiappe, 1992. Enantiornithine (Aves) tarsometatarsi and the avian affinities of the Late Cretaceous Avisauridae. Journal of Vertebrate Paleontology. 12(3), 344-350.
Chiappe, 1993. Enantiornithine (Aves) tarsometatarsi from the Cretaceous Lecho Formation of Northwestern Argentina. American Museum Novitates. 3083, 39 pp.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
Chiappe and Walker, 2002. Skeletal morphology and systematic of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). pp 240-267. in Chiappe and Witmer, (eds.). Mesozoic Birds – Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.
Hartman, Mortimer, Wahl, Lomax, Lippincott and Lovelace, 2019. A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight. PeerJ. 7:e7247.

Lenesornis Kurochkin, 1996
L. maltshevskyi (Nessov, 1986) Kurochkin, 1996
= Ichthyornis maltshevskyi Nessov, 1986
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (ZIN PO 3434) (~330 mm) anterior synsacrum (~39 mm)
Comments- Kurochkin (1996) removed maltshevskyi from Ichthyornis and placed it in a new genus, which seems correct as Lenesornis differs in having broader anterior sacral centra which are ventrally grooved, a lower anterior articular surface, and a fourth sacral transverse process which is not short and dorsally directed. The latter character excludes it from Carinatae sensu Cracraft. Kurochkin noted Lenesornis is very similar to Gobipteryx, only differing in being less concave ventrally and having a broader anterior articular surface (height 73% of width instead of ~82%). Gargantuavis shares broad and low centra with a ventral groove and transverse processes which are similar where known, but differs in that it is very decurved anteriorly, lacks pleurocoels, has a smaller neural canal, and has a ventral keel on the first several vertebrae. Noguerornis differs in having amphiplatyan centra, while Iberomesornis has broader anterior sacral centra with a ventral median prominence. Hebeiornis' sacrum is poorly preserved, but shares the ventral groove with Gobipteryx, Pengornis, Enantiornis and Lenesornis. The sacra of Zhyraornis and the Lecho enantiornithine PVL-4041-4 differ in having narrower anterior sacral centra without ventral grooves. Patagopteryx is similar in having a ventral sulcus, broad anterior surface and slight ventral concavity, though the centra appear broader compared to their length. Archaeorhynchus and Apsaravis also have broadly similar sacra in relative centrum width and at least Archaeorhynchus seems to have a ventral sulcus, though further details in either genus are unknown. Hesperornithines and neornithines differ in having a heterocoelous anterior articulation, while hesperornithines also differ in being non-pneumatic. Both Gansus and Guildavis have narrower centra without a ventral sulcus. Confuciusornis lacks a ventral sulcus anteriorly, though confuciusornithids do share a relatively broad sacrum with concave anterior articulation with Lenesornis. The third sacral rib is larger than in Sapeornis or Shenzhouraptor, though sacra of those taxa are only available in dorsal view, limiting comparisons. Non-avialans have less extensively fused sacra, especially at such small sizes. An exception is Avimimus, which is similar in having a lateral fossa in the first centrum and a ventral sulcus starting on the second centrum.
In conclusion, Lenesornis is most similar to some enantiornithines and basal euornithine, but is not an ornithurine, and is probably closer to Passer than to Archaeopteryx. However, comparisons with non-ornithothoracine birds are limited and the possibility Lenesornis is a very small and highly fused non-bird maniraptoriform like Avimimus cannot be excluded. Though it is distinguishable from other well described theropod sacra (contra O'Connor, 2009), most are too poorly preserved or described.
References- 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, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.

Platanavis Nessov, 1992
P. nana Nessov, 1992
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (ZIN PO 4601) (~150 mm) mid synsacrum (~18 mm)
Diagnosis- sacral pleurocoels present in midsacral vertebrae; sacral pleurocoels directed strongly ventrally; sacral pleurocoels very dorsoventrally compressed; extremely deep median ventral sulcus on mid sacrum (also in Gobipteryx).
Comments- Nessov (1992) included two additional characters in his diagnosis, but dorsoventrally compressed sacral centra are common in birds as are large neural canals.
Mourer-Chauvire (1989) first announced the discovery of this specimen in 1989 as "part of the strange flat sacrum of a small new bird." This taxon is based only on the mid portion of a synsacrum, containing two complete and two partial vertebrae. It was small, as the complete vertebrae are 2.9 and 2.5 mm long each. The vertebrae are dorsoventrally compressed (~64% as tall as wide) and elongate (1.18-1.4 times longer than maximum height). The preserved sequence is only very slightly concave ventrally, and each centrum has a straight ventral margin. The ventral surface features a narrow median sulcus, giving the appearance to paired ridges. There is a low and deep pleurocoel in each complete centrum which opens lateroventrally due to the especially broad dorsal area. The neural canal is very wide, at least as broad as the centra.
Both Nessov (1992) and Kurochkin (2000) have assigned it to Aves incertae sedis without comment. Indeed, the fused sacral vertebrae are too small to derive from adult non-avialan theropods. Even tiny Caenagnathasia and Ceratonykus would have had sacra three times larger, while Microraptor and Jinfengopteryx were twice as large. The large neural canal, dorsoventral compression and ventral groove are common in maniraptoriforms, including many basal birds. Unfortunately, most Mesozoic birds have poorly preserved sacra, and are often undescribed or only visible in dorsal view. Those of Confuciusornis are similar in having lateral fossae and a ventral groove, but the fossae are limited anteriorly while the groove is limited posteriorly. Zhyraornis' sacrum is more concave ventrally, has narrower centra and lacks a groove. It does have pleurocoels anteriorly, but these differ in being laterally directed. The Lecho Formation enantiornithine PVL-4041-4 and Guildavis are also more slender ventrally with no groove, and if they have pleurocoels, they are not directed lateroventrally. Apatornis' sacrum is narrower, especially anteriorly, and lacks pleurocoels. Gansus' sacrum is narrower and not grooved ventrally though it does seem to have somewhat ventrally angled central fossae on the anterior centra. Ichthyornis' sacrum has anterior centra which are too narrow, without a ventral groove, and only the first sacral has a slight central fossa, which is directed laterally. The posterior centra are broader with a slight ventral groove, but lack pleurocoels. Apsaravis has a broad sacrum, but lacks a ventral groove and pleurocoels. Gargantuavis has a broad sacrum with a ventral keel on the posterior half, but lacks pleurocoels. Gobipteryx's and Patagopteryx's sacra are similarly low and broad ventrally with a median groove, but they don't seem to have pleurocoels. Lenesornis' sacrum is similar in being broad and only slightly concave ventrally with a ventral sulcus, but the pleurocoels are limited anteriorly and laterally directed. The ventral grooves of Gargantuavis, Lenesornis and Patagopteryx seem far more shallow than that of Platanavis, while Gobipteryx's is comparably deep. Thus the closest similarity is with various ornithothoracines, though its relationships cannot be determined further given the fragmentary material and lack of many comparable taxa. It may end up being synonymous with one of the Bissekty's numerous enantiornithines, such as the comparably sized Explorornis nessovi or Incolornis silvae.
References- Mourer-Chauvire, 1989. Society of Avian Paleontology and Evolution Information Newsletter. 3.
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.

"Smallornis" Zhang, 2007
"S. liaoningica" Zhang, 2007
Barremian-Albian, Early Cretaceous
Yixian, Jehol Group?, Liaoning, China
Material- skull, mandible, cervical series, coracoid, humeri, radii, ulnae, proximal manus, ilium, pubis, incomplete femora, incomplete tibia, metatarsus, pedal digits I-IV, body feathers, remiges
Comments- Zhang (2007) provided this brief description (translated) - "The parietal bones are well developed, the posterior edge of the orbit is concave, the eye holes are large, the beak is long, and the fingers and claws are particularly curved. The forelimbs are covered with very delicate feathers, and the down feathers on the head are more beautifully decorated. Smallornis liaoningica is a very small arboreal bird."
The available image quality means that it can't be determined whether this is an enantiornithine or euornithine, although the coracoid structure shows it is ornithothoracine. None of the listed characters are diagnostic past Pennaraptora, but I expect enough is preserved to make it valid compared to named Jehol taxa. Until we have a better scan of its skeleton, I'd say leave it as Ornithurothoraces incertae sedis. It is a nomen nudum as there is no "explicit fixation of a holotype, or syntypes" (ICZN Article 16.4.1).
Reference- Zhang, 2007. The Fossils of China. China University of Geosciences Press. 502 pp.

Wyleyia Harrison and Walker, 1973
W. valdensis Harrison and Walker, 1973
Late Berriasian-Valanginian, Early Cretaceous
Hastings Beds, England
Holotype- (NHMUK A3658) incomplete humerus (42.4 mm)
Comments- Harrison and Walker (1973) initially described Wyleyia as a bird, noting similarities to both Archaeopteryx and Ichthyornis. Glut (1982) notes Brett-Surman proposed this was a non-avian dinosaur at the 1978 Society of Vertebrate Paleontology meeting, "an opinion supported by Dr. Storrs Olson and Dr. R. T. Bakker." Harrison (1991) referred it to Enantiornithes, while Kurochkin (1995) referred it to Palaeognathae. Naish (2002) believed Wyleyia was a non-enantiornithine bird, and later (2011) classified it as Maniraptora indet.. Inclusion of Wyleyia in a TWG based matrix suggests it is most likely an ornithothoracine.
References- Harrison and Walker, 1973. Wyleyia: A new bird humerus from the Lower Cretaceous of England. Palaeontology. 16(4), 721-728.
Glut, 1982. The New Dinosaur Dictionary. Citadel Press. 288 pp.
Norman, 1990. Problematic Theropoda: 'Coelurosauria'. In Weishampel, Dodson and Osmolska, eds. The Dinosauria. University of California Press, Berkeley. 280–305.
Harrison, 1991. Fossil birds. In Brooke and Birkhead, eds. The Cambridge Encyclopedia of Ornithology. Cambridge University Press, Cambridge. 69–76.
Kurochkin, 1995. Synopsis of Mesozoic birds and early evolution of Class Aves. Archaeopteryx. 13, 47–66.
Naish, 2002. The historical taxonomy of the Lower Cretaceous theropods (Dinosauria) Calamospondylus and Aristosuchus from the Isle of Wight. Proceedings of the Geologists' Association. n. 113, p. 153-163.
Naish, 2011. Theropod dinosaurs. In Batten (ed.). English Wealden Fossils. The Palaeontological Association. 526-559.

undescribed probable Ornithothoraces (MOR online)
Late Campanian, Late Cretaceous
Judith River Group, Montana, US
Material- (MOR 023) vertebra
?(MOR 1044) partial skeleton
Comments- MOR 023 was listed as "bird", while MOR 1044 was listed as "theropod, bird?".

undescribed probable Ornithothoraces (MOR online)
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, Montana, US
Material- (MOR 978) distal humerus, femur
(MOR 1086) distal humerus
(MOR 2716) distal metatarsal
(MOR 2917) distal femur
(MOR 2918) coracoid
Comments- These were listed as bird remains on MOR's online specimen catalog, so are probably ornithothoracines based on their age.

unnamed probable ornithothoracine (Nesov, 1984)
Early Cenomanian, Late Cretaceous
Khodzhakul Formation, Uzbekistan
Material- (TsNIGRI 52/11915) dorsal vertebra (9 mm) (Nesov, 1984)
? fragments (Nessov, 1992)
Comments- Discovered in 1975, Nesov (1984) noted this specimen was amphicoelous with a shallower lateral fossa than "Zhyraornis kashkarovi" TsNIGRI 43/11915. It is from an avebrevicaudan due to its large lateral central fossae, probably an ornithothoracine based on its age. Nessov (1992) noted unidentified fragments of small bird bones were found in the same locality.
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, 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.

unnamed Ornithothoraces (Nesov, 1984)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Material- (TsNIGRI 52/11915) pedal phalanx (21.3 mm) (Nesov, 1984)
(ZIN PH 9/109) posterior synsacrum (Zelenkov and Averianov, 2011)
(ZIN PO 3434c) distal humerus (Novas, 1992a)
(ZIN PO 3434f) braincase fragment, atlas, axis (Nessov, 1986)
(ZIN PO 4608) partial dentary (Nessov, 1992a,b)
(ZIN PO 4610) tooth (3.2 mm) (Nessov, 1992a,b)
(ZIN PO 4613) distal humerus (Nessov, 1992a,b)
(ZIN PO 4621) posterior mandible (Nessov, 1992a,b)
(ZIN PO 4821) partial coracoid (Nessov and Panteleev, 1993)
posterior synsacrum (Mourer-Chauvire, 1989)
Comments- TsNIGRI 52/11915 is far more elongate than any non-bird theropod, so may belong to a euornithine or specialized enantiornithine.
Zelenkov and Averianov (2011) determined ZIN PH 9/109 was different than Kuszholia, Zhyraornis, Platanavis, and unnamed posterior synsacrum ZIN PO 4826. They referred it to Ornithothoraces.
Nessov (1992a) illustrated distal humerus ZIN PO 3434c he questionably referred to Alexornithiformes. The humerus does resemble enantiornithines in having a strongly distally projected ventral condyle, but this is seen in Apsaravis as well, leaving the specimen referred to Ornithothoraces incertae sedis.
ZIN PO 3434f was listed as Aves indet. by Nessov (1992a), but could conceivably derive from a small non-avian coelurosaur as well.
Nessov (1992a) noted a possibly ichthyornithiform mandible discovered in 1989, which seems to be the partial dentary ZIN PO 4608 ascribed by him later (1992b) to Ichthyornithiformes. The preserved portion differs from Ichthyornis in being more slender and upcurved. It is not troodontid because it lacks a lateral groove, and differs from that family, Dromaeosauridae and Alvarezsauridae in having distinct alveoli. It is here placed in Ornithothoraces incertae sedis (but is not part of Aves), as no more basal toothed avialans are known to exist by the Turonian.
Nessov (1992a) noted teeth of small birds discovered in 1989, one of which (ZIN PO 4610) was later illustrated by him (1992b) as possibly being ichthyornithiform. Yet the tooth differs from Ichthyornis is being straight, more slender, and having a basally expanded crown, and being uncompressed labiolingually. Those features are more closely approached by Dinosaur Park Formation teeth like RTMP 96.62.51, but it is more compressed as well. Perhaps it is an anterior tooth. If it is indeed a bird and not a mammal or crocodilian, it seems distinct from other well described examples.
Nessov (1992a) noted "part of a humerus of a medium-sized bird with strange morphology (possibly a new group of Aves" discovered in 1989. This is probably the distal humerus ZIN PO 4613 later (1992b) figured by him as possibly enantiornithine. Indeed, the humerus resembles enantiornithines in having a strongly distally projected ventral condyle and transversely oriented dorsal condyle. Yet these are present in Apsaravis as well, leaving the specimen referred to Ornithothoraces incertae sedis.
Nessov (1992a) noted a posterior bird mandible discovered in 1989, which seems to be the one later figured by him as ZIN PO 4621 (Nessov, 1992b). It seems to be ornithothoracine based on the concave dorsal surangular edge, but further comparison is necessary to determine its precise relationships.
ZIN PO 4821 was referred to Enantiornithes by Nessov and Panteleev (1993), then later specifically to Alexornithiformes by Panteleyev (1998). While the deep dorsal fossa is found in enantiornithines, it is also present in Apsaravis, limiting identication of this element to Ornithothoraces incertae sedis.
Mourer-Chauvire (1989) noted an ichthyornithiform sacrum, and Nessov (1992) mentioned a posterior synsacrum discovered in 1989, "possibly with affinities to ichthyornithiformes." Besides the size, said to be similar to a recent coromorant, no further details are known. It may indeed by an ichthyornithine, but could also be a more basal euornithine, an enantiornithine, or even a non-bird theropod.
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, 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. Proceedings of the Zoological Institute, Leningrad. 147, 31-38.
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.
Nessov and Panteleev, 1993. On the similarity of the Late Cretaceous ornithofauna of South America and Central Asia. Trudy Zoologicheskogo Instituta, RAN. 252, 84-94.
Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.
Zelenkov and Averianov, 2011. Synsacrum of a primitive bird from the Upper Cretaceous of Uzbekistan. Paleontological Journal. 45(3), 314-319.

undescribed possible Ornithothoraces (Nessov, 1992)
Early Santonian, Late Cretaceous
Yalovach Formation, Tajikistan
Material- fragments
Comments- Nessov (1992) notes rare fragments of birds are present in this locality (spelled Jalovatsh in his paper).
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 ornithothoracine (Malakhov and Ustinov, 1998)
Maastrichtian, Late Cretaceous
Zhuravlovskaya Svita (not Eginsaiskaya Svita), Kazakhstan
Material- (IZASK 4/KM 97) incomplete dentary (?(IZASK 4/KM 97) incomplete dentary
Comments- IZASK 4/KM 97 was referred to Asiahesperornis bazhanovi by Malakhov and Ustinov (1998), but Bell and Chiappe (2020) stated it "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. It is here provisionally placed in Ornithothoaces based on its late age.
References- 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).
Bell and Chiappe, 2020. Anatomy of Parahesperornis: Evolutionary mosaicism in the Cretaceous Hesperornithiformes (Aves). Life. 10(5), 62.

undescribed possible Ornithothoraces (Nessov, 1992)
Late Maastrichtian, Late Cretaceous
Kakanaut Formation, Russia
Comments- Nessov (1992) merely says there are "bones of presumably medium-sized birds" in this locality.
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 Ornithothoraces (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 742) partial furcula
(UA 9603) partial furcula
Comments- The furculae differ from each other, so are from different taxa.
Reference- 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.

unnamed probable Ornithothoraces (Agnolín and Martinelli, 2009)
Campanian-Maastrichtian, Late Cretaceous
Los Alamitos Formation, Río Negro, Argentina
Material- (MACN PV RN 1103) distal pedal phalanx
(MACN PV RN 1104) distal pedal phalanx (?)II-2
(MACN PV RN 1105) pedal ungual I
(MACN PV RN 1106) manual ungual I
(MACN PV RN 1107) distal phalanx II-1
Reference- Agnolín 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.

unnamed probable ornithothoracine (Alves, Bergqvist and Brito, 2016)
Turonian-Santonian, Late Cretaceous
Adamantina Formation of the Bauru Group, Brazil
Material- (UFRJ-DG 06-Av) distal distal pedal phalanx
References- Alves, Bergqvist and Brito, 2016. New occurrences of microvertebrate fossil accumulations in Bauru Group, Late Cretaceous of western São Paulo state, Brazil. Journal of South American Earth Sciences. doi: 10.1016/j.jsames.2016.03.003

unnamed probable Ornithothoraces (Candeiro, Agnolín, Martinelli and Buckup, 2012)
Maastrichtian, Late Cretaceous
Serra da Galga Formation of the Bauru Group, Brazil
Material- (CPP 470) pedal phalanx II-1
(CPP 481) incomplete pedal ungual
Comments- In 2021 the Serra da Galga and Ponte Alta Members of the Marilia Formation were recognized as the Serra da Galga Formation.
Reference- Candeiro, Agnolín, Martinelli and Buckup, 2012. First bird remains from the Upper Cretaceous of the Peirópolis site, Minas Gerais state, Brazil. Geodiversitas. 34(3), 617-624.

Enantiornithes Walker, 1981
Definition- (Enantiornis leali <- Passer domesticus) (modified from Longrich, 2009)
Other definitions- (Cathayornis yandica <- Passer domesticus) (Turner et al., 2012)
(Sinornis santensis <- Passer domesticus) (Sereno, in press; modified from Sereno, 1998)
= Euornithiformes Kurochkin, 1996
= Enantiornithes sensu Sereno, 1998
Definition- (Sinornis santensis <- Passer domesticus) (modified)
= Enantiornithomorpha Chiappe, Ji, Ji and Norell, 1999
= Enantiornithes sensu Turner et al., 2012
Definition- (Cathayornis yandica <- Passer domesticus)
= Pengornithidae Wang et al., 2014
Definition- (Pengornis houi + Eopengornis martini) (Wang et al., 2014)
= Voronidae Zelenkov in Zelenkov and Kurochkin, 2015
Definition- (Vorona berivotrensis <- Patagopteryx deferrariisi) (Zelenkov and Kurochkin, 2015)
Diagnosis- laterally compressed proximal coracoid (also in many Neognathae; absent in Catenoleimus, Explorornis nessovi and Elsornis); m. tibialis cranialis tubercle on tarsometatarsus confined to metatarsal II (also in Velociraptor and Longicrusavis; absent in Vorona, Rapaxavis and Yungavolucris); metatarsal II trochlea transversely expanded (also in Falcarius, some paravians and Zhongjianornis; absent in Alethoalaornis, Longipterygidae and Liaoningornithidae); metatarsal IV reduced in width (also in Archaeopteryx and Zhongjianornis; absent in Iberomesornis, Shanweiniao and Liaoningornithidae).
Comments- Wang et al. (2014) erected Pengornithidae to include Pengornis, Eopengornis and IVPP V18632, as the most basal enantiornithines, even moreso than Protopteryx. Yet their analysis was limited by irrationally only including Jehol enantiornithines. Of their listed characters for Pengornithidae, at least some are obviously primitive (numerous small teeth in upper and lower jaws; no posteromedial sternal processes; posteromedian process broad; fibula almost reaches proximal tarsals), and Cau (online, 2014) found that when the non-Jehol enantiornithines were re-included Pengornithidae was no longer such an exclusive clade.
Voronidae was named by Zelenkov in a Russian book chapter by Zelenkov and Kurochkin (2015) as a family in his parvclass Vorones, also including Mystiornis, Hollanda and Patagopteryx, each given their own order and family. While no internal phylogenetic resolution was suggested for the parvclass, a phylogenetic definition was given for Voronidae as being (translated) "more related to Vorona berivotrensis Forster et al., 1996 than Patagopteryx deferrariisi Alvarenga et Bonaparte, 1992." In this site's topology, this covers all of Enantiornithes.
References- Chiappe, O'Connor and Zhou, 2005. Evolutionary history of the Cretaceous Enantiornithes. Journal of Vertebrate Paleontology. 25(3), 44A.
O'Connor and Chiappe, 2008. Skull morphology of Enantiornithes (Aves: Ornithothoraces). Journal of Vertebrate Paleontology. 28(3), 97A.
Chamero, Marugan-Lobon, Buscalioni and Sanz, 2009. The Mesozoic avian fossils of the Iberian Peninsula. Journal of Vertebrate Paleontology. 29(3), 76A.
Dyke, Osi and Buffetaut, 2009. Large European Cretaceous enantiornithines: Morphometrics, phylogenetics and implications for the biogeography of early birds. Journal of Vertebrate Paleontology. 29(3), 90A.
Martin, 2009. Cyril Walker and the other half of avian evolution. Journal of Vertebrate Paleontology. 29(3), 143A.
Cau, online 2014. http://theropoda.blogspot.com/2014/10/eopengornis-e-la-risoluzione-di.html
Wang, O'Connor, Zheng, Wang, Hu and Zhou, 2014. Insights into the evolution of rachis dominated tail feathers from a new basal enantiornithine (Aves: Ornithothoraces). Biological Journal of the Linnean Society. 113, 805-819.
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.

Abavornis Panteleyev, 1998
A. bonaparti Panteleyev, 1998
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (TsNIGRI 56/11915) (~280 mm) coracoid shaft (~32 mm)
Diagnosis- (after Panteleyev, 1998) significant medial expansion of distal coracoid; deep dorsal coracoid fossa (also in Neuquenornis and Enantiornis); longitudinal groove along ventromedial edge of shaft.
(proposed) laterodistal edge angles medially.
Comments- Originally identified as Aves by Nessov and Borkin (1983) and Nesov (1984), then as Enantiornithes by Nessov and Panteleev (1993). Elzanowski (1995) believed the specimen was nearly identical to Gobipipus (which he referred to juvenile Gobipteryx) and referred it to Gobipterygidae and perhaps Gobipteryx itself. However, it differs from Gobipipus in having the lateral edge angle distomedially, a longer shaft between the dorsal fossa and head, the supracoracoid foramen placed completely proximal to the dorsal fossa, and a rounded proximal edge of the dorsal fossa. In addition to these characters, it differs from adult Gobipteryx in having a wider shaft, deeper dorsal fossa, more distomedial expansion and a ventromedial groove. Kurochkin (1996) referred the coracoid to Enantiornithidae indet., based on the deep and proximally extensive dorsal fossa and convex lateral margin. The former is also found in his alexornithid Neuquenornis however, while the latter is found in his concornithids Concornis and Cathayornis. Panteleyev (1998) described the specimen as the holotype of his new genus Abavornis, which he placed in the Alexornithidae and Alexornithiformes without comment. O'Connor (2009) declared all Bissekty enantiornithines based on coracoids to be nomina dubia, though without detailed comparison.
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.
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 and Panteleev, 1993. On the similarity of the Late Cretaceous ornithofauna of South America and Central Asia. Trudy Zoologicheskogo Instituta, RAN. 252, 84-94.
Elzanowski, 1995. Cretaceous birds and avian phylogeny. Courier Forschungsinstitut Senckenberg. 181, 37-53.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
A? sp. nov. (Panteleyev, 1998)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Material- (ZIN PO 4605) (~180 mm) coracoid shaft (~21 mm)
Comments- Originally identified as Aves by Nessov (1992), then Enantiornithes by Nessov (1997). This is based off the distal part of a coracoid, missing the distolateral corner. It closely resembles Avabornis bonaparti, but the lateral edge is straight, not angled inward distally. Perhaps the edge of A. bonaparti is broken.
References- 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.
Nessov, 1997. [Cretaceous nonmarine vertebrates of northern Eurasia]. Saint Petersburg, Institute of Earth Crust. 1-218.
Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.

Castignovolucris Buffetaut, Angst and Tong, 2023
C. sebei Buffetaut, Angst and Tong, 2023
Late Campanian, Late Cretaceous
Castigno, Grès à Reptiles Formation, Hérault, France
Holotype- (MC-VCZ2-6) incomplete coracoid (~82 mm)
Diagnosis- (after Buffetaut et al., 2023) coracoid head wide, with a broadly pointed acrocoracoid process bearing a proximally-placed tubercle; very deep and narrow groove between the triangular scapular articular facet and the acrocoracoid process; shaft broad and relatively short, with a D-shaped cross-section and parallel longitudinal grooves on its ventral surface; supracoracoid foramen slit-like, lying in a medial position on the shaft and ending distally at the level of the apex of the dorsal fossa; dorsal fossa deeply concave; well-marked distolateral convexity; medial wall of dorsal fossa thickened proximally.
Comments- This was first published by Buffetaut et al. (2021), as "Enantiornithes: represented by a large coracoid found in 2019, indicating a new taxon" and figured as "right enantiornithe coracoid, dorsal view - Musée de Cruzy, VC-Z2-6" (translated). Buffetaut et al. (2023) stated "it seems to show similarities with some large forms from North America, such as specimen RAM 14306 from the Campanian Kaiparowits Formation of Utah."
References- Buffetaut, Angst, Claude, Tong, Amoros, Boschetto, Chenet, Clavel, Maggia, Roques and Sèbe, 2021. Les niveaux à vertébrés fossiles du Crétacé supérieur de Castigno et Combebelle (Villespassans, Hérault): historique et nouvelles découvertes. Carnets natures. 8, 33-47.
Buffetaut, Angst and Tong, 2023. A new enantiornithine bird from Upper Cretaceous non-marine deposits at Villespassans (Hérault, southern France). Annales de Paléontologie. 109(1), 102585.

Catenoleimus Panteleyev, 1998
C. anachoretus Panteleyev, 1998
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (ZIN PO 4606) (~220 mm) coracoid shaft (~25 mm)
Comments- Originally identified as Enantiornithes in Nessov (1992). O'Connor (2009) declared all Bissekty enantiornithines based on coracoids to be nomina dubia, though without detailed comparison.
References- 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.
Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.

Cuspirostrisornithidae Hou, 1997
Cuspirostrisornis Hou, 1997
C. houi Hou, 1997
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V10897) (~140 mm, 70 g) incomplete skull (~27 mm), dentaries, four or five cervical vertebrae, five or six dorsal vertebrae, sacrum, several caudal vertebrae, pygostyle, partial coracoid, sternum (~23 mm), humeri (29 mm), radii (29.5 mm), ulnae (32 mm), carpometacarpus (14 mm), manual ungual, ilium, pubis, ischium, femora (27.3 mm), tibiotarsi (32.5 mm), fibulae (~8.5 mm), tarsometatarsi (19 mm), pedal phalanges, pedal ungual I (8 mm), pedal ungual II (8 mm), pedal ungual III (9 mm), pedal ungual IV (6 mm)
Diagnosis- distal portion of posterolateral sternal processes not fused to sternum.
Reference- Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.

Enantiophoenix Cau and Arduini, 2008
E. electrophyla Cau and Arduini, 2008
Middle Cenomanian, Late Cretaceous
Ouadi al Gabour, Lebanon
Holotype- (MSNM V3882) rib fragments, synsacrum, scapula (21.3 mm), coracoids (one partial; 19.4 mm), partial furcula, partial sternum, ilial fragment, incomplete pubis, ischial fragments, incomplete tarsometatarsi (~28 mm), four pedal phalanges, four pedal unguals, long bone shafts, two distal phalanges, two unguals, feathers
Comments- This specimen was briefly described as an enantiornithine but unnamed by Dalla Vecchia and Chiappe (2002), then described in detail and named by Cau and Arduini (2008). Cau and Arduini assigned Enantiophoenix to the Avisauridae based on their phylogenetic analysis.
References- Dalla Vecchia and Chiappe, 2002. First avian skeleton from the Mesozoic of Northern Gondwana. Journal of Vertebrate Paleontology. 22(4), 856-860.
Cau and Arduini, 2008. Enantiophoenix electrophyla gen. et sp. nov. (Aves, Enantiornithes) from the Upper Cretaceous (Cenomanian) of Lebanon and its phylogenetic relationships. Atti Soc. it. Sci. nat. Museo civ. Stor. nat. Milano. 149(II), 293-324.

"Enantiornis" walkeri Nessov and Panteleev, 1993
= Explorornis walkeri (Nessov and Panteleev, 1993) Panteleyev, 1998
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (ZIN PO 4825) (~300 mm) proximal coracoid (~35 mm)
Diagnosis- (proposed) acrocoracoid process dorsoventrally deep (>50% as deep at level of junction between scapular facet and acrocoracoid as the coracoid head is long); coracoid lateral convexity begins on shaft proximal to dorsal fossa.
Other diagnoses- Nessov and Panteleev (1993) distinguished walkeri from Enantiornis leali based on several characters. The coracoid process is not narrower however. The acrocoracoid process is not actually shorter than in Enantiornis, but appears so due to its depth. The proximal shaft is transversely wider, but this is plesiomorphic. The elongate supracoracoid foramen seems to be the medial exit, which is also elongate in Enantiornis.
Kurochkin (2000) listed two features in his diagnosis to separate walkeri from leali. The coracoid process is even more stout in Explorornis, and equally so in Incolornis, Neuquenornis and Catenoleimus. The proximal shaft is more gracile dorsoventrally, but this is also true of Gurilynia, Gobipteryx and Explorornis.
Comments- This specimen was discovered in 1991 and named "Enantiornis" walkeri by Nessov and Panteleev (1993). While the quotation marks suggest they did not believe the species to actually be Enantiornis, they did place it within the Enantiornithiformes. Kurochkin (1996) removed the quotation marks, as he believed it was referrable to Enantiornis based on the obtuse acrocoracoid tip, stout coracoid process and proximally (dorsoventrally?) thick shaft. However, the acrocoracoid tip is no more obtuse than Explorornis, Incolornis martini and Alexornis, the coracoid process is less stout in Enantiornis than in Explorornis, Incolornis, Catenoleimus, Otogornis or Neuquenornis, and the shaft isn't thick as in Enantiornis and is much thinner than in Incolornis. Kurochkin (2000) later kept the species in Enantiornis and added a couple coracoid features to his diagnosis of the genus- short coracoid shaft; stout acrocoracoid process. The former is plesiomorphic, while the latter is also present in Otogornis and Incolornis. Panteleyev (1998) transferred walkeri to his new genus Explorornis (within Alexornithidae and Alexornithiformes) without justification, though it does share that genus' primitive dorsoventrally compressed coracoid shaft and shallow dorsal fossa. Yet it lacks the apomorphic dorsolateral ridge of Explorornis. walkeri does not seem to be definitively referrable to either genus. O'Connor (2009) declared all Bissekty enantiornithines based on coracoids to be nomina dubia, though without detailed comparison.
References- Nessov and Panteleev, 1993. On the similarity of the Late Cretaceous ornithofauna of South America and Central Asia. Trudy Zoologicheskogo Instituta, RAN. 252, 84-94.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.
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.
E? sp. (Panteleyev, 1998)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Material- (ZIN PO 4817) proximal coracoid (~28 mm)
Comments- This coracoid is not figured, but Panteleev says it resembles walkeri more than E. nessovi or the other Explorornis species. Its true relationships remain unknown.
Reference- Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.

Evgenavis O'Connor, Averianov and Zelenkov, 2014
E. nobilis O'Connor, Averianov and Zelenkov, 2014
Barremian, Early Cretaceous
Ilek Formation, Russia
Holotype- (ZIN PH 1/154) incomplete tarsometatarsus (48.68 mm)
Diagnosis- (after O'Connor et al., 2014) metatarsals fused only proximally; tarsometatarsus plantarly excavated; metatarsal II trochlea wide and angled so that lateral condyle extends farther than medial condyle; medial condyle of metatarsal II trochlea strongly projected plantarily; dorsal and plantar depressions of metatarsal II trochlea well developed; tubercle on proximal dorsal surface of metatarsal III, with another just distal to it on metatarsal II; plantar surface of metatarsal III strongly medially excavated proximal to trochlea; distal vascular foramen closed by medial projection of metatarsal IV; metatarsal IV with small, non-perforating, plantar foramina; metatarsal IV trochlea non-ginglymous; metatarsal V present.
Comments- The holotype was discovered in 2007. Despite stating "Evgenavis differs from Confuciusornis only in size and proportions, being larger and more slender and waisted than the latter", O'Connor et al. recovered it as an enantiornithine in their analysis (based on O'Connor's matrix). They ended up merely placing it in Aves incertae sedis. The fact that the four taxa this paper added to O'Connor's matrix ended up in a clade together when implied weights were used could suggest systematic coding errors/differences compared to O'Connor's original taxa. As Cau (online, 2014) recovered Evgenavis as an enantiornithine as well, it is tentatively placed in that clade here.
References- Cau, online 2014. http://theropoda.blogspot.com/2014/05/evgenavis-fortunguavis-tianyuornis.html
O'Connor, Averianov and Zelenkov, 2014. A confuciusornithiform (Aves, Pygostylia)-like tarsometatarsus from the Early Cretaceous of Siberia and a discussion of the evolution of avian hind limb musculature. Journal of Vertebrate Paleontology. 34(3), 647-656.

Feitianius O'Connor, Li, Lamanna, Wang, Harris, Atterholt and You, 2015
F. paradisi O'Connor, Li, Lamanna, Wang, Harris, Atterholt and You, 2015
Late Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Holotype- (CAGS-IG-05-CM-004) (male?) last five dorsal vertebrae, two dorsal ribs, dorsal rib fragments, gastralia, synsacrum, five or six caudal vertebrae, pygostyle, chevrons, partial ilium, incomplete pubes (23.4 mm), ischia (13.7 mm), femora (27.1 mm), tibiotarsi (35.7 mm), fibulae, metatarsals I (4.7 mm), phalanges I-1 (5.1 mm), pedal unguals I (~5.5 mm), tarsometatarsi (22.7 mm; II ~20.5, III 22.7, IV 21.3 mm), phalanges II-1 (4.5 mm), phalanges II-2 (6.2 mm), pedal unguals II (~5 mm), phalanges III-1 (6.3 mm), phalanges III-2 (5.5 mm), phalanges III-3 (6.2 mm), pedal unguals III (~6 mm), phalanges IV-1 (3.2 mm), phalanges IV-2 (2.8 mm), phalanges IV-3 (3.1 mm), phalanges IV-4 (4.7 mm), pedal unguals IV (~5.5 mm), pedal claw sheaths, collagen, uropygium, body feathers, retrices
Diagnosis- (after O'Connor et al., 2015) shallow lateral dorsal fossae; very small cuppedicus fossa; robust, curved, weakly retroverted pubis; dorsally tapered pubic boot; ischium weakly sigmoid; ischium with delicate ridge on anterior half of lateral surface; medial plantar crest well developed on tarsometatarsus; lateral plantar crest minimally developed; penultimate pedal phalanges the longest in each digit; pedal phalanges II-1 and II-2 dorsoventrally compressed and mediolaterally wide; pedal unguals large and relatively weakly recurved; pedal unguals with long sheaths; several different rectricial morphotypes.
Comments- This specimen was discovered in 2005 and first noted in Lamanna et al. (2009) and O'Connor (2009). O'Connor et al. (2015) named and described it as an enantiornithine in a basal polytomy (possibly caused by the inclusion of other partial specimens).
References- Lamanna, Li, Harris, Atterholt and You, 2009. Exceptionally preserved Enantiornithes (Aves: Ornithothoraces) from the Early Cretaceous of Northwestern China. Journal of Vertebrate Paleontology. 29(3), 131A.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
O'Connor, Li, Lamanna, Wang, Harris, Atterholt and You, 2015. A new Early Cretaceous enantiornithine (Aves, Ornithothoraces) from northwestern China with elaborate tail ornamentation. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1054035

Gracilornis Li and Hou, 2011
G. jiufotangensis Li and Hou, 2011
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (PMOL-AB00170) skull (~34.1 mm), mandibles, eleven cervical vertebrae, three dorsal vertebrae, dorsal ribs, eight sacral vertebrae, six caudal vertebrae, pygostyle (12.8 mm), scapulae, coracoids (14.5 mm), furcula (15.5 mm), sternum (14.6 mm), humeri (24.4 mm), radii (24.3 mm), ulnae (26.3 mm), pisiform, metacarpals I (1.9 mm), phalanges I-1 (~4.1 mm), manual ungual I (~.7 mm), carpometacarpus (II 10.4, III 12.5 mm), phalanges II-1 (6.9 mm), phalanges II-2 (4.1 mm), manual ungual II (1.5 mm), phalanges III-1 (3.4 mm), ilia, pubes (19.4 mm), ischium, femora (21.1 mm), tibiotarsi (27.2 mm), fibula (6.5 mm), metatarsals I (3.1 mm), phalanges I-1 (3.9 mm), pedal unguals I (4.3 mm), tarsometatarsi (III 14.2, III 15.1, IV 14.1 mm), phalanges II-1 (3.5 mm), phalanges II-2 (4.7 mm), pedal unguals II (4.6 mm), phalanges III-1 (4.6 mm), phalanges III-2 (4.1 mm), phalanges III-3 (4.1 mm), pedal ungual III (4.2 mm), phalanx IV-1 (2.4 mm), phalanx IV-2 (2.1 mm), phalanx IV-3 (2.1 mm), pedal ungual IV (3.9 mm)
Diagnosis- (after Li and Hou, 2011) slender skeleton; small sternum (sternum length/trunk length ~0.11, sternum width/trunk length ~0.13); well developed arthroses of limbs.
Comments- The diagnosis is vague except for sternum size, which increases in ontogeny.
Reference- Li and Hou, 2011. Discovery of a new bird (Enantiornithines) from Lower Cretaceous in Western Liaoning, China. Journal of Jilin University (Earth Science Edition). 41(3), 759-763.

Huoshanornis Wang, Zhang, Gao, Hou, Meng and Liu, 2010
H. huji Wang, Zhang, Gao, Hou, Meng and Liu, 2010
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (D2126) skull, mandible, seven cervical vertebrae, three dorsal vertebrae, dorsal ribs, synsacrum, four caudal vertebrae, pygostyle (9.4 mm), scapula, coracoids (14.1 mm), incomplete furcula, incomplete sternum, humeri (21.3 mm), radii, ulnae (24.5 mm), pisiform, phalanges I-1 (3.9 mm), manual unguals I, metacarpals II (13.9 mm), phalanges II-1, phalanges II-2, manual unguals II, metacarpals III, phalanges III-1, pubes, ischium, femora (20.8 mm), tibiotarsi (27.5 mm), metatarsals I, phalanges I-1, pedal unguals I, tarsometatarsi (15.5 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
Diagnosis- (after Wang et al., 2010) intermetacarpal space broad; phalanx I-1 greatly reduced, roughly one fourth the length of the carpometacarpus; phalanx III-1 as long as and almost as wide as II-1; posterolateral sternal process slightly shorter than posteromedian process, with remarkable triangular expansion at its distal end.
Comments- This specimen was discovered before 2010 and was originally described in an elusive thesis by an unknown author.
References- Wang, Zhang, Gao, Hou, Meng and Liu, 2010. A new enantiornithine bird from the Early Cretaceous of Western Liaoning, China. The Condor. 112(3), 432-437.
?, 20??. Description of a new enantiornithine bird from the Early Cretaceous of western Liaoning, China. Masters Thesis. 66 pp.

Iberomesornithiformes Sanz and Bonaparte, 1992
Definition- (Iberomesornis romeralii < Cathayornis yandica, Gobipteryx minuta, Enantiornis leali) (Martyniuk, 2012)
Iberomesornithidae Sanz and Bonaparte, 1992
References- Sanz and Bonaparte, 1992. A new order of birds (Class Aves) from the Lower Cretaceous of Spain. In Campbell (ed.). Papers in Avian Paleontology Honoring Pierce Brodkorb. Proceedings of the II International Symposium of the Society of Avian Paleontology and Evolution. 38-49.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Iberomesornis Sanz and Bonaparte, 1992
I. romerali Sanz and Bonaparte, 1992
Late Barremian, Early Cretaceous
Calizas de La Huerguina Formation, Spain
Holotype- (LH-22) (87 mm) fragment of sixth cervical vertebra, seventh cervical vertebra (2.3 mm), eighth cervical vertebra (2.2 mm), ninth cervical vertebra (1.9 mm), tenth cervical vertebra (1.8 mm), first dorsal vertebra (1.7 mm), second dorsal vertebra (1.7 mm), third dorsal vertebra (1.7 mm), fourth dorsal vertebra (1.7 mm), fifth dorsal vertebra (1.7 mm), sixth dorsal vertebra (1.7 mm), seventh dorsal vertebra (1.7 mm), eighth dorsal vertebra (1.8 mm), ninth dorsal vertebra (1.8 mm), tenth dorsal vertebra (1.7 mm), eleventh dorsal vertebra (1.7 mm), thirteen dorsal ribs, dorsal rib fragments, first sacral vertebra (1.4 mm), second sacral vertebra (1.4 mm), third sacral vertebra, fourth sacral vertebra (~1.3 mm), fifth sacral vertebra (~1.3 mm), sixth sacral vertebra (1.2 mm), seventh sacral vertebra (1 mm), eighth sacral vertebra (.9 mm), first caudal vertebra (.9 mm), second caudal vertebra (.9 mm), third caudal vertebra (.9 mm), fourth caudal vertebra (.9 mm), fifth caudal vertebra (.9 mm), sixth caudal vertebra (.8 mm), six chevrons, pygostyle (9.2 mm), partial scapula (10.1 mm), coracoids (9.9 mm), furcula, partial sternum, eight sternal ribs, incomplete humerus (~17.6 mm), radius (18.2 mm), incomplete ulna (~19.2 mm), partial ilia (10.3 mm), partial pubes, ischia, incomplete femora (16.4 mm), tibiotarsi (20 mm), metatarsal I (2.4 mm), phalanx I-1 (2.9 mm), pedal ungual I (2.5 mm), metatarsal II (11.2 mm), phalanx II-1 (2.3 mm), phalanx II-2 (3.5 mm), pedal ungual II (2.2 mm), metatarsal III (11.8 mm), phalanx III-1 (3.2 mm), phalanx III-2 (2.8 mm), phalanx III-3 (3.4 mm), pedal ungual III (2.3 mm), metatarsal IV (11.5 mm), phalanx IV-1 (1.9 mm), phalanx IV-2 (1.6 mm), phalanx IV-3 (1.7 mm), phalanx IV-4 (2.4 mm), pedal ungual IV (1.8 mm)
Referred- ?(LH-8200) metatarsal I, pedal phalanx I-1, pedal ungual I, tarsometatarsus (14 mm), pedal phalanx II-1, pedal phalanx II-2, pedal ungual II, pedal phalanx III-1, pedal phalanx III-2, pedal phalanx III-3, pedal ungual III, pedal phalanx IV-1, pedal phalanx IV-2, pedal phalanx IV-3, pedal phalanx IV-4, pedal ungual IV (Sanz and Buscalioni, 1994)
Diagnosis- pubic peduncle of ilium directed anteroventrally.
References- Sanz, Bonaparte and Lacasa, 1988. Unusual Early Cretaceous birds from Spain. Nature. 331, 433-435.
Sanz and Bonaparte, 1992. A new order of birds (Class Aves) from the Lower Cretaceous of Spain. In Campbell (ed.). Papers in Avian Paleontology Honoring Pierce Brodkorb. Proceedings of the II International Symposium of the Society of Avian Paleontology and Evolution. 38-49.
Sanz and Buscalioni, 1994. An isolated bird foot from the Barremian (Lower Cretaceous) of Las Hoyas (Cuenca, Spain). Geobios. 16, 213-217.
Sereno, 2000. Iberomesornis romerali (Ornithothoraces, Aves) re-evaluated as an enantiornithine bird. Neues Jahrbuch für Geologie und Paléontologie Abhandlungen. 215, 365-395.
Sanz, Pérez-Moreno, Chiappe and Buscalioni, 2002. The birds from the Lower Cretaceous of Las Hoyas (Privince of Cuenca, Spain). In Chiappe and Witmer (eds.). Mesozoic Birds: Above the Heads of Dinosaurs. University of California Press. 209-229.

"Ichthyornis" minusculus Nessov, 1990
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistanan
Holotype- (ZIN PO 3941) (~205 mm) dorsal vertebra (4 mm)
Comments- Mourer-Chauvire (1989) mentioned this as a "vertebra of an Ichthyornithiform the size of a thrush." This specimen can be assigned to Enantiornithes based on its centrally located parapophysis.
References- Mourer-Chauvire, 1989. Society of Avian Paleontology and Evolution Information Newsletter. 3.
Nessov, 1990. Small ichthyornithiform bird and other bird remains from Bissekty Formation (Upper Cretaceous) of central Kyzylkum Desert. Proceedings of the Zoological Institute, Leningrad. 210, 59-62 (in Russian).
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.

Incolornis Panteleyev, 1998
Diagnosis- (proposed) very deep coracoid shaft (>40% of proximodistal head length); proximodorsal bump located on shaft just distal to scapular facet.
Other diagnoses- Panteleyev (1998) listed three diagnostic characters for Incolornis. Of these, the ventral longitudinal ridge on the coracoid shaft is also present in Iberomesornis, Enantiornis and Gobipteryx. The narrow coracoid tubercle is found in a wide range of taxa (e.g. Catenoleimus, Elsornis, Gurilynia, Enantiornis, Eocathayornis, Cathayornis). Finally, the supracoracoid foramen has its proximal exit on the middle of the medial side of the shaft in Enantiornis, Otogornis and Neuquenornis as well. O'Connor (2009) declared all Bissekty enantiornithines based on coracoids to be nomina dubia, though without detailed comparison.
Reference- Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
I. silvae Panteleyev, 1998
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (ZIN PO 4604) (~135 mm) proximal coracoid (~15 mm)
Diagnosis- (after Panteleyev, 1998) smaller than I. martini.
(proposed) proximodorsal coracoid bump placed further distally than in I. martini.
Comments- This was discovered in 1989 and originally identified as Enantiornithes(?) by Nessov and Panteleev (1993) and Nessov (1997). Panteleyev (1998) made it the type species of his new genus Incolornis. While O'Connor (2009) stated the proximodorsal bump was similar to Protopteryx, the latter's process is medial instead of dorsal so topologically congruent with the procoracoid process.
References- Nessov and Panteleev, 1993. On the similarity of the Late Cretaceous ornithofauna of South America and Central Asia. Trudy Zoologicheskogo Instituta, RAN. 252, 84-94.
Nessov, 1997. [Cretaceous nonmarine vertebrates of northern Eurasia]. Saint Petersburg, Institute of Earth Crust. 1-218.
Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
I. martini (Nessov and Panteleev, 1993) Panteleyev, 1998
= Enantiornis martini Nessov and Panteleyev, 1993
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (ZIN PO 4609) (~220 mm) proximal coracoid (~25 mm)
Diagnosis- (after Panteleyev, 1998) larger than I. silvae.
(proposed) proximodorsal coracoid bump placed further proximally than in I. silvae.
Other diagnoses- Kurochkin (1996) listed the narrow coracoid tubercle as a diagnostic feature, but as noted in the genus diagnosis, this is widespread in enantiornithines. He also listed the stout shaft, which is covered in the genus diagnosis above.
Panteleyev (1998) also distinguishes I. martini from I. silvae based on the supposedly less transversely flattened coracoid shaft, but this seems untrue as I. martini has a width/depth ratio of 69% while I. silvae's is 74%. His final character is the larger groove between the glenoid and acrocoracoid in I. martini, but this could be due to erosion in I. silvae's holotype.
Comments- This was discovered in 1989 and originally figured as a scapula of Enantiornithidae indet. by Nessov (1992). It was later described as "Enantiornis" martini by Nessov and Panteleev (1993), which may indicate they did not feel it belonged in that genus. Kurochkin (1996) believed it was Enantiornis based on the obtuse acrocoracoid tip and stout coracoid process. However, the acrocoracoid tip is no more obtuse than Explorornis, walkeri, and Alexornis, and the coracoid process is less stout in Enantiornis than in Explorornis, Catenoleimus, Otogornis or Neuquenornis. Kurochkin (2000) later kept the species in Enantiornis and added a couple coracoid features to his diagnosis of the genus- short coracoid shaft; stout acrocoracoid process. The former is plesiomorphic, while the latter is also present in Otogornis and walkeri. Panteleev (1998) referred this species to his new genus Incolornis, based on I. silvae, which seems correct despite his listed diagnosis for the genus being problematic.
References- 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.
Nessov and Panteleev, 1993. On the similarity of the Late Cretaceous ornithofauna of South America and Central Asia. Trudy Zoologicheskogo Instituta, RAN. 252, 84-94.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.
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.

"Jinzhouornis" "delicates" Zhang, 2007
Barremian-Aptian, Early Cretaceous
Yixian, Yixian Formation, Liaoning, China
Material- (juvenile) incomplete skull, cervical series, dorsal series, dorsal ribs, sacrum, caudal series, pygostyle, scapulae, coracoids, sternum(?), humeri, radii, ulnae, manus (one partial), ilia, femora, tibiae, metatarsus, pedal digits I-IV, body feathers, remiges
Comments- Zhang (2007) provided this brief description (translated) - "The primitive bird whose individual is smaller than the petite Liaoxiornis, belongs to the Enantiornithes group. The head is short and round, the skull is relatively developed, and the jaw has teeth. The outer body is feathered, and the forelimbs have become wings. There are 3 curved finger claws, which are relatively developed, the sternal keel is prominent, the caudal vertebra have fused, and the tail is short. ... This fossil is the smallest bird fossil discovered in the Late Jurassic-Early Cretaceous Yixian Formation of western Liaoning, China, and it remains to be studied."
The generic assignment is odd because Jinzhouornis is a confuciusornithid, but this is stated to be an enantiornithine. That identification seems to be correct, given the short fused premaxillae preserved left of the main skull, coracoid and humeral shape, tiny diamond-shaped sternum, and manus with short digit I and reduced ungual and seemingly long metacarpal III projecting past II. In addition to the sternal anatomy, the poorly ossified ends of elements and stated small size strongly suggests a young age. The description seems inaccurate in that the round head is probably due to beak elements overlapping the posterior cranium, the manual unguals are not well developed or necessarily three in number, and the sternum shows no sign of a keel. The other details are congruent with a juvenile enantiornithine, and this specimen is likely indeterminate as are most other juvenile enantiornithines ( e.g. Liaoxiornis, Dalingheornis, GMV-2158 and 2159). It is a nomen nudum as there is no "explicit fixation of a holotype, or syntypes" (ICZN Article 16.4.1).
Reference- Zhang, 2007. The Fossils of China. China University of Geosciences Press. 502 pp.

Longchengornis Hou, 1997
L. sanyanensis Hou, 1997
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V10530) (~110 mm, 86 g) frontals, parietals, axis (3 mm), postaxial cervical vertebrae, dorsal vertebrae, dorsal ribs, sacrum (14 mm), fifteen caudal vertebrae, scapula, coracoids (17 mm), furcula, sternum, humeri (32.5 mm), radius (29 mm), ulna, scapholunare, pisiform, metacarpal I, phalanx I-1, manual ungual I, carpometacarpus (15 mm), manual phalanx II-1, partial ilium (17 mm), pubis (~21 mm), ischium (~11 mm), femur (21.5 mm), tibiotarsi (~34 mm), fibula, pedal phalanx I-1 (5.5 mm), pedal ungual I (7 mm), tarsometatarsus (~21.5 mm), pedal phalanx II-1, pedal phalanx II-2, pedal ungual II (8 mm), pedal phalanx III-1, pedal phalanx III-2, pedal phalanx III-3, pedal ungual III, pedal phalanx IV-1, pedal phalanx IV-2, pedal phalanx IV-3, pedal phalanx IV-4, pedal ungual IV
Diagnosis- large foramen in proximal humerus.
Comments- Pittman et al. (2020) listed Longchengornis as a junior synonym of Cathayornis without comment.
References- Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.
Pittman, O'Connor, Tse, Makovicky, Field, Ma, Turner, Norell, Pei and Xu, 2020. The fossil record of Mesozoic and Paleocene pennaraptorans. In Pittman and Xu (eds.). Pennaraptoran Theropod Dinosaurs: Past Progress and New Frontiers. Bulletin of the American Museum of Natural History. 440(1), 37-95.

Yuanjiawaornis Hu, Liu, Li, Xu and Hou, 2015
Y. viriosus Hu, Liu, Li, Xu and Hou, 2015
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (PMOL AB00032) (subadult) seven dorsal vertebrae, dorsal ribs, gastralia, synsacrum, six caudal vertebrae, chevrons, pygostyle (22.5 mm), scapulae (one incomplete), coracoids (28 mm), furcula, sternum (34 mm), sternal ribs, humeri (51 mm), radii (49 mm), ulnae (53 mm), scapholunare, pisiform, proximal carpal fragments, metacarpal I (5.5 mm), phalanx I-1 (11 mm), manual unguals I (4.5 mm), metacarpal II (~21.5 mm), phalanx II-2, metacarpals III (one incomplete; 22.5 mm), phalanx III-1, ilia (29 mm), pubes (36 mm), ischia, incomplete femora (43 mm), tibiotarsi (50.5 mm), fibulae (20.5 mm), metatarsal I (6.5 mm), phalanx I-1 (7 mm), pedal unguals I (9 mm), tarsometatarsi (mtII 24.5, mtIII 27, mtIV 25 mm), pedal phalanx, pedal ungual II/III/IV (9 mm)
Diagnosis- (after Hu et al., 2015) large size (but smaller than Pengornis); ventral surface of synsacrum grooved longitudinally (ridged in Bohaiornis and Parabohaiornis); transverse processes of last sacral vertebra robust and long (those of penultimate sacral vertebra robust and long in Zhouornis, Parabohaiornis and Longusunguis); acromion process tapered anterodorsally (nearly parallel to scapular shaft in bohaiornithids except Longusunguis); lateral margin of coracoid straight (strongly convex in Pengornis, Shenqiornis, Sulcavis and Longusunguis); clavicular rami medially curved and omal tips tapered (clavicular rami straight and omal tips expanded laterally in bohaiornithids); sternum oval in outline with posterolateral processes slightly expanded distally (processes strongly expanded distally in most bohaiornithids, and anterolateral margin of sternum angular in Zhouornis); forelimb and hind limb subequal in length (forelimb much longer than hind limb in Pengornis); humeral head flat (convex in Pengornis and concave in bohaiornithids except Zhouornis); deltopectoral crest gradually decreases in height distally (abruptly decreases distally in Shenqiornis, Sulcavis and Longusunguis).
Comments- The holotype was discovered in 2005. It was assigned to Enantiornithes and said to resemble bohaiornithids, but was not included in a phylogenetic analysis.
Reference- Hu, Liu, Li, Xu and Hou, 2015. Yuanjiawaornis viriosus, gen. et sp. nov., a large enantiornithine bird from the Lower Cretaceous of western Liaoning, China. Cretaceous Research. 55, 210-219.

unnamed Enantiornithes (Morrison, Dyke and Chiappe, 2005)
Late Campanian, Late Cretaceous
Northumberland Formation of the Nanaimo Group, British Columbia, Canada
Material- (RBCM.EH2005.003.0002.A) incomplete radius (106 mm) (Morrison, Dyke and Chiappe, 2005)
(RBCM.EH2005.003.0002.B) proximal coracoid (Morrison, Dyke and Chiappe, 2005)
(RBCM.EH2009.021.0001) incomplete femur (70 mm), proximal tibiotarsus, partial fibula (Dyke, Wang and Kaiser, 2011)
References- Morrison, Dyke and Chiappe, 2005. Cretaceous fossil birds from Hornby Island (British Columbia). Canadian Journal of Earth Sciences. 42, 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, 1489-1496.

unnamed enantiornithine (Currie and Padian, 1983)
Late Campanian, Late Cretaceous
Dinosaur Park Formation, Alberta, Canada
Material- (RTMP 79.14.247) distal tibiotarsus (11 mm wide)
Comments- This was originally identified as a pterosaur tibiotarsus by Currie and Padian (1983).
References- Currie and Padian, 1983. A new pterosaur record from the Judith River (Oldman) Formation of Alberta. Journal of Paleontology, 57(3), 599-600,
Buffetaut, 2010. A basal bird from the Campanian (Late Cretaceous) of Dinosaur Provincial Park (Alberta Canada). Geological Magazine. 147(3), 469-472.

unnamed possible Enantiornithes (Cumbaa and Tokaryk, 1993)
Middle Cenomanian, Late Cretaceous
Carrot River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
Material- (RSM P2077.66) distal metatarsal III (Tokaryk, Cumbaa and Storer, 1997)
Middle Cenomanian, Late Cretaceous
Bainbridge River, Belle Fourche Member of the Ashville Formation, Saskatchewan, Canada
(RSM P2989.26) proximal scapula (Sanchez, 2010)
Comments- Cumbaa and Tokaryk (1993) referred to a "presumed enantiornithine" at the Carrot River site. It was later described by Tokaryk et al. (1997) as a possible enantiornithine based on the lack of distal fusion. However, this is a primitive character, so it should be compared to other theropod metatarsi.
Sanchez (2010) lists RSM P2989.26 as "Enantiornithes?".
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.
Sanchez, 2010. Late Cretaceous (Cenomanian) Hesperornithiformes from the Pasquia Hills, Saskatchewan, Canada. Masters thesis, Carleton University. 238 pp.

unnamed enantiornithine (Longrich, Tokaryk and Field, 2011)
Late Maastrichtian, Late Cretaceous
Frenchman Formation, Saskatchewan, Canada
Material- (NMC 9528; Lancian Enantiornithine A) proximal coracoid
Reference- Longrich, Tokaryk and Field, 2011. Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary. Proceedings of the National Academy of Sciences of the United States of America. 108(37), 15253-15257.

unnamed enantiornithine (Longrich, Tokaryk and Field, 2011)
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, Montana, US
Material- (YPM 57823; Lancian Enantiornithine B) proximal coracoid
Comments- This differs from YPM 57235, which Longrich et al. (2011) refer to Avisaurus archibaldi due to its large size.
Reference- Longrich, Tokaryk and Field, 2011. Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary. Proceedings of the National Academy of Sciences of the United States of America. 108(37), 15253-15257.

unnamed enantiornithine (Hutchison, 1993)
Late Campanian, Late Cretaceous
Kaiparowitz Formation, Utah, US
Material- (RAM 14306) proximal coracoid (Farke and Patel, 2012)
Comments- Atterholt et al. (2018) found this differs from the contemporaneous Mirarce in having an angular acrocoracoid, and deeper groove between the scapular cotyla and glenoid.
Reference- Farke and Patel, 2012. An enantiornithine bird from the Campanian Kaiparowits Formation of Utah, USA. Cretaceous Research. 37, 227-230.
Atterholt, Hutchison and O'Connor, 2018. The most complete enantiornithine from North America and a phylogenetic analysis of the Avisauridae. PeerJ. 6:e5910.

undescribed enantiornithine (Galton, Dyke and Kurochkin, 2009)
Berriasian, Early Cretaceous
Purbeck Limestone Group, England
Material- humerus
Reference- 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.

unnamed Enantiornithes (Sanz, Chiappe, Fernadez-Jalvo, Ortega, Sanchez-Chillon, Poyato-Ariza and Perez-Moreno, 2001)
Late Barremian, Early Cretaceous
Calizas de La Huerguina Formation, Spain
Material- (LH 11386 bird 3) (juvenile) distal tibia, astragalus, phalanx I-1, pedal ungual I, metatarsal II, metatarsal III, metatarsal IV, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, pedal phalanges, pedal ungual (Sanz, Chiappe, Fernadez-Jalvo, Ortega, Sanchez-Chillon, Poyato-Ariza and Perez-Moreno, 2001)
(MCCMLH31444) incomplete radius, incomplete ulna, incomplete carpometacarpus, phalanx I-1, incomplete manual ungual I, phalanx II-1, phalanx II-2, manual ungual II, manual claw sheath, phalanx III-1, phalanx III-2, skin, muscles, body feathers, remiges (Navalon, Marugon-Lobon, Chiappe, Sanz and Buscalioni, 2015)
Comments- LH 11386 bird 3 is one of the two most fragmentary of four juvenile birds found associated in a theropod or pterosaur pellet. It was only identified as a bird by Sanz et al. (2001), and is the specimen on the right which is colored black in their illustration. The medial tibiotarsal condyle being wider than the lateral one is only seen in Patagopteryx among euornithines. Also, the proximal end of metatarsal III is in the same plane as metatarsals II and IV, which is only seen in Patagopteryx, Archaeorhynchus and Hongshanornis among euornithines. Metatarsal IV being so narrow compared to II and III is uniquely enantiornithine. Where exactly it fits among Enantiornithes must await further description or better illustration.
References- Sanz, Chiappe, Fernadez-Jalvo, Ortega, Sanchez-Chillon, Poyato-Ariza and Perez-Moreno, 2001. An Early Cretaceous pellet. Nature. 409, 998-999.
Navalon, Marugon-Lobon, Chiappe, Sanz and Buscalioni, 2015. Soft-tissue and dermal arrangement in the wing of an Early Cretaceous bird: Implications for the evolution of avian flight. Scientific Reports. 5, 14864.

unnamed Enantiornithes (Buffetaut, 1998)
Late Campanian-Early Maastrichtian, Late Cretaceous
Massecaps, Hérault, France
Material- (ACAP-M 192) incomplete coracoid
(ACAP-M 193) proximal femur
Comments- These were described by Buffetaut (1998) as enantiornithines and stated to resemble Enantiornis most closely. Walker et al. (2007) noted they could be referrable to the similarly sized Martinavis from the same strata, and described more precise similarities between ACAP-M 192 and Enantiornis, and ACAP-M 193 and unnamed Lecho Formation femora. Whether these similarities (reduced acrocoracoid; robust coracoid head; supracoracoid foramen does not open into dorsal fossa; well developed trochanteric crest; deeply excavated proximolateral surface of femur) are synapomorphic requires further study.
References- Buffetaut, 1998. First evidence of enantiornithine birds from the Upper Cretaceous of Europe: Postcranial bones from Cruzy (Hérault, Southern France). Oryctos. 1, 131-136.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.

unnamed Enantiornithes (Osi, 2004)
Santonian, Late Cretaceous
Csehbanya Formation, Hungary
Material- (MTM V.2002.05) incomplete femur (22 mm) (Osi, 2004)
(MTM V.2009.39.1) distal humerus (Dyke and Osi, 2010)
References- Osi, 2004. Enantiornithine bird remains from the Late Cretaceous of Hungary. Sixth International Meeting of the Society of Avian Palaeontology and Evolution, Abstracts. 50.
Osi, 2008. Enantiornithine bird remains from the Late Cretaceous of Hungary. Oryctos. 7, 55-60.
Dyke and Osi, 2010. A review of Late Cretaceous fossil birds from Hungary. Geological Journal. 45(4), 434-444.

unnamed probable enantiornithine (Nessov, 1988)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Material- (ZIN PO 3473) axis (13.5 mm)
Comments- Nessov (1988, 1992a) originally assigned this axis to Aves, then later (1992b) stated it was similar to Gaviidae. Kurochkin (1996) assigned it to Alexornithidae within Enantiornithines. This was based on several characters- general elongation; poorly developed prezgyapophyseal facets; lateral extensions of the prezgyapophyseal facets; broad neural arch; dorsally flat posterior neural arch that is projected posteriorly; low neural spine; shallow lateral central fossa. These were compared favorably to Gobipteryx (his Nanantius valifanovi) which he included in Alexornithidae, but it should be noted how few enantiornithine axes are known and described. The axis of Hebeiornis shares the poorly developed prezygapopgyses, lateral prezgyapophyseal extensions and broad neural arch, though it is less elongate and seemingly has a less posteriorly extensive neural arch. That of LP-4450-IEI has the broad neural arch and low neural spine, but is less elongate. Those of GMV-2158, Eocathayornis and Eoenantiornis are much shorter, but cannot be compared otherwise. Additionally, many of the characters have a broader distribution. Both Confuciusornis and Patagopteryx have axes with low neural spnes and shallow lateral fossae, for instance. It is tentatively retained here as an enantiornithine closer to Gobipteryx than the other taxa mentioned above based on elongation, but it should be compared to a wider range of coelurosaurs as well.
References- Nessov, 1988. [New Cretaceous and Paleogene birds of Soviet Middle Asia and Kazakhstan and their environments] Trudy Zoologicheskogo Instituta. 182, 31-38.
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, Palaeontological Institute, special issue. 50 pp.

unnamed enantiornithine (Balanoff, Norell, Grellet-Tinner and Lewin, 2008)
Santonian-Campanian?, Late Cretaceous
Javkhlant Formation, Mongolia
Material- (IGM 100/2010) (embryo) quadrate?, occiput or cervical neural arch, three dorsal vertebrae, two dorsal centra, partial scapula?, coracoids (one partial), furcular fragement?, humeri (~17-18 mm), radius (18.5 mm), ulnae, femora (13.4, 13 mm), tibiae (15.5, 15.6 mm), metatarsi (8.8, 8.3 mm), fragments, egg (~47.5x22.3 mm)
Comments- Balanoff and Norell (2006) and Balanoff et al. (2008) originally described and assigned this specimen to Neoceratopsia, but reidentified as an enantiornithine by Varricchio et al. (2015). The humeri, femora, tibiae and fibula were reidentified as the femora, humeri, ulnae and radius respectively, and cervical vertebrae were reidentified as dorsals. The supposed predentary may be the median area of a furcula, the supposed qudrate may be correctly identified, and the occiput may be that or a cervical neural arch.
References- Balanoff and Norell, 2006. Embryonic ornithischian from the Upper Cretaceous on Mongolia. Journal of Vertebrate Paleontology. 26(3), 38A-39A.
Balanoff, Varricchio and Norell, 2008 online. Enantiornithine Bird, Digital Morphology. http://digimorph.org/specimens/enantiornithine_embryo/
Balanoff, Norell, Grellet-Tinner and Lewin, 2008. Digital preparation of a probable neoceratopsian preserved within an egg, with comments on microstructural of ornithischian eggshells. Naturwissenschaften. 95, 493-500.
Varricchio, Balanoff and Norell, 2015. Reidentification of avian embryonic remains from the Cretaceous of Mongolia. PLoS ONE. 10(6), e0128458.

unnamed Enantiornithes (Kurochkin, 1999)
Late Campanian-Early Maastrichtian, Late Cretaceous
Gurilin Tsav, Nemegt Formation, Mongolia
Material- (PIN 4499-15) distal radius
(PIN 4499-16) distal ulna
(PIN 4499-18) distal carpometacarpus
Reference- Kurochkin, 1999. A new large enantiornithid from the Upper Cretaceous of Mongolia (Aves, Enantiornithes). Russian Academy of Sciences, Proceedings of the Zoological Institute. 277, 130-141.

undescribed enantiornithine (Hu, Gao, Xu and Hou, 2015)
Late Hauterivian, Early Cretaceous
Sichakou Sedimentary Member of the Huajiying Formation, Hebei, China
Material- (CSFM-B00002) (juvenile) incomplete skeleton including skull, mandible, sacrum, coracoid, sternum, forelimb, hindlimb and retrices
Diagnosis- (after Hu et al., 2015) snout half length of skull; upper teeth more numerous than dentary teeth; lateral margin of coracoid straight; posterior end of posteromedian sternal process forked laterally in goblet-like shape; forelimb ~115% of hindlimb length; manual digit I not extending to end of metacarpal II; metatarsals III and IV subequal in length; pedal digit III longer than metatarsal III; pair of strap-like retrices tapered distally.
Reference- Hu, Gao, Xu and Hou, 2015. A new enantiornithine specimen from the Lower Cretaceous of northern Hebei, China. Journal of Vertebrate Paleontology. Program and Abstracts 2015, 147.

undescribed Enantiornithes (Zheng, Zhou, Wang, Zhang, Zhang, Wang, Wei, Wang and Xu, 2013)
Barremian-Albian, Early Cretaceous
Jehol Group, China
Material- (STM 7-05) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-10) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-38) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-40) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-43) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-44) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-46) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-47) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-49) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-50) skull, mandible, cervical vertebrae, dorsal vertebrae, dorsal ribs, synsacrum, caudal vertebrae, pygostyle, coracoids, furcula, humerus, radius, ulnae, incomplete manus, pubes, femur, tibiotarsus, fibulae, pedal ungual I, tarsometatarsi, phalanx II-1, phalanx II-2, pedal ungual II, phalanx III-1, phalanx III-2, phalanx III-3, pedal ungual III, pedal phalanges, pedal unguals, pedal claw sheaths, body feathers, retrices, remiges (Zheng, Zhou, Wang, Zhang, Zhang, Wang, Wei, Wang and Xu, 2013)
(STM 7-54) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-61) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-62) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-66) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-63) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-68) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-72) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-73) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-78) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-93) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-98) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-104) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-108) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-113) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-116) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-121) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-123) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-112) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-123) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-136) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-138) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-160) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-161) skull, mandibles, cervical vertebrae, dorsal vertebrae, pygostyle, partial scapulae, partial coracoids, furcula, humeri, radii, ulnae, manus, femora, tibiotarsi, metatarsals I, phalanges I-1, pedal ungual I, tarsometatarsi, phalanges II-1, phalanges II-2, pedal ungual II, phalanges III-1, phalanx II-2, phalanges IV-1, body feathers, remiges (Zheng, Zhou, Wang, Zhang, Zhang, Wang, Wei, Wang and Xu, 2013)
(STM 7-162) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-168) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-175) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-176) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-177) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-184) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-188) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-189) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-191) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-192) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-194) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-200) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-204) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-209) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-210) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-213) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-214) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-215) cervical vertebrae, synsacrum, caudal vertebrae, pygostyle, humeri, ulnae, manus, femur, tibiotarsi, metatarsals I, phalanges I-1, pedal ungual I, tarsometatarsi, phalanx II-1, phalanx II-2, pedal ungual II, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-4, pedal unguals IV, body feathers, retrices, remiges (Zheng, Zhou, Wang, Zhang, Zhang, Wang, Wei, Wang and Xu, 2013)
(STM 7-219) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-226) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-227) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-230) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-235) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-237) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-243) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-244) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-256) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-258) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-261) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-262) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-267) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-269) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-270) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-271) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-273) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-274) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-280) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-281) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-283) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-284) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 7-286) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-12) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-16) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-19) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-23) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-28) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-31) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-33) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-34) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-45) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-63) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-64) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-79) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-82) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-85) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-89) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-100) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-102) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-106) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-108) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-121) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-122) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-136) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-137) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-140) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-142) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 8-143) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-4) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-5) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-8) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-10) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-11) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-19) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-22) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-29) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-33) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-36) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 10-38) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-1) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-4) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-5) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-6) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-7) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-8) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-9) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-10) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-11) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-13) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-14) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-15) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-17) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-18) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-81) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-85) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-86) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-95) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-103) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-125) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-127) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-134) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-151) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-154) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-156) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-163) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-165) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-167) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-171) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-172) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-179) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-184) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-186) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-188) specimen including dorsal vertebrae, dorsal ribs, scapulae, coracoids, furcula, sternum, anterolateral sternal process, sternal ribs and humeri (Zheng, Wang, O'Connor and Zhou, 2012)
(STM 11-199) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-201) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-204) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-210) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 11-213) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 24-1) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 25-6) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 25-8) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 29-8) (female) specimen including pygostyle, humerus, ovarian follicles and retrices (Zheng, O'Connor, Wang, Pan, Wang, Wang and Zhou, 2017)
(STM 34-1) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 34-7) specimen including pygostyle and retrices (Wang et al., 2021 online)
(STM 34-12) specimen including pygostyle and retrices (Wang et al., 2021 online)
References- Zheng, Wang, O'Connor and Zhou, 2012. Insight into the early evolution of the avian sternum from juvenile enantiornithines. Nature Communications. 3, 1116.
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, Wang, Pan, Wang, Wang and Zhou, 2017. Exceptional preservation of soft tissue in a new specimen of Eoconfuciusornis and its biological implications. National Science Review. 4(3), 441-452.
Wang, O'Connor, Zhao, Pan, Zheng, Wang and Zhou, 2021 online. An Early Cretaceous enantiornithine bird with a pintail. Current Biology. Online now. DOI: 10.1016/j.cub.2021.08.044

unnamed enantiornithine (Chiappe and Ji, 2002)
Late Barremian-Early Aptian, Early Cretaceous
Jianshangou Beds of Yixian Formation, Liaoning, China
Material- (GMV-2158) (juvenile) incomplete skull, incomplete mandibles, incomplete hyoid, nine cervical vertebrae, ten or eleven dorsal vertebrae, dorsal ribs, gastralia, six sacral vertebrae, seven or eight caudal vertebrae, chevrons, incomplete scapulae (~9.9, ~10.2 mm), partial coracoids (~7mm), furcula, incomplete sternum, lateral sternal ossification, sternal ribs, incomplete humeri (15.5, 15.7 mm), incomplete radii (14.6, 14.7 mm), partial ulna (15.6 mm), scapholunare, pisiform, semilunate carpal, distal carpal III, metacarpal I (1.4 mm), phalanx I-1 fragment, metacarpal II (6.9 mm), metacarpal III (7.2 mm), partial ilium, pubes (~9.5 mm), ischia, femora (14.3 mm), incomplete tibiae (18 mm), fibula (4.3 mm), astragalus, calacaneum, metatarsals I (2.6 mm), fragmentary phalanges I-1, partial pedal ungual I, metatarsals II (one incomplete; 10.1, 10.2 mm), phalanges II-1, phalanges II-2 (one partial), pedal ungual II, incomplete metatarsals III (11, 11.2 mm), phalanges III-1 (one fragmentary), phalanx II-2, phalanx III-3, incomplete metatarsals IV, incomplete phalanges IV-1, phalanx IV-2, partial phalanx IV-3, incomplete phalanx IV-4, incomplete pedal ungual IV, incomplete phalanx, partial ungual, remiges, retrices
References- Chiappe and Ji, 2002. Enantiornithine (Aves) neonates from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(3), 43A.
Chiappe, Ji and Ji, 2007. Juvenile birds from the Early Cretaceous of China: Implications for enantiornithine ontogeny. American Museum Novitates. 3594, 46 pp.

unnamed enantiornithine (Chiappe and Ji, 2002)
Early Aptian, Early Cretaceous
Dawangzhangzi Beds of Yixian Formation, Liaoning, China
Material- (GMV-2159) (juvenile) incomplete skull, sclerotic ring, mandibles, seven cervical vertebrae, twelve dorsal vertebrae, dorsal ribs, seven sacral vertebrae, six caudal vertebrae, pygostyle, scapula, coracoids (9.7, 9.8 mm), furcula, anterior sternal ossification, sternum, lateral sternal ossification, sternal ribs, humeri (20.7, 20.5 mm), radii (19.4, 19.6 mm), ulnae (20.8, 21.1 mm), scapholunares, pisiform, semilunate carpals, partial phalanges I-1, manual unguals I, metacarpals II (9, 8.8 mm), phalanges II-1, phalanges II-2, manual unguals II (9.2 mm), metacarpals III, phalanx III-1, pubes (12.5 mm), femora (17.2 mm), tibiae (20.1, 21.6 mm), astragalus, metatarsals I (2.8, 2.7 mm), phalanges I-1, pedal unguals I, metatarsals II (10.8, 10.7 mm), phalanges II-1, phalanges II-2, pedal unguals II, metatarsals III (11.8, 11.8 mm), phalanges III-1, phalanges II-2, phalanges III-3, pedal unguals III, phalanx IV-3, phalanx IV-4, pedal ungual IV, remiges, retrices
References- Chiappe and Ji, 2002. Enantiornithine (Aves) neonates from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(3), 43A.
Chiappe, Ji and Ji, 2007. Juvenile birds from the Early Cretaceous of China: Implications for enantiornithine ontogeny. American Museum Novitates. 3594, 46 pp.

undescribed Enantiornithes (Zhang and Zhou, 2004)
Mid Aptian, Early Cretaceous
Jingangshan Beds of Yixian Formation, Liaoning, China
Material- (IVPP V13939) skeleton including dorsal vertebrae, dorsal ribs, synsacrum, four or five caudal vertebrae, pygostyle, radius, ulna, manus, ilia, pubes, ischia, femora, tibiotarsi, tarsometatarsi, pedes, body feathers, remiges (Zhang and Zhou, 2004)
(IVPP V14238) (embryo) skull, mandible, eight cervical vertebrae, eleven dorsal vertebrae, dorsal ribs, six sacral vertebrae, nineteen caudal vertebrae, scapula, coracoids, furcula, humeri, radius, ulna, semilunate carpal, metacarpal I, phalanx I-1, manual ungual I, metacarpal II, phalanx II-1, phalanx II-2, manual ungual II, metacarpal III, ilium, pubes, ischium, femora, tibiae, metatarsal I, phalanx I-1?, metatarsals II, phalanx II-1, metatarsals III, phalanges III-1, phalanx III-2, phalanx III-3, pedal ungual III, metatarsals IV, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, remiges, retrices (egg ~35x20 mm) (Zhou and Zhang, 2004)
References- Zhang and Zhou, 2004. Leg feathers in an Early Cretaceous bird. Nature. 431, 925.
Zhou and Zhang, 2004. A precocial avian embryo from the Lower Cretaceous of China. Science. 306(5696), 653.

unnamed Enantiornithes (Hou, 1997)
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Material- (CNUVB-1001) skull, eight cervical vertebrae, dorsal vertebrae, dorsal ribs, three uncinate processes, four caudal vertebrae, pygostyle, scapulae, coracoids, furcula, sternum, sternal ribs, humeri (55.6 mm), radii, ulnae (60.8 mm), scapholunare, pisiform, carpometacarpi (26.4 mm), phalanges I-1, manual unguals I, phalanges II-1, phalanges II-2, manual ungual II, phalanges III-1, ilium, pubis, ischium, femora (40.4 mm), tibiotarsi (44.7 mm), fibula, 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 (Zhang, Chen, Zhang and Hou, 2014)
(DNHM D2130) incomplete skeleton including incomplete skull (O'Connor, 2009)
(DNHM D2836) incomplete skeleton including incomplete skull (O'Connor, 2009)
(DNHM D2884) incomplete skull, mandibles, cervical vertebrae, dorsal vertebrae, dorsal ribs, uncinate processes, sacrum, caudal vertebrae, pygostyle, coracoid, furcula, sternal ribs, humeri, radii, ulnae, pisiform, carpometacarpi, phalanges I-1, manual unguals I, phalanges II-1, phalanges II-2, phalanges III-1, ilia, femora, tibiotarsi, metatarsal I, phalanges I-1, pedal unguals I, tarsometatarsi, phalanges III-1, phalanges III-2, phalanx III-3, pedal ungual III, pedal phalanges, pedal unguals, body feathers, remiges and retrices (O'Connor, 2009)
(DMNH D2952; DMNH D2953) incomplete skeleton including incomplete skull (O'Connor, 2009)
(IVPP coll.) ?(IVPP coll.) ilium, pubis, ischium (Hou, 1997)
(STM 10-45) (female subadult) (105 g) skull, mandibles, five cervical vertebrae, dorsal vertebra, three caudal vertebrae, pygostyle, scapulae, coracoids, furcula, sternum, sternal ribs, humeri (40.4 mm), radii, ulnae, scapholunares, pisiforms, semilunate carpals, metacarpals I, phalanges I-1, manual unguals I, metacarpals II, phalanges II-1, phalanges II-2, manual ungual II, metacarpals III, phalanges III-1, femora (31.5 mm), tibiae, proximal tarsals, phalanx I-1, pedal ungual I, tarsometatarsi, phalanx II-2, pedal ungual II, phalanx III-3, pedal ungual III, phalanx IV-4, pedal ungual IV, pedal phalanges, ovarian follicles (Zheng et al., 2013)
(STM 29-8) (female adult) (126 g) skull, mandible, hyoid, six cervical vertebrae, dorsal vertebra, dorsal ribs, synsacrum, caudal vertebrae, pygostyle, furcula, humeri (44.8 mm), radii, ulnae, scapholunare, pisiform, carpometacarpi, phalanges I-1, manual unguals I, phalanges II-1, phalanges II-2, manual ungual II, phalanx III-1, ilium, pubis, ischium, femora (40.2 mm), tibiotarsi, pedal ungual I, tarsometatarsi, phalanx II-2, pedal ungual II, pedal phalanx fragments, body feathers, remiges, ovarian follicles (Zheng et al., 2013)
(STM 34-2) (juvenile) dorsal vertebrae, dorsal ribs, sacrum, caudal vertebrae, pygostyle, scapulae, coracoids, furcula, sternum, lateral sternal ossifications, sternal ribs, humeri, radii (one incomplete), ulnae (one incomplete), metacarpal I, phalanx I-1, manual ungual I, metacarpal II, phalanx II-1, phalanx II-2, manual ungual II, metacarpal III, ischia, femora, tibiae, metatarsal I, metatarsal II, phalanx II-1, metatarsal III, phalanx III-1, metatarsal IV, phalanx IV-1, body feathers, remiges (Zheng, Wang, O'Connor and Zhou, 2012)
(STM 34-9) (juvenile) skull, mandible, cervical vertebrae, dorsal vertebrae, dorsal ribs, sacrum, caudal vertebrae, pygostyle, scapulae, coracoids, anterior sternal ossification, sternum, lateral sternal ossification, sternal ribs, humeri, radii, ulnae, scapholunare, pisiforms, semilunate carpals, metacarpals I, phalanges I-1, manual unguals I, metacarpals II, phalanges II-1, phalanges II-2, manual ungual II, metacarpals III, phalanges III-1, iliu, incomplete pubis, ischium, femora, tibiae, metatarsal 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 unguals III, metatarsals IV, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, pedal claw sheaths, body feathers, retrices (Zheng, Wang, O'Connor and Zhou, 2012)
skeleton including skull, tibiotarsus, pes, body feathers and retrices (Peteya, Clarke, Li and Shawkey, 2015)
Early Albian, Early Cretaceous
Jiufotang Formation, Inner Mongolia, China
(IVPP V15036) (juvenile) specimen including dorsal vertebrae, dorsal ribs, scapulae, coracoids, furcula, lateral sternal ossification, sternal rib and humeri (Zheng, Wang, O'Connor and Zhou, 2012)
(IVPP V15564) (juvenile) specimen including dorsal vertebrae, dorsal ribs, coracoids, furcula, sternum, lateral sternal ossifications, sternal ribs and humerus (Zheng, Wang, O'Connor and Zhou, 2012)
(STM 34-1) (juvenile) skull, mandibles, hyoids, cervical vertebrae, dorsal vertebrae, dorsal ribs, gastralia, sacrum, caudal vertebrae, chevrons, pygostyle, scapula, coracoid, anterior sternal ossification, sternum, lateral sternal ossification, sternal ribs, humeri, radii, ulnae, metacarpals II, phalanx II-1, phalanx II-2, manual ungual II, metacarpals III, phalanx III-1, ilia, pubes, ischia, femora, tibiae, astragalocalcaneum, metatarsal I, phalanges I-1, pedal ungual I, metatarsals II, phalanges II-1, phalanges II-2, pedal unguals II, metatarsals III, phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, metatarsals IV, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, body feathers, remiges (Zheng, Wang, O'Connor and Zhou, 2012)
(STM 34-7) (juvenile) skull, cervical vertebrae, dorsal vertebrae, dorsal ribs, sacrum, caudal vertebrae, pygostyle, coracoids, furcula, anterior sternal ossification, sternum, lateral sternal ossification, sternal ribs, humeri, radii, ulnae, semilunate carpal, metacarpal I, phalanx I-1, manual ungual I, metacarpals II, phalanges II-1, phalanges II-2, manual unguals II, metacarpals III, phalanges III-1, ilia, femora, tibiae (one incomplete), phalanx I-1, metatarsi, pedal phalanges, pedal unguals, body feathers, retrices, remiges (Zheng, Wang, O'Connor and Zhou, 2012)
Comments- Hou (1997) includes a photograph of an articulated pelvis (IVPP coll.) which was illustrated as Cathayornis yandica by Zhou (1999) and Zhou and Hou (2002) without comment. It has a highly convex dorsal postacetabular margin and large amount of taper, unlike Cathayornis, so is probably wrongly referred.
Zhang et al. (2014) described a specimen they state is most similar to Pengornis (large size; hooked acromion; large interclavicular angle; forelimb/hindlimb ratio minus phalanges 1.32), but differs in- posteromedial sternal processes; more robust ulna; longer hallux.
References- Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.
Zhou, 1999. Early evolution of birds and avian flight- Evidence from Mesozoic fossils and modern birds. PhD thesis, University of Kansas. 216 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, Berkeley, Los Angeles, London. 160-183.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
O'Connor, Chiappe, Chuong, Bottjer and You, 2012. Homology and potential cellular and molecular mechanisms for the development of unique feather morphologies in early birds. Geosciences. 2, 157-177.
Zheng, Wang, O'Connor and Zhou, 2012. Insight into the early evolution of the avian sternum from juvenile enantiornithines. Nature Communications. 3, 1116.
Zheng, O'Connor, Huchzermeyer, Wang, Wang, Wang and Zhou, 2013. Exceptional preservation of ovarian follicles in Early Cretaceous birds and implications for early evolution of avian reproductive behaviour. Nature. 495, 507-511.
O'Connor, Wang, Zheng, Wang and Zhou, 2014. The histology of two female Early Cretaceous birds. Vertebrata PalAsiatica. 52(1), 112-128.
Zhang, Chen, Zhang and Hou, 2014. A large enantiornithine bird from the Lower Cretaceous of China and its implication for lung ventilation. Biological Journal of the Linnean Society. 113, 820-827.
Peteya, Clarke, Li and Shawkey, 2015. New details on the plumage and coloration of an Early Cretaceous enantiornithine bird. Journal of Vertebrate Paleontology. Program and Abstracts 2015, 194.

unnamed Enantiornithes (O'Connor, Chiappe, Ji and You, 2004)
Late Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Material- (CAGS-IG-02-0901) incomplete scapula, coracoid (19 mm), humerus (47.7 mm), radius (47.4 mm), ulna (49.4 mm), scapholunare, pisiform, carpometacarpus (I 3.7, II 19, III 21.5 mm), phalanx I-1, phalanx II-1 (11.1 mm), phalanx II-2 (7.9 mm), manual ungual II (6.6 mm), phalanx III-1 (4.6 mm), fragments (O'Connor, Chiappe, Ji and You, 2004)
(CAGS-IG-04-CM-023) partial humerus, radius (32.2 mm), ulna (33.6 mm), scapholunare, pisiform, carpometacarpus (17.1 mm; I 2.8, II 14.1 mm), phalanx I-1 (5.6 mm), manual ungual I (4.1 mm), phalanx II-1 (7.9 mm), phalanx II-2 (6.1 mm), manual ungual II (5.2 mm), phalanx III-1 (5 mm), phalanx III-2 (Harris, Lamanna, You, Ji and Ji, 2006)
(CAGS-IG-05-CM-012) pelvis, partial hindlimbs (O'Connor, 2009)
(CAGS-IG-07-CM-001) dorsal vertebra, dorsal rib fragment, synsacrum, caudal vertebrae, pygostyle, ilia, ischium (14.2 mm), femora (26.3 mm), tibiotarsi (34.4 mm), fibula, metatarsals I (~5.4 mm), phalanges I-1 (5.4 mm), pedal unguals I (5.2 mm), tarsometatarsi (21.6 mm; II 20.4, III 21.6, IV 20.8 mm), phalanges II-1 (4.7 mm), phalanges II-2 (5.8 mm), pedal unguals II (5.9 mm), phalanges III-1 (5.9 mm), phalanges III-2 (5.3 mm), phalanges III-3 (5.9 mm), pedal unguals III (5.8 mm), phalanges IV-1 (3.4 mm), phalanges IV-2 (2.7 mm), phalanges IV-3 (3.1 mm), phalanges IV-4 (4.3 mm), pedal unguals IV (~5.1 mm), body feathers, retrices (O'Connor, 2009)
(CAGS coll.) two specimens (Lamanna et al., 2009)
Comments- Note Ji et al. (2011) later described the Xiagou Qiliania as an enantiornithine, though it is placed more conservatively as Pygostylia incertae sedis here. Given that it is based on two specimens, this leaves six undescribed enantiornithines noted by Lamanna et al. (2009) (out of their 11 total). The three numbered specimens listed by O'Connor (2009) probably encompass the two posterior skeletons (one including retrices, another including feathers and pedal claw sheaths) mentioned by Lamanna et al. (2009). Indeed, CAGS-IG-07-CM-001 can be inferred to be the specimen including retrices by its mention and illustration in O'Connor et al. (2012), and its measurements are listed in O'Connor et al. (2015). The other specimen is confirmed to be CAGS-IG-05-CM-004 by O'Connor et al. (2015), who described it as Feitianius. CAGS-IG-05-CM-030 being described as Dunhuangia (Wang et al., 2015) further lowers the number of unpublished specimens. Avimaia was described based on IVPP 25371 with the paratype CAGS-IG-04-CM-007 orioginally being described without a name by Lammana et al. (2006).
References- O'Connor, Chiappe, Ji and You, 2004. New enantiornithine bird from the Early Cretaceous of Gansu Province, Northwestern China. Journal of Vertebrate Paleontology. 24(3), 244A-245A.
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, Lamanna, You, Ji and Ji, 2006. A second enantiornithean (Aves: Ornithothoraces) wing from the Early Cretaceous Xiagou Formation near Changma, Gansu Province, People’s Republic of China. Canadian Journal of Earth Sciences. 43, 547-554.
Lamanna, You, Harris, Chiappe, Ji, Lü and Ji, 2006. A partial skeleton of an enantiornithine bird from the Early Cretaceous of northwestern China. Acta Palaeontologica Polonica. 51(3), 423-434.
Lamanna, Li, Harris, Atterholt and You, 2009. Exceptionally preserved Enantiornithes (Aves: Ornithothoraces) from the Early Cretaceous of Northwestern China. Journal of Vertebrate Paleontology. 29(3), 131A.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
Ji, Atterholt, O'Connor, Lammana, Harris, Li, You and Dodson, 2011. A new, three-dimensionally preserved enantiornithine bird (Aves: Ornithothoraces) from Gansu Province, north-western China. Zoological Journal of the Linnean Society. 162, 201-219.
O'Connor, Chiappe, Chuong, Bottjer and You, 2012. Homology and potential cellular and molecular mechanisms for the development of unique feather morphologies in early birds. Geosciences. 2, 157-177.
O'Connor, Li, Lamanna, Wang, Harris, Atterholt and You, 2015. A new Early Cretaceous enantiornithine (Aves, Ornithothoraces) from northwestern China with elaborate tail ornamentation. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1054035
Wang, Li, O'Connor, Zhou and You, 2015. Second species of enantiornithine bird from the Lower Cretaceous Changma Basin, northwestern China with implications for the taxonomic diversity of the Changma avifauna. Cretaceous Research. 55, 56-65.

undescribed enantiornithine (Zheng, Zhang and Hou, 2007)
Early Aptian, Early Cretaceous
Qiaotou Member of the Huajiying Formation, Hebei, China
Material- (STM V001) incomplete skull, sclerotic ring, seven cervical vertebrae, incomplete coracoid, proximal humerus, body feathers
Comments- Zheng et al. (2007) state the skull of Paraprotopteryx's holotype "seems not to be the same individual as the postcranial bones after careful examination", and the portion of the slab containing the skull and cervical vertebrae does seem to contain an additional left coracoid.
Reference- Zheng, Zhang and Hou, 2007. A new enantiornithine bird with four long retrices from the Early Cretaceous of Northern Hebei, China. Acta Geologica Sinica. 81(5), 703-708.

unnamed enantiornithine (Zhang, Zhang, Li and Li, 2010)
Early Cretaceous
Jingchuan Formation, Inner Mongolia, China
Material- (OFMB-3) two vertebrae, four dorsal ribs, furcula, sternum (23.1 mm), five sternal ribs (Zhang et al., 2010)
Comments- Zhang et al. (2010) referred a new specimen (OFMB-3) from the same locality to Cathayornis chabuensis, interpreting the differences (broadly triangular distal expansions of the posterolateral sternal processes; post-costal sternal processes) as being due to greater ontogenetic age. Wang and Liu (2016) suggested this could not be demonstrated, and given the lack of shared characters with chabuensis, declared OFMB-3 indeterminate.
References- Zhang, Zhang, Li and Li, 2010. New discovery and flying skills of Cathayornis from the Lower Cretaceous strata of the Otog Qi in Inner Mongolia, China. Geological Bulletin of China. 29(7), 988-992.
Wang and Liu, 2016 (online 2015). Taxonomical reappraisal of Cathayornithidae (Aves: Enantiornithes). Journal of Systematic Palaeontology. 14(1), 29-47.

undescribed possible enantiornithine (Unwin and Matsuoka, 2000)
Valanginian-Hauterivian, Early Cretaceous
Kuwajima Formation of the Tetori Group, Japan
Material- (SBEI 307) fragmentary humerus
Comments- Originally described in Japanese by Unwin and Matsuoka (2000), who also figured the bone. Matsuoka et al. (2002) referred to this as a bird based on its lack of torsion and Enantiornithes based on the lack of an anteriorly bulbous head. However, the former is actually present in most enantiornithines (with some exceptions like Elsornis, Neuquenornis and Enantiornis) and the latter character is symplesiomorphic for theropods. Unwin and Matsuoka's figure shows a capital groove and concave proximal border to the humeral head though, which agree with enantiornithine anatomy.
References- Unwin and Matsuoka, 2000. Pterosaurs and birds. In Matsuoka (ed.). Fossils of the Kuwojima "Kasekikabe" (Fossil-bluff): Scientific report on a Neocomian (Early Cretaceous) fossil assembrage from the Kuwajima Formation, Tetori Group, Shiramine, Ishikawa, Japan. Shiramine Village Board of Education, Ishikawa. 99-104.
Matsuoka, Kusuhashi, Takada and Setoguchi, 2002. A clue to the Neocomian vertebrate fauna: Initial results from the Kuwajima 'Kaseki-kabe' (Tetori Group) in Shiramine, Ishikawa, central Japan. Memoirs of the Faculty of Science, Kyoto University, Series of Geology and Mineralogy. 59(1), 33-45.

undescribed Enantiornithes (Li and Gao, 2007)
Barremian-Albian, Early Cretaceous
Sinuiju Series, North Korea
Material- ? distal tibiotarsus, metatarsal I, phalanx I-1, pedal ungual I, metatarsals II, phalanges II-1, phalanges II-2, metatarsals III, phalanges III-1, phalanges III-2, phalanges III-3, metatarsals IV, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal ungual IV (Gao et al., 2009)
? specimen including caudal vertebrae, pygostyle (~35 mm), forelimb material including manual ungual, manual claw sheath, partial ilium, femur, tibiotarsus (~50 mm), tarsometatarsus and pedal ungual (Gao et al., 2009)
several specimens (Li and Gao, 2007)
Comments- Li and Gao (2007) reported several enantiornithine specimens are known from the Sinuijiu Series, two of which are illustrated and commented on by Gao et al. (2009). The latter referred the hindlimb specimen to Enantiornithes based on- unfused metatarsus; metatarsal II much shorter than III or IV; metatarsals III and IV equal in length. Yet these are primitive characters, and as the fourth metatarsal isn't very reduced in width, this may be another kind of bird such as a confuciusornithid. The large pedal ungual I indicates this is probably an ornithine though. The second photographed specimen isn't identified past being a bird, but while the long pygostyle suggests it is enantiornithine or confuciusornithid, the large manual ungual is more similar to the latter clade.
References- Li and Gao, 2007. Lower Cretaceous vertebrate fauna from the Sinuiju basin, North Korea as evidence of geographic extension of the Jehol biota into the Korean peninsula. Journal of Vertebrate Paleontology. 27(3), 106A.
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 Enantiornithes (Xing, McKellar, Wang, Bai, O'Connor, Benton, Zhang, Wang, Tseng, Lockley, Li, Zhang and Xu, 2016)
Early Cenomanian, Late Cretaceous
Angbamo, Myanmar
Material- (DIP-V-15100) (juvenile) incomplete radius, incomplete ulna, metacarpal I (1.00 mm), phalanx I-1 (1.83 mm), manual ungual I (1.28 mm), metacarpal II (4.17 mm), phalanx II-1 (2.22 mm), phalanx II-2 (1.78 mm), manual ungual II (1.28 mm), metacarpal III (3.72 mm), phalanx III-1 (1.00 mm), manual claw sheaths, skin, contour feathers, remiges (Xing, McKellar, Wang, Bai, O'Connor, Benton, Zhang, Wang, Tseng, Lockley, Li, Zhang and Xu, 2016)
(DIP-V-15101) (juvenile) distal metacarpal I?, phalanx I-1, manual ungual I (1.81 mm), metacarpal II (4.95 mm), phalanx II-1 (3.10 mm), phalanx II-2 (2.57 mm), manual ungual II (2.14 mm), metacarpal III (6.24 mm), phalanx III-1 (1.38 mm), manual claw sheaths, skin, contour feathers, remiges (Xing, McKellar, Wang, Bai, O'Connor, Benton, Zhang, Wang, Tseng, Lockley, Li, Zhang and Xu, 2016)
?(DIP-V-15102) posterodorsal skull, about five cervical vertebrae, nine-ten dorsal vertebrae, sacral vertebra, few caudal vertebrae, pygostyle, distal humerus, radius, ulna, scapholunare, proximal carpometacarpus, phalanx I-1?, ilia, pubes, ischium, femur, contour feathers, remiges (Xing, O'Connor, McKellar, Chiappe, Bai, Tseng, Zhang, Yang, Fang and Li, 2018)
(DIP-V-15105a) metatarsal I, phalanx I-1, pedal ungual I, distal metatarsal II, phalanx II-1, phalanx II-2, pedal ungual II, distal metatarsal III, phalanx III-1, phalanx III-2, phalanx III-3, proximal pedal ungual III, distal metatarsal IV, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, proximal pedal ungual IV, pedal claw sheaths, contour feathers, skin, scutellae
....(DIP-V-15105b) partial remiges (Xing, McKellar, O'Connor, Bai, Tseng and Chiappe, 2019a)
(HPG-15-1) (hatchling) skull, mandibles, dentary beak, atlas, axis, third to sixth cervical vertebrae, cervical ribs, distal radius, distal ulna, scapholunare, pisiform, metacarpal I, phalanx I-1, manual ungual I, metacarpal II, phalanx II-1, phalanx II-2, manual ungual II, metacarpal III, phalanx III-1, proximal femur, distal tibia, astragalus, ascending process, calcaneum, distal tarsal IV, partial phalanges I-1, pedal unguals I (one incomplete), distal tarsal III fused with metatarsal IIs (one partial), phalanges II-1, phalanges II-2, pedal unguals II (one proximal), metatarsals III (one partial), phalanx III-1, proximal phalanx III-2, phalanx III-3, pedal ungual III, metatarsal IV (one partial), phalanx IV-1, phalanges IV-2, phalanges IV-3 (one proximal), phalanges IV-4, pedal unguals IV, pedal claw sheaths, skin, scutellae, contour feathers, remiges, retrix (Xing, O'Connor, McKellar, Chiappe, Tseng, Li and Bai, 2017)
Comments- All of these specimens are preserved in amber, as were the named Fortipesavis prehendens (YLSNHM01001; Clark and O'Connor, 2021) and Elektorornis chenguangi (HPG-15-2; Xing et al., 2019c).
DIP-V-15100 and 15101 were found in 2015 and consist of juvenile wings (Xing et al., 2016). "Preserved feather colour in DIP-V-15100 appears dark brown in the alula, and is slightly paler in the primaries and secondaries ... Dorsal contour feathers are generally dark in colour, but those basal to the alula may have been pale or white ... Ventrally, the surface of the wing has a strong contrast between white or pale contour feathers and down adjacent to the dark brown contour feathers along the anterior margin of the wing." "DIP-V-15101 shares a pale or white spot among the feathers just basal to its well-developed alula ... better-defined bands of pale feathers extend across the dorsal surface of DIP-V-15101, posteriorly and distally from the apex of the alula, and along the trailing edge of the wing." On "the ventral wing surface ... the base of the alular digit is clearly surrounded by white under marginal coverts (Fig. 3c), and this plumage continues posteriorly, as a mixture of pale or white plumulaceous feathers."
Xing et al. (2017) describe enantiornithine hatchling HPG-15-1 discovered by January 2017. "Unfeathered regions ... include most of the postauricular, auricular (anterior to the external ear opening), malar, and submalar areas", while "the ventral surface of the manus lacks plumage, and the exposed skin has a mottled grey, tan, and black surface." "The individual feathers in each [cervical] tract are dark brown in color", "feathers from the lateral pectoral tract are ... elongate, pale or white contours", "plumage within the femoral and crural tracts ... are nearly transparent, suggesting that they were pale or white" and "interspersed among the neoptile [hindlimb] plumage are isolated bristle-like filaments (IBFs) of a medium brown color." Considering wing and tail color, "each of the complete primaries is preserved with visible color patterning that consists of a walnut brown color interrupted by a pale feather apex and two pale transverse bands in the distal half of the feather", "the central core and apical margin of each secondary feather is preserved with a pale brown color, while the lateral margins of each vane are preserved with amuch darker walnut brown color", and "the lateral margins [of the tail] bear a row of unpigmented (pale or white) feathers."
Xing et al. (2018) describe poorly preserved specimen DIP-V-15102. "The barbule apices among the head feathers are preserved with a diffuse, dark brown pigmentation, while the barbule bases and barb rami appear to have been pale or unpigmented." On feathers which "presumably stem from the shoulder or breast regions" pigmentation "is uniform across all feather regions, appearing pale brown and diffuse." In primary remiges "barbules, rami, and rachises are all diffuse, pale brown in colour", while secondaries "may have more of a reddish-brown apparent coloration."
Xing et al. (2019a) describe enantiornithine pes and wing fragment DIP-V-15105. On the foot "contour feathers are preserved with a dark brown overall colouration", while filaments between scutellae "were either white or pale in life." The pedal proportions are different from Elektorornis or HPG-15-1, while there are ten primaries unlike DIP-V-15100 or 15101 which each have nine.
References- Xing, McKellar, Wang, Bai, O'Connor, Benton, Zhang, Wang, Tseng, Lockley, Li, Zhang and Xu, 2016. Mummified precocial bird wings in mid-Cretaceous Burmese amber. Nature Communications. 7:12089.
Xing, O'Connor, McKellar, Chiappe, Tseng, Li and Bai, 2017. A mid-Cretaceous enantiornithine (Aves) hatchling preserved in Burmese amber with unusual plumage. Gondwana Research. 49, 264-277.
Xing, O'Connor, McKellar, Chiappe, Bai, Tseng, Zhang, Yang, Fang and Li, 2018. A flattened enantiornithine in mid-Cretaceous Burmese amber: Morphology and preservation. Science Bulletin. 63(4), 235-243.
Xing, McKellar, O'Connor, Niu and Mai, 2019b. A mid-Cretaceous enantiornithine foot and tail feather preserved in Burmese amber. Scientific Reports. 9:15513.
Xing, McKellar, O'Connor, Bai, Tseng and Chiappe, 2019a. A fully feathered enantiornithine foot and wing fragment preserved in mid-Cretaceous Burmese amber. Scientific Reports. 9:927.
Xing, O’Connor, Chiappe, McKellar, Carroll, Hu, Bai and Lei, 2019c. A new enantiornithine bird with unusual pedal proportions found in amber. Current Biology. 29(14), 2396-2401.e2.
Clark and O'Connor, 2021. Exploring the ecomorphology of two Cretaceous enantiornithines with unique pedal morphology. Frontiers in Ecology and Evolution. 9:654156.

unnamed Enantiornithes (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 747; Humeral Taxon C) humerus (44.6 mm) (O'Connor and Forster, 2010)
(FMNH PA 752) femur (32.5 mm) (O'Connor and Forster, 2010)
(FMNH PA 753) incomplete metatarsal III, partial metatarsal IV (O'Connor and Forster, 2010)
(FMNH PA 780) carpometacarpus (23.2 mm) (O'Connor and Forster, 2009; described by O'Connor and Forster, 2010)
(UA 9605; Humeral Taxon D) partial humerus (O'Connor and Forster, 2010)
(UA 9606; Humeral Taxon E) humeral fragment (O'Connor and Forster, 2010)
(UA 9608) proximal ulna (O'Connor and Forster, 2010)
Comments- Forster and O'Connor (2000) first reported most Maevarano bird elements were enantiornithine, referencing what are probably humeral taxa C and D (small, with large bicipital crests, ventral tubers, and m. coracobrachialis scars). Carpometacarpus FMNH PA 780 was reported by O'Connor and Forster (2009) as enantiornithine. The carpometacarpus may belong to Vorona, though the other remains are clearly not Rahonavis or Vorona.
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 enantiornithine (Schweitzer, Jackson, Chiappe, Calvo and Rubilar, 2001)
Santonian, Late Cretaceous
Bajo de la Carpa Formation of the Rio Colorado Subgroup, Neuquen, Argentina
Material- (MUCPv-284) (embryo) coracoid, partial furcula, incomplete humerus, proximal radius, proximal ulna, ischia (~5 mm), distal femur, tibiae (one fragmentary), egg (45x27 mm)
(MUCPv-305) egg
(MUCPv-306) egg
(MUCPv-350) partial egg
(MUCPv-351) partial egg
(MUCPv-352) partial egg
(MUCPv-353) partial egg
(MUCPv-354) partial egg
(MUCPv-355) partial egg
Comments- Schweitzer et al. (2001, 2002) referred this specimen to Enantiornithes. The strut-like coracoid indicates these are avialan eggs, while the large proximodorsal ischial process is similar to non-euornithine avialans. The laterally excavated furcula is only known in enantiornithines. The dorsally projected deltopectoral crest is unlike Aves as well as most more basal euornithines (except ambiortids, Gansus and Ichthyornis). The slender radius (compared to ulnar width) does not indicate bird affinities though, as it is also found in many more basal maniraptorans. The specimens could belong to the enantiornithine Neuquenornis from the same locality. While the prismatic structure of the eggshell was noted as being like neognaths, Gobipipus and troodontids are now known to have a similar construction. The third structural layer is otherwise unique to euornithines where definitely associated with skeletal material however.
References- Schweitzer, Jackson, Chiappe, Calvo and Rubilar, 2001. Cretaceous avian eggs and embryos from Argentina. Journal of Vertebrate Paleontology. 21(3), 99A.
Schweitzer, Jackson, Chiappe, Schmitt, Calvo and Rubilar, 2002. Late Cretaceous avian eggs with embryos from Argentina. Journal of Vertebrate Paleontology. 22(1), 191-195.
Grellet-Tinner, 2005. A phylogenetic analysis of oological characters: A case study of saurischian dinosaur relationships and avian evolution. PhD thesis, University of Southern California. 221 pp.
Grellet-Tinner, Chiappe, Norell and Bottjer, 2006. Dinosaur eggs and nesting behaviors: A paleobiological investigation. Palaegeography, Palaeoclimatology, Palaeoecology. 232, 294-321.

undescribed enantiornithine (Debee, Lawver, Clarke and Guillermo, 2010)
Maastrichtian, Late Cretaceous
La Colonia Formation, Chubut, Argentina
Material- (MPEF-PV 2359) distal humerus
Diagnosis- (after Debee et al., 2010) thin crest on ventral margin of humerus (raised margin of m. brachialis insertion).
Comments- Debee et al. (2010) referred this specimen to Euenantiornithes.
Reference- Debee, Lawver, Clarke and Guillermo, 2010. A new enantiornithine (Theropoda, Avialae) from the Upper Cretaceous La Colonia Formation of Patagonia, Argentina. Journal of Vertebrate Paleontology. Program and Abstracts 2010, 80A.

unnamed Enantiornithes (Walker, 1981)
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Material- (MACN-S-02) (Chiappe, 1996)
(PVL-4026) (Chiappe, 1996)
(PVL-4030) distal tibiotarsus (~57 mm) (Chiappe and Walker, 2002)
(PVL-4031) ulna (70.8 mm) (Chiappe, 1996)
(PVL-4032) distal ulna (~98 mm), proximal tibiotarsus (~92 mm) (Chiappe, 1996)
(PVL-4034) incomplete scapula (62 mm), coracoid (50 mm) (Chiappe and Walker, 2002)
(PVL-4036) femur (55 mm) (Chiappe and Calvo, 1994)
(PVL-4037) femur (77.8 mm) (Walker, 1981)
(PVL-4038) femur (75.6 mm) (Chiappe and Calvo, 1994)
(PVL-4044) proximal ulna (~106 mm) (Chiappe, 1996)
(PVL 4049) carpometacarpus (Walker, 1981)
(PVL-4056) radius (117.8 mm) (Chiappe, 1996)
(PVL-4060) proximal femur (~53 mm) (Chiappe and Calvo, 1994)
(PVL-4273) proximal femur (~60 mm) (Chiappe and Calvo, 1994)
(PVL-4180) proximal humerus (Chiappe, 1996)
(PVL-4265) proximal humerus (Walker and Dyke, 2009)
(PVL-4269) (Chiappe, 1996)
(PVL-4691) (Chiappe, 1996)
(PVL-4693) (Chiappe, 1996)
(PVL-4694) (Chiappe, 1996)
(PVL-4695) (Chiappe, 1996)
(PVL-4696) (Chiappe, 1996)
(PVL-4697) (Chiappe, 1996)
(PVL-4698) posterior mandible (Chiappe, 1996)
(PVL-4703) (Chiappe, 1996)
Comments- A large amount of mostly disarticulated enantiornithine specimens have been found in the Lecho Formation. Most have been described and illustrated by Walker and Dyke (2009), though some have only appeared as specimen numbers in Chiappe (1996). Seven humeral morphologies are known from the site (Enantiornis leali, E? sp. nov., Martinavis? vincei, M? saltariensis, M? minor, M? whetstonei and Elbretornis), and three tarsometatarsal morphologies (Lectavis, Yungavolucris and Soroavisaurus). These specimens probably belong to those taxa, though determining their exact allocation is difficult. Several specimens (PVL-4030-4032, 4034, 4036-4038, 4044, 4049, 4056, 4060 and 4273) were referred to Martinavis sp. by Walker and Dyke, though none of the Lecho species are here thought to belong to that genus. Still, these specimens are too small to be Enantiornis or Elbretornis, and several (e.g. PVL-4030, 4036, 4060) are so small they probably belong to minor or whetstonei.
PVL-4049 was originally illustrated by Walker (1981) then referred to Enantiornis by Chiappe and Walker (2002). Walker and Dyke (2009) placed it in Martinavis instead, as it is much smaller than Enantiornis.
PVL-4036 was photographed by Chiappe (1996), PVL-4037 was illustrated by Walker (1981) and Chiappe and Walker (2002), and PVL-4038 was first noted by Chiappe and Calvo (1994) and photographed in Chiappe (1996; as PVL-4048). Walker et al. (2007) stated PVL-4037 is consistant in size with both Enantiornis and Martinavis? vincei from the same locality, and Walker and Dyke (2009) referred all three specimens to Martinavis sp..
The proximal end of PVL-4060 was illustrated schematically by Chiappe and Calvo (1994), and based on its small size thought to belong to Martinavis? minor or M? whetstonei by Walker and Dyke (2009).
PVL-4273 was illustrated by Chinsamy et al. (1995) and its histology was examined.
Chiappe and Walker (2002) referred PVL-4030 to Soroavisaurus and illustrated it. Walker and Dyke (2009) reassigned the tibiotarsus to Martinavis sp., though they mislabeled it PVL-4031 in their materials list.
References- Walker, 1981. New subclass of birds from the Cretaceous of South America. Nature. 292, 51-53.
Chiappe and Calvo, 1994. Neuquenornis volans, a new Enantiornithes (Aves) from the Upper Cretaceous of Patagonia (Argentina). Journal of Vertebrate Paleontology. 14, 230–246.
Chinsamy, Chiappe and Dodson, 1995. Mesozoic avian bone microstructure: Physiological implications. Paleobiology. 21(4), 561-574.
Chiappe, 1996. Late Cretaceous birds of southern South America: anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. Munchner Geowissenschaftliche Abhandlungen (A). 30, 203-244.
Chiappe and Walker, 2002. Skeletal morphology and systematic of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). pp 240-267. in Chiappe and Witmer, (eds.). Mesozoic Birds – Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

unnamed Enantiornithes ( Moyano-Paz, Rozadilla, Agnolín, Vera, Coronel, Varela, Gomez-Dacal, Aranciaga-Rolando, D'Angelo, Perez-Loinaze, Richiano, Chimento, Motta, Sterli, Manabe, Tsuihiji, Isasi, Poire and Novas, 2022)
Late Campanian-Early Maastrichtian, Late Cretaceous
Chorrillo Formation, Santa Cruz, Argentina
Material- (MPM-PV-22866) distal pedal phalanx
(MPM-PV-22867) incomplete pedal ungual ?I
(MPM-PV-22868) incomplete pedal ungual
Comments- MPM-PV-22866-22868 were discovered in March 2020 and referred to Enantiornithes by Moyano-Paz et al. (2022) based on "having poorly developed flexor tubercles, a ventral "V" shaped groove delimiting the flexor tubercle and dorsoventrally high and subrectangular-shaped proximal articular surface."
Reference- Moyano-Paz, Rozadilla, Agnolín, Vera, Coronel, Varela, Gomez-Dacal, Aranciaga-Rolando, D'Angelo, Perez-Loinaze, Richiano, Chimento, Motta, Sterli, Manabe, Tsuihiji, Isasi, Poire and Novas, 2022. The uppermost Cretaceous continental deposits at the southern end of Patagonia, the Chorrillo Formation case study (Austral-Magallanes Basin): Sedimentology, fossil content and regional implications. Cretaceous Research. 130, 105059.

unnamed enantiornithine (Alvarenga and Nava, 2005)
Turonian-Santonian, Late Cretaceous
Adamantina Formation of the Bauru Group, Brazil
Material- (MZ coll.) vertebrae, ribs
References- Alvarenga, and Nava, 2005. Aves Enantiornithes do Cretaceo Superior da Formacao Adamantina do Estado de São Paulo, Brasil. II Congresso Latino-Americano de Paleontologia de Vertebrados (Rio de Janeiro), Boletim de Resumos. 20.
Candeiro, Martinelli, Avilla and Rich, 2006. Tetrapods from the Upper Cretaceous (Turonian-Maastrichtian) Bauru Group of Brazil: A reappraisal. Cretaceous Research. 27(6), 923-946.

unnamed enantiornithine (Candeiro, Agnolín, Martinelli and Buckup, 2012)
Maastrichtian, Late Cretaceous
Serra da Galga Formation of the Bauru Group, Brazil
Material- (CPP 482) incomplete metatarsal III
Comments- In 2021 the Serra da Galga and Ponte Alta Members of the Marilia Formation were recognized as the Serra da Galga Formation.
Reference- Candeiro, Agnolín, Martinelli and Buckup, 2012. First bird remains from the Upper Cretaceous of the Peirópolis site, Minas Gerais state, Brazil. Geodiversitas. 34(3), 617-624.

unnamed Enantiornithes (Close, Vickers-Rich, Trusler, Chiappe, O'Connor, Rich, Kool and Komarower, 2009)
Aptian, Early Cretaceous
Wonthoggi Formation of the Strzelecki Group, Victoria, Australia
Material- (P 208183) partial furcula (Close, Vickers-Rich, Trusler, Chiappe, O'Connor, Rich, Kool and Komarower, 2009)
incomplete tibiotarsus (Close and Vickers-Rich, 2009)
References- Close and Vickers-Rich, 2009. Australia's Mesozoic birds: New material from the Early Cretaceous of Victoria. Journal of Vertebrate Paleontology. 29(3), 80A.
Close, Vickers-Rich, Trusler, Chiappe, O'Connor, Rich, Kool and Komarower, 2009. Earliest Gondwanan bird from the Cretaceous of Southeastern Australia. Journal of Vertebrate Paleontology. 29(2), 616-619.

Brevirostruavis Li, Wang, Stidham, Zhou and Clarke, 2022
= "Brevirostruavis" Li, Wang, Stidham, Zhou and Clarke, 2021 online
B. macrohyoideus Li, Wang, Stidham, Zhou and Clarke, 2022
= "Brevirostruavis macrohyoideus" Li, Wang, Stidham, Zhou and Clarke, 2021 online
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Material- (IVPP V13266) skull (40.40 mm), mandibles, hyoids (28.4, 25.0 mm), atlantal neural arch, axis, axial ribs, eight cervical vertebrae, four posterior dorsal vertebrae, dorsal ribs, gastralia, synsacrum, five caudal vertebrae, pygostyle (19.8 mm), proximal scapula, coracoids (~22.3 mm), furcula, sternum (25.3 mm), sternal ribs, incomplete humeri (39.2 mm), incomplete radii, incomplete ulnae (38.6 mm), scaptholunare, pisiforms, carpometacarpi (mcI 2.9, 2.6; mcII 14.9, 15.0; mcIII 15.8, 17.7 mm), phalanges I-1 (6.6, 6.9 mm), manual unguals I (3.5 mm), phalanges II-1 (8.8, 9.6 mm), phalanges II-2 (5.5, 6.3 mm), manual unguals II (3.3 mm), phalanges III-1 (4.6, 4.6 mm), manual claw sheaths, ilium, pubes, ischia, femora (28.3 mm), tibiotarsi (40.0 mm), fibulae (~29.3 mm), metatarsals I (5.1 mm), phalanges I-1 (5.3 mm), pedal unguals I (8.3 mm), tarsometatarsi (one incomplete; mtII 18.8, mtIII 20.4, mtIV 18.7 mm), phalanges II-1 (5.0 mm), phalanges II-2 (6.2 mm), pedal unguals II (7.7 mm), phalanges III-1 (6.8 mm), phalanges III-2 (5.3 mm), phalanges III-3 (5.9 mm), pedal unguals III (8.4 mm), phalanges IV-1 (2.6 mm), phalanges IV-2 (3.1 mm), phalanges III-3 (3.4 mm), phalanges IV-4 (4.3 mm), pedal unguals IV (6.8 mm), pedal claw sheaths, body feathers, remiges
Diagnosis- (after Li et al., 2021 online) short and pointed rostrum lined with small peg-shaped teeth; extremely long ceratobranchials, 63-71% of skull length; axial postzygapophyseal facet tear-drop shaped; third cervical vertebra with sub-rounded postzygapophyseal facet; elongate anterior cervical prezygapophyses; well-extended anterolateral sternal processes; posterolateral sternal processes with expanded triangular distal ends; ischium with pronounced proximodorsal process; distal tibiotarsus with knob on its anterior surface; fibula ~70% of tibiotarsal length (73%); pedal digit I more robust than other pedal digits; tarsometatarsus ~50% of tibiotarsal length (51%); medial rim of metatarsal III trochlea larger than lateral rim.
Comments- Li et al. (2021 online) named and described this taxon, but the paper has no mention of ZooBank so 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"), "Brevirostruavis macrohyoideus" Li et al., 2021 was a nomen nudum that became valid in April 2022 when the physical volume was published.
Li et al. (2022) added it to O'Connor's bird analysis and found it resolves at the base of Enantiornithes in a polytomy with other enantiornithines- Cruralispennia, Eoenantiornis, Eocathayornis, Protopteryx, Pterygornis, pengornithids, longipterygids, bohaiornithids and a derived clade including avisaurids.
Reference- Li, Wang, Stidham, Zhou and Clarke, 2022 (online 2021). Novel evolution of a hyper-elongated tongue in a Cretaceous enantiornithine from China and the evolution of the hyolingual apparatus and feeding in birds. Journal of Anatomy. Early View. 240(4), 627-638.

Cruralispennia Wang, O'Connor, Pan and Zhou, 2017
C. multidonta Wang, O'Connor, Pan and Zhou, 2017
Late Hauterivian, Early Cretaceous
Sichakou Sedimentary Member of the Huajiying Formation, Hebei, China
Holotype- (IVPP V21711) (<1 year old subadult) partial skull, dentary surangular, several cervical vertebrae, five dorsal vertebrae, dorsal ribs, gastralia, partial synsacrum(?), two caudal vertebrae, pygostyle (5.58 mm), scapulae, coracoids (12.37 mm), sternum, sternal ribs, humeri (19.35 mm), radii (21.35 mm), ulnae (22.48 mm), partial ilium, pubis (18.12 mm), ischium (6.82 mm), femur (19.75 mm), tibiotarsus (23.08 mm), fibula, tarsometatarsus (19.71 mm), nine pedal phalanges (?), four pedal unguals (?), body feathers, remiges
Diagnosis- (after Wang et al., 2017) 14 dentary teeth; abbreviated, plough-shaped pygostyle with a pygostyle/tarsometatarsus length ratio of about 0.28; coracoid mediolaterally narrow with the
sternal margin measuring only one quarter of the proximodistal length; sternum bearing a V-shaped posterior margin and subequal posteromedial and posterolateral processes; postacetabular process of ilium short and strongly ventrally directed; proximodorsal process of ischium distally placed; pubis without distal expansion.
Other diagnoses- Wang et al. (2017) listed manus shorter than humerus as diagnostic, but the hands appear to be faked (see below).
Comments- This specimen was discovered before August 2016. Note the labels for the pubic and ischial peduncles in supp. fig. 1b are reversed. The pedal phalanges appear to be partially fake, with e.g. the right pes illustrated by the authors (supp. fig. 2) as having at least 16 non-ungual phalanges and five unguals when it should have ten and four respectively. In this pes, the supposedly articulated toes and pedal ungual I don't seem to consist of real bone, while five phalanges and three unguals are real but may have been displaced or even added from another fossil. In the less clearly photographed left pes, 14 non-ungual phalanges are illustrated of which four seem to be genuine. This calls into question the veracity of other portions of the holotype, such as the hands which each appear poorly defined with differing metacarpal II lengths and a more robust first digit than expected in an ornithothoracine. Most of the left hindlimb may similarly be artificial or at least heavily reconstructed. The identity of the large masses by the supposed proximal left femur is uncertain, but may indeed be at least partially synsacral pieces as labeled in figure 1b.
Wang et al. addded Cruralispennia to O'Connor's avialn matrix and recovered it sister to bohaiornithids.
Reference- 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.

Eopengornis Wang, O'Connor, Zheng, Wang, Hu and Zhou, 2014
= "Eopengornis" Zheng, O'Connor, Wang, Wang, Zhang and Zhou, 2014
E. martini Wang, O'Connor, Zheng, Wang, Hu and Zhou, 2014
Late Hauterivian, Early Cretaceous
Luozigou, Sichakou Sedimentary Member of the Huajiying Formation, Hebei, China
Holotype- (STM24-1) (subadult) skull, sclerotic plates, mandibles (one partial), six cervical vertebrae, cervical ribs, several dorsal vertebrae, dorsal ribs, gastralia, sacral vertebrae, seven caudal vertebrae, pygostyle, scapulae (one partial), coracoids, furcula, sternum, posterolateral sternal processes, three to six sternal ribs, humeri (38 mm), radii (one incomplete, one partial), incomplete ulnae (42.4 mm), scapholunare, pisiforms, semilunate carpals, metacarpals I, phalanges I-1, manual unguals I, metacarpals II (19.97 mm), phalanges II-1, phalanges II-2, manual unguals II, fragmentary metacarpals III, phalanges III-1, phalanges III-2, pubes, femora (one incomplete, one partial; 27 mm), tibiae (31 mm), fibulae (one partial), proximal tarsals, metatarsals I (6.9 mm), phalanges I-1 (7.8 mm), pedal unguals, metatarsals II (15.9 mm), phalanges II-1, phalanges II-2, pedal unguals II, metatarsals III (17.81 mm), phalanges III-1, phalanges III-2, phalanges III-3, pedal unguals III, metatarsals IV, phalanges IV-1, phalanges IV-2, phalanges III-3, phalanges IV-4, pedal unguals IV, metatarsals V, remiges, retrices (~123 mm), body feathers
Diagnosis- (after Wang et al., 2014) accessory foramina piercing nasal absent; numerous, small, occlusally tapered and slightly recurved teeth in upper and lower jaws; fibula ends in rounded expansion; elongate hallux with metatarsal I and phalanx I-1 each almost half length of metatarsal II.
Comments- The name "Eopengornis" was first published by Zheng et al. (2014), which was online on September 8th and in print on September 23rd. While a few basic details were given along with photos, the paper was clearly meant to be published after Wang et al.'s (2014) official description which appeared on October 17th. The absence of a species name (ICZN Article 13.3), listed holotype (Article 16.4) and explicit statement about it being a new genus (Article 16.1) means this early occurance of the genus name is a nomen nudum.
The holotype was purchased from a collector. Xu et al. (2023) list the holotype's appendicular lengths as- humerus (35.6 mm), ulna (39.8 mm), femur (24.1 mm), tibia (31.7 mm).
Wang et al. (2014) found this was sister to Pengornis in a version of O'Connor's bird analysis that excluded all non-Jehol enantiornithines.
References- Wang, O'Connor, Zheng, Wang, Hu and Zhou, 2014. Insights into the evolution of rachis dominated tail feathers from a new basal enantiornithine (Aves: Ornithothoraces). Biological Journal of the Linnean Society. 113, 805-819.
Zheng, O'Connor, Wang, Wang, Zhang and Zhou, 2014. On the absence of sternal elements in Anchiornis (Paraves) and Sapeornis (Aves) and the complex early evolution of the avian sternum. Proceedings of the National Academy of Sciences. 111(38), 13900-13905.
Xu, Wang, Chen, Dong, Lin, Xu, Tang, You, Zhou, Wang, He, Li, Zhang and Zhou, 2023. A new avialan theropod from an emerging Jurassic terrestrial fauna. Nature. 621, 336-343.

Explorornis Panteleyev, 1998
Diagnosis- (after Panteleyev, 1998) coracoid shaft primitively not narrower than deep (also in Elsornis, walkeri and Catenoleimus).
(proposed) crest along the dorsolateral edge of the shaft (also in Eocathayornis).
Other diagnoses- Panteleyev (1998) also listed the broad distal expansion in his diagnosis, but this is primitive for ornithothoracines. The low coracoid tubercle is not different from Incolornis, Otogornis or Neuquenornis. The gradually rising edge of the dorsal coracoid fossa is also present in walkeri, Incolornis, Elsornis, Shanweiniao, Cathayornis and Eocathayornis. The coracoid glenoid facet is generally rather flat in enantiornithines, and is eroded in Explorornis nessovi, so Panteleev's characterization of a convex glenoid in the taxon seems questionable.
Comments- Panteleyev also referred another species to this genus- E. walkeri. While walkeri shares the plesiomorphic dorsoventrally flattened coracoid shaft and shallow dorsal fossa of nessovi, there are no shared derived characters yet identified that could unite the species. O'Connor (2009) declared all Bissekty enantiornithines based on coracoids to be nomina dubia, though without detailed comparison.
E. nessovi Panteleyev, 1998
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (ZIN PO 4819) (~165 mm) distally incomplete coracoid (18.8 mm)
Diagnosis- (proposed) compared to E. sp. nov., lateral and medial edges around dorsal coracoid fossa thin; coracoid shaft thinner; lateral edge of coracoid completely concave.
Comments- This was collected in 1991 and originally identified as Enantiornithes by Nessov and Panteleev (1993) and Nessov (1997). Panteleyev (1998) and it and referred it to Alexornithidae within Alexornithiformes without comment. Nessov (1996) referred the then unnamed specimen to Alexornithidae based on the narrow shaft, shallow dorsal coracoid fossa and "slightly projected lateral margin". Yet Nessov's classification is flawed, as for instance his enantiornithid Enantiornis has a narrower shaft and less projected lateral margin than Explorornis, while his concornithids such as Iberomesornis and Cathayornis are comparable in these regards, and the latter also has a shallow dorsal fossa. The coracoid fossa does indicate this is an enantiornithine, as Apsaravis differs in having a concave scapular facet. Within Enantiornithes, the concave lateral edge and shallow dorsal fossa may mean this is a relatively basal taxon.
References- Nessov and Panteleev, 1993. On the similarity of the Late Cretaceous ornithofauna of South America and Central Asia. Trudy Zoologicheskogo Instituta, RAN. 252, 84-94.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
Nessov, 1997. [Cretaceous nonmarine vertebrates of northern Eurasia]. Saint Petersburg, Institute of Earth Crust. 1-218.
Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
E. sp. nov. (Panteleyev, 1998)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Material- (ZIN PO 4818) (~165 mm) incomplete coracoid (~19 mm)
Diagnosis- (proposed) compared to E. nessovi, lateral and medial edges around dorsal coracoid fossa thick; coracoid shaft thicker; lateral; edge of coracoid distally convex.
Comments- This was originally identified as Enantiornithes by Nessov and Panteleev (1993) and Nessov (1997). It was described as Explorornis sp. 1 by Panteleyev (1998), which seems valid since it has the apomorphic crest of that genus. However, the other shared character (shaft broader than deep) is plesiomorphic and the slightly convex laterodistal edge might indicate it is more derived. Kurochkin (1996) referred it to Alexornithiformes fam. indet. without justification.
References- Nessov and Panteleev, 1993. On the similarity of the Late Cretaceous ornithofauna of South America and Central Asia. Trudy Zoologicheskogo Instituta, RAN. 252, 84-94.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
Nessov, 1997. [Cretaceous nonmarine vertebrates of northern Eurasia]. Saint Petersburg, Institute of Earth Crust. 1-218.
Panteleyev, 1998. New species of enantiornithines (Aves: Enantiornithes) from Upper Cretaceous of central Kyzylkum. Russian Journal of Ornithology. Express-issue 35, 3-15.

Mirusavis Wang, O'Connor, Bailleul and Li, 2020
= "Mirusavis" Wang, O'Connor, Bailleul and Li, 2019 online
M. parvus Wang, O'Connor, Bailleul and Li, 2020
= "Mirusavis parvus" Wang, O'Connor, Bailleul and Li, 2019 online
Early Albian, Early Cretaceous
Sihedang, Jiufotang Formation, Liaoning, China
Holotype- (IVPP V18692) (~16 g; subadult female) axis, third to tenth cervical vertebrae, six dorsal ribs, two uncinate processes, gastralia, scapulae (one incomplete), coracoids (one partial; 16.30 mm), furcula, partial sternum, several sternal ribs, humerus (30.02 mm), radius (~29.87 mm), ulna (31.71 mm), scapholunare, metacarpal I (2.56 mm), phalanx I-1 (4.85 mm), manual ungual I (1.45 mm), carpometacarpus (13.21 mm), phalanx II-1 (7.43 mm), phalanx II-2 (4.38 mm), proximal manual ungual II, phalanx III-1 (3.36 mm), femur (27.33 mm), proximal tibiotarsus, proximal fibula
Diagnosis- (Wang, O'Connor, Bailleul and Li, 2020) sternum with anterolateral processes (also in Shangyang and Concornis); elongated posteromedial process of sternum posterolaterally directed; proximodistally short humeral deltopectoral crest; distal margin of humerus strongly angled ventrodistally; ulna with well-developed bicipital tubercle; ulna with distinct olecranon process; dorsal cotyle of ulna convex; radius with bicipital tubercle; interosseous surface of radius smooth; manual ungual II larger than manual ungual I.
Comments- This specimen was discovered prior to August 2019. It was first published as unnamed enantiornithine IVPP V18692 in Wang et al.'s (2020a) phylogenetic analysis, added to O'Connor's avialan analysis. The paper describing it was published online on December 19 2019 but does not contain reference to a ZooBank registration, so the name was a nomen nudum (ICZN Article 8.5.3. states names published electronically 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") until the volume was physically released in June 2020.
Wang et al. (2020b) used Mirusavis to O'Connor's avialan analysis and recovered it sister to Shangyang in Enantiornithes more derived than pengornithids, Protopteryx and Monoenenatiornis.
References- Wang, O'Connor, Bailleul and Li, 2020a (online 2019). Evolution and distribution of medullary bone: Evidence from a new Early Cretaceous enantiornithine bird. National Science Review. 7(6), 1068-1078.
Wang, O'Connor, Zhou and Zhou, 2020b (online 2019). New toothed Early Cretaceous ornithuromorph bird reveals intraclade diversity in pattern of tooth loss. Journal of Systematic Palaeontology. 18(8), 631-645.

Noguerornis Lacasa-Ruiz, 1989
N. gonzalezi Lacasa-Ruiz, 1989
Late Berriasian-Early Barremian, Early Cretaceous
La Pedrera de Rubies Lithographic Limestones, Spain
Holotype- (LP.1702) last dorsal vertebra (1.6 mm), three dorsal rib fragments, first sacral vertebra (2 mm), second sacral vertebra (2.4 mm), incomplete furcula, humeri (22.8 mm), radii (23.1, 23.2 mm), ulna (24.3 mm), scapholunare, pisiform, carpometacarpus, proximal phalanx I-1, ischium, partial tibia, long bone shaft, coverts, secondary remiges
Diagnosis- ischial symphysis present.
References- Lacasa-Ruiz, 1986. Nota preliminar sobre el hallazgo de restos keos de un ave fosil en el yacimiento neocomiense del Montsec. (Prov .Lerida, Espafia). Ilerdu. 47, 203-206.
Lacasa-Ruiz, 1989. An Early Cretaceous fossil bird from Montsec Mountain (Lleida, Spain). Terra Nova. 1(1), 45-46.
Lacasa-Ruiz, 1989. Nuevo genero de ave fosil del yacimiento Neocomiense del Montsec (Provincia de Lerida, Espana). Estudios Geologicos. 45, 417-425.
Chiappe and Lacasa-Ruiz, 2002. Noguerornis gonzalezi (Aves: Ornithothoraces) from the Early Cretaceous of Spain. 230-239. in Chiappe and Witmer, (eds.). Mesozoic Birds: Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.

Orienantius Liu, Chiappe, Zhang, Serrano and Meng, 2019
= "Orienantius" Liu, Chiappe, Zhang, Serrano and Meng, 2018
O. ritteri Liu, Chiappe, Zhang, Serrano and Meng, 2019
= "Orienantius ritteri" Liu, Chiappe, Zhang, Serrano and Meng, 2018
Late Hauterivian, Early Cretaceous
Sichakou Sedimentary Member of the Huajiying Formation, Hebei, China
Holotype- (BMNHC Ph 1156a/b) (juvenile) skull, mandibles, hyoids, seven to eight cervical vertebrae, eleven dorsal vertebrae, dorsal ribs, synsacrum, six caudal vertebrae, pygostyle (14.6 mm), scapulae, coracoids (~13.5 mm), furcula, sternum, sternal ribs, humeri (29.2 mm), radii (27.2 mm), ulnae (29.4 mm), scapholunare, pisiform, semilunate carpals, metacarpal I (2.2 mm), phalanges I-1 (5.1 mm), manual unguals I (3.1 mm), metacarpals II (12.9 mm), phalanges II-1 (7.7 mm), phalanges II-2 (5.1 mm), manual unguals II (3.1 mm), metacarpals III (13.7 mm), phalanges III-1 (3.8 mm), phalanges III-2 (0.8 mm), manual claw sheaths, ilia, pubes (20.3 mm), ischium, femora (25.1 mm), (tibiotarsus 31.1 mm) tibiae, astragalacalcanea, distal tarsals III, metatarsals I, phalanges I-1 (4.3 mm), pedal unguals I (6.1 mm), metatarsals II, phalanges II-1 (4.1 mm), phalanges II-2 (5.2 mm), pedal unguals II (6.8 mm), metatarsals III (17.3 mm), phalanges III-1 (5.5 mm), phalanges III-2 (4.5 mm), phalanges III-3 (4.8 mm), pedal unguals III (6.0 mm), metatarsals IV, phalanges IV-1 (2.9 mm), phalanges IV-2 (2.6 mm), phalanges III-3 (2.3 mm), phalanges IV-4 (3.0 mm), pedal unguals IV (5.4 mm), pedal claw sheaths, body feathers, remiges, retrices, skin
Paratype- (BMNHC Ph 1154a/b) (juvenile) posterior skull, posterior mandible, cervical series, dorsal series, dorsal ribs, gastralia, synsacrum, free caudal series, pygostyle (14.9 mm), coracoids (13.3 mm), sternum, sternal ribs, humeri (28.5 mm), radii (29.5 mm), ulnae (29.8 mm), scapholunares, pisiforms, semilunate carpals, metacarpals I (2.4 mm), phalanges I-1 (4.9 mm), manual unguals I (2.5 mm), metacarpals II (~13 mm), phalanges II-1 (7.5 mm), phalanges II-2 (5.1 mm), manual unguals II (2.1 mm), metacarpals III (~14 mm), phalanges III-1 (4.1 mm), phalanx III-2 (~0.7 mm), pubis (~18 mm), ischium, femora (24.2 mm), (tibiotarsus 31.9 mm) tibiae (one partial), metatarsals I, phalanges I-1 (4.2 mm), pedal unguals I (5.4 mm), metatarsals II, phalanges II-1 (4.0 mm), phalanges II-2 (4.8 mm), pedal unguals II (6.2 mm), metatarsals III (17.4 mm), phalanges III-1 (5.3 mm), phalanges III-2 (4.5 mm), phalanges III-3 (4.5 mm), pedal unguals III (6.1 mm), metatarsals IV, phalanges IV-1 (3.0 mm), phalanges IV-2 (~1.8 mm), phalanges III-3 (2.4 mm), phalanges IV-4 (3.2 mm), pedal unguals IV (4.9 mm), pedal claw sheaths, body feathers, remiges, retrices, skin
Diagnosis- (after Liu et al., 2019) posterior end of dentary with a weak fork; reduced number of maxillary and dentary teeth (not many more than 3 in the maxilla and 6 in the dentary); ventral median groove on synsacral vertebrae; long and narrow pygostyle (>80% the length of the tarsometatarsus); furcula with very long hypocleidium (>80% length of furcular rami); sternum with slightly deflected posterolateral processes ending in triangular distal expansions, short posteromedial processes, and a narrow posteromedian process that projects posteriorly beyond the level of the posterolateral processes; semilunate carpal with distal projection overlapping metacarpal III; short manual digit I (digit I/metacarpal II length ratio 0.39); gently expanded pubic boot.
Comments- The specimens were discovered before March 2018. The description of Orienantius was first released online as an Accepted Manuscript on October 25 2018, but this did not contain reference to a ZooBank registration, so the name was a nomen nudum (ICZN Article 8.5.3. states names published electronically 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") until the volume was physically released in March 2019.
Liu et al. did not add Orienantius to a phylogetic analysis, but proposed it was more similar to Jehol enantiornithines than Protopteryx and pengornithids.
Reference- Liu, Chiappe, Zhang, Serrano and Meng, 2019 (online 2018). Soft tissue preservation in two new enantiornithine specimens (Aves) from the Lower Cretaceous Huajiying Formation of Hebei Province, China. Cretaceous Research. 95, 191-207.

Pengornis Zhou, Clarke and Zhang, 2008
= Parapengornis Hu, O'Connor and Zhou, 2015a
= "Chiappeavis" O'Connor, Wang, Zheng, Hu, Zhang and Zhou, 2015 online
= Chiappeavis O'Connor, Wang, Zheng, Hu, Zhang and Zhou, 2016
= Yuanchuavis Wang, O'Connor, Zhao, Pan, Zheng, Wang and Zhou, 2021
P. houi Zhou, Clarke and Zhang, 2008
= Parapengornis eurycaudatus Hu, O'Connor and Zhou, 2015a
= "Chiappeavis magnapremaxillo" O'Connor, Wang, Zheng, Hu, Zhang and Zhou, 2015 online
= Chiappeavis magnapremaxillo O'Connor, Wang, Zheng, Hu, Zhang and Zhou, 2016
= Yuanchuavis kompsosoura Wang, O'Connor, Zhao, Pan, Zheng, Wang and Zhou, 2021
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V15336) (440 g) skull (~54.7 mm), mandibles, eleven cervical vertebrae, few dorsal vertebrae, dorsal ribs, gastralia, synsacrum (~27.1 mm), six caudal vertebrae, proximal pygostyle, scapulae, coracoids (37.9 mm), incomplete furcula, humeri (64.3 mm), radii (66.7 mm), ulnae (70.7 mm), scapholunares, pisiforms, carpometacarpi (34.3 mm; mcII 27 mm, mcIII 31.1 mm), phalanges II-1 (16.3 mm), phalanx II-2, phalanx III-1, manual ungual, ilium, partial pubes (~49.2 mm), femora (48 mm), tibiotarsi (50.4 mm), fibula (~44.5 mm), metatarsal I (8.7 mm), pedal ungual I, tarsometatarsi (26.5 mm), phalanx II-1 (5.9 mm), phalanx II-2 (8.1 mm), pedal ungual II (12.4 mm), phalanx III-1 (8.6 mm), phalanx III-2 (7.9 mm), phalanx III-3 (8.8 mm), pedal ungual III (11.7 mm), phalanx IV-1 (5.2 mm), phalanx IV-2 (~3.8 mm), phalanx IV-3 (4.1 mm), phalanx IV-4 (5.9 mm), pedal ungual IV (9.9 mm), ungual
Referred- (IVPP V18632) (subadult) skull (39.7 mm), sclerotic ossicles, mandibles, seven cervical vertebrae, two anterior dorsal vertebrae, four posterior dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, eight sacral vertebrae (sacrum 22.1 mm), eight caudal vertebrae (series 15.3 mm), pygostyle (9.2 mm), partial scapulae (34.9 mm), partial coracoids, incomplete furcula, sternum (22.8 mm), sternal ribs, humeri (one incomplete; 45.7 mm), radii (45.5 mm), ulnae (49 mm), scapholunare, pisiform, semilunate carpal, metacarpals I (4.2 mm), phalanx I-1 (10.7 mm), manual ungual I (5.5 mm), metacarpals II (one partial; 20.1 mm), phalanges II-1 (one partial; 12.5 mm), phalanges II-2 (8.8 mm), manual unguals II (4.5 mm), metacarpals III (19.7 mm), phalanges III-1 (one partial; 6.3 mm), phalanx III-2 (1 mm), incomplete ilia, pubes (one incomplete; 38.4 mm), ischia (one partial), femora (34.8 mm), tibiae (37.7 mm), fibulae (26.5 mm), astragali, calcanea, metatarsal I (6.6 mm), phalanx I-1 (5.8 mm), pedal ungual I (8.2 mm), metatarsal II (19.1 mm), phalanx II-2 (6.1 mm), pedal ungual II (7 mm), metatarsal III (19.7 mm), phalanx III-1 (6.8 mm), phalanx III-2 (6 mm), phalanx III-3 (6.4 mm), pedal ungual III (5.2 mm), partial metatarsal IV, phalanx IV-1 (3.8 mm), phalanx IV-2 (3.1 mm), phalanx IV-3 (2.8 mm), phalanx IV-4 (4.4 mm), pedal ungual IV (6.5 mm), metatarsal V(?), pedal claw sheaths, remiges, retrix (Hu, Zhou and O'Connor, 2014)
(IVPP V18687; holotype of Parapengornis eurycaudatus) (<1 year old juvenile) skull (39.9 mm), mandibles, hyoids, axis, third cervical vertebra, fourth cervical vertebra, fifth cervical vertebra, sixth cervical vertebra, seventh cervical vertebra, eighth cervical vertebra, ninth cervical vertebra, first dorsal vertebra, second dorsal vertebra, third dorsal vertebra, five mid-posterior dorsal vertebrae, dorsal ribs, several uncinate processes, gastralia, synsacrum, seven or eight caudal vertebrae, pygostyle (8.4 mm), scapulae (one incomplete; 46.3 mm), coracoids (26.3 mm), furcula, incomplete sternum, at least eight sternal ribs, humeri (52.1 mm), radii (53.7 mm), ulnae (54.9 mm), scapholunare, pisiform, semilunate carpal, metacarpal I (5.3 mm), phalanx I-1 (11.4 mm), manual ungual I (6.7 mm), metacarpal II (24.8 mm), phalanges II-1 (12.7 mm), phalanges II-2 (9.2 mm), manual unguals II (4.8 mm), metacarpal III (27.4 mm), phalanges III-1 (8.1 mm), phalanx III-2 (1.2 mm), ilia, pubes (37.2 mm), ischia, femora (39.8 mm), tibiae (40.4 mm), fibulae (34.6 mm), astragali, calcaneum, proximal tarsal, metatarsals I (one incomplete; 8.6 mm), phalanges I-1 (one incomplete; 9.2 mm), pedal unguals I (one incomplete; 7.4 mm), metatarsals II (one incomplete; ~19.5 mm), phalanges II-1 (5.2 mm), phalanges II-2 (one partial; 7 mm), pedal unguals II (one partial; 8.2 mm), metatarsals III (one incomplete; ~20.5 mm), phalanges III-1 (6.6 mm), phalanges III-2 (one fragmentary; 6.3 mm), phalanges III-3 (6.4 mm), pedal unguals III (one incomplete; 8.2 mm), metatarsals IV (one incomplete; 19.1 mm), phalanges IV-1 (one fragmentary; 4.8 mm), phalanges IV-2 (one fragmentary; 2.7 mm), phalanges IV-3 (3.2 mm), phalanges IV-4 (4.5 mm), pedal unguals IV (one partial; 5.8 mm), pedal claw sheaths, metatarsals V, body feathers, retrices, remiges (144.2 mm) (Hu, O'Connor and Zhou, 2015a)
(IVPP V27883; holotype of Yuanchuavis kompsosoura) skull, sclerotic plates, mandibles, atlas, axis, third-tenth cervical vertebrae, first-tenth dorsal vertebrae, several partial cervical ribs, few uncinate processes, synsacrum, first-seventh caudal vertebrae, pygostyle (18 mm), two chevrons, ilia (34.62 mm), pubes (46.81 mm), ischia (31.78 mm), femora (one incomplete; 45.37 mm), tibiotarsi (one incomplete; 50.79 mm), fibulae, metatarsals I (one distal; 10.42 mm), phalanges I-1 (11.32 mm), partial pedal ungual I, metatarsals II (25.03 mm), distal phalanx II-1, phalanges II-2 (one proximal; 10.19 mm), pedal ungual II (6.72 mm), metatarsals III (~27.07 mm), phalanx III-1 (8.64 mm), phalanges III-2 (one distal; 7.73 mm), phalanx III-3 (8.54 mm), metatarsals IV (26.21 mm), phalanx IV-1 (5.0 mm), phalanges IV-2 (3.97 mm), proximal phalanges IV-3, metatarsals V (6.52 mm), body feathers, retrices (Wang, O'Connor, Zhao, Pan, Zheng, Wang and Zhou, 2021 online)
(STM 29-11; holotype of Chiappeavis magnapremaxillo) (juvenile) skull, sclerotic plates, mandible, several cervical vertebrae, six dorsal vertebrae, dorsal ribs, synsacrum. caudal vertebrae, pygostyle (~18 mm), chevron, incomplete scapulae, coracoids, furcula, sternum, sternal ribs, humeri (58.13 mm), radii, ulnae (64.59 mm), scapholunare, pisiform, carpometacarpi (31.12 mm), fragmentary phalanx II-1, distal phlannx II-2, manual ungual II, phalanges III-1, ilia (one incomplete), pubes, femora (42.9 mm), tibiae (46.7 mm), astragalocalcanea, phalanx I-1, pedal unguals I, metatarsals II, metatarsals III (22.5 mm), metatarsals IV, numerous pedal phalanges, five pedal unguals, pedal claw sheaths, remiges, retrices (56-74 mm) (O'Connor, Sullivan, Zhou and Zheng, 2015; described by O'Connor, Wang, Zheng, Hu, Zhang and Zhou, 2015)
?(STM 29-15) (juvenile) dorsal vertebrae, dorsal ribs, gastralia, synsacrum, caudal fragments, pygostyle (8.7 mm), scapulae (one incomplete, one proximal; 26 mm), incomplete coracoids, sterna, sternal ribs, humeri (48.2 mm), partial radii, ulnae (one incomplete, one partial), scapholunare, pisiform, semilunate carpal, metacarpal I, phalanges I-1 (11.5 mm), manual ungual I (5.8 mm), metacarpals II (one incomplete; 25.6 mm), phalanges II-1 (12.4 mm), phalanges II-2 (7.9 mm), manual unguals II (3.9 mm), metacarpals III (one partial; 27.6 mm), phalanx III-1 (6.9 mm), ilia, pubes, ischia, femora (37.2 mm), tibiae (39.5 mm), fibula, astragalocalcanea, distal tarsal, metatarsals I (8.5 mm), phalanges I-1 (8.7 mm), pedal unguals I, metatarsals II (18.5 mm), phalanx II-1, phalanx II-2, pedal ungual II, metatarsals III, phalanx III-1, phalanx III-2, phalanx III-3, pedal ungual III, metatarsals IV, phalanx IV-?, pedal ungual IV, remiges (O'Connor et al., 2015)
Early Albian, Early Cretaceous
Chifeng, Jiufotang Formation, Inner Mongolia, China
?(IVPP V15576) (subadult female) femur (38.8 mm), incomplete tibiotarsus, partial fibula, metatarsal I 8.4 mm), fragmentary phalanx I-1, fragmentary pedal ungual I, tarsometatarsus (21.9 mm), phalanx II-1, phalanx II-2, pedal ungual II, phalanx III-1, phalanx III-2, phalanx III-3, pedal ungual III, phalanx IV-1, pahalnx IV-2, phalanx IV-3, pahalnx IV-4, pedal ungual IV, pedal claw sheaths, metatarsal V, body feathers (O'Connor, Erickson, Norell, Bailleul, Hu and Zhou, 2018)
Diagnosis- (after Zhou et al., 2008) premaxillae unfused; hooked scapular acromion; globose humeral head that projects further proximally than the deltopectoral crest.
(after Hu et al., 2014) 9-13 dentary teeth that are small, stout, and unrecurved.
Comments- Hu et al. (2014) described the new specimen IVPP V18632 which they considered a subadult individual of a new species of Pengornis. The differences they viewed as non-ontogenetic (nasal process of maxilla more delicate; dorsal process of maxilla pointed rather than rodlike [not comparable states]; furcula more slender with interclavicular angle of 75 degrees rather than 65 [ontogenetic?]; humeral head flat rather than globose [not apparent]; deltopectoral crest weaker and narrower [ontogenetic?]; pubis straight [in anterior view in IVPP V18687?]) seem to be minor and comparable to those I consider individual variation in other paravian species, so I refer IVPP V18632 to P. houi. Note too that the interclavicular angle and humeral head convexity is intermediate in IVPP V18687.
O'Connor et al. (2015a) described a skeleton lacking the skull and neck (STM 29-15) as Pengornithidae indet., with unspecified differences "in pedal morphology and inferred adult body size" suggesting it was not conspecific with IVPP V18632. As STM 29-15 is from the Jiufotang Formation (O'Connor pers. comm., 2015), it is here tentatively assigned to the only pengornithid from that formation that I recognize, Pengornis itself.
O'Connor et al. (2018) describe a hindlimb with medullary bone as Pengornithidae indet., but given this is from the Jiufotang Formation it is here tentaively referred to Pengornis.
Parapengornis- Hu et al. (2015a) described a new genus of pengornithid, Parapengornis eurycaudatus based on basically complete specimen IVPP V18687. Xu et al. (2023) gave different appendicular measurements- humerus (51.82 mm), ulna (55.65 mm), metacarpus (27.12 mm), femur (39.2 mm), tibia (40.42 mm), metatarsus (18.9 mm). Note the supposed quadratojugal is almost certainly a postorbital, while the supposed palatines are likely postdentary mandibular elements. They suggested several diagnostic characters and referred IVPP V18632 to the taxon. Of their diagnostic characters, the teeth of all birds are basally constricted, and those of Parapengornis are not more numerous than Pengornis (9 vs.13 in the dentary). The width of the pygostyle, lateral expansion of the distal processes and and concavity of the posterior margin cannot be evaluated in the laterally preserved element of Pengornis. The furculae of all enantiornithines are Y-shaped, and that of Parapengornis is not noticably more slender or straighter than Pengornis. Hu et al. stated "pedal phalanx I-1 is longer than metatarsal I and approximately half the length of metatarsal III", but I-1 seems to be unpreserved in Pengornis. The more slender and recurved teeth could be ontogenetic (as in the Eichstatt Archaeopteryx vs. the London specimen), as could the less elongated anterior cervical vertebrae (as in many living birds). Contra the text, the maxillary fenestra doesn't seem to be larger or more anteriorly positioned than in Pengornis, nor does the femoral head seem less developed. The quadrate was said to differ from Pengornis in being straight posteriorly, but the shape difference is due to it being in anterior instead of lateral view. The lower deltopectoral crest is potentially ontogenetic as in IVPP V18632. Stated proportional differences (coracoid length/width ratio 192% vs. 202%; ulnohumeral ratio 105% vs. 108%) are easily explainable by individual variation. This leaves the following as potentially supporting Parapengornis' validity- shorter posterodorsal lacrimal process; pygostyle shorter than half the length of metatarsal III (41% vs. >73%); metatarsal I >40% of metatarsal II length. IVPP V18632 cannot be shown to have more recurved and slender teeth, as the apices are flat (taphonomic), its elongated anterior cervicals (contra Hu et al.) and short metatarsal I are like Pengornis. It does resemble Parapengornis' type in having a short posterodorsal lacrimal process and pygostyle shorter than half metatarsal III's length (47%). Given the intermediate characters of IVPP V18632, it's viewed as most probable the three specimens are conspecific.
Chiappeavis- O'Connor et al. (2016) described another new genus of pengornithid, Chiappeavis magnapremaxillo, based on almost complete specimen STM 29-11. Note the electronic version was published on December 31, 2015 and did not mention ZooBank, and the paper version was not published until January 11, 2016. Thus ICZN Article 8.5.3 (a 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") made "Chiappeavis magnapremaxillo" O'Connor et al. 2015 a nomen nudum until 2016. Xu et al. (2023) provide appendicular measurements. Several characters were listed as supposedly diagnostic here as well. The premaxilla was said to have a larger body and convex ventral margin, but the convex element has far too long of a ventral margin to be a premaxilla, so is more likely an incomplete maxilla with the base of the ascending process. The actual right premaxilla is then just the small anterodorsal portion right below the partially preserved left premaxilla, and has no visible ventral margin. The posterodorsal premaxillary process was claimed to be longer than other pengornithids, almost reaching the frontals. Yet this bone is highly abraded just posterior to figure 2A's 'l pm' label, so that this posterior portion could easily belong to the right nasal instead. This is bolstered by the fact it's the same width as the left nasal and that the right nasal is otherwise missing. The synsacrum has eight vertebrae (as in IVPP V18632), while the authors claim Pengornis' holotype has seven. Yet the description of the latter says only that seven are visible, but that the anterior end is covered, and indeed there could easily be another one beneath the ilium. STM 29-15 only has seven but is obviously younger based on its unfused sterna. The "median trabeculae" [sic = posteromedian process] of Chiappeavis is said to have diagnostic concave lateral margins, but this is also true in IVPP V18632 (though not STM 29-15) and is unpreserved in Parapengornis, while Pengornis' holotype doesn't preserve the sternum. The posteromedian angle of the sternum is said to be narrow, but while its 53 degree angle is a bit less than IVPP V18632's (at 68) or STM 29-15's (at 66), Parapengornis' holotype could have an identical angle if complete, and again Pengornis' holotype doesn't preserve the element. Finally, the authors claim the proximal articular surface of the tibia is laterodistally inclined, but this is only true of the left tibia, with the right tibia having a right angle between the surface and the long axis of the bone. Furthermore, Pengornis' holotype and IVPP V18632 both have inclined surfaces, though Parapengornis' holotype lacks them. Given the variation in Chiappeavis' holotype, the variation is likely due to perspective or taphonomy. Besides the characters listed in the diagnosis, O'Connor et al. note the short anterior cervicals are like the Parapengornis holotype but unlike Pengornis' holotype. As the latter is larger than the others, this may support ontogenetic cervical elongation. They also correctly note the long pygostyle is like Pengornis' holotype, but unlike IVPP V18632 or Parapengornis' holotype. Finally, the short metatarsal I is said to be like Pengornis' holotype, and is additionally like IVPP V18632 but unlike Parapengornis' holotype or STM 29-15. Thus the only real difference from Pengornis' holotype is the shorter anterior cervicals, and while there are a few differences from other pengornithid specimens (laterally concave posteromedian sternal process unlike STM 29-15; narrower posterior sternal angle than STM 29-15 and IVPP V18632; long pygostyle unlike STM 29-15, IVPP V18632 and Parapengornis' type; short metatarsal I unlike STM 29-15 and Parapengornis' type), there's no pattern of character distribution that would suggest separate pengornithid species (e.g. Parapengornis shares the cervical length and probably sternal angle, while IVPP V18632 is different in cervical length but shares metatarsal I length). Thus all Jiufotang pengornithids are still retained in Pengornis houi.
Yuanchuavis- Wang et al. (2021) described a supposed new taxon of pengornithid- Yuanchuavis kompsosoura based on IVPP V27883, a skeleton missing pectoral girdles and forelimbs. Regarding its validity, the premaxilla is said to have five teeth but the medial view of the right premaxilla in figure S1B shows the last tooth is upside down so that the root protrudes ventrally as if it's a crown tip in lateral view, and so is probably a dentary tooth. Similarly, the same figure shows the edentulous tip of the bone is exaggerated by the first tooth being displaced and artificially angled posteriorly. The actual edentulous portion is only two FABLs long, similar to Pengornis, IVPP V18632 and Parapengornis (right premaxilla; first tooth displaced and loose in left element). The supposedly short anterior and posterior lacrimal processes are similar to Parapengornis, IVPP V18632 and Pengornis except that the posterior process of the latter is longer as interpreted by O'Connor. The large hypapophyses on dorsals one and two are difficult to evaluate in other Pengornis as anterior dorsals are usually disarticulated and oriented at odd angles when exposed at all. Contra the authors, the dorsoventral depth of the dorsal central fossae (e.g. D5) are similar to IVPP V18632, Parapengornis and Chiappeavis. Finally, the short anterodorsal pygostyle processes are also present in Parapengornis and Chiappeavis (eroded in Pengornis), while the elongate anteroventral process is also present in Parapengornis, partly exposed in Pengornis and probably hidden under caudal vertebrae in Chiappeavis. Of the variable characters noted above for Parapengornis and Chaippeavis, the pygostyle/metatarsus ratio is intermediate (66%), metatarsal I is 42% the length of metatarsal II, and anterior cervicals are elongate, again showing no pattern and no distinct separated groups of ratios. Thus like other Jiufotang pengornithids, Yuanchuavis is synonymized with Pengornis here.
Relationships- Zhou et al. (2008) found Pengornis to be more derived than Protopteryx, but outside a clade containing Concornis, Gobipteryx, Neuquenornis and Cathayornis when entered into Clarke's matrix. Hu et al. (2014) entered the holotype and their new specimen into O'Connor's matrix and found them to be the most basal non-Protopteryx, non-longipterygid enantiornithines. This is the same result as found in the more extensive analysis of Wang et al. (2014), where it is mislabeled IVPP V18631. Hu et al. (2015) added the Parapengornis specimen and three characters, and found pengornithids to be more deeply nested in Enantiornithes than before, though the authors doubted this was true.
References- Zhou, Clarke and Zhang, 2008. Insight into diversity, body size and morphological evolution from the largest Early Cretaceous enantiornithine bird. Journal of Anatomy. 212, 565-577.
Hu, Zhou and O'Connor, 2014. A subadult specimen of Pengornis and character evolution in Enantiornithes. Vertebrata PalAsiatica. 52(1), 77-97.
Wang, Zhou, O'Connor and Zelenkov, 2014. A new diverse enantiornithine family (Bohaiornithidae fam. nov.) from the Lower Cretaceous of China with information from two new species. Vertebrata PalAsiatica. 52(1), 31-76.
Hu, O'Connor and Zhou, 2015a. A new species of Pengornithidae (Aves: Enantiornithes) from the Lower Cretaceous of China suggests a specialized scansorial habitat previously unknown in early birds. PLoS ONE. 10(6), e0126791.
Hu, O'Connor and Zhou, 2015b. A new species of Pengornithidae (Aves: Enantiornithes) from the Lower Cretaceous of China suggests a specialized scansorial habitat previously unknown in early birds. Journal of Vertebrate Paleontology. Program and Abstracts 2015, 147.
O'Connor, Sullivan, Zhou and Zheng, 2015b. Evolution and functional significance of derived sternal ossification patterns in ornithothoracine birds. Journal of Vertebrate Paleontology. Program and Abstracts 2015, 189.
O'Connor, Zheng, Sullivan, Chuong, Wang, Li, Wang, Zhang and Zhou, 2015a. Evolution and functional significance of derived sternal ossification patterns in ornithothoracine birds. Journal of Evolutionary Biology. 28(8), 1550-1567.
O'Connor, Wang, Zheng, Hu, Zhang and Zhou, 2016 (online 2015). An enantiornithine with a fan-shaped tail, and the evolution of the rectricial complex in early birds. Current Biology. 26(1), 114-119.
O'Connor, Erickson, Norell, Bailleul, Hu and Zhou, 2018. Medullary bone in an Early Cretaceous enantiornithine bird and discussion regarding its identification in fossils. Nature Communications. 9:5169.
Wang, O'Connor, Zhao, Pan, Zheng, Wang and Zhou, 2021. An Early Cretaceous enantiornithine bird with a pintail. Current Biology. 31, 1-8.
Xu, Wang, Chen, Dong, Lin, Xu, Tang, You, Zhou, Wang, He, Li, Zhang and Zhou, 2023. A new avialan theropod from an emerging Jurassic terrestrial fauna. Nature. 621, 336-343.

Protopterygiformes Zhang and Zhou, 2006
Protopterygidae Zhang and Zhou, 2006
Protopteryx Zhang and Zhou, 2000
P. fengningensis Zhang and Zhou, 2000
Late Hauterivian, Early Cretaceous
Sichakou Sedimentary Member of the Huajiying Formation, Hebei, China
Holotype- (IVPP V11665) (~130 mm; 70 g, juvenile?) skull (28.3 mm), mandible, seven or eight cervical vertebrae (18.5), twelve dorsal vertebrae (33.9 mm), dorsal ribs, sacrum, seven free caudal vertebrae (9.4 mm), pygostyle (11.3 mm), scapulae (21.7 mm), coracoids, furcula (14.7 mm), sternum, humeri (27.5 mm), radii, ulnae (28.1 mm), semilunate carpal, distal carpal III, metacarpal I, phalanx I-1, manual ungual I, metacarpal II (15.75 mm), phalanx II-1, phalanx II-2, manual ungual II, metacarpal III, phalanx III-1, phalanx III-2, ilium (15.3 mm), pubis (22.3 mm), ischium (12.9 mm), femur (19.8 mm), tibia (30.9 mm), fibula, astragalus, calcaneum, distal tarsal, tarsometatarsus (16.23 mm), pedal phalanges, pedal unguals, feather impressions
Paratype- (IVPP V11844) (~130 mm; juvenile?) incomplete skeleton including skull, mandible, seven or eight cervical vertebrae (19.1), twelve dorsal vertebrae (34 mm), dorsal ribs, seven free caudal vertebrae, pygostyle, coracoids (12.7 mm), furcula (14 mm), sternum (15.9 mm), sternal ribs, forelimbs, ilium (14.8 mm), feather impressions
Diagnosis- (proposed) scapulocoracoid articulation flat; procoracoid process; wide interclavicular angle (ontogenetic?); carpometacarpus unfused (ontogenetic?); distal tarsals unfused to tarsometatarsus (ontogenetic?).
Comments- Jin et al. (2008) reidentified the horizon of Protopteryx as the Huajiying Formation, instead of the Yixian Formation as stated by Zhang and Zhou (2000) or the Dabeigou Formation as in Zhang et al. (2008). Wang et al. (2017) lists the holotype's pygostyle and tarsometatarsus lengths as 21.32 and 30.90 mm respectively, but these are clearly far too large. Xu et al. (2023) includes several appendicular measurements for the holotype.
References- Zhang and Zhou, 2000. A primitive enantiornithine bird and the origin of feathers. Science. 290, 1955-1959.
Jin, Zhang, Li, Zhang, Li and Zhou, 2008. On the horizon of Protopteryx and the early vertebrate fossil assemblages of the Jehol Biota. Chinese Science Bulletin. 53(18), 2820-2827.
Zhang, Zhou and Benton, 2008. A primitive confuciusornithid bird from China and its implications for early avian flight. Science in China Series D: Earth Sciences. 51(5), 625-639.
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.
Xu, Wang, Chen, Dong, Lin, Xu, Tang, You, Zhou, Wang, He, Li, Zhang and Zhou, 2023. A new avialan theropod from an emerging Jurassic terrestrial fauna. Nature. 621, 336-343.

Shangyang Wang and Zhou 2019
S. graciles Wang and Zhou, 2019
Early Albian, Early Cretaceous
Mutouchengzi, Jiufotang Formation, Liaoning, China
Holotype- (IVPP V25033) (adult) skull, mandibles, 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, first dorsal vertebra, four posterior dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, synsacrum (17.2 mm), six caudal vertebrae, pygostyle (13.9 mm), scapulae (~23.6 mm), coracoids (16.6, 16.7 mm), furcula, sternum, sternal ribs, humeri (28.4, ~28 mm), radii (28.9, 28.6 mm), ulnae (30.5, ~30.2 mm), scapholunares, pisiforms, carpometacarpi (mcI 2.4 mm; 14.0 mm), phalanges I-1 (4.9, 5.0 mm), manual unguals I (2.0, ~1.7 mm), phalanges II-1 (one distal; ~7.7 mm), phalanges II-2 (one distal; 5.1 mm), manual ungual II (1.5 mm), phalanx III-1 (4.2 mm), ilia (17.5 mm), pubes (22.6 mm), ischium, femora (25.5 mm), tibiotarsi (31.0, 31.2 mm), fibulae, metatarsals I, phalanges I-1 (4.2, 4.1 mm), pedal unguals I (3.9, 3.8 mm), tarsometatarsi (17.2 mm), phalanges II-1 (3.8, 3.8 mm), phalanges II-2 (5.0, 4.8 mm), pedal unguals II (3.9, 3.6 mm), phalanges III-1 (5.5, 5.6 mm), phalanges III-2 (4.9, 4.9 mm), phalanges III-3 (5.2, 5.1 mm), pedal unguals III (4.5, 4.1 mm), phalanges IV-1 (3.0 mm), phalanges IV-2 (2.7, 2.8 mm), phalanges III-3 (3.1, 3.0 mm), phalanges IV-4 (4.2, 3.9 mm), pedal unguals IV (3.2, 3.3 mm), pedal claw sheaths
Diagnosis- (after Wang and Zhou, 2019) fully fused premaxillae (also in Gobipteryx); eleven cervical vertebrae; eight fused sacrals; hypocleidium very short; sternum with anterolateral processes (also in Pterygornis, Piscivorenantiornis, Cathayornis and Rapaxavis); coracoid slender; pubis sigmoid in lateral view; metatarsal II wider than metatarsal III; pedal digit II shorter than IV.
Comments- This was discovered prior to May 2018.
Wang and Zhou added Shangyang to O'Connor's avialan analysis and recovered it sister to Eocathayornis plus Longipterygidae.
Reference- Wang and Zhou 2019. A new enantiornithine (Aves: Ornithothoraces) with completely fused premaxillae from the Early Cretaceous of China. Journal of Systematic Palaeontology. 17(15), 1299-1312.

unnamed clade
= Longipterygidae sensu O'Connor et al. 2009
Definition- (Longipteryx chaoyangensis + Longirostravis hani)

Alexornithiformes Brodkorb, 1976
Definition- (Alexornis antecedens <- Coracias garrulus, Picus viridis, Gobipteryx minuta) (Martyniuk, 2012)
Alexornithidae Brodkorb, 1976
References- Brodkorb, 1976. Discovery of a Creteceous bird, apparently ancestral to the orders Coraciiformes and Piciformes (Aves: Carinatae). in Olson (ed.). Collected papers in avian phylogeny honoring the 90th birthday of Alaxander Wetmore. Smithsonian Contributions to Paleobiology. 27, 67-73.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Alexornis Brodkorb, 1976
A. antecedens Brodkorb, 1976
Campanian, Late Cretaceous
Bocana Roja Formation, Mexico
Holotype- (LACM 33213 in part) distal humerus (~105 mm)
Paratype- ....(LACM 33213 in part) distal humerus
Referred- ....(LACM 32213 in part) proximal scapula, proximal coracoid (~12 mm), proximal ulna, distal femur, proximal tibia, >20 fragments (Brodkorb, 1976)
Diagnosis- anterior cnemial crest present.
Reference- Brodkorb, 1976. Discovery of a Creteceous bird, apparently ancestral to the orders Coraciiformes and Piciformes (Aves: Carinatae). In Olson (ed.). Collected Papers in Avian Phylogeny Honoring the 90th Birthday of Alaxander Wetmore. Smithsonian Contributions to Paleobiology. 27, 67-73.

Cratoavis Carvalho, Novas, Agnolín, Isasi, Freitas and Andrade, 2015b
C. cearensis Carvalho, Novas, Agnolín, Isasi, Freitas and Andrade, 2015b
Late Aptian, Early Cretaceous
Nova Olinda Member of the Crato Formation, Brazil
Holotype- (UFRJ-DG 031 Av) (~60 mm, juvenile) incomplete skull, sclerotic ossicles, partial mandible, five cervical vertebrae, six dorsal vertebrae, several partial dorsal ribs, (caudal series 8.3 mm) eight partial to complete caudal vertebrae, pygostyle (9.4 mm), scapula, coracoids (7.7 mm), few sternal ribs, humeri (14 mm), radii, ulnae (13.3 mm), phalanx I-1, carpometacarpi (one fragmentary; 7.2 mm), metacarpal I fragment?, phalanx II-1, phalanx II-2, manual ungual II, partial phalanx III-1 (3.2 mm), fragmentary ilia, incomplete pubes, femora (12.8, ~11.7 mm), tibiotarsi (~12 mm), metatarsals I, phalanges I-1 (2.6 mm), pedal unguals I (3.5 mm), metatarsals II (one partial), phalanges II-1 (one fragmentary), partial pedal unguals II, metatarsals III (one partial; 8.9 mm), phalanges III-1 (one partial), phalanx III-2, phalanges III-3 (one incomplete), pedal unguals III, metatarsal IV, phalanges IV-1, phalanges IV-2, phalanx IV-3, phalanges IV-4 (one partial), incomplete pedal unguals IV, pedal claw sheaths, body feathers, remiges, retrices (79.9 mm)
Diagnosis- (after Carvalho et al., 2015b) maxillary teeth; dorsal vertebrae with fan-shaped and very well-developed neural spines; caudal neural spines transversely thick; strongly concave medial margin of coracoid; proximally rounded humeral head; tibiotarsus shorter than femur and subequal in length to metatarsals; very elongate pedal digit III phalanges; very long rectrices, much longer than total body size.
Comments- Carvalho et al. (2015a) described UFRJ-DG 031 Av as Euenantiornithes indet., finding it to be more derived than Protopteryx and Elsornis. It was diagnosed and named by Carvalho et al. (2015b) in a paper with identical authorship submitted five weeks after the original was accepted, and approved a week before the original was published.
References- Carvalho, Novas, Agnolín, Isasi, Freitas and Andrade, 2015a. A Mesozoic bird from Gondwana preserving feathers. Nature Communications. 6, 7141.
Carvalho, Novas, Agnolín, Isasi, Freitas and Andrade, 2015b. A new genus and species of enantiornithine bird from the Early Cretaceous of Brazil. Brazilian Journal of Geology. 45(2), 161-171.

Grabauornis Dalsatt, Ericson and Zhou, 2014
= "Grabauornis" Dalsatt, 2012
G. lingyuanensis Dalsatt, Ericson and Zhou, 2014
= "Grabauornis lingyuanensis" Dalsatt, 2012
Early Aptian, Early Cretaceous
Dawangzhangzi Beds of Yixian Formation, Liaoning, China
Holotype- (IVPP V14595) (235 mm adult) partial skull (32.2 mm), mandibles (one partial; 15.2 mm), nine to ten cervical vertebrae, seven dorsal vertebrae, partial dorsal ribs, gastralia, synsacrum, four caudal vertebrae, pygostyle (14.8 mm), incomplete scapulae (24.2, 26.3 mm), incomplete coracoids (20.1, 20 mm), partial furcula (11.5 mm), sternum, sternal ribs, incomplete humeri (33.5 mm), radii (one incomplete, one fragmentary; 31.7 mm), incomplete ulna (35.2 mm), scapholunare, carpometacarpus (4.6, 17.5, 16.6 mm), phalanx I-1 (7.3 mm), proximal manual ungual I, phalanx II-1 (6.4 mm), phalanx II-2 (6.2 mm), manual ungual II (2.1 mm), ilia, femora (31.3 mm), tibiotarsi (one partial; 36.2 mm), fibula, metatarsals I (4.1, 4.2 mm), phalanges I-1 (5, 5 mm), pedal unguals I (7.6, 7.2 mm), tarsometatarsi (II 18.6, 18.4; III 19.7, 19.4 mm; IV 18.3, 18.3 mm), phalanges II-1 (4.7, 4.2 mm), phalanges II-2 (6.8, 6.4 mm), pedal unguals II (6.2, 4.5 mm), phalanges III-1 (6.5, 7 mm), phalanges III-2 (5.3, 4.6 mm), phalanx III-3 (5.2 mm), pedal ungual III (6.5 mm), phalanges IV-4 (3.2 mm), phalanx IV-2 (3.8 mm), phalanx IV-3 (2.8 mm), phalanx IV-4 (3.7 mm), body feathers, remiges
Diagnosis- (after Dalsatt et al., 2014) small teeth; well developed acrocoracoid process; long posterolateral steranl process and very short posteromedial sternal process; posterolateral process expanded distally; metacarpals II and III nearly equal in width with almost no intermetacarpal space; humerus with prominent head and much shorter than ulna.
Comments- This taxon was initially announced in a thesis (Dalsatt, 2012) then described in a rather poorly translated paper (Dalsatt et al., 2014), and found to be an enantiornithine more derived than Protopteryx and Pengornis using a version of Clarke's bird analysis.
Reference- Dalsätt, 2012. Fossil birds: Contributions to the understanding of avian evolution. PhD thesis. Stockholm University. 35 pp.
Dalsatt, Ericson and Zhou, 2014. A new Enantiornithes (Aves) from the Early Cretaceous of China. Acta Geologica Sinica (English Edition). 88(4), 1034-1040.

Halimornis Chiappe, Lamb and Ericson, 2002
H. thompsoni Chiappe, Lamb and Ericson, 2002
Early-Middle Campanian, Late Cretaceous
Mooreville Chalk Formation, Alabama, US
Holotype- (D2K 035) two dorsal vertebrae, caudal vertebra, pygostyle, proximal humerus, distal femur
....(UAMNH PV996.1.1) dorsal centrum, dorsal neural arch, proximal scapula
Reference- Chiappe, Lamb and Ericson, 2002. New enantiornithine bird from the marine Upper Cretaceous of Alabama. Journal of Vertebrate Paleontology. 22(1), 170-174.

Kizylkumavis Nesov, 1984a
K. cretacea Nesov, 1984a
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (TsNIGRI 51/11915) (~110 mm) distal humerus (~27 mm)
Comments- O'Connor (2009) proposed Kizylkumavis is a nomen dubium as it is indistinguishable from Alexornis. The latter seems true except for the slightly narrower ectocondyle in Kizylkumavis, though more detailed comparison to other enantiornithines is necessary.
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.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.

Sazavis Nessov vide Nessov and Jarkov, 1989
S. prisca Nessov vide Nessov and Jarkov, 1989
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Holotype- (ZIN PO 3472) (~185 mm) distal tibiotarsus (4.5 mm wide)
Other diagnoses- Nessov and Jarkov (1989) initially included characters now known to be more widespread in enantiornithines. They said the retinaculum tuberosity is poorly developed and distally placed, but there are two tuberosities, the weaker of which is proximally placed as in e.g. Gobipteryx, Nanantius and Qiliania. The distal tuberosity is actually more prominent than the former two, though comparable and plesiomorphic in any case. The distal transverse width (222% of minimal shaft width) is not greater than e.g. Nanantius or ?Soroavisaurus PVL-4033. The medial condyle (misidentified as lateral by the authors) is less broad than e.g. Gobipteryx or PVL-4033. The medial condyle also has a rounded proximal margin in e.g. Gobipteryx, Qiliania and PVL-4033.
Kurochkin (1996) listed a few new characters to distinguish Sazavis from Gobipteryx (as his new taxon Nanantius valifanovi). Of these, the supposedly more abrupt transition from tibiotarsal shaft to condyles isn't different from e.g. Qiliania or PVL-4033. The medial condyle is more circular in these two specimens as well. Finally, the intercondylar fossa is more medially placed in e.g. Qiliania and Nanantius, and is symplesiomorphic.
Comments- Nessov and Jarkov (1989) initially assigned Sazavis to ?Alexornithidae within Enantiornithes, but mistook the medial condyle for the lateral and vice versa. O'Connor (2009) declared Sazavis a nomen dubium because she misunderstood "the distinguishing characteristic of the specimen" as being "the transverse paracondylar expansion" as opposed to being "only medially expanded in Gobipteryx." She correctly noted the former morphology is also present in the then unnamed Qiliania. Yet this was not a character mentioned by Nessov and Jarkov in their initial diagnosis nor one mentioned by Kurochkin as differing from Gobipteryx (his Nanantius valifanovi). Yet Sazavis differs from Qiliania in having a less anteriorly projected lateral condyle, a larger medial condyle (56% of distal width vs. 53%) especially visible as its distal boundary, and more developed distal retinaculum tuberosity. Resolving whether Sazavis is diagnostic compared to other enantiornithines requires a more detailed comparison of tibiotarsi.
References- Nessov and Jarkov, 1989. New Cretaceous-Paleogene birds of the USSR and some remarks on the origin and evolution of the class Aves. Proceedings of the Zoological Institute, Leningrad. 197, 78-97.
Elzanowski, 1995. Cretaceous birds and avian phylogeny. Courier Forschungsinstitut Senckenberg. 181, 37-53.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.

Yatenavis Herrera, Agnolín, Rozadilla, Coco, Manabe, Tsuihiji and Novas, 2022 online
Y. ieujensis Herrera, Agnolín, Rozadilla, Coco, Manabe, Tsuihiji and Novas, 2022 online
Early Maastrichtian, Late Cretaceous
Estancia La Anita, Chorrillo Formation, Santa Cruz, Argentina
Holotype- (MPM-PV-23086) distal humerus (6.2 mm trans)
Diagnosis- (after Herrera et al., 2023) humeral shaft narrow (less than half the maximum width of the distal end of the humerus); humeral shaft slightly bowed anteroposteriorly; dorsal supracondylar process prominent
and slightly concave (also in Alexornis, Kizylkumavis and Martinavis); m. brachialis fossa wide, deep and proximally extended; m. brachialis fossa medially positioned and laterally delimited by a ridge; well-defined fossa proximal to distal condyles, and dorsally separated from m. brachialis fossa through a wide and prominent ridge; anteroposterior ridge along distal margin of ventral condyle (also in Alexornis, Kizylkumavis and Martinavis); D-shaped distal fossa delimited laterally by ridge of ventral condyle and separated from olecranal fossa; distal end of humerus almost perpendicular to longitudinal axis of bone.
Comments- The holotype was discovered in March 2022. Herrera et al. (2022) found "the latter caudal ridge [on the ventral condyle distally] is perpendicular to the cranial margin of the ventral condyle and together forms a L-shaped prominence when viewed distally in Yatenavis, a trait shared with MPEF-PV 2359 and Martinavis vincei, but not with Kizylkumavis." Furthermore "Yatenavis differs from the enantiornithines, excepting MPEF-PV 2359, in that the site of origin for m. brachialis is positioned at the craniomedial surface of the humerus."
Reference- Herrera, Agnolín, Rozadilla, Coco, Manabe, Tsuihiji and Novas, 2023 (2022 online). New enantiornithine bird from the uppermost Cretaceous (Maastrichtian) of southern Patagonia, Argentina. Cretaceous Research. 144, 105452.

Boluochiformes Zhou and Zhang, 2006
Boluochidae Zhou and Zhang, 2006
Boluochia Zhou, 1995
B. zhengi Zhou, 1995
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V9770) (~155 mm) incomplete premaxilla, nasal fragments, partial dentaries, teeth, dorsal rib fragments, incomplete sacrum, six caudal vertebrae, pygostyle (21.5 mm), posterior sternum, three sternal ribs?, posterior ilium (~7.5 mm), pubes (one fragmentary; 25.15 mm), ischia (17 mm), distal femora, incomplete tibiotarsi (~37 mm), metatarsal I (4.1 mm), tarsometatarsi (17.4, 17.7 mm; II 17.2 mm, III 17.4 mm, IV 17.5 mm), at least seventeen pedal phalanges, six pedal unguals
Diagnosis- (after O'Connor et al., 2011) premaxilla anterior to external nares imperforate with parallel dorsal and ventral margins; dorsal surface of premaxilla with slight concavity just anterior to the nasal processes; premaxilla with large, recurved teeth; large and robust pygostyle 20% longer than tarsometatarsus; metatarsals II–III subequal in length and ending distally at approximately the same level; metatarsal IV longer than II and III and laterally deflected along the distal fifth of the tarsometatarsus.
Comments- This specimen was found by Zhou in 1990 along with the holotype of Cathayornis and an unidentified sternal impression (IVPP V 9941). It is mostly preserved as a natural mold. O'Connor et al. (2011) redescribed it, noting the supposedly curved toothless premaxilla was misinterpreted and contains several teeth. In addition, the specimen is very similar to Longipteryx and may be a senior synonym.
References- Zhou, 1995. Discovery of a new enantiornithine bird from the Early Cretaceous of Liaoning, China. Vertebrata PalAsiatica. 33(2), 99-113.
Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park. 221 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.
O'Connor, Zhou and Zhang, 2010. A new look at 'old' birds from the Jehol fauna. Journal of Vertebrate Paleontology. Program and Abstracts 2010, 141A.
O'Connor, Zhou and Zhang, 2011. A reappraisal of Boluochia zhengi (Aves: Enantiornithes) and a discussion of intraclade diversity in the Jehol avifauna, China. Journal of Systematic Palaeontology. 9(1), 51-63.

Longipterygiformes Zhang, Zhou, Hou and Gu, 2001
Definition- (Longipteryx chaoyangensis <- Cathayornis yandica, Iberomesornis romeralii, Enantiornis leali) (Martyniuk, 2012)
Longipterygidae Zhang, Zhou, Hou and Gu, 2001
Other definitions- (Longipteryx chaoyangensis + Longirostravis hani) (O'Connor, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009)
Longipteryginae Zhang, Zhou, Hou and Gu, 2001 vide Stidham and O'Connor, 2021
Longipteryx Zhang, Zhou, Hou and Gu, 2001
= "Camptodontus" Li, Gong, Zhang, Yang and Hou, 2010 (preoccupied Dejean, 1826)
= Camptodontornis Demirjian, 2019
References- Dejean, 1826. Species general des coleopteres, de la collection de M. le Comte Dejean. Tome second. Crevot, Paris. 501 pp.
Zhang, Zhou, Hou and Gu, 2001. Early diversification of birds: Evidence from a new opposite bird. Chinese Science Bulletin. 46(11), 945-950.
Li, Gong, Zhang, Yang and Hou, 2010. A new enantiornithine bird from the Early Cretaceous of Liaoning, China. Acta Palaeontologica Sinica. 49(4), 524-531.
Demirjian, 2019. Camptodontornis gen. nov., a replacement name for the bird genus Camptodontus Li, Gong, Zhang, Yang, and Hou, 2010, a junior homonym of Camptodontus Dejean, 1826. Zootaxa. 4612(3), 440.
Stidham and O'Connor, 2021. The evolutionary and functional implications of the unusual quadrate of Longipteryx chaoyangensis (Avialae: Enantiornithes) from the Cretaceous Jehol Biota of China. Journal of Anatomy. 239(5), 1066-1074.
L. chaoyangensis Zhang, Zhou, Hou and Gu, 2001
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V12325) (~190 mm, 190 g) skull (55.06 mm), mandible, hyoids, seven cervical vertebrae, at least five dorsal vertebrae, sixteen dorsal ribs, ten uncinate processes, six rows of gastralia, sacrum, six caudal vertebrae, pygostyle (21.38 mm), scapulae, incomplete coracoids (19.86 mm), furcula, sternal fragments, four sternal ribs, incomplete humeri (43.48, ~42.03 mm), incomplete radii (~43.48 mm), incomplete ulnae (44.26, ~47.1 mm), scapholunare, pisiform, semilunate carpal, metacarpal I (4.4 mm), phalanx I-1 (8.5 mm), manual ungual I (7.7 mm), metacarpal II (17 mm), phalanx II-1 (10 mm), phalanx II-2 (9.3 mm), manual ungual II (8.5 mm), metacarpal III (18 mm), phalanx III-1 (5.1 mm), phalanx III-2 (1.5 mm), ilia, incomplete pubes, incomplete ischium, incomplete femora (28.26, 28.77 mm), incomplete tibiae (30.07 mm), fibulae (12 mm), proximal tarsals, metatarsal I (4.8 mm), phalanx I-1, pedal ungual I, tarsometatarsus (metatarsal II 20 mm; III 20.5 mm; IV 21 mm), phalanx II-1, phalanx II-2, phalanx III-1, proximal phalanx III-2, phalanges from digit IV, feather impressions
Paratypes- (IVPP V12552) (juvenile) (93% size of holotype) complete skeleton including skull and sternum
(IVPP V12553) furcula, humerus
(IVPP V12554) ulna
Diagnosis- scapula distally broad; wide interclavicular angle (ontogenetic?); metatarsal IV longer than III (also in Boluochia and Alethoalaornis).
References- Zhang, Zhou, Hou and Gu, 2001. Early diversification of birds: Evidence from a new opposite bird. Chinese Science Bulletin. 46(11), 945-950.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD Thesis. University of Southern California. 586 pp.
L? yangi (Li, Gong, Zhang, Yang and Hou, 2010) new combination
= "Camptodontus" yangi Li, Gong, Zhang, Yang and Hou, 2010
= Camptodontornis yangi (Li, Gong, Zhang, Yang and Hou, 2010) Demirjian, 2019
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (SG2005-B1) skull (56 mm), mandibles, four cervical vertebrae, synsacrum, scapulae (one partial), coracoids (19 mm), furcula, sternum (18 mm), humerus (42 mm), radius (42 mm), ulna (46 mm), partial pubis, fragments
Referred- (DNHM D2566) incomplete skeleton including incomplete skull (O'Connor, 2009)
Barremian-Aptian, Early Cretaceous
Yixian Formation?, Liaoning, China
(DNHM D2889) (adult) skull (70 mm), mandibles, atlas, axis, five cervical vertebrae, at least ten dorsal vertebrae, dorsal ribs, gastralia, synsacrum, at least five caudal vertebrae, pygostyle, scapulae (one incomplete), coracoids (24 mm), furcula, partial sternum, humeri (40 mm), radii (40 mm), ulnae (42 mm), pisiform, carpometacarpi (mcI 5, mcII 17, mcIII 23 mm), phalanges I-1 (9 mm), manual unguals I (8 mm), phalanges II-1 (12 mm), phalanges II-2 (11 mm), manual unguals II (7 mm), phalanges III-1 (one fragmentary), partial pubis, ischium, femora (31 mm), tibiotarsi (38 mm), fibula (~15 mm), metatarsal I, phalanx I-1 (7 mm), pedal ungual I (6 mm), tarsometatarsi (24 mm; one incomplete), phalanges II-1 (4 mm), phalanges II-2 (6 mm), pedal unguals II (7 mm), phalanges III-1 (5 mm), phalanges III-2 (4 mm), phalanges III-3 (7 mm), pedal unguals III (7 mm), phalanges IV-1 (5 mm), phalanges IV-2 (4 mm), phalanges IV-3 (4 mm), phalanges IV-4 (6 mm), pedal unguals IV (9 mm), pedal claw sheaths (O'Connor, 2009; described by Wang et al., 2015)
Diagnosis- (after Li et al., 2010) skull three times longer than tall; large conical premaxillary teeth; widely spaced premaxillary teeth; teeth strongly recurved; frontal broad and flat; dentary long; dentary teeth similar to but shorter than those of premaxilla; anterior cervical centra heterocoelous; posterior sternal carina; posterolateral sternal process slender with slightly expanded distal end; posteromedial sternal process short; ulnohumeral ratio ~110%; radius about 75% as wide as ulna.
Comments- Li et al. (2020) assigned "Camptodontus" yangi to Longipterygidae based on the "long and thick beak, similar sternum and furcula", but it has not been included in a phylogenetic analysis. They described it as a new genus of enantiornithine, but the name is preoccupied by a carabid beetle named 184 years earlier (Martyniuk, 2012) so was replaced by Camptodontornis (Demirjian, 2019). Wang et al. (2014) referred the holotype to Longipteryx based on the "large teeth strongly curved caudally [and] lateral trabecula of sternum slightly laterally directed with simple distal expansion", though they did not state whether the species was valid or use the new combination Longipteryx yangi posited above. Martyniuk proposed a possible synonymy with Boluochia based on tooth size. The latter genus itself has been compared favorably to Longipteryx by O'Connor, and the relationship between these specimens is presently uncertain.
This is seemingly the same taxon as DNHM D2889, a specimen called Longipteryx sp. by O'Connor (O'Connor, 2009; O'Connor and Chiappe, 2011), both of which have larger premaxillary teeth than the L. chaoyangensis holotype or IVPP V12552. Wang et al. (2015) fully described it, referring it to Yuanjiawa in the Yixian Formation, whereas O'Connor listed it as from the Jiufotang Formation like other specimens with this morphology. Wang et al. referred DNHM D2889 to Longipteryx chaoyangensis while noting some differences (forelimb/hindlimb ratio 1.2 vs. 1.5; femorotibiotarsal ratio .8 vs. 1.0; femorohumeral ratio .8 vs. .6; clavicular arm / hypocleidium ratio 1.1 vs. .8), which they ascribed to age.
O'Connor (2009) also referred DNHM D2566 to Longipteryx sp..
References- Dejean, 1826. Species general des coleopteres, de la collection de M. le Comte Dejean. Tome second. Crevot, Paris. 501 pp.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD Thesis. University of Southern California. 586 pp.
Li, Gong, Zhang, Yang and Hou, 2010. A new enantiornithine bird from the Early Cretaceous of Liaoning, China. Acta Palaeontologica Sinica. 49(4), 524-531.
O'Connor and Chiappe, 2011. A revision of enantiornithine (Aves: Ornithothoraces) skull morphology. Journal of Systematic Palaeontology. 9(1), 135-157.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Wang, Zhou, O'Connor and Zelenkov, 2014. A new diverse enantiornithine family (Bohaiornithidae fam. nov.) from the Lower Cretaceous of China with information from two new species. Vertebrata PalAsiatica. 52(1), 31-76.
Wang, Zhao, Shen, Liu, Gao, Cheng and Zhang, 2015. New material of Longipteryx (Aves: Enantiornithes) from the Lower Cretaceous Yixian Formation of China with the first recognized avian tooth crenulations. Zootaxa. 3941(4), 565-578.
Demirjian, 2019. Camptodontornis gen. nov., a replacement name for the bird genus Camptodontus Li, Gong, Zhang, Yang, and Hou, 2010, a junior homonym of Camptodontus Dejean, 1826. Zootaxa. 4612(3), 440.
Yun, 2019. Comments on the taxonomic validity of Camptodontornis yangi (Li, Gong, Zhang, Yang, and Hou, 2010) and its relationships to Longipteryx chaoyangensis Zhang, Zhou, Hou, and Gu, 2000 and Boluochia zhengi Zhou, 1995. Zootaxa. 4652(2), 391-392.

Shengjingornis Li, Wang, Zhang and Hou, 2012
S. yangi Li, Wang, Zhang and Hou, 2012
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (PMOL AB00179) skull (~46.6 mm), mandibles, atlas, axis, seven cervical vertebrae, seven dorsal vertebrae, dorsal ribs, gastralia, synsacrum, four caudal vertebrae, pygostyle, scapulae, coracoids (18.7 mm), furcula, sternum (31.6 mm), sternal ribs, humeri (41 mm), radii (43 mm), ulnae (42 mm), scapholunares, pisiform, metacarpals I (3.8 mm), phalanges I-1 (8.8 mm), manual unguals I (5.1 mm), carpometacarpi (mcII 18.5, mcIII 22.8 mm), phalanx II-1, phalanx II-2 (8 mm), phalanx III-1 (8.8 mm), phalanx III-2 (5.1), ilia, pubes (29.4 mm), ischia, femora (37.5 mm), tibiotarsi (44.1 mm), fibulae (21.2 mm), metatarsals I (4.4 mm), phalanges I-1 (4.1 mm), pedal unguals I (6.8 mm), tarsometatarsi (mtII 21.1, mtIII 23.5, mtIV 22 mm), phalanges II-1 (5.3 mm), phalanges II-2 (6.7 mm), pedal unguals II (7.6 mm), phalanges III-1 (7.1 mm), phalanges III-2 (6.2 mm), phalanges III-3 (6.5 mm), pedal unguals III (7.5 mm), phalanges IV-1 (3.8 mm), phalanx IV-2 (~3.1 mm), phalanges IV-3 (3.3 mm), phalanges IV-4 (3.5 mm), pedal unguals IV (6.1 mm)
Diagnosis- (after Li et al., 2012) long, tapering, slightly curved beak; teeth anteriorly; short nasal; slender jugal; high frontal; Y-shaped furcula with distally expanded hypocleidium; short coracoids; low and posteriorly restricted sternal keel; humerus nearly as long as radius and ulna; carpometacarpus fused; at least two manual unguals; femoral head developed; fibula nearly half length of tibiotarsus; metatarsus proximally fused.
Comments- Li et al. (2012) entered Shengjingornis into O'Connor's matrix and found it to be sister to Longirostravis. Note most of the supposed diagnostic characters are symplesiomorphies for enantiornithines.
Reference- Li, Wang, Zhang and Hou, 2012. A new enantiornithine bird from the Lower Cretaceous Jiufotang Formation in Jinzhou area, Western Liaoning Province, China. Acta Geologica Sinica. 86(5), 1039-1044.

Longirostravisiformes Zhou and Zhang, 2006
Longirostravisidae Zhou and Zhang, 2006
= Longirostrisavinae Zhou and Zhang, 2006 vide Stidham and O'Connor, 2021
Diagnosis- manual ungual I absent; manual ungual II absent; longitudinal crest on the central portion of its pedal unguals' sides.
References- Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.
Stidham and O'Connor, 2021. The evolutionary and functional implications of the unusual quadrate of Longipteryx chaoyangensis (Avialae: Enantiornithes) from the Cretaceous Jehol Biota of China. Journal of Anatomy. 239(5), 1066-1074.

Shanweiniao O'Connor, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009
S. cooperorum O'Connor, Wang, Chiappe, Gao, Meng, Cheng and Liu, 2009
Early Aptian, Early Cretaceous
Dawangzhangzi Beds of Yixian Formation, Liaoning, China
Holotype- (DMNH D1878) (adult) skull (31.36 mm), sclerotic ring, mandibles, nine cervical vertebrae, six dorsal vertebrae, partial dorsal ribs, gastralia, partial synsacrum, several caudal vertebrae, pygostyle (12.37 mm), scapula, coracoids (~12.61 mm), furcula (~8.95 mm), sternum, sternal ribs, humeri (~21.31, 22.43 mm), radii (~22.53 mm), ulnae (~23.36 mm), partial proximal carpal, phalanx I-1, manual ungual I, partial metacarpal II, phalanges II-1 (4.55 mm), phalanges II-2 (2.62 mm), phalanx III-1 (2.33 mm), partial ilium, partial pubes, femora (~17.6 mm), tibiotarsi (22.61, 22.41 mm), fibula, partial metatarsals I, phalanges I-1 (3.71 mm), pedal unguals I, tarsometatarsi (11.9, 11.75 mm; mtII 9.3, 10.05 mm, mtIII 11.16, 20.84 mm, mtIV 10.98, 10.72 mm), phalanges II-1 (2.75 mm), phalanges II-2 (4.4, 4.44 mm), pedal unguals II (6.51, 6.54 mm), phalanges III-1 (~2.71 mm), phalanges III-2 (2.98 mm), phalanges III-3 (~3.99 mm), pedal unguals III (~5.67, 5.19 mm), phalanges IV-1 (1.82 mm), phalanges IV-2 (1.28 mm), phalanges IV-3 (2.15 mm), phalanges IV-4 (3.23 mm), pedal unguals IV (~5.54, 5.8 mm), pedal claw sheaths, body feathers, remiges, retrices
Diagnosis- (after O'Connor et al., 2009) intermembral index (humerus+ulna/.femur+tibiotarsus) 1.23.
Other diagnoses- O'Connor et al. (2009) also list several other characters in the diagnosis which they state are found in related taxa as well. The snout length (62% of skull length) is overlapped by Longirostravis (60-64%) and very similar to Longipteryx (64%) and Rapaxavis (65%). Manual phalanx II-2 is reduced and wedge-shaped in Longirostravis and Rapaxavis too. The low interclavicular angle (~40 degrees) is also present in Iberomesornis and Concornis. The length of the hypocleideum being shorter than the interclavicular symphysis is not necessarily true, as the authors state the hypocleideal length is unknown. The distallly non-branched posterolateral sternal processes are plesiomorphic for enantiornithines. Metatarsal III is longest plesiomorphically for theropods. O'Connor et al. note Rapaxavis also has a longitudinal crest on the central portion of its pedal unguals' sides. Two pairs of elongate retrices are also present in Paraprotopteryx. The pedal ungual and claw curvature is similar to that of Rapaxavis.
References- O'Connor, Meng, Wang and Chiappe, 2006. Longirostrine enantiornithine birds; Information from a new Chinese specimen. Journal of Vertebrate Paleontology. 26(3), 106A.
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.

unnamed clade (Longirostravis hani + Rapaxavis pani)
Diagnosis- less than eight sacral vertebrae; posterolateral sternal process with tribranched distal tip.

Longirostravis Hou, Chiappe, Zhang and Chuong, 2004
= "Longirostravis" Hou, Chiappe, Zhang and Chuong, 2003 online
L. hani Hou, Chiappe, Zhang and Chuong, 2004
= "Longirostravis hani" Hou, Chiappe, Zhang and Chuong, 2003 online
Late Barremian-Early Aptian, Early Cretaceous
Jianshangou or Dawangzhangzi Beds of Yixian Formation, Liaoning, China
Holotype- (IVPP V11309) (~105 mm, 39 g) skull (~32.86 mm), mandibles, cervical vertebrae, dorsal vertebrae, dorsal ribs, gastralia, sacrum, five caudal vertebrae, pygostyle (13.57 mm), scapulae (19.2 mm), coracoids (13.57, ~11.86 mm), furcula (10.71 mm), sternum (17 mm), humeri (23.51, ~25.71 mm), radii (~21.43, 24.57 mm), ulnae (~24.11, ~25.14 mm), proximal carpal, carpometacarpus, manual phalanges?, ilium (13.8 mm), pubis, ischium, femora (19.43 mm), tibiotarsi (25.17, 25 mm), fibulae, metatarsal I, tarsometatarsus (13.74 mm), pedal phalanges, feather impressions
Diagnosis- (after Hou et al., 2004) posterolateral sternal process with cladogram-like three-branched distal end.
(proposed) seven sacral vertebrae (also in Protopteryx).
Other diagnoses- Hou et al. (2004) included two other characters in their diagnosis. The long tapered snout is also present in Longipteryx, Shanweiniao and Rapaxavis, while Longipteryx's and Rapaxavis' are also decurved. Shanweiniao and Rapaxavis share dentation which is as anteriorly limited.
Comments- The description was first released online on December 2003 but not officially published until January 2004.
References- Hou, Chiappe, Zhang and Chuong, 2004. New Early Cretaceous fossil from China documents a novel trophic specialization for Mesozoic birds. Naturwissenschaften. 91(1), 22-25.
Zhou and Zhang, 2006. Mesozoic birds of China- A synoptic review. Vertebrata PalAsiatica. 44(1), 60-98.

Rapaxavis Morschhauser, Varricchio, Gao, Liu, Wang, Cheng and Meng, 2009
R. pani Morschhauser, Varricchio, Gao, Liu, Wang, Cheng and Meng, 2009
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (DMNH D2522) (47 g, subadult) skull, mandibles, hyoid, eight cervical vertebrae, four dorsal vertebrae, dorsal ribs, gastralia, synsacrum, six caudal vertebrae, pygostyle, anterior scapula, coracoids, furcula, sternum, anterolateral sternal ossifications, nine sternal ribs (4.7-9.7 mm), humeri, radii, ulnae, pisiforms, metacarpals I, phalanges I-1, metacarpals II, phalanges II-1, phalanges II-2, metacarpals III, phalanges III-1, phalanges III-2, ilia, pubes, ischia, femora, tibiae, fibulae, astragalocalcanea, fused distal tarsals III+IV, 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 unguals III, metatarsals IV, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, pedal claw sheaths
Diagnosis- (after Morschhauser et al., 2009) six sacral vertebrae; posterolateral sternal processes with two prominent branches and a smaller third branch; anterolateral sternal ossifications (also in Concornis).
(after O'Connor et al., 2011) rostrum ~60% of skull length; dentition anteriorly restricted; premaxillary process of maxilla approximately three times longer than the jugal process; nasals lacking maxillary process, external nares schizorhinal; furcula with short interclavicular symphysis and interclavicular angle of 50 degrees; coracoid lateral and sternal margins straight; coracoidal facets of sternum defining an obtuse angle of approximately 110 degrees; femur 80% the length of the tibiotarsus; penultimate pedal phalanges longer than preceding phalanges.
Other diagnoses- Morschhauser et al. (2009) list several other characters in their diagnosis as well. The long and slightly curved snout is also present in Longipteryx and Longirostravis. Shanweiniao seems to have as few dentary teeth as Rapaxavis. Boluochia, Dapingfangornis, Jibeinia, Longipteryx, Pengornis and Sinornis also have six free caudal vertebrae. The lack of Longirostravis' antler-shaped posterolateral sternal processes is plesiomorphic, as is the unexpanded posteromedian sternal process. The lack of manual unguals I and II is shared with Longirostravis and Shanweiniao. Having hindlimbs longer compared to the forelimbs than in Longipteryx is plesiomorphic, with Longirostravis having a similar ratio. Longirostravis has a similarly long hallux compared to tarsometatarsal length, as opposed to Longipteryx and Shanweiniao.
Comments- This specimen was first reported by Morschhauser et al. (2006) as a juvenile Longirostravis or a new related taxon, and was used in the phylogenetic analysis of O'Connor et al. (2009) before it was named. This found it to be a longipterygid sister to Longirostravis (though it was misspelled DMNH D2567/8 in figure 8 and switched with Zhongornis), which Morschhauser et al. (2009) agreed with when they named and described the taxon a few months later. O'Connor et al. (2011) redescribed the specimen once it was fully prepared.
References- Morschhauser, Liu, Meng and Varricchio, 2006. Anatomical details from a well preserved specimen of Longirostravis (Aves, Enantiornithes) from the Jiufotang Formation, Liaoning Province, China. Journal of Vertebrate Paleontology. 26(3), 103A.
Morschhauser, Varricchio, Gao, Liu, Wang, Cheng and Meng, 2009. Anatomy of the Early Cretaceous bird Rapaxavis pani, a new species from Liaoning Province, China. Journal of Vertebrate Paleontology. 29(2), 545-554.
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, Chiappe, Gao and Zhao, 2011. Anatomy of the Early Cretaceous enantiornithine bird Rapaxavis pani. Acta Palaeontologica Polonica. 56(3), 463-475.

unnamed clade

Alethoalaornithidae Li, Hu, Duan, Gong and Hou, 2007
Alethoalaornis Li, Hu, Duan, Gong and Hou, 2007
A. agitornis Li, Hu, Duan, Gong and Hou, 2007
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (LPM coll.; LPM 00009) incomplete skull (27 mm), mandible, nine cervical vertebrae, nine dorsal vertebrae, dorsal rib fragments, six caudal vertebrae, pygostyle (16 mm), scapulae, coracoids, furcula, sternum, humeri (24 mm), radii, ulnae (26 mm), scapholunares, pisiforms, carpometacarpi (23 mm), phalanges I-1, manual unguals I, phalanges II-1 + III-1, phalanges II-2, manual unguals II, pubes, femora (24 mm), tibiotarsi (27 mm), fibula, phalanx I-1, pedal ungual I, tarsometatarsi (17 mm), phalanx II-1, phalanx II-2, pedal ungual II, phalanges III-1, phalanges III-2, phalanges III-3, pedal ungual III, phalanges IV-1, phalanges IV-2, phalanges IV-3, phalanges IV-4, pedal unguals IV, body feathers, remiges
Paratype- (LPM 00038) specimen including skull, cervical vertebrae, dorsal vertebrae, dorsal ribs, synsacrum, pectoral elements, humeri, radii, ulnae, carpometacarpi, phalanges I-1, manual ungual I, phalanges II-1, phalanges II-2, phalanges III-1, partial ilia, pubis(?), femora, tibiotarsi, metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsi, pedal phalanges, pedal unguals
Referred- ?(LPM 00032) (subadult) specimen including synsacrum, pygostyle, humeri, radius, ulnae, carpometacarpus, phalanx I-1, femur, tibiotarsu, phalanx I-1, pedal ungual I, tarsometatarsus, 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 (Li, Hu, Duan, Gong and Hou, 2007)
(LPM 00053) specimen including dorsal ribs, gastralia, synsacrum, caudal vertebrae, pygostyle (~12 mm), incomplete humerus, radius, ulna, partial carpometacarpus, phalanx II-1, ilium, pubis, femora (one partial), tibiotarsi (one incomplete; ~26 mm), fibula, metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsi, phalanx II-1, phalanx II-2, pedal ungual II, phalanx III-1, phalanx III-2, phalanx IIII-3, pedal ungual III, pedal digit IV (Li, Hu, Duan, Gong and Hou, 2007)
?(LPM B00017; = LPM 00040) specimen including skull, mandibles, cervical vertebrae, dorsal vertebrae, synsacrum, scapula, coracoid, sternum, humeri, radii, ulnae, pisiform, metacarpal I, phalanx I-1, manual ungual I, carpometacarpus, phalanx II-1, phalanx II-2, phalanx III-1, partial femur, tibiotarsus, fibula, 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(Li, Hu, Duan, Gong and Hou, 2007)
Diagnosis- (after Li et al., 2007) hypcleidium equals clavicular ramus in length.
(after O'Connor, 2009; based on LPM B00017) low and delicate spinal crest on synsacrum; coracoid with convex lateral margin; sternal margin of coracoid slightly ventrally concave; lateral corner of distal coracoid distal to medial corner; sternum with posterolateral processes projecting posteriorly further than posteromedian process; pneumotricipital fossa rudimentary; deltopectoral crest tapering distally; manual digit I ~50% length of metacarpal II; manual ungual I larger than ungual II; tibiotarsus proximal surface angled so that medial margin is elevated compared to lateral margin; pedal ungual III less recurved than II and IV; proximal half of pedal unguals with laterally projecting ridges.
Other diagnoses- Li et al. (2007) listed numerous other characters in their diagnosis of Alethoalaornis and Alethoalaornithidae. The beak does not seem longer than most enantiornithines (and O'Connor 2009 states preservation prevents determination of its length), while its apparent sharpness in LPM 00038 is due to preparation and that of LPM 00040 could be due to that or preservation. Two to three pairs of premaxillary teeth seem to be present in Pengornis. Heterocoelous cervical vertebrae and thin hypocleidia are present in most enantiornithines. A "well developed" sternal carina and "metacarpal formed" are too vague to evaulate. Deep capital grooves are present in all enantiornithines except Elsornis. O'Connor notes pneumatic foramina are absent in referred specimen LPM B00017 at least. The manual unguals on digits I and II are reduced a similar amount in Hebeiornis and Shanweiniao, while many derived enantiornithines lack an ungual on digit III. Contra their description, the illustration suggests that the metatarsals increase in length laterally instead of being equally long. This is also present in Longipteryx and Boluochia. O'Connor states metatarsal III is longest in LMP B00017 while II and IV are subequal, which is primitive for theropods. Pedal unguals are longer than their pedal phalanges in most enantiornithines, including Pengornis, Shanweiniao and Sinornis.
Comments- Li et al. (2007) named this taxon in a description which was largely published in Chinese, with only a short English summary. They erected the new family Alethoalaornithidae for the genus, which they placed in Cathayornithiformes. This latter assignment was based on "similar length of trochlea at distal end of tarsometatarsus." If this refers to equal width, it is unlike Sinornis, which has trochlea II widest, and if it refers to distal extent, it is also unlike Sinornis which has trochlea III longest (whereas Alethoalaornis is illustrated as having trochlea IV longest, though LPM B00017 has III longest). O'Connor (2009) notes the holotype has a new collection number (unknown to her) as LPM 00009 is now a Confuciusornis specimen. She noted the only specimen available for study (LPM B00017) is distinguishable from other enantiornmithines, but because Li et al.'s "diagnosis does not match observations in LPMB00017, it is possible this specimen is not referable to Alethoalaornis agitornis, or that the original diagnosis is inaccurate."
Hu et al. (2013) mentioned LPM 00032 (as PMOL-AB00032) as a new enantiornithine taxon similar to Bohaiornis in size and limb element ratios, but diagnosed it based on- neural spines of dorsal vertebrae with anteroposteriorly strongly expanded tips; longitudinally grooved ventral surface of synsacrum; coracoid with straight lateral margin; clavicular rami medially curved; oval outline of sternum with posteromedian process distinctly wider than posteroolateral processes; forelimb and hind limb subequal in length; humeral head flat; manual digit I extending almost as far distally as metacarpal II.
References- Li, Hu, Duan, Gong and Hou, 2007. Alethoalaornithidae fam. nov.: A new family of enantiornithine bird from the Lower Cretaceous of Western Liaoning. Acta Palaeontologica Sinica. 46(3), 365-372.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
Hu, Liu, Li, Hou and Xu, 2013. A new large enantiornithine bird from the Lower Cretaceous of Western Liaoning, China. Journal of Vertebrate Paleontology. Program and Abstracts 2013, 145.

Gurilynia Kurochkin, 1999
G. nessovi Kurochkin, 1999
Late Campanian-Early Maastrichtian, Late Cretaceous
Gurilin Tsav, Nemegt Formation, Mongolia
Holotype- (PIN 4499-12) proximal humerus
Paratypes- ....(PIN 4499-13) (~510 mm) proximal coracoid (~58 mm)
....(PIN 4499-14) distal humerus
Diagnosis- (after Kurochkin, 1999) acute top of the coracoid process; very thin dorsal portion of the coracoid shaft; nearly equal length of both branches in the humeral head, which form an obtuse angle; small anterior fossa distal to the top of the humeral head angle; absence of a tuberosity depression on the posterior side of the deleopectoral crest; very shallow posterior depression on the distal humerus.
(after O'Connor, 2009) proximal anterior surface concave and posterior surface convex; proximal margin convex on midline, rising dorsally and ventrally; deltopectoral crest projecting proximally to same level as humeral head; anterior margin shallow capital incision; proximoventrally restricted ventral tubercle; oval impression for m. coracobrachialis cranialis demarcated ventrally by defined ridge.
References- Kurochkin, 1999. A new large enantiornithid from the Upper Cretaceous of Mongolia (Aves, Enantiornithes). Russian Academy of Sciences, Proceedings of the Zoological Institute. 277, 130-141.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.

Avimaia Bailleul, O'Connor, Zhang, Li, Wang, Lamanna, Zhu and Zhou, 2019
A. schweitzerae Bailleul, O'Connor, Zhang, Li, Wang, Lamanna, Zhu and Zhou, 2019
Late Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Holotype- (IVPP 25371) (1+ year old female) last seven dorsal vertebrae, several dorsal ribs, synsacrum, two caudal vertebrfae, pygostyle, ilia, pubes, ischium, incomplete femora, tibiotarsi, proximal fibula, metatarsal I, phalanges I-1, pedal unguals I, tarsometatarsi (one proximal), phalanx II-1, phalanx II-2, pedal ungual II, phalanges III-1 (one distal), phalanges III-2, phalanges III-3, pedal unguals III, phalanges IV-1 (one distal), phalanges IV-2 (one proximal), phalanges IV-3, phalanges IV-4, pedal unguals IV, body feathers, partial egg
Paratype- (CAGS-IG-04-CM-007) fused ilial and ischial fragments, pubes, femora (one partial; 24 mm), tibiotarsi (one proximal; ~29.2 mm), proximal fibula, metatarsal I, phalanx I-1 (4.3 mm), pedal ungual I (~3.9 mm), tarsometatarsus (II 19.6, III 20.3, IV 19.1 mm), phalanx II-1 (3.6 mm), phalanx II-2 (4.9 mm), pedal ungual II (4.4 mm), phalanx III-1 (4.8 mm), phalanx III-2 (4 mm), phalanx III-3 (5 mm), pedal ungual III (4.4 mm), phalanx IV-1 (2.8 mm), phalanx IV-2 (2 mm), phalanx IV-3 (2.2 mm), phalanx IV-4 (3.7 mm), pedal ungual IV (~4.7 mm), fragment, feathers (Lamanna, You, Harris, Chiappe, Ji, Lü and Ji, 2006)
Diagnosis- (after Bailleul et al., 2019) pubis delicate and strongly curved so that the posterior margin is concave throughout; distal end of ischium dorsally curved.
Comments- Bailleul et al. (2019) added this to O'Connor's bird analysis and recovered it deeply nested in Enantiornithes in a polytomy with CAGS-IG-07-CM-001, Concornis, Enantiophoenix, Eoenantiornis and Neuquenornis.
References- Lamanna, You, Harris, Chiappe, Ji, Lü and Ji, 2006. A partial skeleton of an enantiornithine bird from the Early Cretaceous of northwestern China. Acta Palaeontologica Polonica. 51(3), 423-434.
Bailleul, O'Connor, Zhang, Li, Wang, Lamanna, Zhu and Zhou, 2019. An Early Cretaceous enantiornithine (Aves) preserving an unlaid egg and probable medullary bone. Nature Communications. 10:1275.

"Cathayornis" aberransis Hou, Zhou, Zhang and Gu, 2002
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V12353; lost) skull (28 mm), gastralia, coracoids (16 mm), incomplete furcula?, sternum, forelimb elements including humerus (30 mm) and ulnae (29 mm), carpometacarpi (15 mm), pubes (24.5 mm), proximal tibia, fibula, numerous other elements
Comments- Described by Hou et al. (2002) in a book which has not yet been translated to English, making information on this specimen extremely limited. Of the characters in the original diagnosis, toothed jaws, a well developed posteriorly distributed sternal keel, humerus slightly shorter than ulna and distally fused pubes are all plesiomorphic for Enantiornithes. Cathayornis yandica only differs from these in that its ulna is slightly shorter than its humerus, but variations of 5-10% are known for other basal birds, so this doesn't guarantee a valid distinguishing characteristic. The longitudinal ridge between the frontals (absent according to O'Connor and Dyke, 2010), and tubercles on "both sides of the frontal" are difficult to evaluate given taphonomy and the lack of frontal description and preservation in most enantiornithines. The last proposed diagnostic feature- posterolateral sternal processes shorter than posteromedian processes, does appear to be valid. This is also present in Protopteryx, probably Elsornis, Eoenantiornis and Hebeiornis though. O'Connor and Dyke said further preparation and examination are needed to validate the species, though Wang and Liu (2016) state the holotype is lost.
Reference- Hou, Zhou, Zhang and Gu, 2002. Mesozoic birds from western Liaoning in China. ISBN 7-5381-3392-5. 120 pp.
O'Connor and Dyke, 2010. A reassessment of Sinornis santensis and Cathayornis yandica (Aves: Enantiornithes). Records of the Australian Museum. 62, 7-20.
Wang and Liu, 2016 (online 2015). Taxonomical reappraisal of Cathayornithidae (Aves: Enantiornithes). Journal of Systematic Palaeontology. 14(1), 29-47.

"Cathayornis" chabuensis Li, Li, Zhang, Zhou, Bai, Zhang and Ba, 2008
Early Cretaceous
Jingchuan Formation, Inner Mongolia, China
Holotype- (BMNHC Ph 000110) (subadult) ten cervical vertebrae, two cervical ribs, six dorsal vertebrae, nine dorsal ribs, scapulae (one incomplete; 23 mm), coracoids (17.6 mm), sternum (21 mm), humeri (one incomplete; 31.8 mm) radii (34.4 mm), ulnae (36.5 mm), carpometacarpi (one incomplete; 15 mm), phalanx II-1, phalanx II-2, phalanx III-1, femora (30.8 mm), tibiotarsi (38.6 mm), metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsi (one partial; 19 mm), phalanx II-1, phalanx II-2, pedal ungual II, phalanx III-1, phalanx III-2, phalanx III-3, pedal ungual III, feathers
Diagnosis- (after Wang and Liu, 2016) differs from Cathayornis in- distal edge of posterolateral sternal process rounded (also in Longipteryx; ontogenetic?); posteromedian sternal process distally blunt; lateral process at base of posterolateral sternal process absent.
Other diagnoses- Li et al. (2008) use the posteriorly diverging posterolateral sternal processes to distinguish this species from Cathayornis yandica, but this is true of most enantiornithines (e.g. Alethoalaornis, Boluochia, Houornis, Concornis, Dapingfangornis, Elsornis, Eocathayornis, Eoenantiornis, Hebeiornis, Jibeinia). The authors also distinguished it by its posteromedian sternal process which extends posteriorly past the posterolateral processes. This is also found in Protopteryx, Eocathayornis, Eoenantiornis, Hebeiornis, Shanweiniao and probably Elsornis.
Comments- Li et al. discovered this specimen in 2002 and described it as a new species of Cathayornis in 2008. They assigned it to Cathayornis based on several characters. The longitudinal radius groove is present in all enantiornithines more derived than Longipteryx. Cathayornis actually has a broad intermetacarpal space (contra Li et al.), with the illusion of a nearly absent space in some enantiornithines due to postmortem distortion of the flattened third metacarpal. Several other enantiornithines have only one phalanx on manual digit III (Alethoalaornis, Concornis, Eoalulavis, Eoenantiornis, Gobipteryx, Hebeiornis, Sinornis), which is often closely appressed to phalanx II-1 when articulated (e.g. Eoalulavis, Hebeiornis, Sinornis) and is actually fused in Alethoalaornis based on its figure. Finally, Li et al. state "proportions of limb bones" are similar between Cathayornis and chabuensis. The ulnohumeral ratios are indeed quite similar (98% vs. 97%), but so are those of Houornis (100%), Rapaxavis (100%) and Longirostravis (98%). The humerofemoral ratio of chabuensis (113%) is similar to Cathayornis (117%), but so are Houornis (113%), Eoenantiornis (111%) and Sinornis (114%). The tibiofemoral ratio of 127% is again close to Cathayornis' (126%), but so are Dapingfangornis (126%), Jibeinia (126%), Shanweiniao (128%), Longirostravis (129%) and Sinornis (124%). The tarsometatarsofemoral ratio of 63% is a bit lower than Cathayornis' (~66%), with Houornis (63%), Gobipteryx (~69%), Largirostrornis (67%), Shanweiniao (68%), and Shenquiornis (64%) all being at least as similar to Cathayornis in this regard. Thus there are no unique shared characters with Cathayornis and while the limb proportions are mostly similar, they are not necessarily derived. It is here excluded from Cathayornis. O'Connor and Dyke (2010) and Wang and Liu (2016) agreed the characters did not justify referral to Cathayornis. Both papers agreed it could be distinguished from Cathayornis, though the latter paper declared it a nomen dubium without stating which taxa it could not be distinguished from. Wang and Liu found chabuensis to be more closely related to Hebeiornis than to Cathayornis.
Zhang et al. (2010) referred a new specimen (OFMB-3) from the same locality to Cathayornis chabuensis, interpreting the differences (broadly triangular distal expansions of the posterolateral sternal processes; post-costal sternal processes) as being due to greater ontogenetic age. Wang and Liu (2016) suggested this could not be demonstrated, and given the lack of shared characters with chabuensis, declared OFMB-3 indeterminate.
References- Li, Li, Zhang, Zhou, Bai, Zhang and Ba, 2008. A new species of Cathayornis from the Lower Cretaceous of Inner Mongolia, China and its stratigraphic significance. Acta Geologica Sinica. 82(6), 1115-1123.
O'Connor and Dyke, 2010. A reassessment of Sinornis santensis and Cathayornis yandica (Aves: Enantiornithes). Records of the Australian Museum. 62, 7-20.
Zhang, Zhang, Li and Li, 2010. New discovery and flying skills of Cathayornis from the Lower Cretaceous strata of the Otog Qi in Inner Mongolia, China. Geological Bulletin of China. 29(7), 988-992.
Wang and Liu, 2016 (online 2015). Taxonomical reappraisal of Cathayornithidae (Aves: Enantiornithes). Journal of Systematic Palaeontology. 14(1), 29-47.

Cathayornithiformes Zhou, Jin and Zhang, 1992a
Definition- (Cathayornis yandica <- Iberomesornis romeralii, Longipteryx chaoyangensis, Gobipteryx minuta, Enantiornis leali) (Martyniuk, 2012)
Cathayornithidae Zhou, Jin and Zhang, 1992a
References- Zhou, Jin and Zhang, 1992a. [Preliminary report on a Mesozoic bird from Liaoning, China]. Chinese Science Bulletin. 5, 435-437.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Cathayornis Zhou, Jin and Zhang, 1992a
C. yandica Zhou, Jin and Zhang, 1992a
?= Cathayornis "shanwangensis" Xu, Yang and Deng, 1999
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V 9769) (63 g) incomplete skull (28.1 mm), mandibles, five cervical vertebrae (2.7, 2.5 mm), ?fourth dorsal vertebra (2.5 mm), dorsal ribs, synsacrum (13.1 mm), first caudal vertebra (2 mm), second caudal vertebra, third caudal vertebra, fourth caudal vertebra, fifth caudal vertebra (1.6 mm), sixth caudal vertebra, pygostyle (14.4 mm), scapulae (20.4 mm), incomplete coracoids, furcula, partial sternum (21 mm), sternal rib, humeri (25.7 mm), radii (24.9 mm), ulnae (26.2 mm), scapholunares, pisiforms, carpometacarpi (12.3 mm; metacarpal I 2.2 mm, metacarpal III 12.6 mm), phalanges I-1 (4.6 mm), manual unguals I (1.6 mm), phalanges II-1 (6.8 mm), phalanges II-2 (4.3 mm), manual ungual II (1.1 mm), phalanges III-1 (3.1 mm), ilia (13.9 mm), pubis (~15.4 mm), ischia, femora (23 mm), tibiotarsi (one incomplete; 29.4 mm), fibulae, metatarsal I (3 mm), partial tarsometatarsus (mtII 14.8 mm), several pedal phalanges, three pedal unguals
Referred- ?(DNHM 2510; DNHM 2511) incomplete skeleton including incomplete skull (O'Connor, 2009)
?(DNHM 2567; DNHM 2568) incomplete skeleton including incomplete skull, scapula, coracoid, furcula and sternum (O'Connor, 2009)
?(IVPP V9936) tarsometatarsus (mtII ~21.6, mtIII ~22.5, mtIV ~22.3 mm), phalanx II-1, phalanx II-2, two phalanges III-?, three phalanges IV-?, two pedal unguals, pedal claw sheath (Zhou, 1999)
?(IVPP V10896) specimen including premaxilla, dentary and coracoid (Martin and Zhou, 1997)
Diagnosis- (after Zhou et al., 1992) transverse processes of seventh and eighth sacral vertebrae fusing distally.
(after Zhou, 1999) manual ungual I slightly longer than ungual II [145%] (also in Bohaiornis 125-150% and Sulcavis 135%).
(after O'Connor and Dyke, 2010) postacetabular process with almost straight dorsal margin (also in bohaiornithids and Eoalulavis); postacetabular process less tapered than Sinornis (also in Zhouornis and Eoalulavis).
(after Wang and Liu, 2016) postcostal sternal process.
Other diagnoses- Zhou et al. (1992) included numerous ornithothoracine symplesiomorphies in their original diagnosis- cranial elements "seldom fused"; premaxilla toothed; dentary toothed; pygostyle long; "straight and slender" scapula; strut-like coracoid; sternal keel low; low and flat humeral head; very small pneumotricipital fossa; semilunate dorsal ulnar condyle; carpometacarpus; manual unguals present; pelvic bones unfused; fibula "weak" and unfused with tibia; pedal unguals strongly curved and pointed; pedal unguals with "undeveloped" extensor tubercles. Other characters are common in enentiornithines- synsacrum including 8 vertebrae; posterolateral and posteromedial sternal processes. The foramen magnum is unpreserved, so Zhou et al's listing it as posteroventrally oriented cannot be verified. Contra Zhou et al., the metatarsus is fused.
Hou (1997) also included more characters symplesiomorphic for ornithothoracines- rostrum relatively long and low; pygostyle present; scapula with oblique acromion process; humeral head small or undeveloped; humeral medial and lateral tuberosities distinct; ulna robust and slightly curved; small olecranon process; radius slender with expanded proximal end; carpal trochlea; reduced unguals on first and second manual digits; fibula is long and "conical" (actually transversely flattened); pedal unguals not "extremely curved". Other characters used by Hou are common in enantiornithines- posterolateral sternal processes well developed with termini expanded as oblique triangles; humerus and ulna equivalent in length [u/h 102%].
Zhou (1999) listed a supracetabular crest that is anterodorsally developed, but among advanced enantiornithines this is only otherwise determinable in Sinornis (present) and Bohaiornis (absent). Other characters listed are common in enantiornithines- large and shallow metacarpal incision in pisiform; phalanx III-1 ~50% [46%] of II-1 length; phalanx III-1 expanded proximally. The supposedly absent antitrochanter is due to damage (O'Connor and Dyke, 2010).
O'Connor and Dyke (2010) listed other characters which differ from Sinornis, but of these the supposedly blunter postacetabular process tip seems comparable, and the other two are common in enantiornithines- pygostyle longer [63% of femur vs. 55%]; manual phalanx III-1 straight.
Wang and Liu (2016) also listed posterolateral sternal process extends further posteriorly than posteromedian process, which is found in several other derived enantiornithines. A tapered posteromedian sternal process is primitive. The supposedly unforked jugal whose posterior end curves dorsally is problematic. The presence of a posterior process is unclear, and the dorsal half of the apparant dorsal process may be another element.
Comments- The holotype was discovered in 1990 and first mentioned in an abstract by Zhou (1992) before being named and described by Zhou et al. (1992). It was later redescribed in both Hou (1997) and Zhou's (1999) thesis. Cathayornis yandica was considered a junior synonym of Sinornis santensis by Sereno et al. (2002), but was revalidated by O'Connor (2009; published as O'Connor and Dyke, 2010).
Xu et al. (1999) listed Cathayornis shanwangensis as a fossil bird along with Archaeopteryx, Ichthyornis and Hesperornis in their announcement of Hebeiornis, but this is near certainly an error (in both the Chinese and English). As the other three listed genera are famous, the similarly well known Cathayornis yandica would be expected as opposed to a new species. It's possible the authors were thinking of the phasianid Shandongornis shanwanensis from the Miocene Shanwan Series of Shandong, China.
Referred specimens- Hou (1997) includes a photograph of an articulated pelvis (IVPP coll.) which was illustrated as Cathayornis yandica by Zhou (1999) and Zhou and Hou (2002) without comment. Martin and Zhou (1997) refer IVPP V10896 and V10916 to Cathayornis. The latter was made the holotype of Eocathayornis in 2002, while V10896 was listed as Cathayornis indet. by O'Connor and Chiappe (2011). Zhou reported "over a dozen" Cathayornis specimens were known, though he only lists IVPP V10896 and V9936 as referred specimens, the latter photographed as a referred specimen by Zhou and Hou. O'Connor and Dyke (2010) incorrectly say Hou referred IVPP V10533 and V10904 to Cathayornis yandica, but he actually referred these to C. caudatus (now Houornis). O'Connor (2009) lists DNHM 2510/1 and 2567/8 in her thesis as Cathayornis sp., but otherwise only refers to them as Enantiornithes or Euenantiornithes indet..
Besides noting basic surangular morphology, DNHM 2510/1 remains undescribed and is unillustrated, so cannot be evaluated from publications unless O'Connor's data matrix is examined.
DNHM 2567/8 has postcostal sternal processes, so may be correctly referred to Cathayornis.
IVPP V9936 is 46% larger than the holotype, but difficult to compare otherwise as the type's metatarsus is only partially preserved and the few phalanges preserved in each specimen are disarticulated.
IVPP V10896 was listed as preserving a premaxilla and dentary by O'Connor and Chiappe, and to have a coracoid 2.5 times longer than wide by Zhou (2002). The coracoid's dimensions in the holotype are uncertain (estimated at 2.3 by Zhou, 1999), as the preserved coracoid is broken in two with an unknown amount under the sternum. Wang and Liu (2016) said V10896 "preserves an articulated pelvic girdle", but this is probably an error referring to the unnumbered IVPP specimen.
The IVPP articulated pelvis has a highly convex dorsal postacetabular margin and large amount of taper, unlike Cathayornis, so is probably wrongly referred. It's listed as an unnamed Jiufotang enantiornithine here.
References- Zhou, 1992. Discovery of new Cretaceous birds in China. Abstracts of the Third Symposium of the Society of Avian Paleontology and Evolution.
Zhou, Jin and Zhang, 1992a. [Preliminary report on a Mesozoic bird from Liaoning, China]. Chinese Science Bulletin. 5, 435-437.
Zhou, Jin and Zhang, 1992b. Preliminary report on a Mesozoic bird from Liaoning, China. Chinese Science Bulletin. 37(16), 1365-1368.
Zhou, 1995. The discovery of Early Cretaceous birds in China. Courier Forschungsinstitut Senckenberg. 181, 9-22.
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, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.
Martin and Zhou, 1997. Archaeopteryx-like skull in enantiornithine bird. Nature. 389, 556.
Xu, Yang and Deng, 1999. First discovery of Mesozoic bird fossils in Hebei Province and its significance. Regional Geology of China. 18(4), 444-448.
Zhou, 1999. Early evolution of birds and avian flight- Evidence from Mesozoic fossils and modern birds. PhD thesis, University of Kansas. 216 pp.
Sereno, Rao and Li, 2002. Sinornis santensis (Aves: Enantiornithes) from the Early Cretaceous of Northeastern China. In Chiappe and Witmer (eds.). Mesozoic Birds - Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London. 184-208.
Zhou, 2002. A new and primitive enantiornithine bird from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(1), 49-57.
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.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
O'Connor and Dyke, 2010. A reassessment of Sinornis santensis and Cathayornis yandica (Aves: Enantiornithes). Records of the Australian Museum. 62, 7-20.
O'Connor and Chiappe, 2011. A revision of enantiornithine (Aves: Ornithothoraces) skull morphology. Journal of Systematic Palaeontology. 9(1), 135-157.
Wang and Liu, 2016 (online 2015). Taxonomical reappraisal of Cathayornithidae (Aves: Enantiornithes). Journal of Systematic Palaeontology. 14(1), 29-47.

Concornithidae Kurochkin, 1996
Concornis Sanz and Buscalioni, 1992
C. lacustris Sanz and Buscalioni, 1992
Late Barremian, Early Cretaceous
Calizas de La Huerguina Formation, Spain
Holotype- (LH-2814) (~130 mm, 70 g) four posterior dorsal vertebrae, dorsal rib fragments, posterior sacrum, first caudal vertebra, second caudal vertebra, partial scapulae, coracoids, furcula, anterolateral sternal ossification, sternum, sternal ribs, humerus, incomplete radius, incomplete ulna, carpometacarpus, phalanx I-1, manual ungual I, phalanx II-1, phalanx II-2, manual ungual II, phalanx III-1, pubes, ischia, femora (24 mm), tibiotarsi (36 mm), metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsus (22 mm), phalanx II-1, phalanx II-2, partial pedal ungual II, proximal phalanx III-1, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, feather impressions
References- 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.
Sanz, Chiappe and Buscalioni, 1995. The osteology of Concornis lacustris (Aves: Enantiornithes) from the Lower Cretaceous of Spain and a reexamination of its phylogenetic relationships. American Museum Novitates. 3133, 23 pp.
Sanz, Pérez-Moreno, Chiappe and Buscalioni, 2002. The birds from the Lower Cretaceous of Las Hoyas (Privince of Cuenca, Spain). In Chiappe and Witmer (eds.). Mesozoic Birds: Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London. 209-229.

Dalingheornis Zhang, Hou, Hasegawa, O'Connor, Martin and Chiappe, 2006
D. liweii Zhang, Hou, Hasegawa, O'Connor, Martin and Chiappe, 2006
Early Aptian, Early Cretaceous
Dawangzhangzi Beds of Yixian Formation, Liaoning, China
Holotype- (CNU VB2005001) (juvenile) skull (20 mm), mandibles, ten cervical vertebrae, cervical ribs, eleven dorsal vertebrae, eighteen dorsal ribs, sternal ribs, eight sacral vertebrae, twenty caudal vertebrae (17.5 mm), chevrons, scapulae (8 mm), coracoids (6 mm), furcula (5 mm), posterolateral sternal processes, humeri (14 mm), radii, ulnae (14 mm), scapholunare, pisiform, semilunate carpal, metacarpal I, phalanx I-1, metacarpal II (6 mm), phalanx II-1, phalanx II-2, manual ungual II, metacarpal III (6 mm), ilia (8 mm), pubis (8 mm), ischium (4 mm), femora (11 mm), tibiae (16 mm), astragalus, calcaneum, metatarsal I, phalanx I-1, pedal ungual I, metatarsal II, phalanx II-1, phalanx II-2, pedal ungual II, metatarsal III (9 mm), phalanx III-1, phalanx III-2, proximal phalanx III-3, pedal ungual III, metatarsal IV, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, feather impressions
Comments- O'Connor (2009) considers this to be a nomen dubium and a nomen nudum as it is supposedly in a private collection, but the original description has it placed in a university, and the repository is unrelated to validity.
References- Zhang, Hou, Hasegawa, O'Connor, Martin and Chiappe, 2006. The first Mesozoic heterodactyl bird from China. Acta Geologica Sinica. 80(5), 631-635.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.

Dapingfangornis Li, Duan, Hu, Wang, Cheng and Hou, 2006
D. sentisorhinus Li, Duan, Hu, Wang, Cheng and Hou, 2006
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (LPM 00039) skull (28 mm), sclerotic plates, mandibles, hyoids, cervical vertebrae, dorsal vertebrae, dorsal ribs, sacrum, six caudal vertebrae, pygostyle (15 mm), furcula, sternum (17 mm), scapulae, coracoids (15 mm), humeri (22 mm), radii, ulnae (27 mm), phalanx I-1, manual ungual I, carpometacarpi (11 mm), phalanx II-1, phalanx II-2, manual ungual II, phalanx III-1, ilia, pubes, ischia, femora (23 mm), tibiotarsi (29 mm), fibula, metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsi (16 mm), 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, feather impressions
Diagnosis- (after Li et al., 2006) straight lateral coracoid edge; short hypocleidium; articular surfaces for coracoids on sternum at small angle (~100 degrees) to each other; distal expansion of posterolateral sternal process hooked anterolaterally; elongate ulna (>107% of humeral length); extremely slender radius (~30% of ulnar width) (?); elongate metacarpal I (~34-40% of metacarpal II length) (?); metatarsal II trochlea not significantly wider than metatarsal III trochlea (?).
Other diagnoses- Li et al. (2006) listed numerous features in their diagnosis. The supposedly sharp rostrum is due to the dorsal snout being either crushed or missing. The supposed median nasal horn is questionable. I wouldn't be surprised if it were the standard maniraptoriform laterally projected lacrimal 'horn', viewed ventrally. This would make sense, because the frontal's concave upper margin would then be the lateral orbital margin in life. O'Connor (2009) agrees, saying "a nasal crest cannot be confirmed although at this time, it also cannot be entirely refuted." The frontal is domed posteriorly as typical for birds, not flat. O'Connor notes the dentary is not longer than in other enantiornithines, nor are the teeth more widely spaced. The "high feathered crown" is a taphonomic illusion often seen in feathered Jehol specimens.
Description- What appear to be parietals are preserved posterior to the skull, as seen in the photo of the skeleton (though they aren't illustrated). The ventral margin of the skull is very well preserved, with a maxilla strongly resembling Hebeiornis' and a typical bowed enantiornithine-grade jugal with an expanded anterior end. The 'tympanic' is actually one of the few well preserved enantiornithine-grade quadratojugals. O'Connor (2009) notes at least three maxillary teeth and seven dentary teeth are preserved, contra the at least six maxillary and ten dentary teeth reported by Li et al. (2006). The described 'palatines' are closer in position to pterygoids. The fenestra posteroventral to the 'nasal horn' appears to be a broken or disarticulated space between the frontal and nasal/lacrimal. Two sclerotic plates are apparent, but I don't know what Li et al. identified as a vomer or lacrimal.
The dentaries seem to have an elongate posterodorsal process, which combined with the surangular's outline, indicate a large external mandibular fenestra. I can't identify what Li et al. describe as a prearticular or articular.
The cervical vertebrae are described as heterocoelous, but this could be only partial heterocoely. The presence of at least eight sacral vertebrae indicate an ornithothoracine, while the long pygostyle is characteristic of basal avebrevicaudans.
The furcula is said to have a short hypocleidium, which would be atypical of enantiornithine-grade birds (though known in juveniles and Aberratiodontus). Notably there is no other evidence this is a young individual, as the sternal posterolateral processes are present, the carpometacarpus and tarsometatarsus are fused, and the pygostyle is completely fused. There is a furcula-shaped structure in the illustration, but it's so atypical (one clavicular branch more slender and drawn unfused to the rest; hypocleidium extends posterolaterally; interclavicular angle comparable to basal pygostylians) that either it was drawn exceedingly poorly or not all of it is supposed to be a furcula (or both).
The short sternum with fused distal posterolateral processes indicate an enantiornithine-grade bird. The anterior margin is more acute than most eumaniraptorans, with the exceptions of Longirostravis, Aberratiodontus, Cuspirostrisornis, Yanornis and Ambiortus. The posterolateral processes end in small expansions, as in Jibeinia, Protopteryx, Boluochia, Hebeiornis and Aberratiodontus. However, Dapingfangornis' are apomorphically hooked anterolaterally. The posteromedial processes are very poorly developed, as in Protopteryx, Longipteryx and Hebeiornis (Aberratiodontus lacks them entirely). The posteromedian process is unexpanded, as in Jibeinia, Protopteryx, Longipteryx, Boluochia, Hebeiornis, Eoenantiornis, Cathayornis and Aberratiodontus.
The illustration would suggest an ulnar sesamoid and three elongate metacarpals (II-IV), but I ascribe this to the artist instead of the specimen. The radius is drawn as much more slender than most Mesozoic birds, and this could be due to artistic inaccuracy as well. The first metacarpal as illustrated is longer than any other birds except confuciusornithids. Phalanx I-1 is comparable in length to Jibeinia and enantiornithine-grade birds (except Protopteryx, Longipteryx and Eoalulavis). Phalanx II-2 is shorter (compared to II-1) than other coelurosaurs except Jibeinia, Hebeiornis, Cathayornis, Sinornis and Eocathayornis. Metacarpal III is illustrated as subequal or barely passing metacarpal II distally, which would be odd for an enantiornithine-grade bird and more like euornithines and more basal birds. It may be due to inaccurate illustration. Digit III seems to only have one phalanx, though I wouldn't be surprised if a tiny second one were present but not illustrated. This would be unlike Jibeinia and most more basal birds.
Relationships- Li et al. assign Dapingfangornis to the Eoenantiornithiformes because of a short skull, larger nasals and similar sternum. I disagree. The craniofemoral ratio of Dapingfangornis is 1.22, while Eoenantiornis' is 1.32. These are longer than Aberratiodontus (1.07), Hebeiornis (1.05) and Cuspirostrisornis (.99), but comparable to Cathayornis (1.22) and Sinornis (1.26). Protopteryx (~1.42), Longipteryx (1.90) and Longirostravis (1.80) have longer skulls. Even assuming the nasals are correctly identified in Dapingfangornis, elongate nasals are primitive for birds. The sterna are not very similar, as noted above. Eoenantiornis has a more obtuse anterior margin, large distal expansions on the posterolateral processes (contra Hou et al., 1999), and prominant posteromedial processes. Li et al. distinguish the genera by Dapingfengornis' dubious nasal horn, primitive (and overemphasized by taphonomy) sharp snout, apparently short hypocleidium, and sternal keel (which is unknown in Eoenantiornis because the sternum is in dorsal view; contra Hou et al.,1999).
Reference- Li, Duan, Hu, Wang, Cheng and Hou, 2006. New eoenantiornithid bird from the Early Cretaceous Jiufotang Formation of Western Liaoning, China. Acta Geologica Sinica. 80(1), 38-41.

Dunhuangia Wang, Li, O'Connor, Zhou and You, 2015
D. cuii Wang, Li, O'Connor, Zhou and You, 2015
Late Aptian, Early Cretaceous
Xiagou Formation, Gansu, China
Holotype- (CAGS-IG-05-CM-030) gastralia, scapulae (one incomplete), coracoids (18.3 mm), partial furcula, sternum (24.1 mm), sternal ribs, incomplete humeri, incomplete radii, incomplete ulnae, pisiforms, carpometacarpi (17.1 mm; mcI 2.9 mm), phalanx I-1 (4.8 mm), manual ungual I (2.5 mm), phalanges II-1 (8.8 mm), phalanges II-2 (6.1 mm), manual ungual II (2.6 mm), phalanges III-1 (3.7 mm)
Diagnosis- (after Wang et al., 2015) dorsal fossa of coracoid defined laterally by thick ridge which extends further laterally and forms dorsoventrallycompressed lateral margin; sternum bearing elongated posterolateral process measuring more than half length of sternum.
Comments- Discovered in 2005, this was described as a new taxon of enantiornithine sister to Fortunguavis by Wang et al. (2015).
Reference- Wang, Li, O'Connor, Zhou and You, 2015. Second species of enantiornithine bird from the Lower Cretaceous Changma Basin, northwestern China with implications for the taxonomic diversity of the Changma avifauna. Cretaceous Research. 55, 56-65.

Elbretornis Walker and Dyke, 2009
E. bonapartei Walker and Dyke, 2009
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Holotype- (PVL-4022) scapula, incomplete coracoid, humerus (90.2 mm), proximal radius, proximal ulna
Referred- ?(PVL 4027) distal tibiotarsus (78.5 mm) (Chiappe, 1996)
?(PVL-4041-2) two dorsal vertebrae
....(PVL-4041-4) dorsal rib fragment, sacrum fused to ilia (41 mm), femur (Chippe and Walker, 2002)
?(PVL-4047) dorsal vertebrae (Chiappe and Calvo, 1994)
?(PVL-4051) six dorsal vertebrae
Diagnosis- (after Walker and Dyke, 2009) dorsal tuberculum of humerus strongly projected; mediolateral angle of proximal humerus slanted; large and deeply excavated pneumatic fossa on proximal end containing a deep, rounded and wide pneumatic foramen that undercuts the shaft; pneumatic foramen located distally within fossa; absence of an olecranon fossa on the caudal face of the distal humerus; condylus dorsalis bulbous and not angled transversely; absence of a bridge crossing the caudal portion of the shaft of the coracoid; welldeveloped and caudally orientated processus lateralis of coracoid; well-developed and concave sternal facet of coracoid turned somewhat onto the dorsal face; very large circular foramen nervi supracoracoidei that opens into the dorsal fossa of the coracoid; external cotyla of ulna deep and cup-shaped; ulna shorter than humerus; radius two-thirds the width of the ulna.
Comments- PVL-4022 includes a humerus illustrated by Chiappe and Walker (2002), though noted (without reference to a specimen number) as early as Walker (1981) for being unique among Lecho enantiornithines in having a pneumotricipital foramen. It's an enantiornithine based on- well-developed fossa on the midline of the proximal humerus making the articular surface appear V-shaped in proximal view; ventrodistal margin of humerus projected significantly distal to dorsodistal margin, distal margin angling strongly ventrally (also in Piksi and Apsaravis); proximoposterior surface of deltopectoral crest concave (also in Confuciusornis, Apsaravis and Ichthyornis); long axis of dorsal condyle of humerus almost transversely oriented (also in Yanornis and Apsaravis). Within Enantiornithes, it is derived based on the proximal edge of humeral head which is centrally concave and the hypertrophied bicipital crest.
PVL-4041 and 4051 were first reported and commented on by Chiappe and Calvo (1994), and later illustrated by Chiappe and Walker (2002). Both of these specimens are Enantiornithes at least as derived as Iberomesornis due to the centrally located posterior dorsal parapophyses.
PVL-4041-4 is a synsacrum and articulated ilia illustrated by Chiappe and Walker (2002). The ilia contact over the sacrum, which is otherwise only known in neognaths (Chiappe and Walker note it may be due to distortion). However, the ilium does not extend anterior to the sacral vertebrae, unlike Gansus and Aves. Furthermore, the postacetabular process is vertically oriented, unlike Carinatae sensu Chiappe. The presence of eight sacral vertebrae establishes the specimen as an enantiornithine as derived as Iberomesornis or an ornithothoracine.
References- Walker, 1981. New subclass of birds from the Cretaceous of South America. Nature. 292, 51-53.
Chiappe and Calvo, 1994. Neuquenornis volans, a new Enantiornithes (Aves) from the Upper Cretaceous of Patagonia (Argentina). Journal of Vertebrate Paleontology. 14, 230–246.
Chiappe, 1996. Late Cretaceous birds of southern South America: anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. Munchner Geowissenschaftliche Abhandlungen (A). 30, 203–244.
Chiappe and Walker, 2002. Skeletal morphology and systematic of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). pp 240-267. in Chiappe and Witmer, (eds.). Mesozoic Birds – Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

Elektorornis Xing, O'Connor, Chiappe, McKellar, Carroll, Hu, Bai and Lei, 2019
E. chenguangi Xing, O'Connor, Chiappe, McKellar, Carroll, Hu, Bai and Lei, 2019
Early Cenomanian, Late Cretaceous
Angbamo, Myanmar
Holotype- (HPG-15-2) (subadult or adult) forelimb fragments(?), distal femora, tibiotarsi, fibula, metatarsals I, phalanges I-1, pedal unguals I, tarsometatarsi (7.7 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, pedal claw sheaths, skin, body feathers, remiges
Diagnosis- (after Xing et al., 2019) pedal digit III 20% longer than tarsometatarsus; hallux more than 86% length of pedal digit II; pedal digit II 59% length of digit III.
Comments- Discovered prior to January 2019. "Diffuse traces of pigments within the barbules give the wing an overall dark brown color, with paler barb rami and rachises, and with two large-scale pale wing spots visible anteriorly. Entire barb apices within the posterior vanes of the primaries are either pale or white in color, which would have made the underside of the wing pale or striped." Xing et al. (2019) added this to O'Connor's avialan matrix and recovered it as a euenantiornithine in a polytomy with Elsornis, Enantiophoenix, Eoenantiornis, Halimornis and avisaurids.
Reference- Xing, O'Connor, Chiappe, McKellar, Carroll, Hu, Bai and Lei, 2019. A new enantiornithine bird with unusual pedal proportions found in amber. Current Biology. 29(4), 2396-2401.e2.
Clark and O'Connor, 2021. Exploring the ecomorphology of two Cretaceous enantiornithines with unique pedal morphology. Frontiers in Ecology and Evolution. 9:654156.

Elsornis Chiappe, Suzuki, Dyke, Watabe, Tsogtbaatar and Barsbold, 2007
= "Elsornis" Chiappe, Suzuki, Dyke, Watabe, Tsogtbaatar and Barsbold, 2006 online
E. keni Chiappe, Suzuki, Dyke, Watabe, Tsogtbaatar and Barsbold, 2007
= "Elsornis keni" Chiappe, Suzuki, Dyke, Watabe, Tsogtbaatar and Barsbold, 2006 online
Late Campanian, Late Cretaceous
Tugrikin Shire, Djadokhta Formation, Mongolia
Holotype- (MPD-b 100/201; 980725 TS-V Bird SZK) two posterior cervical vertebrae, two anterior dorsal vertebrae, few dorsal ribs, partial scapulae (63 mm), coracoids (41.7 mm), incomplete furcula, incomplete sternum (>58.55 mm), humeri (77.3 mm), radii (60.65, 60.48 mm), ulnae (66.68 mm), partial carpometacarpi, three pedal phalanges, four pedal unguals, fragments
Diagnosis- (after Chiappe et al., 2007) brachial index (humeral length:ulnar length ratio) substantially greater than 1; scapular shaft with an abrupt bend on its cranial quarter; cranial margin of sternum subdivided in three distinct segments due to widely spaced coracoidal sulci; distal symphysis of the major and minor metacarpals extending for at least one-third the total length of the carpometacarpus.
Comments- The holotype was discovered on August 25 1998 and first reported in a few meeting abstracts in 1999 (Suzuki and Watabe, 1999; Suzuki et al., 1999a, b). It was first photographed (as "Forelimb bones of an enantiornithine bird at Tugrikin Shire") by Suzuki and Watabe (2000). The description was first available online December 2006 but was not officially published until May 2007.
References- Suzuki and Watabe, 1999. New occurrence of enantiornithine bird from the Upper Cretaceous of Mongolia. Paleontological Society of Japan Annual Meeting, Abstracts. 48.
Suzuki, Watabe and Tsogtbaatar, 1999a. A new enantiornithine bird from the Upper Cretaceous Djadokhta Formation of Gobi desert, Mongolia. Geological Society of Japan Annual Meeting 104, Abstracts. 209.
Suzuki, Watabe and Tsogtbaatar, 1999b. A new enantiornithine bird from the Upper Cretaceous Djadokhta Formation of Gobi desert, Mongolia. Journal of Vertebrate Paleontology. 19(3), 79A.
Suzuki and Watabe, 2000. Report on the Japan-Mongolia Joint Paleontological Expedition to the Gobi desert, 1998. Hayashibara Museum of Natural Sciences Research Bulletin. 1, 83-98.
Chiappe, Suzuki, Dyke, Watabe, Tsogtbaatar and Barsbold, 2007. A new enantiornithine bird from the Late Cretaceous of the Gobi Desert. Journal of Systematic Palaeontology. 5(2), 193-208.

Enantiornithiformes Martin, 1983
Definition- (Enantiornis leali <- Gobipteryx minuta) (Martyniuk, 2012)
"Enantiornithidae" Nessov and Borkin, 1983
Enantiornithidae Nesov, 1984
Comments- Nessov and Borkin (1983) mentioned the proximal tarsometatarsus ZIN PO 3494 as a member of Enantiornithidae, but as they do not list a diagnosis or definition for the family, it was a nomen nudum at the time. This makes the nominal author Nesov (1984), who references the Martinavis? vincei humerus and notes enantiornithid humeri have dorsal condyles more transversely oriented than in alexornithids.
References- Martin, 1983. The origin and early radiation of birds. in Brush and Clark, (eds.). Perspectives in Ornithology. 291-338.
Nessov and Borkin, 1983. New records of bird bones from Cretaceous of Mongolia and Middle Asia. Trudy Zoologicheskogo Instituta AN SSSR. 116, 108-110.
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.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Enantiornis Walker, 1981
E. leali Walker, 1981
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Holotype- (PVL-4035) (~1.0 m) proximal scapula (~89 mm), coracoid (77.2 mm), proximal humerus (~151 mm)
Referred- (PVL-4020) scapula (75.4 mm), incomplete coracoid (66.4 mm), humerus (141.2 mm), proximal radius (142.1 mm), ulnae (one proximal; 146 mm), scapholunare, pisiform, proximal carpometacarpus, phalanx I-1 (lost), manual ungual I (lost) (Chiappe, 1996)
(PVL-4029) incomplete coracoid (~65 mm) (Chiappe and Calvo, 1994)
(PVL-4039) scapula (89 mm) (Walker, 1981)
(PVL-4055) scapula (78.5 mm) (Chiappe, 1996)
(PVL-4181) ulna (Chiappe, 1996)
(PVL-4266) proximal humerus (Chiappe, 1996)
(PVL-4267) ulna (Chiappe, 1996)
(PVL-4271) coracoid (Chiappe, 1996)
Diagnosis- (after Walker and Dyke, 2009) large perforating, pneumatic foramen on distal ulna; scapula with distinct depression in the acromion process (anterior to the coracoid articulation), and a narrow notch just ventral to it; coracoid with fenestra in the medial wall of the neck; humerus with narrow pneumatic fossa, sometimes perforated by a canal running proximodistally through the internal tuberosity; bicipital crest markedly projected cranially; external
tuberosity rises above the level of the humeral head in caudal view; medial edge of the internal condyle of the ulna straight; large pit present in ventral view above the distal articulation of the ulna (this contains the large foramen)
Comments- Walker (1981) named this taxon and based it on PVL-4035, of which only the coracoid was illustrated. The Lecho enantiornithine was described briefly, but the only explicit mention of Enantiornis' characters were several features in a table. Chiappe (1996) described the taxon more fully and listed other specimens as being referred, illustrating the rest of the holotype. Some referred elements were later illustrated by Chiappe and Walker (2002). PVL-4029 was illustrated by Chiappe and Calvo (1994) as an enantiornithine, and was referred to Enantiornis by Walker and Dyke (2009). PVL-4266 is a proximal humerus photographed by Chiappe (1996) which was assigned to E. leali by Walker and Dyke. While PVL-4049 was originally illustrated by Walker (1981) then referred to Enantiornis by Chiappe and Walker (2002), Walker and Dyke (2009) placed it in Martinavis instead.
References- Walker, 1981. New subclass of birds from the Cretaceous of South America. Nature. 292, 51-53.
Chiappe and Calvo, 1994. Neuquenornis volans, a new Enantiornithes (Aves) from the Upper Cretaceous of Patagonia (Argentina). Journal of Vertebrate Paleontology. 14, 230-246.
Chiappe, 1996. Early avian evolution in the southern hemisphere: The fossil record of birds in the Mesozoic of Gondwana. Memoirs of the Queensland Museum. 39(3), 533-554.
Chiappe and Walker, 2002. Skeletal morphology and systematic of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). pp 240-267. in Chiappe and Witmer, (eds.). Mesozoic Birds – Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.
E? sp. nov. (Chiappe, 1991)
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Material- ?(PVL-4023) proximal ulna (~165 mm) (Chiappe, 1996)
(PVL-4043) proximal humerus (~156 mm) (Chiappe, 1991)
Comments- The proximal humerus PVL-4043 was photographed by Chiappe (1991) and is an enantiornithine based on the well-developed fossa on the midline of the proximal humerus, making the articular surface appear V-shaped in proximal view. Additional characters shared with derived enantiornithines include the proximally concave humeral head and hypertrophied bicipital crest. Walker and Dyke (2009) tentatively assigned it to Enantiornis leali, but noted it was anatomically distinct and probably a different taxon.
The proximal ulna PVL-4023 was referred to E. leali by Chiappe (1996), and later more tentatively referred to the species by Walker and Dyke (2009). The latter authors find it is larger than other specimens and differs in the shape of its internal cotyla. As PVL-4043 also differs from E. leali in minor details and is larger, they are both provisionally listed here in the same species.
Reference- Chiappe, 1991. Cretaceous birds of Latin America. Cretaceous Research. 12(1), 55-63.
Chiappe, 1996. Early avian evolution in the southern hemisphere: The fossil record of birds in the Mesozoic of Gondwana. Memoirs of the Queensland Museum. 39(3), 533-554.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.
E. sp. indet. (Walker, 1981)
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Material- ?(PVL-4021-2) fragmentary sternum (Chiappe and Calvo, 1994)
?(PVL-4042) incomplete pelvis (ilium 64 mm) (Walker, 1981)
?(PVL-4045) synsacrum (Chiappe, 1996)
?(PVL-4050) fifth or sixth cervical vertebra (Chiappe, 1996)
?(PVL-4057) mid cervical vertebra (Chiappe, 1996)
?(PVL-4058) distal tarsometatarsus (Chiappe, 1996)
?(PVL-4272) partial coracoid (Walker and Dyke, 2009)
Comments- This material was referred to Enantiornis sp. by Walker (unpublished) and later Walker and Dyke (2009) based on size. Walker also initially referred the hindlimb material that was later named Lectavis and Yungavolucris to Enantiornis. Walker and Dyke (2009) later noted it was likely that Lectavis is Enantiornis based on size and associations.
PVL-4021-2 is a sternum noted by Chiappe and Calvo (1994) as having deep posterior notches. It shares the same specimen number with Lectavis, though Walker (unpublished) considered the association doubtful.
PVL-4042 is a pelvis missing most of the pubis and the distal ischium, illustrated by Walker (1981) and later Chiappe and Walker (2002) (where it is mislabeled PVL-4032-3). Walker et al. (2007) stated it was consistant in size with Enantiornis, which was formalized by Walker and Dyke (2009). The complete pelvic fusion is more similar to euornithines than enantiornithines, though the elongate proximodorsal ischial process is only known in confuciusornithids and enantiornithines and the m. cuppedicus fossa is unlike euornithines. The low pointed postacetabular process is a symplesiomorphy only retained in Archaeorhynchus among euornthines, though found in most enantiornithines (except Gobipteryx).
PVL-4050 and 4057 are mid cervical vertebrae noted by Chiappe (1996) and Chiappe and Walker (2002) which are avialan due to their heterocoelous anterior surfaces, but unlike most euornithines (except Archaeorhynchus, Yixianornis, Gansus and Ichthyornis) in lacking heterocoelous posterior surfaces. Their centra are highly compressed tranversely, as in enantiornithines and Ichthyornis.
References- Walker, 1981. New subclass of birds from the Cretaceous of South America. Nature. 292, 51-53.
Chiappe and Calvo, 1994. Neuquenornis volans, a new Enantiornithes (Aves) from the Upper Cretaceous of Patagonia (Argentina). Journal of Vertebrate Paleontology. 14, 230-246.
Chiappe, 1996. Late Cretaceous birds of southern South America: anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. Munchner Geowissenschaftliche Abhandlungen (A). 30, 203-244.
Chiappe and Walker, 2002. Skeletal morphology and systematic of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). pp 240-267. in Chiappe and Witmer, (eds.). Mesozoic Birds – Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

Eocathayornis Zhou, 2002
= "Eocathayornis" Zhou, 1999
E. walkeri Zhou, 2002
= "Eocathayornis walkeri" Zhou, 1999
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V10916) (56 g) premaxilla, maxilla, lacrimal?, jugal?, quadratojugal?, frontal, parietals, quadrate, basicranium?, dentaries, articular, hyoid, six cervical vertebrae, dorsal vertebrae, several partial dorsal ribs, four caudal vertebrae, proximal pygostyle, scapula, coracoids (13.6 mm), sternum (18.5 mm), sternal ribs, humeri (23.5 mm), radii (25.6 mm), ulnae (26 mm), scapholunare, pisiform, carpometacarpus (14 mm), phalanx I-1 (6 mm), manual ungual I (2.1 mm), phalanx II-1 (7 mm), phalanx II-2 (4.3 mm), manual ungual II (2.4 mm), phalanx III-1 (2.5 mm), manual ungual III (1.3 mm)
Comments- Collected in 1994, Martin and Zhou (1997) first referred this specimen to Cathayornis. Zhou (1999) described it in his thesis before its official publication in 2002.
References- Martin and Zhou, 1997. Archaeopteryx-like skull in enantiornithine bird. Nature. 389, 556.
Zhou, 1999. Early evolution of birds and avian flight- Evidence from Mesozoic fossils and modern birds. PhD thesis, University of Kansas. 216 pp.
Zhou, 2002. A new and primitive enantiornithine bird from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(1), 49-57.

Eoenantiornithiformes Hou, Martin, Zhou and Feduccia, 1999
Definition- (Eoenantiornis buhleri <- Cathayornis yandica, Iberomesornis romeralii, Enantiornis leali) (Martyniuk, 2012)
Eoenantiornithidae Hou, Martin, Zhou and Feduccia, 1999
Definition- (Eoenantiornis buhleri <- Longipteryx chaoyangensis, Cathayornis yandica, Enantiornis leali) (Martyniuk, 2012)
References- Hou, Martin, Zhou and Feduccia, 1999. Archaeopteryx to opposite birds - missing link from the Mesozoic of China. Vertebrata PalAsiatica. 37(2), 88–95.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Eoenantiornis Hou, Martin, Zhou and Feduccia, 1999
E. buhleri Hou, Martin, Zhou and Feduccia, 1999
Late Barremian-Early Aptian, Early Cretaceous
Jianshangou Beds of Yixian Formation, Liaoning, China
Holotype- (IVPP V11537) (135 mm, 80 g) incomplete skull (22 mm), mandibles, hyoid, eleven cervical vertebrae (~29 mm), dorsal vertebrae, several dorsal ribs, two uncinate processes, gastralia, anterior sacrum, several caudal vertebrae, distal pygostyle, scapula, coracoids (12.5 mm), furcula, sternum, humerus (29.5 mm), partial radii, incomplete ulnae (31 mm), scapholunare?, pisiforms, carpometacarpi (12 mm), phalanx I-1, manual ungual I, phalanx II-1, phalanx II-2, manual ungual II, phalanx III-1, partial ilium, distal pubes, distal ischium, incomplete femur (26.5 mm), tibiotarsus (31 mm), metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsus (22.3 mm), phalanx II-1, phalanx II-2, pedal ungual II, phalanx III-1, feather impressions
Comments- Hou et al. (1999) initially interpreted the sternum as lacking posterolateral processes, but Zhou et al. (2005) reinterpreted a supposed distal humerus as one. This was later called into question by O'Connor (2012).
References- Hou, Martin, Zhou and Feduccia, 1999. Archaeopteryx to opposite birds - Missing link from the Mesozoic of China. Vertebrata PalAsiatica. 37(2), 88-95.
Zhou, Chiappe and Zhang, 2005. Anatomy of the Early Cretaceous bird Eoenantiornis buhleri (Aves: Enantiornithes) from China. Canadian Journal of Earth Sciences. 42, 1331-1338.
O'Connor, 2012. A revised look at Liaoningornis longidigitrus (Aves). Vertebrata PalAsiatica. 50(1), 25-37.

Flexomornis Tykoski and Fiorillo, 2010
F. howei Tykoski and Fiorillo, 2010
Middle Campanian, Late Cretaceous
Lewisville Member of the Woodbine Formation, Texas, US
Holotype- (DMNH 18137) incomplete scapula (~64 mm), distal ?humerus, proximal carpometacarpus, proximal tibiotarsus, several fragments
Diagnosis- (after Tykoski and Fiorillo, 2010) scapular blade dorsoventrally broad and mediolaterally laminar; scapula lacks a medial longitudinal groove; scapula has a distinct ventral bend in the blade axis in mediolateral view; crests along the anterodorsal margins of metacarpals II and III.
Comments- This was described as an enantiornithine perhaps related to Elsornis based on the ventrally bent scapula and bowed carpometacarpus.
Reference- Tykoski and Fiorillo, 2010. An enantiornithine bird from the lower middle Cenomanian of Texas. Journal of Vertebrate Paleontology. 30(1), 288-292.

Fortunguavis Wang, O'Connor and Zhou, 2014
F. xiaotaizicus Wang, O'Connor and Zhou, 2014
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V18631) (adult) skull, mandibles, atlas, several cervical vertebrae, eight dorsal vertebrae, dorsal ribs, gastralia, synsacrum, four-six caudal vertebrae, pygostyle (19.84 mm), incomplete scapula, coracoids (22.5 mm), incomplete furcula, incomplete sternum, sternal ribs, humeri (one partial; 43.6 mm), radii (46.8 mm), ulnae (one partial), scapholunare, pisiform, carpometacarpi (21.9, 21.4 mm), phalanges I-1 (9.9, 9.8 mm), manual unguals I (4.8 mm), phalanges II-1 (11, 10.9 mm), phalanges II-2 (6.8, 7 mm), partial manual ungual II, phalanges III-1 (6, 5.7 mm), phalanx III-2, manual claw sheaths, ilium, pubes, ischia, femora (~41 mm), tibiotarsi (47, 49.2 mm), fibulae, metatarsals I, phalanges I-1 (5.9 mm), pedal unguals I (7.1 mm), tarsometatarsi (25.3, 25.6 mm), phalanx II-1 (6 mm), phalanges II-2 (8.5 mm), pedal unguals II (10 mm), phalanges III-1 (7.6 mm), phalanges III-2 (6.8 mm), phalanges III-3 (6.8 mm), pedal unguals III (~7.4 mm), phalanx IV-1 (4.5 mm), phalanx IV-2 (3.8 mm), phalanx IV-3 (3.1 mm), phalanx IV-4 (4.1 mm), phalanx IV-?, pedal unguals IV (~5.2 mm), pedal claw sheaths, body feathers, remiges
Diagnosis- (after Wang et al., 2014) dorsoventrally bowed clavicular ramus; straight to weakly concave lateral margin of coracoid; well-developed alular digit with large and strongly recurved ungual; large pubic foot with recurved tip; metatarsal II reduced, not reaching proximal margin of metatarsal IV trochlea; stout and robust pedal phalanges; strongly recurved pedal unguals.
Comments- Wang et al. (2014) entered Fortunguavis into O'Connor's analysis and found it to emerge in a polytomy with most enantiornithines except non-longipterygid-grade taxa, Protopteryx, Elsornis and Iberomesornis.
References- Wang, O'Connor and Zhou, 2014. A new robust enantiornithine bird from the Lower Cretaceous of China with scansorial adaptations. Journal of Vertebrate Paleontology. 34(3), 657-671.
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.

Gobipipus Kurochkin, Chatterjee and Mikhailov, 2013
= "Gobipipus" Mourer-Chauvire, 1995
G. reshetovi Kurochkin, Chatterjee and Mikhailov, 2013
= "Gobipipus reshetovi" Mourer-Chauvire, 1995
Late Campanian, Late Cretaceous
Khermeen Tsav, Baruungoyot Formation, Mongolia
Holotype- (PIN 4492-3) (embryo) partial skull (16 mm), mandible, seven cervical vertebrae, four anterior dorsal vertebrae, scapulae (9 mm), coracoids (6 mm), clavicle, sternum, humeri (13 mm), radii (14 mm), ulna (15 mm), scapholunare, pisiform, carpometacarpus (7.2 mm), phalanx I-1, phalanx II-1
Paratypes- (PIN 4492-4) (embryo) verteabrae, ilium (7 mm), (?)pubis (6 mm), femur (9 mm), tibia (13 mm), fibula (12 mm), eggshell
numerous eggs (30-36 x 20-24 mm)
Diagnosis- (after Kurochkin et al., 2013) toothless; upturned rostrum; maxilla forms an inner and lower flange of the external naris; anterior part of mesethmoid has a ventral flange within antorbital fenestra; lateral surface of dentary shows deep horizontal groove posteriorly and two rows of vascular pits anteriorly; mandibular symphysis; acromial process of scapula has medioventral projection for procoracoid process; preserved manual phalangeal formula is 1-1-0, with digit 1 much longer than digit 2.
Comments- Several embryos were described by Elzanowski (1981) and tentatively referred to Gobipteryx minuta. Chatterjee and Kurochkin (1994) and Kurochkin (1995, 1996) separated ZPAL MgR-I/33 and two new specimens in the PIN collections from ZPAL MgR-I/34 as a new taxon of palaeognath. This was to be described in Nature by Chatterjee, Kurochkin and Mikhailov as "Gobipipus reshetovi" (Mourer-Chauvire, 1995). Indeed, such a reference is cited as a manuscript by Kurochkin (1996) and Starck and Ricklefs (1998) and "in press" in Nature by Kurochkin (1995). The name "Gobipipus reshetovi" was published by Mourer-Chauvire (1995) and later by Chatterjee (1997), though only as nomina nuda. Ford (www.paleofile.com) lists "Gobipipus elzanowskii" as a nomen nudum ascribed to Chatterjee in 1994, though the 'Chatterjee, 1994' entry in his bibliography is a miscitation of Chatterjee and Kurochkin, 1994. That species name has not been published to my knowledge. By 2000, Kurochkin (2000, 2004) no longer believed the PIN specimens and ZPAL-MgR-I/33 were a separate taxon from the enantiornithine specimens. The differences were ascribed to ontogeny. Kurochkin (2000, 2004) felt these embryos were a new taxon of enantiornithine which could be distinguished from Gobipteryx based on several characteristics. The official description was finally published in 2013 by Kurochkin et al. after Kurochkin's death, though only the PIN specimens were now referred to the new taxon, with the rest being retained in Gobipteryx. Kurochkin et al. include Gobipipus in a version of Clarke's analysis and find it to be a basal enantiornithine.
The eggs have been named Gobioolithus minor and are laevisoolithid (Mikhailov, 1996).
References- Elzanowski, 1981. Embryonic bird skeletons from the Late Cretaceous of Mongolia. Palaeontologica Polonica. 42, 147-176.
Chatterjee and Kurochkin, 1994. An new embryonic bird from the Cretaceous of Mongolia. Journal of Vertebrate Paleontology. 14(3), 20A.
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.
Mourer-Chauviré, 1995. Society of Avian Paleontology and Evolution. Information Newsletter.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
Mikhailov, 1996. The eggs of birds in the Upper Cretaceous of Mongolia. Paleontologichesky Zhurnal. 1, 19-121. [in Russian]
Chatterjee, 1997. The Rise of Birds. 312 pp.
Starck and Ricklefs, 1998. Patterns of development: The altricial-precocial spectrum. in Starck and Ricklefs (eds.). Avian Growth and Development. Evolution within the altricial precocial spectrum. University Press, New York. pp 3-30.
Kurochkin, 2000. Mesozoic birds of Mongolia and the former USSR. in Benton et al., eds. The Age of Dinosaurs in Russia and Mongolia. 533-559.
Kurochkin, 2004. The truth about Gobipteryx. Sixth International Meeting of the Society of Avian Paleontology and Evolution. Abstracts. 33-34.
Kurochkin, Chatterjee and Mikhailov, 2013. An embryonic enantiornithine bird and associated eggs from the Cretaceous of Mongolia. Paleontological Journal. 47(11), 1252-1269.

Gobipterygiformes Elzanowski, 1974
Gobipterygidae Elzanowski, 1974
Gobipteryx Elzanowski, 1974
G. minuta Elzanowski, 1974
= Nanantius valifanovi Kurochkin, 1996
Late Campanian, Late Cretaceous
Khulsan, Baruungoyot Formation, Mongolia
Holotype- (ZPAL MgR-I/12) (~190 mm) premaxillae, quadrate, vomeral fragment(?), palatine, partial ectopterygoid, partial pterygoids, mandibles (38 mm), cervical vertebral fragments
Referred- (ZPAL MgR-I/32) premaxillae, maxillae, nasal fragment, partial vomer, palatine, partial pterygoids, dentaries, surangular, angular (Elzanowski, 1976)
Late Campanian, Late Cretaceous
Khermeen Tsav, Baruungoyot Formation, Mongolia
?(PIN 4492-1; holotype of Nanantius valifanovi) (~175 mm) anterior premaxillae, frontals, pterygoids, parabasisphenoid, anterior dentaries, axis (6.2 mm), seven incomplete cervical vertebrae (5.2 mm), incomplete anterior dorsal vertebra, sacrum (15 mm), four caudal vertebrae, pygostyle (8.6 mm), proximal scapula, partial coracoids (~30.8 mm), partial furcula, incomplete humeri (~44 mm), incomplete radius (~43 mm), incomplete ulnae (~57 mm), distal metacarpal II, phalanx II-1 (11.3 mm), distal metatarsal III, phalanx III-1 (4.3 mm), partial ilia, distal pubes, partial femur (~36 mm), femoral fragment, incomplete tibiotarsus (~59.9 mm), tibiotarsal fragments, incomplete fibulae, metatarsal I (4.1 mm), proximal phalanx I-1, pedal ungual I (8 mm), incomplete tarsometatarsi (metatarsal II 24.1 mm, metatarsal III 25 mm, metatarsal IV 23.7 mm), proximal phalanx II-1, phalanx II-2, pedal ungual II (8.5 mm), phalanx III-1, proximal phalanx III-2, distal phalanx III-3, pedal ungual III (7.8 mm), pedal digit IV phalanges, pedal ungual IV (7.6 mm), thirty eggshell fragments (Kurochkin, 1996)
(ZPAL MgR-I/33) (embryo) (skull ~20 mm) premaxillae, maxilla, nasals, frontal, squamosal, quadrate, ectethmoid, exoccipital, basioccipital, posterior mandibular fragment, atlas(?), anterior cervical neural arch, eighth cervical neural arch, ninth cervical neural arch, fragmentary tenth cervical neural arch, several cervical centra, eleventh dorsal neural arch, twelfth dorsal neural arch, first dorsal neural arch, second dorsal neural arch, third dorsal neural arch, fourth dorsal neural arch, fifth dorsal neural arch, sixth dorsal neural arch, seventh dorsal neural arch, four dorsal rib fragments, scapulae (11 mm), coracoid fragments, incomplete humeri (14 mm), incomplete radius (15.9 mm), incomplete ulna (16.1 mm), metacarpal II, metacarpal III (7.5 mm), distal femur, proximal tibia, pedal phalanx, pedal ungual, eggshells (Elzanowski, 1981)
(ZPAL MgR-I/34) (embryo) quadrate fragment, pterygoid fragment, parabasisphenoid, braincase fragments, mandibular fragment, atlas, axis, third cervical vertebra, fourth cervical vertebra (1.3 mm), fifth cervical vertebra (1.3 mm), sixth cervical vertebra, seventh cervical vertebra (1.7 mm), eighth cervical vertebra (1.7 mm), ninth cervical vertebra, tenth cervical vertebra, eleventh cervical vertebra, twelfth cervical vertebra (1.3 mm), first dorsal vertebra (1.3 mm), second dorsal vertebra (1.6 mm), third dorsal neural arch fragment, five anterior dorsal ribs, incomplete scapulae, coracoids, partial furcula, proximal humeri (~18.7 mm), distal radius, distal ulna, pisiform, distal carpals, phalanx I-1 (~2.6 mm), manual ungual I (~1.3 mm), metacarpal II (11.1 mm), metacarpal III (11.8 mm), eggshells (Elzanowski, 1981)
(ZPAL MgR-I/88) (embryo) (skull ~88 mm) premaxillae, maxillae, nasal, frontal, ectethmoid, anterior mandibles, penultimate pedal phalanx (3.6 mm), pedal ungual (3.3 mm), eggshells (Elzanowski, 1981)
(ZPAL MgR-I/89) (embryo) three dorsal neural arches, fragmentary humerus(?), fragmentary radius(?), fragmentary ulna(?), metacarpal II, metacarpal III, eggshells (Elzanowski, 1981)
(ZPAL MgR-I/90) (embryo) fragmentary tibia(?), pedal ungual, eggshells (Elzanowski, 1981)
(ZPAL MgR-I/91) (embryo) posterior skull fragment, fragmentary humerus, fragmentary radius, fragmentary ulna, fragmentary metacarpal II, fragmentary metacarpal III, eggshells (Elzanowski, 1981)
(ZPAL MgR-I/92) (embryo) fragmentary coracoid(?), fragmentary humerus(?), fragmentary metacarpal II, two pedal phalanges, eggshells (Elzanowski, 1981)
Late Campanian, Late Cretaceous
Ukhaa Tolgod, Djadokhta Formation, Mongolia
?(IGM 100/1011) premaxillae, maxillae, partial nasals, vomer, palatines, pterygoid, ectethmoid, nine sclerotic ossicles, anterior dentary (Chiappe, Norell and Clark, 2001)
Comments- While Chiappe et al. (2001) synonymized Nanantius valifanovi with Gobipteryx minuta, Kurochkin (2004) kept them separate and referred IGM 100/1011 to a new species of Nanantius instead of G. minuta. This was based on an unpublished character analysis, with only a few supposedly distinguishing characters listed. N. valifanovi was said to differ from Gobipteryx in the thin and sharp tomium, dorsal premaxillary groove, and absence of a ventral symphyseal crest on the dentary. Kurochkin et al. (2013) later kept the two synonymized, though this was published after Kurochkin's death so may be Mikhailov's opinion instead.
The eggshells associated with PIN 4492-1 have been assigned to the ootaxon Subtilioolithus multituberculatus in the Laevisoolithidae by Mikhailov (1996).
Several embryos were described by Elzanowski (1981), tentatively referred to Gobipteryx minuta because of several cranial features. Martin (1983, 1995) and Elzanowski (1995) followed this assignment.
References- Elzanowski, 1974. Preliminary note on the palaeonathous bird from the Upper Cretaceous of Mongolia. Results of the Polish-Mongolian Paleontological Expeditions - Part V. Palaeontologica Polonica. 30, 103-109.
Elzanowski, 1976. Palaeognathous bird from the Cretaceous of central Asia. Nature. 264, 51-53.
Elzanowski, 1977. Skulls of Gobipteryx (Aves) from the Upper Cretaceous of Mongolia. Results of the Polish-Mongolian Paleontological Expeditions - Part VII. Palaeontologica Polonica. 37, 153-165.
Elzanowski, 1981. Embryonic bird skeletons from the Late Cretaceous of Mongolia. Palaeontologica Polonica. 42, 147-176.
Elzanowski, 1995. Cretaceous birds and avian phylogeny. Courier Forschungsinstitut Senckenberg. 181, 37-53.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
Mikhailov, 1996. The eggs of birds in the Upper Cretaceous of Mongolia. Paleontologichesky Zhurnal. 1, 19-121. [in Russian]
Chiappe, Norell and Clark, 2001. A new skull of Gobipteryx minuta (Aves: Enantiornithes) from the Cretaceous of the Gobi Desert. American Museum Novitates. 3346, 1-15.
Kurochkin, 2004. The truth about Gobipteryx. Sixth International Meeting of the Society of Avian Paleontology and Evolution. Abstracts. 33-34.
Kurochkin, Chatterjee and Mikhailov, 2013. An embryonic enantiornithine bird and associated eggs from the Cretaceous of Mongolia. Paleontological Journal. 47(11), 1252-1269.

Gretcheniao Chiappe, Meng, Serrano, Sigurdsen, Wang, Bell and Liu, 2019
G. sinensis Chiappe, Meng, Serrano, Sigurdsen, Wang, Bell and Liu, 2019
Barremian-Aptian, Early Cretaceous
Huludao, Yixian Formation, Liaoning, China
Holotype- (BMNHC Ph 829) (236 g) incomplete skull, mandibles, hyoid, eight cervical vertebrae, elven dorsal vertebrae, partial dorsal ribs, synsacrum, five acuadl vertebrae, pygostyle (~20.6 mm), two chevrons, scapulae (~36.8 mm), coracoids (29.3, 29.3 mm), furcula, sternum, humeri (49.7, ~50.0 mm), radii (49.2 mm), ulnae (52.9 mm), scapholunares, pisiform, carpometacarpi (27.9 mm), phalanges I-1 (~11.2, ~9.7 mm), manual ungual I (~4.9 mm), phalanx II-1 (12.3 mm), phalanx II-2 (7.4 mm), manual ungual II, phalanx III-1 (6.6 mm), phalanx III-2?, ilia, pubes (38.8, ~35.9 mm), ischia, femora (41.1, 43.2 mm), tibiotarsi (49.6, 50.6 mm), fibulae, metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsi (26.9 mm), phalanx II-1, phalanges II-2, pedal ungual II, phalanges III-1, phalanges III-2, phalanx III-3, pedal ungual III, phalanx IV-1, phalanges IV-2, phalanx IV-3, phalanges IV-4, pedal ungual IV, pedal claw sheaths, feathers
Diagnosis- (after Chiappe et al., 2019) slightly tapered omal ends of the furcular rami; ventral tubercle at the convergence of the furcular rami; slender coracoid with a sternal margin that is slightly more than 1/3 the length of the bone; coracoid with straight lateral margin; humeral bicipital area scarred by a large cranioventrally facing fossa; significantly elongated carpometacarpus; metacarpal II carrying a protuberance on its dorsal surface.
Comments- Gretcheniao was discovered prior to March 2019. Chiappe et al. (2019) state "there is only a single phalanx of the minor digit" but their figure 7C illustrates an impression of phalanx III-2. The photograph itself shows what could be the impression, or could be an artifact in the sediment.
Chiappe et al. added Gretcheniao to Chiappe's avialan analysis and recovered it closer to avisaurids and 'bohaiornithids' than to longipterygids, closest to Junornis.
Reference- Chiappe, Meng, Serrano, Sigurdsen, Wang, Bell and Liu, 2019. New Bohaiornis-like bird from the Early Cretaceous of China: Enantiornithine interrelationships and flight performance. PeerJ. 7:e7846.

Hebeiornis Yan vide Xu, Yang and Deng, 1999
= Vescornis Zhang, Ericson and Zhou, 2004
H. fengningensis Yan vide Xu, Yang and Deng, 1999
= Vescornis hebeiensis Zhang, Ericson and Zhou, 2004
Early Aptian, Early Cretaceous
Qiaotou Member of the Huajiying Formation, Hebei, China
Holotype- (NIGP 130722) (125 mm; 50 g, subadult) skull, mandibles, hyoid, atlas, axis, third cervical vertebra, fourth cervical vertebra, fifth cervical vertebra, sixth cervical vertebra, seventh cervical vertebra, eighth cervical vertebra, ninth cervical vertebra, several dorsal vertebrae, dorsal ribs, gastralia, sacrum, pygostyle (10.72 mm), scapulae (13 mm), coracoids, furcula, sternum, sternal ribs, humeri (25 mm), radii, ulnae (30 mm), scapholunares, pisiforms, metacarpal I, phalanx I-1, manual ungual I, carpometacarpus, phalanx II-1, phalanx II-2, manual ungual II, phalanx III-1, partial ilium, partial pubes, incomplete ischium, femora (25 mm), tibiotarsi (30 mm), proximal tarsals, metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsi (16.00 mm), 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
Comments- Jin et al. (2008) reassign Hebeiornis' horizon to the Qiaotou Member of the Huajiying Formation, as opposed to the Yixian Formation which was stated in Xu et al. (1999) and Zhang et al. (2004).
This specimen was initially very briefly described in an obscure paper as Hebeiorins fengningensis (Xu et al., 1999). They list it as gen. et sp. nov. and attribute it to Yan, 1999, which I assume to mean they are the only author (perhaps a mispelling of Yang You-shi?) taking credit for the name, as opposed to there being a separate Yan, 1999 publication that has not been located. The photograph in Xu et al. is extremely poor, and only labeled "Bird fossils in the bottom of the Jurassic Yixian Formation". However, only one Yixian bird specimen is described there, and the pose described for Hebeiornis is the same (complete specimen exposed ventrally, neck curving to its left). In 2006, Mortimer (DML) realized it was a photograph of the holotype of Vescornis hebeiensis, which was described in detail by Zhang et al. (2004). The latter taxon was also thought to be from the Yixian Formation of Senjitsu in Fengning County, though that horizon has recently been changed (see above). The measurements match fairly well with Vescornis (skull ~24 vs. 27 mm; scapula ~17 vs. 13 mm; humerus ~24 vs. 25 mm; ulna ~25 vs. 30 mm; femur ~24 vs. 25 mm; tibia ~30 vs. 30 mm), as do the few osteological details with the exception of the pygostyle. As Babelfish translates, Hebeiornis "does not have the tail synthesis bone", while Vescornis has a pygostyle. Then again, the authors were apparently unfamiliar with the numerous basal pygostylians with elongate pygostyles (with the exception of Cathayornis, which they never discuss, only list), so perhaps Vescornis' elongate pygostyle was too dissimilar to ornithurine sensu Gauthier and de Queiroz pygostyles for them to count it. Jin et al. (2008) confirm they are the same specimen, though they regard Hebeiornis as a nomen nudum. More recently, Hebeiornis has become the accepted name, being used in several of O'Connor's publications.
One issue is that the only time Hebeiornis is used in Xu et al.'s (1999) paper, it is misspelled Hebeiorins. However, ICZN Article 32.5.1 states "If there is in the original publication itself, without recourse to any external source of information, clear evidence of an inadvertent error, such as a lapsus calami or a copyist's or printer's error, it must be corrected." Xu et al. say "Hebeiorins fengningensis Yan 1999 (gen et sp nov), namely Hebei Fengning bird (new genus and new species)." Since the suffix for "bird" is "-ornis" not "-orins", and the difference is a simple switching of n and i, that seems to be clear evidence of a lapsus calami. Even if this were not the case, it would still be correct to use Hebeiornis. Several publications have since used Hebeiornis, but only one I know of has used Hebeiorins (Ji et al., 2008). If Hebeiorins was the correct original spelling, the uses of Hebeiornis would be incorrect subsequent spellings. These are defined by ICZN Article 33.3 as "any subsequent spelling of a name different from the correct original spelling, other than a mandatory change or an emendation". Article 33.3.1 states "when an incorrect subsequent spelling is in prevailing usage and is attributed to the publication of the original spelling, the subsequent spelling and attribution are to be preserved and the spelling is deemed to be a correct original spelling." Since Hebeiornis is in prevailing usage and attributed to Xu et al., it's deemed to be the correct original spelling.
References- Xu, Yang and Deng, 1999. First discovery of Mesozoic bird fossils in Hebei Province and its significance. Regional Geology of China. 18(4), 444-448.
Zhang, Ericson and Zhou, 2004. Description of a new enantiornithine bird from the Early Cretaceous of Hebei, northern China. Canadian Journal of Earth Sciences. 41(9), 1097-1107.
Mortimer, DML 2006. https://web.archive.org/web/20160806075437/http://dml.cmnh.org/2006Dec/msg00079.html
Jin, Zhang, Li, Zhang, Li and Zhou, 2008. On the horizon of Protopteryx and the early vertebrate fossil assemblages of the Jehol Biota. Chinese Science Bulletin. 53(18), 2820-2827.
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.

Holbotia Zelenkov and Averianov, 2015
= "Holbotia" Kurochkin, 1982 vide Kurochkin, 1991
= "Kholbotiaka" Kurochkin, 1994
H. ponomarenkoi Zelenkov and Averianov, 2015
= "Holbotia ponomarenkoi" Kurochkin, 1982 vide Kurochkin, 1991
Hauterivian-Barremian, Early Cretaceous
Andaikhudag Formation, Mongolia
Holotype- (PIN 3147-200) (subadult) partial skull, partial mandibles, cervical neural arch, one or two fragmentary dorsal vertebrae, last dorsal centrum, partial dorsal ribs, fragmentary synsacrum, incomplete caudal vertebra, furcula, sternal fragment, four sternal ribs, ?phalanx II-1, incomplete ?phalanx II-2, fragmentary ilia, pubic fragment, partial ischium, partial femur, tibia (~33 mm), astragalus, calcaneum, distal tarsal, metatarsal I, phalanx I-1, pedal ungual I, metatarsal II, phalanx II-1, partial phalanx II-2, pedal ungual II, metatarsal III, phalanx III-1, phalanx III-2, phalanx III-3, pedal ungual III, metatarsal IV, phalanx IV-1/2/3 fragments, partial phalanx IV-4, pedal ungual IV, pedal claw sheaths, body feathers
Diagnosis- (after Zelenkov and Averianov, 2015) prenarial portion of premaxilla low with subparallel dorsal and ventral margins; dentary with widely spaced, small teeth; at least one cervical vertebra with most anterior part of prezygapophyseal articular surface facing ventrally; posterior surface of distal tibia with laterally located robust crest; metatarsus at least eight times longer than wide proximally.
Comments- Fragmentary manual elements were identified as distal metacarpals II and III and an incomplete II-1 by Zelenkov and Averianov (2015), but in my opinion the supposed metacarpals look more similar to a broken II-1, with the supposed II-1 being II-2. The authors stated "poor preservation of this area precludes equivocal interpretation of these bone fragments", which I agree with.
The specimen was discovered in 1977 and initially identified as a bird by Kurochkin (1979) before he misidentified it as a pterosaur. It was first published by Kurochkin (1991), who included a photo of the specimen with the caption "Part of the skeleton of a tiny pterosaur (Mongolia). Bone surrounded [by] convert organic matter to the side [that] shows two fingerprint feathers. Original." Next to the slab in the photo is a card with "Holbotia ponomarenkoi Kurochkin, 1982" written on it. Kurochkin (1993) later reidentified the specimen as a bird in his thesis, as did Unwin (1993). Unwin was the first author to publish the name Holbotia ponomarenkoi in text, and identified it as probably ambiortid and possibly Ambiortus, though further study has shown this to be untrue (Kurochkin, 1995a; etc.). Kurochkin (1994) mentions the Early Cretaceous "Mongolian Kholbotiaka" as an enantiornithine, but this is a literal translation from Cyrillic and not a newly proposed genus name. Kurochkin (1995a, b; 1996; 2000) and Bakhurina and Unwin (1995) provided further details of Holbotia as an enantiornithine similar to other Early Cretaceous taxa. Note however, that Bakhurina and Unwin were incorrect in stating Holbotia has subequal tarsometatarsus and tibiotarsus (actual ratio ~68%) and penultimate pedal phalanges "no longer than any of the preceding phalanges" (at least phalanx III-3 is longer than III-2). Also contra Kurochkin (1996), no coracoid is preserved. More recently, Zelenkov and Averianov (2014) discuss the specimen in an abstract, misspelling the genus as 'Holobotia'. The official description appeared the following year, with Zelenkov and Averianov (2015) finding Holbotia to be most closely related to Neuquenornis, Concornis and Qiliania using O'Connor's bird matrix.
References- Kurochkin, 1979. Fossil avifauna of Mongolia. Basic results of the Joint Soviet-Mongolian Palaeontological Expedition for 1969-1969. Palaeontological Institute, Moscow. 9-10.
Kurochkin, 1991. Protoavis, Ambiortus, and other palaeornithological rarities. Priroda. 1991(12), 43-53 [In Russian].
Kurochkin, 1993. [The principle stages in evolution of class Aves]. Thesis, Palaeontological Institute, RAS, Moscow. 64 pp.
Unwin, 1993. Chapter 40. Aves. In Benton (ed.). The Fossil Record 2. Chapman and Hall, NY. 717-738.
Kurochkin, 1994. Synopsis and Evolution of Mesozoic Birds. Journal für Ornithologie. 135.
Bakhurina and Unwin, 1995. Survey of pterosaurs from the Jurassic and Cretaceous of the former Soviet Union and Mongolia. Historical Biology. 10, 197-245.
Kurochkin, 1995a. Synopsis of Mesozoic Birds and Early Evolution of Class Aves. Archaeopteryx. 13, 47-66.
Kurochkin, 1995b. 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, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, 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.
Zelenkov and Averianov, 2014. A historical specimen of enantiornithine bird from the Early Cretaceous of Mongolia. 4th International Paleontological Congress, Abstract Volume. 148.
Zelenkov and Averianov, 2015. A historical specimen of enantiornithine bird from the Early Cretaceous of Mongolia representing a new taxon with a specialized neck morphology. Journal of Systematic Palaeontology. DOI:10.1080/14772019.2015.1051146

Houornis Wang and Liu, 2015
= "Similicathayornis" Wang and Liu, 2015 online
H. caudatus (Hou, 1997) Wang and Liu, 2015
= Cathayornis caudatus Hou, 1997
= "Similicaudipteryx" caudatus (Hou, 1997) Wang and Liu, 2015 online
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V10917) incomplete skull (26.4 mm), partial mandibles (~21 mm), gastralia, four caudal vertebrae, partial pygostyle, partial ?coracoid, incomplete sternum (21.5 mm), humeri (one partial; 25.5 mm), radii (~25 mm), ulnae (~26.5 mm), pisiform, carpometacarpi (II 12.2, III 12.7 mm), phalanx II-1 (6.9 mm), phalanx II-2 (4.3 mm), manual ungual II (1.7 mm), phalanx III-1 (3.4 mm), pubes (one partial), femora (one partial; ~22.9 mm), tibiotarsi (28.5 mm), fibula (~7 mm), metatarsals I, phalanges I-1, pedal ungual I (5 mm), tarsometatarsi (II 14.2, III 15.6, IV 14.8 mm), phalanx II-1, phalanx II-2, pedal unguals II, phalanx III-1, phalanx III-2, phalanx III-3, pedal unguals III, phalanx IV-4, pedal unguals IV, five pedal phalanges, pedal claw sheaths
Paratypes- (IVPP V10533) synsacrum (15.5 mm), several caudal vertebrae, pygostyle, ilia (13 mm), pubes (one partial), femora (one partial; 24.5 mm), tibiotarsi (30.5 mm), fibulae (9 mm), tarsometatarsi (16 mm), pedal phalanges, pedal unguals (5 mm), seeds?
?(IVPP V10904) gastralia, tibiotarsi (34.5 mm), fibula, tarsometatarsi (19 mm), pedal phalanges, pedal unguals (8 mm)
Diagnosis- (after Wang and Liu, 2016) pygostyle longer than tarsometatarsus; sternum with anterior spine and concave costal margin; posterolateral process with large fan-shaped distal expansion; pubic peduncle of ilium well developed and approaching ischiadic peduncle in length; pubic peduncle strongly posteriorly directed; postacetabular process weakly curved ventrally; distal ends of metatarsals II and III deflected medially; metatarsal IV trochlea less than half width metatarsal III trochlea.
Other diagnoses- Hou (1997) included several characters in caudatus' diagnosis which are problematic. The supposed transverse trough lying between the frontal and parietal is either an area where the bone has broken away or due to disarticulation of those elements. A minimum of three pairs of dentary teeth, "relatively well developed" sternal carina, and elongated tarsometatarsus that exceeds half tibiotarsal length are true of most enantiornithines. Hou's interpretation of the caudal vertebrae as unfused is due to misidentifying the partial left femur as the caudal series, as detailed by Wang and Liu (2016).
Comments- The holotype was discovered in 1993 and described by Hou (1997) as a new species of Cathayornis based on numerous symplesiomorphies. O'Connor and Dyke (2010) identified the pygostyle, viewing Hou's supposed string of unfused caudal vertebrae as the left pubis. They considered the species a nomen dubium pending further study. Wang and Liu (2016) performed that study, finding caudatus to be valid though not necessarily closely related to Cathayornis. Thus they placed it in a new genus Houornis. Their redescription could not verify the presence of dorsal vertebrae, sacral vertebrae or scapula, and found the supposed caudal series was actually the left femur. The supplementary information includes a NEXUS file with the OTU "Similicaudipteryx caudatus", seemingly an earlier idea for the genus name. Their figured cladogram does not place Houornis more precisely than Enantiornithes more derived that Protopteryx and Iberomesornis, and excluded from derived longipterygids and bohaiornithids, though this may be due to including the fragmentary Parvavis and OFMB-3. Wang and Liu confirmed the referral of IVPP V10533 to Houornis based on tarsometatarsal characters, but they did not mention IVPP V10904 which was also referred to the taxon by Hou. While the deflection of metatarsal III is ambiguous in Hou's figure, metatarsal IV does seem to be comparably narrow. It is provisionally retained as Houornis here pending further study.
References- Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.
O'Connor and Dyke, 2010. A reassessment of Sinornis santensis and Cathayornis yandica (Aves: Enantiornithes). Records of the Australian Museum. 62, 7-20.
Wang and Liu, 2016 (online 2015). Taxonomical reappraisal of Cathayornithidae (Aves: Enantiornithes). Journal of Systematic Palaeontology. 14(1), 29-47.

Jibeiniaithiformes Zhou and Wang, 2010
"Jibeiniaithidae" Zhou and Wang, 2010
Comments- "Jibeiniaithidae" is formed incorrectly, as it should be 'Jibeiniidae'. However, it is also a nomen nudum as it is not "accompanied by a description or definition that states in words characters that are purported to differentiate the taxon" (ICZN Article 13.1.1). Jibeiniaithiformes is also formed incorrectly (should be 'Jibeiniiformes'), but orders are not covered by the ICZN.
Reference- Zhou and Wang, 2010. Vertebrate diversity of the Jehol Biota as compared with other lagerstätten. Science China Earth Sciences. 53(12), 1894-1907.
Jibeinia Hou, 2000
= "Jibeinia" Hou, 1997
J. luanhera Hou, 2000
= "Jibeinia luanhera" Hou, 1997
Early Aptian, Early Cretaceous
Qiaotou Member of the Huajiying Formation, Hebei, China
Holotype- (IVPP collection; lost) (juvenile) partial skull, mandible (22 mm), six cervical vertebrae (~2.4 mm), five dorsal vertebrae (~2.9 m), dorsal ribs, gastralia, sacrum, six caudal vertebrae, pygostyle (13 mm), scapula (20 mm), coracoids (11.5 mm), incomplete furcula, sternum (17 mm), humerus (23.3 mm), radius (24.2 mm), ulna (24 mm), semilunate carpal, pisiform, metacarpal I (2 mm), phalanx I-1 (4 mm), manual ungual I (2.5 mm), metacarpal II (9.3 mm), phalanx II-1 (6 mm), phalanx II-2 (3.7 mm), manual ungual II (2.1 mm), metacarpal III (8.3 mm), phalanx III-1 (1.5 mm), phalanx III-2 (2.9 mm), manual ungual III (1 mm), partial ilium, pubis (21 mm), partial ischium, femora (22.2 mm), tibiae (28 mm), astragali, calcanea, distal tarsal, metatarsal I, phalanx I-1, pedal ungual I, metatarsal II, phalanx II-1, phalanx II-2, pedal ungual II, metatarsal III (16.3 mm), phalanx III-1, phalanx III-2, proximal phalanx III-3, pedal ungual III, metatarsal IV, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, feather impressions
Diagnosis- narrow furcular branches; metacarpal II does not extend past metacarpal II (?); three phalanges on manual digit III (?); trochlea of metatarsal II not wider than that of metatarsal III (?).
Other diagnoses- Of the diagnostic characters listed by Hou (1997), most are symplesiomorphic for enantiornithines (numerous unserrated maxillary teeth; large, broad sternum; reduced manual digit III; fused pubic symphysis; metatarsals partially fused proximally and unfused distally; metatarsal II shorter than metatarsal III or IV) or ambiguous (extremely concave cervical centra; unexpanded distal pubes). The narrow posteromedian sternal process is present in almost all enantiornithines as derived as Longipteryx, while the final character (poorly developed posterolateral sternal processes) is problematic. The distal end of the right process is covered by another element, while the right process has a broader base which may be the remains of a large distal expansion. If the right side is more accurate, it would resemble Hebeiornis, while the left side could resemble Eoenantiornis. Another possibility is that the sternum is similar to Cathayornis in possessing a small anterolateral process on the right side, with most of the posterolateral process broken off. Interestingly, if manual phalanx III-1 is actually a broken piece of metacarpal III, both the apparently short metacarpal III and presence of three phalanges on that digit would be resolved and the manus would resemble those of other enantiornithines. Hou previously claims Confuciusornis has five phalanges on manual digit III in the same book (again probably due to a broken element), so such a mistake by him would not be unheard of. It would still have two phalanges on the digit however, which would be like basal enantiornithines but unlike some derived taxa.
Comments- The name "Jibeinia luanhera" was first used in Hou (1997), but only in the captions of three illustrations. In the text, it was merely called Ji Bei bird (this is untrue in the English translation). Because the scientific name was not given in the text itself, "Jibeinia" was a nomen nudum. Later, Hou (2000) used the scientific name in the text of his semipopular Picture Book of Chinese Fossil Birds, with accompanying illustrations and disgnosis. This counts as the first official use of the name. Unfortunately, neither work contains trustworthy descriptions or accurate illustrations. The illustrations in Hou (1997) are hopelessly schematic, while the skeletal reconstructions in Hou (2000) aren't respresentative of bird anatomy, let alone that of Jibeinia itself. Hou's (1997) descriptions contain features not known in birds (e.g. septomaxillae, presternae) as well as numerous characters which clash with those described in more recent and better illustrated papers (e.g. Confuciusornis in Chiappe et al., 1999). In addition, the holotype is presently lost (Hou pers. comm., 2001 to Zhang et al., 2004) and existing casts are of low quality. Thus all morphological details of Jibeinia are suspect, except the few which can be gleaned from published photographs.
Jin et al. (2008) reassign Jibeinia's horizon to the Qiaotou Member of the Huajiying Formation, as opposed to the Yixian Formation which was stated in Hou (1997) and Zhang et al. (2004).
Based on comparison with undoubted juvenile enantiornithines (Dalingheornis, Liaoxiornis, GMV 2158, GMV 2159, etc.), Jibeinia is near certainly a juvenile as well. Characters supporting this conclusion include- unfused sacrum; sternal keel absent; high interclavicular angle; humeral head not concave proximally; humeral distal condyles undeveloped, which in turn causes the ventral condyle to not project distally; carpometacarpus fusion absent; pelvic fusion absent; cnemial crest absent; tibiotarsal, proximal tarsal and distal tarsal fusion absent. Some of these characters are seen in most of the taxa described by Hou (1997), so may be due to the schematic illustration quality or incorrect description instead.
Jibeinia exhibits several primitive characters for an ornithothoracine. It supposedly lacks a sternal keel, has three phalanges on manual digit III, and a metacarpal I which is unfused to the carpometacarpus. In addition, the unfused carpometacarpus and pelvis, absent cnemial crest and unfused tibiotarsus and tarsus are all near certainly juvenile characters, being more primitive than more basal avebrevicaudans like Sapeornis and Confuciusornis. However, Jibeinia exhibits a narrower interclavicular angle (~66 degrees) and less phalanges on manual digit III than confuciusornithids and most more basal maniraptorans. Because Jibeinia is probably a juvenile, it is unclear if some characters it possesses are due to being juvenile or being basal. The posteromedian sternal process is narrow as in enantiornithines, but the ventral humeral condyle doesn't appear to be distally projected, if the illustration can be trusted. The latter is the juvenile condition for enantiornithines, however. Metatarsal IV is reduced in width as in enantiornithines.
Zhang et al. (2004) suggested Jibeinia may be a senior synonym of Hebeiornis (described by those authors as Vescornis), which they described from the same formation. This was based on their identical size and numerous similar characteristics. Besides those characters listed in the diagnosis, Jibeinia differs from Hebeiornis in- more shallow anterior dentary; elongate posteromedial sternal processes; narrow ventral tubercle of humerus; larger manual ungual I. Jibeinia supposedly has amphicoelous cervicals and dorsals, while Hebeiornis has heterocoelous cervicals and an opisthocoelous dorsal (but note the comment above regarding enantiornithine central articulations). Besides the numerous juvenile characters listed above (some of which Hebeiornis shows as well- unfused sacrum, metacarpal I unfused to carpometacarpus, proximal tarsals unfused to tibia), Jibeinia is younger based on supposed foramina between neural arches in the pygostyle, and its undeveloped distal femoral condyles. Based on comparison to Hebeiornis, the proximal coracoid of Jibeinia may be broken off, though Hou does describe it as having a rounded head. If it is complete, it is shorter than in Hebeiornis.
References- Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.
Hou, 2000. Picture Book of Chinese Fossil Birds. Yunnan Science and Technology Press, Kunming, China.
Zhang, Ericson and Zhou, 2004. Description of a new enantiornithine bird from the Early Cretaceous of Hebei, northern China. Canadian Journal of Earth Sciences. 41(9), 1097-1107.
Jin, Zhang, Li, Zhang, Li and Zhou, 2008. On the horizon of Protopteryx and the early vertebrate fossil assemblages of the Jehol Biota. Chinese Science Bulletin. 53(18), 2820-2827.

Junornis Liu, Chiappe, Serrano, Habib, Zhang and Meng, 2017
J. houi Liu, Chiappe, Serrano, Habib, Zhang and Meng, 2017
Barremian-Aptian, Early Cretaceous
Liutaiogou, Yixian Formation, Inner Mongolia, China
Holotype- (BMNHC Ph 919a, b) (30.4 g) skull (30.6 mm), mandibles, hyoids, atlas, axis, six or seven postaxial cervical vertebrae, several dorsal vertebrae, dorsal ribs, gastralia, synsacrum, seven caudal vertebrae, few chevrons?, pygostyle, scapulae (20.1 mm), coracoids (14.1 mm), furcula, sternum (18.5 mm), sternal ribs, humeri (25.9 mm), radii (25.7 mm), ulnae (26.9 mm), scapholunares, pisiform, carpometacarpi (mcI 1.9, mcII 11.7, mcIII 12.6 mm), phalanges I-1 (4.5 mm), manual unguals I (2.8 mm), phalanges II-1 (5.5 mm), phalanges II-2 (4.1 mm), manual unguals II (2.5 mm), phalanges III-1 (3.5 mm), phalanges III-2 (1.1 mm), manual claw sheaths, ilia (~15 mm), pubes (25.5 mm), ischia (~15 mm), femora (23.4 mm), tibiotarsi (28.1 mm), fibulae, metatarsals I, phalanges I-1 (4.3 mm), pedal unguals I (4.8 mm), tarsometatarsi (mtII 15.5, mtIII 16.8, mtIV 16.1 mm), phalanges II-1 (3.1 mm), phalanges II-2 (4.8 mm), pedal unguals II (5.1 mm), phalanges III-1 (4.6 mm), phalanges III-2 (4.1 mm), phalanges III-3 (4.5 mm), pedal unguals III (6.1 mm), phalanges IV-1 (2.8 mm), phalanges IV-2 (2.8 mm), phalanges IV-3 (2.8 mm), phalanges IV-4 (3.1 mm), pedal unguals IV (5.1 mm), pedal claw sheaths, body feathers (6-14 mm), remiges (to ~72.7 mm), retrices (~200 mm)
Diagnosis- (after Liu et al., 2017) costal processes of last two penultimate synsacral vertebrae three times wider than same process of last synsacral vertebra; rounded anterolateral corner of sternum (more angular in Cathayornis and Houornis); distinct trough excavating ventral surface of anteromedial portion of sternum; triangular process at base of sternal posterolateral process (absent in Houornis and Eocathayornis); sternal posterolateral process broad (much wider than in Cathayornis, Eocathayornis and Houornis); sternal posterolateral process laterally deflected (straight in Cathayornis and Eocathayornis); sternal posteromedial process nearly level with mid-shaft of posterolateral process (significantly shorter in Cathayornis, Houornis and Eocathayornis); sternal posteromedian process level with posterolateral process (posterolateral processes project further posteriorly in Houornis and Cathayornis); very broad pelvis.
Comments- The holotype was discovered by June 2016. Liu et al. felt it was most similar to Cathayornis, Eocathayornis and Houornis but did not perform a phylogenetioc analysis.
Reference- Liu, Chiappe, Serrano, Habib, Zhang and Meng, 2017. Flight aerodynamics in enantiornithines: Information from a new Chinese Early Cretaceous bird. PLoS ONE. 12(10): e0184637.

Largirostrornis Hou, 1997
L. sexdentoris Hou, 1997
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V10531) (~160 mm) skull (32 mm), partial mandibles, cervical vertebrae, several dorsal vertebrae, gastralia, sacrum, caudal vertebrae, coracoids (19 mm), partial furcula, sternum (~22 mm), humerus (31 mm), radius, ulna (~31.5 mm), carpometacarpus (15 mm), manual ungual (2 mm), ilia, pubes, ischia, femora (28.5 mm), tibiotarsi (33 mm), fibula, tarsometatarsi (19 mm), pedal phalanges, pedal unguals
Comments- Pittman et al. (2020) listed Largirostrornis as a junior synonym of Cathayornis without comment.
References- Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.
Pittman, O'Connor, Tse, Makovicky, Field, Ma, Turner, Norell, Pei and Xu, 2020. The fossil record of Mesozoic and Paleocene pennaraptorans. In Pittman and Xu (eds.). Pennaraptoran Theropod Dinosaurs: Past Progress and New Frontiers. Bulletin of the American Museum of Natural History. 440(1), 37-95.

Liaoxiornithiformes Hou, Zhou, Zhang and Gu, 2002
Liaoxiornithidae Hou, Zhou, Zhang and Gu, 2002
Liaoxiornis Hou and Chen, 1999a
= Lingyuanornis Ji and Ji, 1999
L. delicatus Hou and Chen, 1999a
= Lingyuanornis parvus Ji and Ji, 1999
Early Aptian, Early Cretaceous
Dawangzhangzi Beds of Yixian Formation, Liaoning, China
Holotype- (NIGP 130723; GMV-2156 is counterpart and holotype of Lingyuanornis parvus) (82 mm; juvenile) skull (20.3 mm), mandible (20 mm), ten cervical vertebrae, cervical rib, twelve dorsal vertebrae, twenty-two dorsal ribs, six sacral vertebrae (11 mm), seven caudal vertebrae (4.1 mm), pygostyle (16 mm), scapulae (10.1, 10.1 mm), coracoids (7.5 mm), furcula (7.6 mm), sternum (3.2 mm), lateral sternal ossification, humeri (15.5, 15.4 mm), radii (14.9 mm), ulnae (15.6 mm), scapholunare, pisiform, semilunate carpal, metacarpal I (1.3 mm), metacarpals II (6.5 mm), manual phalanx II-1 (4.3 mm), metacarpals III (7.4 mm), phalanx III-1, ilia (9-10 mm), pubes (6.6 mm), femora (14.4, 14.5 mm), tibiae (16.5, 17.1 mm), tarsal, metatarsals I, phalanx I-1, pedal unguals I, metatarsals II (9.6 mm), phalanges II-1, phalanges II-2, metatarsals III (10.4 mm), phalanges III-1, phalanx III-2, metatarsals IV (9.6 mm), pedal phalanges, remiges
Comments- Discovered in 1998 or 1999, the part and counterpart of Liaoxiornis were obtained by different museums and described as different taxa. Hou and Chen (1999a,b) of the NIGP (and IVPP) described the part as Liaoxiornis delicatus in early February 1999 (English version appeared in May). Ji and Ji (1999) of the GMV described the counterpart as Lingyuanornis parvus in March 1999. Harris (pers. comm. 2001 to Mortimer (online, 2001) discovered the specimens were from the same individual, while Creisler (online 2001) determined the nomenclatural priority. While at least Hou and Chen viewed Liaoxiornis as an adult, it is clearly a juvenile as confirmed by Chiappe and Ji (2002) and Chiappe et al. (2007). The latter authors argue the holotype is indeterminate and that the name Liaoxiornis delicatus "should be abandoned", placing it in quotes. Yet the taxon is valid under the ICZN and cannot simply be disappeared regardless of how diagnostic its holotype is. Similarly, O'Connor's (2009) claim the taxon is a nomen nudum is incorrect, as it was properly established under ICZN rules.
References- Hou and Chen, 1999a. Liaoxiornis delicatus gen. et sp. nov., the smallest Mesozoic bird. Kexue Tongbao. 44(3), 311-315.
Hou and Chen, 1999b. Liaoxiornis delicatus gen. et sp. nov., the smallest Mesozoic bird. Chinese Science Bulletin. 44(9), 834-838.
Ji and Ji, 1999. A new genus of the Mesozoic birds from Lingyuan, Liaoning, China. Chinese Geology. 26(3) (total issue 262), 45-49.
Creisler, online 2001. https://web.archive.org/web/20160806095206/http://dml.cmnh.org/2001Jun/msg00051.html
Mortimer, online 2001. https://web.archive.org/web/20160806121810/http://dml.cmnh.org/2001Jul/msg00344.html
Chiappe and Ji, 2002. Enantiornithine (Aves) neonates from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 22(3), 43A.
Chiappe and Walker, 2002. Skeletal morphology and systematics of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). In Chiappe and Witmer (eds.). Mesozoic Birds - Above the Heads of Dinosaurs. University of California Press. 240-267.
Hou, Zhou, Zhang and Gu, 2002. Mesozoic birds from Western Liaoning in China. ISBN 7-5381-3392-5. 120 pp.
Chiappe, Ji and Ji, 2007. Juvenile birds from the Early Cretaceous of China: Implications for enantiornithine ontogeny. American Museum Novitates. 3594, 46 pp.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.

Linyiornis Wang, Wang, O'Connor, Wang, Zheng and Zhang, 2016
L. amoena Wang, Wang, O'Connor, Wang, Zheng and Zhang, 2016
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (STM 11-80; = STM 19-8) (adult female) skull, mandible, ten to twelve cervical vertebrae fused with ribs, eight to ten dorsal vertebrae, dorsal ribs, synsacrum, four caudal vertebrae, partial pygostyle, scapulae (38.7 mm), coracoids (25.2 mm), incomplete furcula, fragmentary sternum, humeri (45.2 mm), radii (43.2 mm), ulnae (45.7 mm), radialae, pisiforms, metacarpal I (4.4 mm), phalanges I-1, carpometacarpi (one partial; 19.7 mm), phalanx II-1, phalanx II-2, manual ungual II, phalangeal fragments?, ilia (36.1 mm), pubes (one partial; 47 mm), ischium (19.4 mm), femora (39.7 mm), tibiotarsi (48.3 mm), fibula, metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsi (mtII 21.2, mtIII 23.4, mtIV 22 mm), phalanges II-1, phalanges II-2 (one partial), pedal ungual II, phalanges III-1, phalanges II-2 (one partial), phalanx III-3, pedal unguals III, phalanges IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, pedal phalanges, seven ovarian follicles (5.6-7.1 mm)
Diagnosis- (after Wang et al., 2016) rostrum with dorsoventral height of premaxillary body equal to its anteroposterior length; scapular shaft sagittally curved with blunt distal end; bicipital crest hypertrophied with strong cranial projection relative to humeral shaft; muscle attachment pit massive and craniodistally located on bicipital crest; fossa for capital ligament distinctly absent from femoral head.
Comments- The specimen was discovered prior to 2015. Wang et al. (2016a) found this to be a bohaiornithid using O'Connor's bird matrix. Notably, Wang et al. (2016b) later in a paper describing what would be named Piscivorenantiornis added the OTU STM19-8 to O'Connor's matrix which they referenced as referring to Linyiornis. The scores are identical, so whether STM 19-8 was a typo or the specimen changed numbers is uncertain.
Reference- Wang, Zhou and Sullivan, 2016b. A fish-eating enantiornithine bird from the Early Cretaceous of China provides evidence of modern avian digestive features. Current Biology. 26, 1170-1176.
Wang, Wang, O'Connor, Wang, Zheng and Zhang, 2016a. A new Jehol enantiornithine bird with three-dimensional preservation and ovarian follicles. Journal of Vertebrate Paleontology. 36(2), e1054496.

Martinavis Walker, Buffetaut and Dyke, 2007
Other diagnoses- Walker et al. (2007) note numerous characters which they correctly state are shared with other enantiornithines- proximal margin of humerus concave in its central portion, rising both ventrally and dorsally on either side; bicipital crest prominent; ventral surface of bicipital crest bearing a small fossa for muscle attachment; proximally L-shaped humeral head; well-marked depression underneath the proximal head of the humerus; weakly developed distal condyles; flat distal end that is not deflected dorsally. They also list many characters intended to be apomorphies of Martinavis. The pneumotricipital fossa is no wider in vincei, saltariensis or minor than Elbretornis, Enantiornis, Gurilynia, Halimornis or Otogornis, and is narrow in cruzyensis and whetstonei. It is wide in the American specimen KU-NM-37 though. The lack of a perforated ventral tubercle is plesiomorphic and also present in such taxa as Halimornis and Eoalulavis. Most enantiornithine deltopectoral crests could be described as "flat and broad", while the stated lack of ventral curvature in the crest is difficult to understand since it projects dorsally in enantiornithines. The lack of a marked distal angle between the deltopectoral crest and shaft distally is primitive and also seen in such taxa as Eoalulavis, Eocathayornis, Hebeiornis, Otogornis, Pengornis and Cathayornis, but is absent in saltariensis and not determinable in KU-NM-37. The bicipital crest in cruzyensis and vincei is no smaller than in Gurilynia, while KU-NM-37, minor, saltariensis and whetstonei have large crests. The bicipital crest is indeed more anteriorly angled in vincei and KU-NM-37 than Elbretornis, Enantiornis, Halimornis or Gurilynia, but is less angled than Elsornis. Supposed Martinavis species minor, saltariensis and whetstonei have less angled crests. The condition in cruzyensis is not illustrated, though stated to be less than vincei at least. "Ventral margin of bicipital crest small" is a confusing statement, and the ventrally placed bicipital fossa is also present in Elbretornis, Gurilynia and Halimornis while those of M. cruzyensis, saltariensis and minor are anteroventrally placed. The ventral condyle is as poorly developed in Elbretornis, Elsornis, Eocathayornis, Kizylkumavis and Cathayornis. Note neither this nor the next three characters can be evaluated in minor, whetstonei or KU-NM-37. Alexornis, Elbretornis, Elsornis, Kizylkumavis and Otogornis lack both scapulotricipital and humerotricipital grooves as well. The ventral epicondyle is as large and distally projected in Kizylkumavis and probably Alexornis. A transversely oriented dorsal condyle is present in almost all enantiornithines, even Elbretornis (contra Walker and Dyke). Walker et al. also included a differential diagnosis, though it repeats some characters of the general diagnosis (anteriorly angled bicipital crest; deltopectoral crest smoothly angled; transversely oriented dorsal condyle) and has another which contradicts the general diagnosis (small entepicondyle). Of the remaining characters, the shaft is actually less gracile than Enantiornis (and most other enantiornithines), not more. A laterally positioned ectepicondyle is present in all enantiornithines. Walker and Dyke do not add further characters to the diagnosis.
Comments- Walker et al. (2007) established this genus for several large humeri from the Late Cretaceous of Argentina (M. vincei, PVL-4025, 4028 and 4046), France (M. cruzyensis) and the US (KU-NM-37). Walker and Dyke (2009) later named PVL-4025 M. saltariensis, PVL-4028 M. whetstonei and PVL-4046 M. minor. However, as seen above, none of these specimens share unique apomorphies. In fact, M. cruzyensis lacks two of the supposed Martinavis synapomorphies, saltariensis lacks four, both minor and whetstonei lack at least three, and the American specimen lacks at least one. Walker and Dyke refer numerous additional postcranial elements to Martinavis sp. based on size (PVL-4030-4032, 4034, 4036-4038, 4044, 4049, 4056, 4060 and tentatively 4273), but since there's no evidence that genus was present in Argentina, it seems best to keep these as Enantiornithes indet..
References- Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.
M. cruzyensis Walker, Buffetaut and Dyke, 2007
Late Campanian-Early Maastrichtian, Late Cretaceous
Massecaps, Hérault, France
Holotype- (ACAP-M 1957) humerus (92 mm)
Other diagnoses- Several characters in Walker et al.'s diagnosis are identical to those for their Martinavis generic diagnosis and are present in other taxa as noted above- bicipital crest of humerus strongly projected anteriorly; broad deltopectoral crest; lack of a perforated ventral tubercle; ventral epicondyle enlarged and extended distally. Of the remaining characters, the capital groove is also wide in Gurilynia and Eoalulavis and is also deep in most enantiornithines (except Elsornis; it is actually said to be deeper in M? vincei). The deltopectoral crest is also deeply concave posteriorly in M? vincei and Halimornis. The dorsal and ventral condyles are not enlarged or expanded more than M? vincei, Gurilynia, Kizylkumavis or Alexornis.
Reference- Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.

Martinavis? minor Walker and Dyke, 2009
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Holotype- (PVL-4046) incomplete humerus (~67 mm)
Diagnosis- (after Walker and Dyke, 2009) two-thirds the size of M? vincei and M? saltariensis; head of its humerus less notched on its cranial surface; external tuberosity less bulbous in proximal view.
Comments- PVL-4046 was first listed as Enantiornithes by Chiappe (1996), and later assigned by Walker et al. (2007) to Martinavis sp.. Walker and Dyke (2009) described it as a new species, Martinavis minor. As noted in the Martinavis comments though, minor does not share any known apomorphies with the type species of Martinavis and indeed lacks at least three of that genus' listed apomorphies. Thus there is no reason to refer minor to Martinavis at this time.
References- Chiappe, 1996. Late Cretaceous birds of southern South America: anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. Munchner Geowissenschaftliche Abhandlungen (A). 30, 203–244.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

Martinavis? saltariensis Walker and Dyke, 2009
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Holotype- (PVL-4025) humerus (95.3 mm)
Diagnosis- (after Walker and Dyke, 2009; compared to other Martinavis species) bicipital crest less cranially inclined; distal extremity of deltopectoral crest meets the shaft more abruptly; no depression present in capital groove; base of pneumatic fossa deeper and broader; internal border of shaft proximal to this fossa is more gently sloped; small entepicondyle; more laterally positioned ectepicondyle; more transversely orientated external condyle.
Comments- PVL-4025 is a humerus first photographed as Enantiornithes by Chiappe (1996), and later illustrated by Chiappe and Walker (2002). Walker et al. (2007) assigned it to Martinavis sp. and it was later made the holotype of Martinavis saltariensis by Walker and Dyke (2009). However, saltariensis does not have some supposed Martinavis characters listed by Walker et al. (deltopectoral crest merges smoothly into shaft; bicipital crest small and anteriorly angled; large ventral epicondyle), and there are no characters which it uniquely shares with M. cruzyensis and/or vincei. It seems best to keep this species out of Martinavis, and it could be named as a new genus. Based on size, it may belong to Soroavisaurus.
References- Chiappe, 1996. Late Cretaceous birds of southern South America: anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. Munchner Geowissenschaftliche Abhandlungen (A). 30, 203–244.
Chiappe and Walker, 2002. Skeletal morphology and systematic of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). pp 240-267. in Chiappe and Witmer, (eds.). Mesozoic Birds – Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

Martinavis? vincei Walker, Buffetaut and Dyke, 2007
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Holotype- (PVL-4054) humerus (110 mm)
Paratype- (PVL-4059) distal humerus (~110 mm)
Other diagnoses- The bicipital crest was said to be angled more anteriorly than in M. cruzyensis, but is even more anteriorly angled in Elsornis. The capital groove seem equally deep in Enantiornis and probably Eocathayornis. Finally, the distal condyles do not appear "more distally enlarged" than in M. cruzyensis.
Comments- PVL-4054 was first illustrated by Walker (1981) and later by Chiappe and Walker (2002) as Enantiornithes, and described as the holotype of Martinavis vincei by Walker et al. (2007). Chiappe (1996) listed PVL-4059 as Enantiornithines and it was later made the paratype of M. vincei. However, as noted the the Other diagnoses of Martinavis, none of Walker et al.'s supposed apomorphies for that genus are valid. This makes referring vincei to it problematic and indeed it resembles Gurilynia and Halimornis more than Martinavis in having a broad pneumotricipital fossa and ventrally placed bicipital fossa. Based on size, it may belong to Soroavisaurus.
References- Walker, 1981. New subclass of birds from the Cretaceous of South America. Nature. 292, 51-53.
Chiappe, 1996. Late Cretaceous birds of southern South America: anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. Munchner Geowissenschaftliche Abhandlungen (A). 30, 203–244.
Chiappe and Walker, 2002. Skeletal morphology and systematics of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). pp 240-267. in Chiappe and Witmer (eds.). Mesozoic Birds - Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

Martinavis? whetstonei Walker and Dyke, 2009
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Holotype- (PVL-4028) incomplete humerus (~70 mm)
Diagnosis- (after Walker and Dyke, 2009; compared to other Martinavis species) two-thirds the size of M? vincei and M? saltariensis; short deltoid crest; internally positioned pneumatic fossa; less cranially inclined bicipital crest; more bulbous external tuberosity.
Comments- PVL-4028 was first listed as Enantiornithes by Chiappe (1996), and later assigned by Walker et al. (2007) to Martinavis sp.. Walker and Dyke (2009) described it as a new species, Martinavis whetstonei. As noted in the Martinavis comments though, whetstonei does not share any known apomorphies with the type species of Martinavis and indeed lacks at least three of that genus' listed apomorphies. Thus there is no reason to refer whetstonei to Martinavis at this time.
References- Chiappe, 1996. Late Cretaceous birds of southern South America: anatomy and systematics of Enantiornithes and Patagopteryx deferrariisi. Munchner Geowissenschaftliche Abhandlungen (A). 30, 203–244.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

Microenantiornis Wei and Li, 2017
M. vulgaris Wei and Li, 2017
Early Albian, Early Cretaceous
Chaoyang, Jiufotang Formation, Liaoning, China
Holotype- (PMOL-AB00171) skull (26.5 mm), mandible, atlas, axis, at least eight postaxial cervical vertebrae, posterior three dorsal vertebrae, gastralia, synsacrum, three caudal vertebrae, pygostyle (11.5 mm), scapulae (15.2 mm), coracoids (13.6 mm), furcula, sternum, humeri (23.6 mm), radii (23.0 mm), ulnae (23.7 mm), scapholunares, semilunate carpals, metacarpals I (2.9 mm), carpometacarpi (mcII 7.9, mcIII 9.8 mm), phalanges II-1 (4.3 mm), phalanges II-2 (4.9 mm), manual ungual II, phalanges III-1 (~1.5 mm), incomplete ilium, incomplete pubis, ischium, femora (21.3 mm), tibiotarsi (26.1 mm), fibulae, metatarsals I (2.9 mm), phalanges I-1 (4.5 mm), pedal unguals I (4.6 mm), tarsometatarsi (mtII 16.6, mtIII 17.7, mtIV 17.2 mm), phalanges II-1 (3.8 mm), phalanges II-2 (4.2 mm), pedal unguals II (4.7 mm), phalanges III-1 (4.5 mm), phalanges III-2 (3.6 mm), phalanges III-3 (4.9 mm), pedal unguals III (6.2 mm), phalanx IV-1 (~2.7 mm), phalanges IV-2 (~2.4 mm), phalanges IV-3 (2.1 mm), phalanges IV-4 (3.3 mm), pedal unguals IV (4.1 mm), remiges?
Diagnosis- (after Wei and Lei, 2017) skull high with short snout, orbit ~29% of skull length; no dentary teeth; forelimbs and himdlimbs nearly equal in length; ratio of coracoid length vs. distal width ~2.6; length/width ratio of sternum ~1; anterior margin of sternum rounded; sternal posterolateral processes not expanded distally; sternal posteromedian process slightly expanded distally; sternal keel absent.
Comments- This was described by Wei and Li (2017) as an enantiornithine but the paper has not been fully translated from Chinese. Most of the supposedly diagnostic characters are indicative of a young ontogenetic stage (high skull with large orbit; rounded anterior sternum; small sternal posterolateral process distal expansions; sternal keel absent), which matches the incompletely fused carpometacarpi.
Reference- Wei and Li, 2017. Discovery of a new enantiornithine bird from Lower Cretaceous of western Liaoning, China. Global Geology. 36(3), 655-662.

Monoenantiornis Hu and O'Connor, 2016
M. sihedangia Hu and O'Connor, 2016
Early Albian, Early Cretaceous
Sihedang, Jiufotang Formation, Liaoning, China
Holotype- (IVPP V20289) (subadult) incomplete skull, incomplete mandibles, hyoid, seven cervical vertebrae, six dorsal vertebrae, several dorsal ribs, uncinate processes, synsacrum, three caudal vertebrae, incomplete pygostyle, scapulae (one fragmentary; ~37.1 mm), coracoids (24.4 mm), partial furcula, incomplete sternum, sternal ribs, humeri (45.1 mm), radii (43.3 mm), ulnae (45.6 mm), scapholunares, pisiforms, semilunate carpals, metacarpal I (~5 mm), phalanges I-1 (7.1 mm), manual unguals I (4.2 mm), metacarpals II (19.2 mm), phalanges II-1 (one partial; 10.8 mm), phalanges II-2 (one partial; 11.2 mm), manual unguals II (one partial; 4 mm), metacarpals III (20 mm), phalanx III-1, partial ilia, pubes, femora (38.5 mm), tibiae (45.5 mm), fibulae, astragalocalcaneum, distal tarsals III+IV, metatarsal I, phalanx I-1 (6.4 mm), pedal ungual I (9.1 mm), metatarsals II, phalanges II-1 (5.7 mm), phalanges II-2 (7.9 mm), pedal unguals II (11.2 mm), metatarsals III, phalanges III-1 (7.5 mm), phalanges III-2 (7.2 mm), phalanges III-3 (6.5 mm), pedal ungual III, metatarsals IV, phalanges IV-1 (4.3 mm), phalanges IV-2 (3 mm), phalanges IV-3 (3.4 mm), phalanges IV-4 (2.4 mm), pedal unguals IV, pedal claw sheaths, body feathers, remiges
Diagnosis- (after Hu and O'Connor, 2016) small teeth with unrecurved and pointed apices; premaxillary teeth with lingual grooves; sternum with narrowly vaulted anterior margin; posterolateral sternal processes directed posterolaterally and terminating anterior to distal end of posteromedian process; furcular articular surface of scapula large and triangle-shaped; distal half of lateral coracoid margin strongly convex; extension of metacarpal III beyond metacarpal II >15% length of the latter; single and low cnemial crest present along proximal 30%; extremely robust pedal digit II and delicate pedal digit IV.
Comments- While Hu and O'Connor (2016) assigned Monoenantiornis to the Yixian Formation, it was found in Sihedang, which is here viewed as belonging to the Jiufotang Formation (see Iteravis entry). Using a verson of O'Connor's bird matrix, Hu and O'Connor recovered Monoenantiornis as the most basal enantiornithine more derived than longipterygids.
Reference- Hu and O'Connor, 2016. First species of Enantiornithes from Sihedang elucidates skeletal development in Early Cretaceous enantiornithines. Journal of Systematic Palaeontology. http://dx.doi.org/10.1080/14772019.2016.1246111

Musivavis Wang, Cau, Luo, Kundrat, Wu, Ju, Guo, Liu and Ji, 2022
M. amabilis Wang, Cau, Luo, Kundrat, Wu, Ju, Guo, Liu and Ji, 2022
Early Albian, Early Cretaceous
Shangheshou, Jiufotang Formation, Liaoning, China
Holotype- (MHGU-3000) (subadult) incomplete skull (30 mm), sclerotic plates, mandibles (one partial), partial hyoid, nine cervical vertebrae, three dorsal vertebrae, two dorsal ribs, synsacrum (15 mm), few caudal vertebrae, pygostyle (~12 mm), scapulae (one partial; 26 mm), coracoids (14 mm), furcula, sternum (15 mm), twelve sternal ribs, humeri (30 mm), radii (33 mm), ulnae (33 mm), scapholunare, pisiforms, metacarpals I (4 mm), phalanges I-1 (5 mm), manual unguals I (2 mm), carpometacarpi (mcII 14, mcIII 16 mm), phalanges II-1 (8 mm), phalanges II-2 (one proximal; 5 mm), manual ungual II (2 mm), phalanges III-1 (4 mm), ilial fragment, pubes, distal ischium, femora (27 mm), incomplete tibiotarsi (33 mm), fibulae (~8 mm), metatarsals I (4 mm), phalanges I-1 (5 mm), pedal unguals I (7 mm), tarsometatarsi (mtII 19, mtIII 19, mtIV 18 mm), phalanges II-1 (4 mm), phalanges II-2 (4 mm), pedal unguals II (6 mm), phalanges III-1 (6 mm), phalanges III-2 (5 mm), phalanges III-3 (5 mm), pedal unguals III (5 mm), phalanges IV-1 (3 mm), phalanx IV-2 (3 mm), phalanges IV-3 (3 mm), phalanges IV-4 (4 mm), pedal unguals IV (4 mm)
Diagnosis- (after Wang et al., 2022) pygostyle abruptly tapers distally (also in Gretcheniao); sulcus excavating furcular arms very deep and extends onto the proximal third of the hypocleideum; sharp keel runs along entire ventral surface of furcula, from the junction of the epicleideal rami to the distal tip of the hypocleideum; flat anterior margin of sternum becomes curved near the anterolateral process; sternum possesses anterolaterally projected anterolateral processes; posteromedian process of sternum extends nearly to same level as posterolateral processes and expands as a blunt distal end (also in Bohaiornis); manual phalanx I-1 has a transversally expanded proximal end followed by a gracile shaft, resulting in a concave proximomedial corner of the bone.
Comments- The holotype "was discovered around year 2000, and was at least for a decade in the Museum of Hebei University collection before being studied" (Cau, online 2022).
Wang et al. (2022) used Cau's bird matrix to recover Musivavis as the sister taxon to Dunhuangia in Euenantiornithes.
References- Cau, online 2022. http://theropoda.blogspot.com/2022/02/lamabile-mosaico-di-musivavis.html
Wang, Cau, Luo, Kundrat, Wu, Ju, Guo, Liu and Ji, 2022. A new bohaiornithid-like bird from the Lower Cretaceous of China fills a gap in enantiornithine disparity. Journal of Paleontology. 96(4), 961-976.

Nanantius Molnar, 1986
Diagnosis- (after Kurochkin and Molnar, 1997) laterally convex tibiotarsal shaft; caudal intercotylar prominence on the proximal tibiotarsal articular surface; well expressed fibular crest on lateral edge of tibial shaft; oblong fossae on cranial and caudal sides of the fibular crest.
Comments- The partial skeleton PIN 4492-1 was originally described as a new species, Nanantius valifanovi (Kurochkin, 1996), but has been identified as a specimen of Gobipteryx minuta (Chiappe et al., 2001). This limits known Nanantius specimens to partial tibiotarsi and a vertebra from the Tollebuc Formation of Queensland.
References- Molnar, 1986. An enantiornithine bird from the Lower Cretaceous of Queensland, Australia. Nature 322 736-738.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.
Kurochkin and Molnar, 1997. New material of enantiornithine birds from the Early Cretaceous of Australia. Alcheringa. 21, 291-297.
Chiappe, Norell and Clark. 2001. A new skull of Gobipteryx minuta (Aves: Enantiornithes) from the Cretaceous of the Gobi Desert. American Museum Novitates 3346: 1-15.
N. eos Molnar, 1986
Albian, Early Cretaceous
Toolebuc Formation, Queensland, Australia
Holotype- (QM F12992; lost) (~135 mm) incomplete tibiotarsus (~34 mm)
Referred- ....(QM F12991; lost) cervical vertebra (Kurochkin and Molnar, 1997)
(QM F16811) proximal tibiotarsus (Kear et al., 2003)
Diagnosis- (modified from Kurochkin and Molnar, 1997) lateral cnemial crest absent; absence of long, low lateral eminence in fossa lateral to lateral cnemial crest; cranial cnemial crest on the medial edge of the tibiotarsus; nutrient foramen on caudal side of shaft near termination of fibular crest.
Comments- The cervical vertebra (QM F12991) was found less than 5 cm from the holotype tibiotarsus, so may belong to the same individual and taxon. O'Connor (2009) reports both are lost. The proximal tibiotarsus described by Kear et al. (2003) from ichthyosaur gut contents is more similar to N. eos than QM F31813 in the absence of a lateral cnemial crest and eminence lateral to that. It is provisionally assigned to N. eos here based on provenence.
References- Molnar, 1986. An enantiornithine bird from the Lower Cretaceous of Queensland, Australia. Nature. 322, 736-738.
Kurochkin and Molnar, 1997. New material of enantiornithine birds from the Early Cretaceous of Australia. Alcheringa. 21, 291-297.
Kear, Boles and Smith, 2003. Unusual gut contents in a Cretaceous ichthyosaur. Proceedings of the Royal Society of London B. 270, S206-S208.
O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD thesis, University of Southern California. 586 pp.
N. sp. nov. (Kurochkin and Molnar, 1997)
Albian, Early Cretaceous
Toolebuc Formation, Queensland, Australia
Material- (QM F31813) proximal tibiotarsus (~28 mm)
Diagnosis- (modified from Kurochkin and Molnar, 1997) lateral cnemial crest present; long, low lateral eminence in fossa lateral to lateral cnemial crest; cranial cnemial crest caudal to the medial edge of the tibiotarsus; nutrient foramen on caudal side of shaft near termination of fibular crest absent.
Reference- Kurochkin and Molnar, 1997. New material of enantiornithine birds from the Early Cretaceous of Australia. Alcheringa. 21, 291-297.

Otogornis Hou, 1994
O. genghisi Hou, 1994
Early Cretaceous
Jingchuan (not Yijinholuo) Formation, Inner Mongolia, China
Holotype- (IVPP V9607) (~150 mm, 170 g) scapulae (24 mm), coracoids (22 mm), humeri (31 mm), radii (40, 42 mm), ulnae (43, 50.1 mm), partial carpometacarpus, phalanx I-1(?), manual ungual I(?), feather impressions
Comments- Originally identified as an enantiornithine by Dong (1994), Hou (1994) later named the specimen and placed it as a basal enantiornithine. Kurochkin (1999) believed the taxon to be a palaeognath related to Ambiortus instead, assigning both to the Ambiortiformes.
References- Dong, 1994. A Lower Cretaceous enantiornithine bird from the Ordos Basin of Inner Mongolia, People's Republic of China. Canadian Journal of Earth Sciences. 30(10), 2177-2179.
Hou, 1994. A Late Mesozoic bird from Inner Mongolia. Vertebrata PalAsiatica. 32(4), 258-266.
Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.
Kurochkin, 1999. The relationships of the Early Cretaceous Ambiortus and Otogornis (Aves: Ambiortiformes). Smithsonian Contributions to Paleobiology. 89, 275-284.

Paraprotopteryx Zheng, Zhang and Hou, 2007
P. gracilis Zheng, Zhang and Hou, 2007
Early Aptian, Early Cretaceous
Qiaotou Member of the Huajiying Formation, Hebei, China
Holotype- (STM V001) (subadult) several dorsal vertebrae, partial dorsal ribs, gastralia, pygostyle (12.9 mm), scapula (17.9 mm), coracoids (12.8 mm), partial sternum, sternal rib, incomplete humeri (22.6 mm), radii, ulnae (23.5 mm), scapholunares, pisiforms, carpometacarpi (11.5 mm), manual phalanx I-1 (2.9 mm), manual ungual I, phalanx II-1 (5.5 mm), phalanx II-2 (3.5 mm), manual ungual II, phalanges III-1 (2.9 mm), phalanx III-2, manual claw sheath, incomplete femur (22.2 mm), tibiae (one partial; 26.3 mm), astragalocalcanea, metatarsals I, phalanges I-1, pedal unguals I, tarsometatarsi (15.7 mm), phalanges II-1, phalanges II-2, pedal unguals II, 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 unguals IV, remiges, retrices, body feathers
Other diagnoses- Zheng et al. (2007) list numerous additional characters in their diagnosis. The scapula is no longer (79%) than several other enantiornithines including the contemporaneous Jibeinia (86%). The elongation of the coracoid (length 2.37 times distal width, not 2.5 times as listed in the diagnosis) is very similar to Eoenantiornis (2.34) and in any case is intermediate between ratios in other enantiornithines. The authors state the furcula has two distinguishing features- an interclavicular angle of less than 40 degrees and a highly elongate hypocleideum (three-fourths of clavicular branch length). However, plate II shows that the supposed clavicular branches of the furcula are dorsal ribs while the illustrated hypocleidium is nowhere to be found in the photograph. This would explain the unusually slender clavicular branches in the illustration. The posteromedial sternal process is said to be longer and more robust than the posterolateral process, but the photograph indicates the supposed posterolateral process is probably a sternal rib instead. This leaves the supposed posteromedial process as the posterolateral process while the real posteromedial process is unpreserved with most of the posterior sternum. Manual ungual I is said to be larger than ungual II, but this seems to be merely due to the preserved keratinous sheath on ungual I, though larger manual ungual I's are known in some enantiornithines (e.g. Jibeinia). The length of manual digit I (76%- as measured from the base of the carpometacarpus to the tip of phalanx I-1 compared to the length of the semilunate carpal plus metacarpal II) is very similar to Jibeinia (71%) and especially Eoenantiornis (76%). Metacarpal III being more slender than metacarpal II is found in most theropods. Manual phalanx II-2 being shorter than II-1 is present in many derived enantiornithines. The carpometacarpus being only fused proximally is true in most enantiornithines. The unfused tibiotarsus is probably ontogenetic and is known in the young holotypes of other enantiornithines (Protopteryx, Rapaxavis, Dalingheornis, Jibeinia). Strong, curved pedal unguals and a long pygostyle are present in most enantiornithines. Finally, two pairs of elongate retrices are known in Shanweiniao.
Comments- While Zheng et al. (2007) refer Paraprotopteryx to the Liaoning Formation of Fengning, they also state Protopteryx, Jibeinia and Vescornis (= Hebeiornis) are from this locality. Jin et al. (2008) reassigned it to the Qiaotou Member of the Huajiying Formation. Zheng et al. state the skull "seems not to be the same individual as the postcranial bones after careful examination", and the portion of the slab containing the skull and cervical vertebrae does seem to contain an additional left coracoid.
Zheng et al. stated Paraprotopteryx was most similar to Protopteryx due to several characters. Of these, the unfused tibiotarsus is probably ontogenetic while the carpometacarpus is not unfused in Paraprotopteryx. Elongate paired retrices are also known in Jibeinia, Longirostravis, Shanweiniao and Dapingfangornis and seem standard for enantiornithines. The shared character of "complete manual claws" probably refers to the presence of two phalanges on digit III, which is seen in all basal enantiornithines including Pengornis, Jibeinia, Longipteryx, Longirostravis, Rapaxavis and Eocathayornis.
References- Zheng, Zhang and Hou, 2007. A new enantiornithine bird with four long retrices from the Early Cretaceous of Northern Hebei, China. Acta Geologica Sinica. 81(5), 703-708.
Jin, Zhang, Li, Zhang, Li and Zhou, 2008. On the horizon of Protopteryx and the early vertebrate fossil assemblages of the Jehol Biota. Chinese Science Bulletin. 53(18), 2820-2827.

Parvavis Wang, Zhou and Xu, 2014
P. chuxiongensis Wang, Zhou and Xu, 2014
Turonian-Santonian, Late Cretaceous
Jiangdihe Formation, Yunnan, China
Holotype- (IVPP V18586) (subadult) occiput, several cervical vertebrae, six caudal vertebrae, incomplete pygostyle, humeri (18.4 mm), radius (18.4 mm), ulna (18.6 mm), femur (14.5 mm), tibiotarsi (one partial; 17.7 mm), metatarsals I, phalanges I-1 (2.6 mm), pedal unguals I (3 mm), tarsometatarsi (9.5 mm), phalanges II-1 (2.3 mm), phalanges II-2 (3.1 mm), pedal unguals II (4.5 mm), phalanges III-1 (3.1 mm), phalanges III-2 (2.6 mm), pahlanges III-3 (2.5 mm), pedal unguals III (4.2 mm), phalanges IV-1 (1.7 mm), phalanges IV-2 (1.7 mm), phalanx IV-3 (1.9 mm), phalanges IV-4 (1.9 mm), pedal unguals IV (2.9 mm), feathers
Diagnosis- (after Wang et al., 2014) small, with humerus less than half as long as that of Longipteryx; proximal profile of humerus concave; anterior face immediately distal to head concave; deltopectoral crest narrower than shaft width; ventral side of distal humerus extending more distally than dorsal side; (combination of) metatarsals II and IV and proximal to entire trochlea of metatarsal III; trochlea of metatarsal II broader than those of II and IV (also in many other enantiornithines such as Eoenantiornis and Vescornis); ungual of digit IV reduced (also in in Vescornis and Qiliania).
Comments- The holotype was discovered in 2010 and found by Wang et al. (2014) to be the most basal examined non-longipterygid enantiornithine when entered in O'Connor's analysis.
Reference- Wang, Zhou and Xu, 2014. The first enantiornithine bird from the Upper Cretaceous of China, Journal of Vertebrate Paleontology. 34(1), 135-145.

Piscivorenantiornis Wang and Zhou, 2017
P. inusitatus Wang and Zhou, 2017
Early Albian, Early Cretaceous
Dapingfang, Jiufotang Formation, Liaoning, China
Holotype- (IVPP V22582) premaxillae, frontal, braincase, quadrates, dentary, splenials, surangulars, atlas, eight cervical vertebrae, nine dorsal vertebrae, dorsal ribs, gastralia, synsacrum, six caudal vertebrae, scapula, coracoids (24.4, 24.3 mm), furcula, sternum, humeri (40.5 mm), radii (40.5, 40.6 mm), ulnae (44.2, 43.0 mm), scapholunares, pisiforms, carpometacarpi (mc 4.1, cmc 19.1 mm), phalanx I-1, manual ungual (?)I, pelves (ilium 27.9, pubis 36.2, ischium 22.4 mm), femora (35.0 mm), tibiotarsi (one partial; 4.13 mm), fibulae, metatarsal I, tarsometatarsus (mtII 19.7, mtIII 21.8, mtIV 19.9 mm), six pedal phalanges, two pedal unguals, gastric pellet (22.6 mm)
Early Albian, Early Cretaceous
Sihedang, Jiufotang Formation, Liaoning, China
Referred- (IVPP V23362) incomplete skull, mandible, atlas, four anterior cervical vertebrae, mid cervical vertebra, posterior cervical vertebra, four dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, synsacrum, four caudal vertebrae, pygostyle, scapulae, coracoids, furcula, sternum, humeri (one incomplete), incomplete radii, ulnae (one partial), scapholunare, pisiform, carpometacarpus, phalanx I-1, phalanx II-1, phalanx II-2, incomplete pelves, femora (one partial), tibiotarsi (one incomplete), fibula, tarsometatarsus, six pedal phalanges, two pedal unguals, pedal claw sheaths (Wang and Zhou, 2020)
Diagnosis- (after Wang and Zhou, 2017) premaxillary symphysis notched anteriorly; anterior articular facets of posterior cervical vertebrae dorsoventrally concave and
mediolaterally convex; ventral margin of preacetabular process straight.
(after Wang and Zhou, 2020) exoccipital with pair of round fossae lateral to foramen magnum.
Comments- The holotype was discovered before October 2015 and initially briefly described by Wang et al. (2016) as an enantiornithine for which "a detailed morphological study of the new specimen is in preparation and will be presented in a separated paper." This was published the next year by Wang and Zhou (2017), who officially named and described the taxon. Both papers added it to O'Connor's avialan analysis and recovered it as close to Pterygornis, Dunhuangia and bohaiornithids. Wang and Zhou (2020) described a referred specimen, and using more taxa recovered Piscivorenantiornis sister to Mirusavis plus Shangyang.
References- 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.
Wang and Zhou, 2017. A morphological study of the first known piscivorous enantiornithine bird from the Early Cretaceous of China. Journal of Vertebrate Paleontology. 37(2), e1278702.
Wang and Zhou, 2020. Anatomy of a new specimen of Piscivorenantiornis inusitatus (Aves: Enantiornithes) from the Lower Cretaceous Jehol biota. Journal of Vertebrate Paleontology. 40(3), e1783278.

Pterygornis Wang, Hu and Li, 2015
= "Dispersusia" Wang, Hu and Li, 2015
P. dapingfangensis Wang, Hu and Li, 2015
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V20729) (adult) partial skull, sclerotic ossicles, incomplete mandible, atlas, axis, six postaxial cervical vertebrae, seven dorsal vertebrae, dorsal ribs, synsacrum, six caudal vertebrae, pygostyle (12.3 mm), scapulae, coracoids (15.9 mm), incomplete sternum, sternal ribs, humeri (25.3 mm), radii (26.4 mm), ulnae (28.3 mm), scapholunares, pisiforms, carpometacarpi (13.3 mm, mcI 2.4 mm), phalanx I-1 (4.4 mm), phalanx II-1 (7.1 mm), femora (23.8 mm), tibiotarsi (28.6 mm), fibulae (12.2 mm), metatarsals I, tarsometatarsi (mtII 15.1, mtIII 17, mtIV 15.6 mm), fifteen pedal phalanges, six pedal unguals
Diagnosis- (after Wang et al., 2015) proximal half of coracoid shaft curved medially (also in Cathayornis and Eocathayornis); sternum with external anteromedian spine (possibly external spine also in Eocathayornis and Houornis); sternum with anterolateral processes (also in Rapaxavis and Concornis); metatarsal II strongly ginglymoid articulation; wide articular furrow on plantar surface of metatarsal II.
Other diagnoses- Wang et al. also view the surangular as diagnostic, proposing it has an anteroventrally sloping anterior margin. Yet this would be unlike almost all other theropods, and not match the slope of the dentary (Wang et al. propose they form an autapomorphic overlapping articulation). Note the supposed angular is continuous posteriorly with the surangular, flaring at its posterior end. These facts make it more likely the surangular is a left element in medial view and that the 'angular' is the ridge dorsal to the Meckelian fossa, comparable to Archaeopteryx. The authors also propose the distally fused first and second metacarpals to be unique among Early Cretaceous enantiornithines, but correctly note the condition is present in several Late Cretaceous members of that group.
Comments- The name "Dispersusia" is used and bolded in Wang et al.'s cladogram, no doubt an earlier name for Pterygornis in reference to the dispersed elements of the holotype. Wang et al. entered Pterygornis into a version of O'Connor's bird matrix and found it to be more derived than longipterygids, in a position just closer to avisaurids than to bohaiornithids.
Reference- Wang, Hu and Li, 2015. A new small enantiornithine bird from the Jehol Biota, with implications for early evolution of avian skull morphology. Journal of Systematic Palaeontology. DOI:10.1080/14772019.2015.1073801

Euenantiornithes Chiappe, 2002
Definition- (Sinornis santensis <- Iberomesornis romerali) (modified from Chiappe, 2002)
Sinornithiformes Hou, 1997
"Sinornithidae" Hou, 1997
Comments- As Hou (1997) did not define or diagnose Sinornithidae, it is a nomen nudum (ICZN Article 13.1.1).
References- Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.
Sinornis Sereno and Rao, 1992
S. santensis Sereno and Rao, 1992
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (BPV 538) incomplete skull (~26.5 mm), partial mandibles, eleven dorsal vertebrae (2.4, 2.3 mm; dorsal column ~30.5 mm), dorsal ribs, sacrum (12.9 mm; first sacral 2.5 mm, eighth sacral 1.5 mm), first caudal vertebra (1.6 mm), second caudal vertebra (1.5 mm), third caudal vertebra (1.5 mm), fourth caudal vertebra (1.3 mm), fifth caudal vertebra (1 mm), sixth caudal vertebra (.6 mm), five chevrons, pygostyle (11.5 mm), scapula (~18 mm), partial coracoid, furcula, partial sternum, incomplete humerus (24 mm), partial radii (~22.2 mm), partial ulnae (~19.2 mm), scapholunare, pisiform, carpometacarpus (10.3 mm; metacarpal I ~1.9 mm, metacarpal III ~10.8 mm), phalanx I-1 (4 mm), manual ungual I (1.6 mm), phalanx II-1 (5.4 mm), phalanx II-2 (3.8 mm), manual ungual II (2.1 mm), phalanx III-1 (3.9 mm), incomplete ilium (~13 mm), pubes, ischia, femora (~21 mm), tibiotarsi (25.7, 26.4 mm), fibulae, metatarsal I (3.2 mm), phalanx I-1 (3.7 mm), pedal ungual I (5.6 mm), tarsometatarsi (metatarsal II 14.1 mm, metatarsal III 14.6 mm, metatarsal IV 14.1 mm), phalanx II-1 (3.2 mm), phalanx II-2 (4.1 mm), pedal ungual II (5.8 mm), phalanx III-1 (4.3 mm), phalanx III-2 (3.6 mm), phalanx III-3 (3.9 mm), pedal ungual III (6.7 mm), phalanx IV-1 (2.1 mm), phalanx IV-2 (2.1 mm), phalanx IV-3 (2.1 mm), phalanx IV-4 (3 mm), pedal ungual IV (5.3 mm)
References- Sereno and Rao, 1992. Early evolution of avian flight and perching: New evidence from the Lower Cretaceous of China. Science. 255, 845-848.
Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park, Lugu Hsiang, Taiwan. 221 pp.
Sereno, Rao and Li, 2002. Sinornis santensis (Aves: Enantiornithes) from the Early Cretaceous of Northeastern China. pp 184-208. in Chiappe and Witmer, (eds.). Mesozoic Birds – Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.
Zhou and Hou, 2002. The Discovery and Study of Mesozoic Birds in China. pp 160-183. in Chiappe and Witmer, (eds.). Mesozoic Birds – Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.
O'Connor and Dyke, 2010. A reassessment of Sinornis santensis and Cathayornis yandica (Aves: Enantiornithes). Records of the Australian Museum. 62, 7-20.

Xiangornis Hu, Xu, Hou and Sullivan, 2012
X. shenmi Hu, Xu, Hou and Sullivan, 2012
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (PMOL-AB00245) coracoid (35 mm), incomplete furcula, sternal fragment, proximal humerus, distal radius, distal ulna, incomplete carpometacarpus (38.5 mm), phalanx I-1 (15.2 mm)
Diagnosis- (after Hu et al., 2012) large size; coracoid with medially curved acrocoracoid process; proximally convex humeral head; carpometacarpus longer than coracoid and completely fused both proximally and distally; short metacarpal I (about one-sixth of the length of metacarpal II) completely fused to metacarpal II; large, flange-like extensor process; intermetacarpal space positioned significantly distal to metacarpal I.
Comments- The holotype was discovered in 2005. Hu et al. included it in a version of Clarke's matrix and found it to be an enantiornithine.
Reference- Hu, Xu, Hou and Sullivan, 2012. A new enantiornithine bird from the Lower Cretaceous of western Liaoning, China, and its implications for early avian evolution, Journal of Vertebrate Paleontology. 32(3), 639-645.

Yuornis Xu, Buffetaut, O'Connor, Zhang, Jia, Zhang, Chang and Tong, 2021
Y. junchangi Xu, Buffetaut, O'Connor, Zhang, Jia, Zhang, Chang and Tong, 2021
Late Cretaceous
Qiupa Formation, Henan, China
Holotype- (L-08-7-3) incomplete skull (62 mm), sclerotic plates, mandibles (50 mm), two partial ribs, fragmentary synsacrum, proximal scapulae, proximal coracoid, humeri (73 mm), radii (one fragmentary; 72 mm), ulnae (78 mm), distal metacarpals II, partial phalanges II-1, partial phalanges II-2, manual ungual II, distal metacarpals III, phalanx III-1, ilial fragment, incomplete femur, incomplete tibiotarsus, two phalanges IV-?
Diagnosis- (after Xu et al., 2021) antorbital fenestra and supratemporal fenestra completely confluent with orbit; quadratojugal with hook-like process that curves around the lateral condyle
of the quadrate; acromion process with narrow pedicel with sulcus the lateral surface; deltopectoral crest more than one-third the length of the humerus and separated from the dorsal tubercle. Differs from Gobipteryx in having a proportionately longer and narrower rostrum that is not upturned rostrally; well developed nasal process on maxilla; external nares proportionately narrower.
Comments- Lu et al. (2011) briefly describe this specimen in an abstract and refer it to the Gobipterygidae. Xu et al. (2021) officially described it and recovered Yuornis sister to Gobipteryx using O'Connor's bird analysis.
References- Lu, Xu, Zhang, Jia and Chang, 2011. A new gobipterygid bird from the Late Cretaceous Central China and its biogeographic implications. Journal of Vertebrate Paleontology. Program and Abstracts 2011, 147.
Xu, Buffetaut, O'Connor, Zhang, Jia, Zhang, Chang and Tong, 2021. A new, remarkably preserved, enantiornithine bird from the Upper Cretaceous Qiupa Formation of Henan (central China) and convergent evolution between enantiornithines and modern birds. Geological Magazine. 158(11), 2087-2094.

Yungavolucris Chiappe, 1993
Y. brevipedalis Chiappe, 1993
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Holotype- (PVL-4053) (~340 mm) tarsometatarsus (41.9 mm)
Paratypes- (PVL-4040) incomplete tarsometatarsus (41.6 mm)
(PVL-4052) incomplete tarsometatarsus (51.9 mm) (Chiappe, 1991)
(PVL-4268) distal metatarsal II, distal metatarsal III
(PVL-4692) distal tarsometatarsus (42.8 mm)
Comments- Walker et al. (2007) mistakenly assigned the holotype to Avisaurus. Based on size, it may correspond with Elbretornis.
References- Walker, 1981. New subclass of birds from the Cretaceous of South America. Nature. 292, 51-53.
Chiappe, 1991. Cretaceous birds of Latin America. Cretaceous Research. 12(1), 55-63.
Chiappe, 1993. Enantiornithine (Aves) tarsometatarsi from the Cretaceous Lecho Formation of Northwestern Argentina. American Museum Novitates. 3083, 39 pp.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

undescribed enantiornithine (Martin and Stewart, 1982)
Campanian, Late Cretaceous
Pembina Member of the Vermillion River Formation, Manitoba, Canada
Material- (CFDC B.77.03.07) dorsal vertebra (6 mm)
Comments- Referred to Ichthyornis sp. by Martin and Stewart (1982), and later to Enantiornithes by Clarke (2004) because of its centrally placed parapophyses.
References- Martin and Stewart, 1982. An ichthyornithiform bird from the Campanian of Canada. Canadian Journal of Earth Sciences. 19, 324-327.
Nicholls, 1989. 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. University of Calgary.
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 Enantiornithes (Shufeldt, 1915)
Late Maastrichtian, Late Cretaceous
Lance Formation, Wyoming, US
Material- (USNM 2909) distal metatarsal II, two distal pedal phalanges (Gilmore, 1920)
(YPM 865) distal metatarsal III, two fragments (Shufeldt, 1915)
Comments- USNM 2909 was originally referred to Ornithomimus minutus by Gilmore (1920) but later to Euenantiornithes by Chiappe and Walker (2002). Similarly, Shufeldt (1915) listed YPM 865 as indeterminate fragmentary bird material, but Chiappe and Walker later identified it as euenantiornithine.
References- Shufeldt, 1915. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.
Gilmore, 1920. Osteology of the carnivorous Dinosauria in the United States National Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus. United States National Museum, Bulletin. 110, 1-154.
Chiappe and Walker, 2002. Skeletal morphology and systematics of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). In Chiappe and Witmer (eds.). Mesozoic Birds, Above the Heads of Dinosaurs. University of California Press. 240-267.

unnamed enantiornithine (Walker, Buffetaut and Dyke, 2007)
Campanian, Late Cretaceous
Lance's Quarry, New Mexico, US
Material- (KU-NM-37) proximal humerus
Comments- Walker et al. (2007) refer this to Martinavis sp., but the supposed apomorphies of that genus are not valid (see Martinavis Other diagnoses) and there are no characters which it uniquely shares with M. cruzyensis and/or vincei. The authors confusingly stated it is "the most distinctive of [the] referred specimens" and that it "is indistinguishable from other bones referred here to Martinavis." The broad capital groove is more similar to M. cruzyensis, while the broad pneumotricipital groove is more similar to M? vincei. It seems best to keep this specimen out of Martinavis.
Reference- Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

unnamed enantiornithine (Sanz, Chiappe, Perez-Moreno, Moratalla, Hernandez-Carrasquilla, Buscalioni, Ortega, Poyato-Ariza, Rasskin-Gutman and Martinez-Delclos, 1997)
Late Berriasian-Early Barremian, Early Cretaceous
La Pedrera de Rubies Lithographic Limestones, Spain
Material- (LP-4450-IEI) (juvenile) skull, mandible, hyoids, nine cervical vertebrae, partial dorsal ribs, scapula, coracoid, furcula, humerus, radius, ulna, carpometacarpus, phalanx I-1, manual ungual I, phalanx II-1, phalanx II-2, manual ungual II, feather impressions
References- Morell, 1997. Fossilized hatchling heats up the bird-dinosaur debate. Science. 276, 1501.
Sanz, Chiappe, Perez-Moreno, Moratalla, Hernandez-Carrasquilla, Buscalioni, Ortega, Poyato-Ariza, Rasskin-Gutman and Martinez-Delclos, 1997. A nestling bird from the Lower Cretaceous of Spain: Implications for avian skull and neck evolution. Science. 276, 1543-1546.
Marugan-Lobon, Cambra-Moo, Martinez-Delclos, Sanz and Buscalioni, 2002. Juvenile enantiornithine skeleton from Montsec (Catalonia, Spain) Lower Cretaceous revisited: Taphonomy and morphometrics to access ontogenetic stage. Journal of Vertebrate Paleontology. 22(3), 84A.

undescribed enantiornithine (Sanz, Chiappe, Fernadez-Jalvo, Ortega, Sanchez-Chillon, Poyato-Ariza and Perez-Moreno, 2001)
Late Barremian, Early Cretaceous
Calizas de La Huerguina Formation, Spain
Material- (LH 11386 bird 1) (juvenile) four posterior cervical vertebrae, eleven dorsal vertebrae, dorsal neural spine, six dorsal ribs, sacrum, twelve caudal vertebrae(?), scapulae, coracoids, sternum, sternal ribs, humerus, radius, ulna, pisiform, phalanx I-1, manual ungual I, distal metacarpal II, proximal phalanx II-1, partial ilium, proximal pubis, ischium, partial femur, astragalus, metatarsal I, phalanx I-1, pedal ungual I, metatarsal II, phalanx II-1, phalanges II-2, pedal unguals II, metatarsal III, phalanx III-1, phalanges III-2, phalanges III-3, pedal ungual III, metatarsal IV, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, fragments, remiges
Comments- This specimen is the most complete of four juvenile birds found associated in a theropod or pterosaur pellet. It was only identified as a bird by Sanz et al. (2001), and colored dark gray in their illustration. The strut-like coracoid and tapered distal scapula are like avialans (though confuciusornithids reverse the latter). The fused sterna are similar to euavialans, though its small size and lack of lateral processes are no doubt due to its young age, as seen in juvenile enantiornithines and confuciusornithids. Several characters are unlike most euornithines, but similar to enantiornithines and more basal birds. The absent procoracoid process is only found in Patagopteryx and Apsaravis. The scapula being shorter than the humerus is only found in Archaeorhynchus, Yanornis and Gansus. The medial tibiotarsal condyle being wider than the lateral one is only seen in Patagopteryx. Finally, the proximal end of metatarsal III is in the same plane as metatarsals II and IV, which is only seen in Patagopteryx, Archaeorhynchus and Hongshanornis among euornithines. Other characters are shared only with enantiornithines with a few exceptions. The deep dorsal coracoid fossa and narrow tibiotarsal intercondylar groove (~25% of tibiotarsal width) are only present in enantiornithines and Apsaravis. The narrow sternal xiphoid process is only present in enantiornithines and Hongshanornis. Metatarsal IV being so narrow compared to II and III is uniquely enantionithine. Within Enantiornithes, the specimen may be more derived than Protopteryx, Longipteryx and Eoenantiornis based on its short manual digit I. The sternal xiphoid process is distally expanded as in Longirostravis, Shanweiniao, Eocathayornis, Eoalulavis and Liaoningornis. Yet metatarsal II has a trochlea smaller than III, which among enantiornithines is only known in longipterygids, Vorona and Liaoningornis. It may be most closely related to Vorona, Liaoningornis, or Shanweiniao and Longirostravis.
Reference- Sanz, Chiappe, Fernadez-Jalvo, Ortega, Sanchez-Chillon, Poyato-Ariza and Perez-Moreno, 2001. An Early Cretaceous pellet. Nature. 409, 998-999.

unnamed enantiornithine (Buffetaut, Mechin and Mechin-Salessy, 2000)
Early Maastrichtian, Late Cretaceous
Bastide-Neuve, Provence, France
Material- (Mechin coll. no. 606) tibiotarsus (132 mm)
Comments- Buffetaut et al. (2000) referred this specimen to Enantiornithes incertae sedis. The reduced fibula indicates this is an avialan, while the tubercle on the ascending process is a pygostylian character. Although uncommon, lack of fusion between the astragalocalcaneum and tibia is known in some pygostylians (e.g. Longipteryx, Hebeiornis, Gobipteryx, Vorona) and may be ontogenetic. The lack of medially tapering distal condyles and narrow intercondylar groove are seen in most enantiornithines, but also the basal euornithines Apsaravis and Longicrusavis. The large medial condyle (~200% the width of the lateral one) is characteristic of a subset of enantiornithines, including Nanantius, Gobipteryx and Soroavisaurus.
Reference- Buffetaut, Mechin and Mechin-Salessy, 2000. An archaic bird (Enantiornithes) from the Upper Cretaceous of Provence (Southern France). Comptes Rendus de l'Academie des Sciences. 331, 557-561.

undescribed enantiornithine (Dyke, Vremir, Kaiser and Naish, 2011)
Maastrichtian, Late Cretaceous
Sèbes Formation, Romania
Material- (EME V.314) (adult) scapula, coracoid, partial sternum, humerus, ulna (75 mm), tibiotarsus (75 mm), (nestling) quadrate, cervical vertebra, dorsal vertebrae, proximal scapula, proximal tibia, pedal phalanges, ~50 bone fragments, seven incomplete eggs, thousands of eggshell fragments
Comments- This was hypothesized to be the remains of a nesting colony by Dyke et al. (2012), who suggested the taxon is very closely related to Enantiornis.
References- Dyke, Vremir, Kaiser and Naish, 2011. A drowned Mesozoic bird breeding colony. Journal of Vertebrate Paleontology. Program and Abstracts 2011, 103.
Dyke, Vremir, Kaiser and Naish, 2012. A drowned Mesozoic bird breeding colony from the Late Cretaceous of Transylvania. Naturwissenschaften. 99, 435-442.

unnamed enantiornithine (Nessov and Borkin, 1983)
Mid-Late Turonian, Late Cretaceous
Bissekty Formation, Uzbekistan
Material- (ZIN PO 3494) proximal tarsometatarsus
Comments- Discovered in 1979, this was identified as an enantiornithid by Nessov and Borkin (1983), then as an enantiornithiform by Nesov (1984a,b, 1992). Kurochkin (1996) referred it to Alexornithidae within Enantiornithes. This was based on the strongly reduced metatarsal IV, which however seems to characterize most enantiornithines except for Aberratiodontus, Iberomesornis, Liaoningornis and Vorona. The extremely enlarged medial tibiotarsal condyle (based on the tarsometatarsal cotyla it was ~225% the width of the lateral condyle) is characteristic of a derived set of enantiornithines including Gobipteryx, Nanantius and Soroavisaurus though.
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, 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.
Kurochkin, 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the Infraclass Enantiornithes (Aves). Russian Academy of Sciences, Palaeontological Institute, special issue. 50 pp.

unnamed enantiornithine (Chiappe and Calvo, 1994)
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Material- (MACN-S-01) femur (93.5 mm) (Chiappe and Calvo, 1994)
Comments- MACN-S-01 was first noted by Chiappe and Calvo (1994), while Chinsamy et al. (1995) examined its histology. It is from an enantiornithine based on its hypertrophied posterior trochanter and resembles Vorona, Neuquenornis and Concornis in having a posteriorly projected lateral border on the distal femur.
References- Chiappe and Calvo, 1994. Neuquenornis volans, a new Enantiornithes (Aves) from the Upper Cretaceous of Patagonia (Argentina). Journal of Vertebrate Paleontology. 14, 230-246.
Chinsamy, Chiappe and Dodson, 1995. Mesozoic avian bone microstructure: Physiological implications. Paleobiology. 21(4), 561-574.

unnamed Enantiornithes (Naish, Martill and Merrick, 2007)
Late Aptian, Early Cretaceous
Nova Olinda Member of the Crato Formation, Brazil
Material- (MURJ private coll.) incomplete skull, twenty-two presacral vertebrae, cervical ribs, two dorsal ribs, fragmentary sacrum, three caudal vertebrae, caudal vertebral fragments, chevron, partial ilium, ?ischium, femur (~40 mm), tibiotarsus (~39 mm), phalanx I-1, pedal ungual I, tarsometatarsus (~31 mm), pedal ungual II, phalanx III-1, phalanx III-2, phalanx III-3, pedal ungual III, phalanx IV-4, pedal ungual IV, pedal claw sheaths, body feathers
Comments- Naish et al. (2007) refer a specimen in a private collection to Euenantiornithes based on the centrally placed dorsal parapophyses. The dorsal neural spines are expanded axially at their tips, which Naish et al. notes is similar to Cathayornis (their Sinornis), though it is also present in several other enantiornithines (e.g. Eoalulavis, Fortunguavis, Longusunguis, Noguerornis, Parabohaiornis, Rapaxavis, Shenqiornis, Zhouornis). The authors proposed the presence of two central fossae on the first caudal vertebra could be an autapomorphy.
Reference- Naish, Martill and Merrick, 2007. Birds of the Crato Formation. In Martill, Bechly and Loveridge (eds.). The Crato fossil beds of Brazil: Window into an ancient world. Cambridge University Press. 525-533.

Avisauroidea Paul and Brett-Surman, 1985 vide Martyniuk, 2012
Definition- (Avisaurus archibaldi <- Longipteryx chaoyangensis, Sinornis santensis, Gobipteryx minuta) (Martyniuk, 2012)
Avisauridae Paul and Brett-Surman, 1985
Definition- (Avisaurus archibaldi + Neuquenornis volans) (Chiappe, 1993)
Other definitions- (Avisaurus archibaldi <- Longipteryx chaoyangensis, Sinornis santensis, Gobipteryx minuta) (Cau and Arduini, 2008)
References- Brett-Surman and Paul, 1985. A new family of bird-like dinosaurs linking Laurasia and Gondwanaland. Journal of Vertebrate Paleontology. 5(2), 133-138.
Chiappe, 1993. Enantiornithine (Aves) tarsometatarsi from the Cretaceous Lecho Formation of northwestern Argentina. American Museum Novitates. 3083, 39 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 Soc. it. Sci. nat. Museo civ. Stor. nat. Milano. 149(II), 293-324.
Martyniuk, 2012. A Field Guide to Mesozoic Birds and Other Winged Dinosaurs. Vernon, New Jersey. Pan Aves. 189 pp.
Atterholt, Hutchison and O'Connor, 2018. The most complete enantiornithine from North America and a phylogenetic analysis of the Avisauridae. PeerJ. 6:e5910.

Avisaurus Brett-Surman and Paul, 1985
A. archibaldi Brett-Surman and Paul, 1985
Late Maastrichtian, Late Cretaceous
Hell Creek Formation, Montana, US
Holotype- (UCMP 117600) (~550 mm) tarsometatarsus (mtII 68.7, mtIII 73.9, mtIV 67.8 mm)
Paratype- (PU 17324) tarsometatarsus
Referred- ?(UCMP 171634) (juvenile) metatarsal III (UCMP online; Stidham and Hutchison, 1999?)
?(UCMP 174717) phalanx (UCMP online)
?(YPM 57235) proximal coracoid (Longrich, Tokaryk and Field, 2011)
(large) distal tibiotarsus (Stidham and Hutchison, 2001)
Comments- The holotype was discovered on July 24 1975. Glut (1982) notes Brett-Surman proposed this and an Argentinian form (presumably what would be later named Soroavisaurus) as a new theropod family at the 1978 Society of Vertebrate Paleontology meeting. Brett-Surman and Paul (1985) also designated PVL-4690 and PVL-4048 as paratypes, but they were later made the holotype and paratype respectively of Soroavisaurus australis (Chiappe, 1993).
Stidham and Hutchison (2001) mention "tarsometatarsal fragments representing one or two undescribed taxa" from the Hell Creek Formation of Montana. They (1999) state "A juvenile Avisaurus specimen of an undescribed species from the Maastrichtian Hell Creek Formation of Montana reveals the presence of distal tarsals in enantiomithines." At his 2002 SVP presentation, Stidham used a juvenile avisaurid metatarsal to show that the distal tarsals fused to the metatarsals before the metatarsals fuse to each other in enantiornithines (Mortimer, DML 2002). This may be UCMP 171634, a metatarsal III on the UCMP online database.
References- Glut, 1982. The New Dinosaur Dictionary. Citadel Press. 288 pp.
Brett-Surman and Paul, 1985. A new family of bird-like dinosaurs linking Laurasia and Gondwanaland. Journal of Vertebrate Paleontology. 5(2), 133-138.
Chiappe, 1993. Enantiornithine (Aves) tarsometatarsi from the Cretaceous Lecho Formation of northwestern Argentina. American Museum Novitates. 3083, 39 pp.
Stidham and Hutchison, 1999. The North American avisaurids (Aves: Enantiornithes): New data on morphology and phylogeny. VII International Symposium on Mesozoic Terrestrial Ecosystems, abstracts. 61.
Stidham and Hutchison, 2001. The North American avisaurids (Aves: Enantiornithes): New data on biostratigraphy and biogeography. In Bonaparte (ed.). VII International Symposium on Mesozoic Terrestrial Ecosystems. Asociacion Paleontologica Argentina Publicacion Especial. 7, 175-177.
Mortimer, DML 2002. https://web.archive.org/web/20161206234325/http://dml.cmnh.org/2002Oct/msg00295.html
Stidham, 2002. Evolutionary and developmental origin of the extant bird tarsometatarsus from its theropod dinosaur ancestry. Journal of Vertebrate Paleontology. 22(3), 111A.
Longrich, Tokaryk and Field, 2011. Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary. Proceedings of the National Academy of Sciences of the United States of America. 108(37), 15253-15257.

Gettyia Atterholt, Hutchison and O'Connor, 2018
G. gloriae (Varricchio and Chiappe, 1995) Atterholt, Hutchison and O'Connor, 2018
= Avisaurus gloriae Varricchio and Chiappe, 1995
Middle-Late Campanian, Late Cretaceous
Two Medicine Formation, Montana, US
Holotype- (MOR 553E/6.19.91.64) (~230 mm) tarsometatarsus (mtII 28.4, mtIII 30.9, mtIV 28.5 mm)
Comments- This specimen was discovered in summer 1991 and first referred to as the Two Medicine form in Chiappe (1993).
Diagnosis- (after Varricchio and Chiappe, 1995) mid-length cross-section of tarsometatarsus relatively straight; attachment for the m. tibialis cranialis located beyond the midpoint of the tarsometatarsus; small, medially-curving ridge on the dorsal distal portion of metatarsal II; distal vascular foramen completely closed by metatarsal IV.
(after Atterholt et al., 2018) dorsal surface of the tarsometatarsus strongly inclined.
References- Chiappe, 1993. Enantiornithine (Aves) tarsometatarsi from the Cretaceous Lecho Formation of northwestern Argentina. American Museum Novitates. 3083, 39 pp.
Varricchio and Chiappe, 1995. A new enantiornithine bird from the Upper Cretaceous Two Medicine Formation of Montana. Journal of Vertebrate Paleontology. 15(1), 201-204.
Atterholt, Hutchison and O'Connor, 2018. The most complete enantiornithine from North America and a phylogenetic analysis of the Avisauridae. PeerJ. 6:e5910.

Mirarce Atterholt, Hutchison and O'Connor, 2018
M. eatoni Atterholt, Hutchison and O'Connor, 2018
Late Campanian, Late Cretaceous
Kaiparowitz Formation, Utah, US
Holotype- (UCMP 139500) (adult) axis (18.1 mm), third cervical vertebra, posterior cervical vertebra, two incomplete dorsal vertebrae, pygostyle (37.9 mm), incomplete scapula, partial coracoid, furcula, posterior sternum, humerus (95.9 mm), partial radius, incomplete ulna, carpometacarpal fragment, distal metacarpal II, phalanx II-1, partial pelvis, femora (one fragmentary; 89 mm), fragmentary tibiotarsus, phalanx I-1, pedal ungual I, tarsometatarsi (one proximal; mtII 44.1, mtIII 48.2, mtIV 45.9 mm), phalanges II-1, phalanges II-2, pedal ungual II, phalanges III-1, phalanx III-2, phalanx III-3, pedal ungual III, phalanx IV-1, phalanx IV-3, phalanx IV-4, pedal ungual IV, seven pedal phalanges (incl. unguals)
Diagnosis- (after Atterholt et al., 2018) posterior end of sternum weakly flexed posterodorsally, terminating in a small knob; ulnae with remix papillae present; small, deep, circular pit located just
anterolateral to femoral posterior trochanter; small, triangular muscle scar on medial margin of femoral shaft, just distal to the head, followed distally by much larger proximodistally elongate oval; distinct, rugose ridge-like muscle attachment located on anteromedial margin of femur one fourth from the distal end; tubercle for m. tibialis cranialis located at mid-point of shaft of metatarsal II on the dorsal surface.
Comments- This was discovered on October 12 1992 and initially identified as Avisaurus sp. nov. (Hutchison, 1993), though note that abstract incorrectly claimed evidence of "sharply clawed digits on the wing." Stidham and Hutchison (1999) noted it in an abstract as an "undescribed crowsized partial skeleton of Avisaurus from the Campanian Kaiparowits Formation." Hutchinson (2001) illustrates the proximal femur as Avisaurus and notes a few characters.
References- Hutchison, 1993. Avisaurus: A "dinosaur" grows wings. Journal of Veterbrate Paleontology. 13(3), 43A.
Stidham and Hutchison, 1999. The North American avisaurids (Aves: Enantiornithes): New data on morphology and phylogeny. VII International Symposium on Mesozoic Terrestrial Ecosystems, abstracts. 61.
Hutchinson, 2001. The evolution of femoral osteology and soft tissues on the line to extant birds (Neornithes). Zoological Journal of the Linnean Society. 131, 169-197.
Chiappe and Walker, 2002. Skeletal morphology and systematics of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). In Chiappe and Witmer (eds.). Mesozoic Birds - Above the Heads of Dinosaurs. University of California Press. 240-267.
Atterholt, Hutchison and O'Connor, 2018. The most complete enantiornithine from North America and a phylogenetic analysis of the Avisauridae. PeerJ. 6:e5910.

Soroavisaurus Chiappe, 1993
S. australis Chiappe, 1993
Maastrichtian, Late Cretaceous
Lecho Formation, Salta, Argentina
Holotype- (PVL-4690; paratype of Avisaurus archibaldi) (~345 mm) tarsometatarsus (46.9 mm; metatarsal II 44.2, metatarsal IV 43.3 mm)
Paratype- (PVL-4048; paratype of Avisaurus archibaldi) metatarsal I (12.2 mm), phalanx I-1 (16.2 mm), ungual I (17.3 mm), tarsometatarsus (51.5 mm; metatarsal II 48.9, metatarsal IV 48.4 mm), four pedal phalanges
Referred- ?(PVL-4033) tibiotarsus (85.6 mm) (Walker, 1981)
Comments- Collected between 1974 and 1976, PVL-4048 was originally illustrated by Walker (1981). Glut (1982) notes Brett-Surman proposed what is presumably this and Avisaurus as a new theropod family at the 1978 Society of Vertebrate Paleontology meeting. Brett-Surman and Paul (1985) made it and PVL-4690 paratypes of Avisaurus archibaldi, though they referred to PVL-4690 as Avisaurus sp. and 4048 as Avisauridae in an illustration. They were also referred to Avisaurus sp. by Chiappe (1992) and Chiappe and Calvo (1994). Chiappe (1993) named them both Soroavisaurus australis.
PVL-4033 was also originally illustrated by Walker (and referred to Martinavis by him in his unpublished manuscript), but not referred to Soroavisaurus until Chiappe and Walker (2002). The latter authors also referred PVL-4030 to Soroavisaurus and illustrated both tibiotarsi. Walker and Dyke (2009) reassigned PVL-4030 to Martinavis sp. and assigned PVL-4033 to Martinavis in their measurement table. Walker et al. (2007) stated PVL-4033 is consistant in size with both Enantiornis and Martinavis. The smaller size of Soroavisaurus does suggest it may correspond with humeri of Martinavis? vincei or M? saltariensis, making the assignment of elements like tibiotarsi to either taxon more semantic than scientific.
References- Walker, 1981. New subclass of birds from the Cretaceous of South America. Nature. 292, 51-53.
Glut, 1982. The New Dinosaur Dictionary. Citadel Press. 288 pp.
Brett-Surman and Paul, 1985. A new family of bird-like dinosaurs linking Laurasia and Gondwanaland. Journal of Vertebrate Paleontology. 5(2), 133-138.
Chiappe, 1992. Enantiornithine (Aves) tarsometatarsi and the avian affinites of the Cretaceous Avisauridae. Journal of Vertebrate Paleontology. 12(3), 344-350.
Chiappe, 1993. Enantiornithine (Aves) tarsometatarsi from the Cretaceous Lecho Formation of northwestern Argentina. American Museum Novitates. 3083, 39 pp.
Chiappe and Calvo, 1994. Neuquenornis volans, a new Enantiornithes (Aves) from the Upper Cretaceous of Patagonia (Argentina). Journal of Vertebrate Paleontology. 14, 230–246.
Chiappe and Walker, 2002. Skeletal morphology and systematic of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). pp 240-267. in Chiappe and Witmer, (eds.). Mesozoic Birds – Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.
Walker, Buffetaut and Dyke, 2007. Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina. Geological Magazine. 144(6), 977-986.
Walker and Dyke, 2009. Euenantiornithine birds from the Late Cretaceous of El Brete (Argentina). Irish Journal of Earth Sciences. 27, 15-62.

Neuquenornis Chiappe and Calvo, 1994
N. volans Chiappe and Calvo, 1994
Santonian, Late Cretaceous
Bajo de le Carpa Formation of the Rio Colorado Subgroup, Neuquen, Argentina
Holotype- (MUCPv-142) (~290 mm) posterior skull, five partial dorsal vertebrae, incomplete scapula, coracoids (33.4 mm), furcula, incomplete sternum, sternal ribs, incomplete humeri, incomplete radii (70.5 mm), incomplete ulnae (72.1 mm), pisiform, carpometacarpus, proximal phalanx II-1, pelvic(?) fragment, incomplete femur, partial tibiotarsi (~87.7 mm), metatarsal I (8.3 mm), phalanx I-1 (10.7 mm), pedal ungual I (14.6 mm), incomplete tarsometatarsi (~46.8 mm), phalanx II-1 (6.6 mm), phalanx II-2 (12.3 mm), partial pedal ungual II (11.7 mm), phalanx III-1 (10.7 mm), phalanx III-2
References- Chiappe and Calvo, 1989. El primer Enantiornithes (Aves) del Cretacico de Patagonia. Resumes VI Jornadas Argentinas de Paleontologia de Vertebrados. San Juan. pp. 19-21.
Chiappe, 1991a. Cretaceous birds of Latin America. Cretaceous Research. 12(1), 55-63.
Chiappe, 1991b. Cretaceous avian remains from Patagonia shed new light on the early radiation of birds. Alcheringa. 15, 333-338.
Chiappe, 1992. Enantiornithine (Aves) tarsometatarsi and the avian affinites of the Cretaceous Avisauridae. Journal of Vertebrate Paleontology. 12(3), 344-350.
Chiappe and Calvo, 1994. Neuquenornis volans, a new Late Cretaceous bird (Enantiornithes: Avisauridae) from Patagonia, Argentina. Journal of Vertebrate Paleontology. 14(2), 230-246.

Intiornis Novas, Agnolín and Scanferla, 2010
I. inexpectatus Novas, Agnolín and Scanferla, 2010
Campanian, Late Cretaceous
Las Curtiembres Formation, Salta, Argentina
Holotype- (MAS-P/2 1) distal tibiotarsus, metatarsal I, phalanx I-1, pedal ungual I, tarsometatarsus (21 mm), phalanx II-1, phalanx II-2, pedal ungual II, phalanx III-1, phalanx III-2, proximal phalanx III-3, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV
Diagnosis- (after Novas et al., 2010) tall and cup-like intercotylar prominence, even more developed than in Lectavis; phalanx IV-4 anteroposteriorly short, being subequal in length to phalanx IV-2; phalanx I-1 proportionally short and stout.
Comments- Novas et al. (2010) described this taxon as an avisaurid most closely related to Soroavisaurus.
Reference- Novas, Agnolín and Scanferla, 2010. New enantiornithine bird (Aves, Ornithothoraces) from the Late Cretaceous of NW Argentina. Comptes Rendus Palevol. 9(8), 499-503.

Bohaiornithidae Wang, Zhou, O'Connor and Zelenkov, 2014
Definition- (Bohaiornis guoi + Shenqiornis mengi) (Wang et al., 2014)
Diagnosis- (after Wang et al., 2014) robust rostrum; large, robust, subconical teeth with sharply tapered and slightly distally recurved tips; pygostyle tapered, without abrupt distal constriction; scapular blade with convex dorsal magin and straight to weakly concave ventral margin; omal tips of furcula with blunt expansions visible in ventrolateral view; sternum with posterolateral process strongly projecting posterolaterally; pedal digit II more robust than other digits; pedal unguals extremely elongated with digit III ungual measuring more than 40% length of tarsometatarsus.
Comments- Both Chiappe et al. (2019) and Hartman et al. (2019) failed to recover this clade (as also including Sulcavis, Parabohaiornis, Zhouornis and Longusunguis) without it encompassing most enantiornithines due to the basal position of Shenqiornis in both.
References- Wang, Zhou, O'Connor and Zelenkov, 2014. A new diverse enantiornithine family (Bohaiornithidae fam. nov.) from the Lower Cretaceous of China with information from two new species. Vertebrata PalAsiatica. 52(1), 31-76.
Chiappe, Meng, Serrano, Sigurdsen, Wang, Bell and Liu, 2019. New Bohaiornis-like bird from the Early Cretaceous of China: Enantiornithine interrelationships and flight performance. PeerJ. 7:e7846.
Hartman, Mortimer, Wahl, Lomax, Lippincott and Lovelace, 2019. A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight. PeerJ. 7:e7247. DOI: 10.7717/peerj.7247

Beiguornis Wang, Ju, Wu, Liu, Guo and Ji, 2022
B. khinganensis Wang, Ju, Wu, Liu, Guo and Ji, 2022
Early Aptian, Early Cretaceous
Pigeon Hill, Longjiang Formation, Inner Mongolia, China
Holotype- (MHGU-F307/308) (subadult) partial skull, eight cervical vertebrae, dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, synsacrum, five caudal vertebrae, pygostyle, scapulae, coracoids, furcula, partial sternum, sternal ribs, humeri, radii (one partial), ulnae (one partial), metacarpals I, phalanges I-1, manual unguals I, carpometacarpi, phalanges II-1, phalanges II-2, manual unguals II, phalanges III-1, phalanx III-2, partial ilium, proximal pubis, femora, tibiae, fibula, astragalocalcanea, metatarsal I, phalanges I-1 (one distal) pedal unguals I, tarsometatarsi (one partial), partial phalanx II-2, incomplete pedal ungual II, fragmentary phalanx III-1, incomplete phalanx III-2, proximal phalanx III-3, phalanx IV-1, partial phalanx IV-3, partial phalanx IV-4, pedal claw sheath
Diagnosis- (after Wang et al., 2022) coracoid strongly expanded distolaterally; distal coracoid margin long and straight; anterior margin of sternum sharply angled at median; small notch posterior to costal edge of sternum; posteromedial sternal processes triangular; manual ungual I long and curved; manual ungual II short and robust.
Comments- The interpretation of preserved pedal phalanges here is slightly different than in Wang et al.'s (2022) figure 10, in that III-3 and pedal ungual III are viewed as III-2 and III-3, and IV-4 and pedal ungual IV are viewed as IV-3 and IV-4 . This is based on length in typical enantiornithines, as phalangeal morphology is largely indeterminate due to a lack of preparation.
Wang et al. (2022) add the taxon to O'Connor's bird analysis and find it emerges sister to Sulcavis within Bohaiornithidae.
Reference- Wang, Ju, Wu, Liu, Guo and Ji, 2022. The first enantiornithine bird from the Lower Cretaceous Longjiang Formation in the Great Khingan Range of Inner Mongolia. Acta Geologica Sinica. 96(2), 337-348.

Shenqiornis Wang, O'Connor, Zhao, Chiappe, Gao and Cheng, 2010
= Dalianornis" O'Connor, Chiappe and Bell, 2011
S. mengi Wang, O'Connor, Zhao, Chiappe, Gao and Cheng, 2010
= "Dalianornis mengi" O'Connor, Chiappe and Bell, 2011
Early Aptian, Early Cretaceous
Qiaotou Member of the Huajiying Formation, Hebei, China
Holotype- (DNHM D2950-2951) (subadult) incomplete skull (~41.8 mm), sclerotic plates, incomplete mandibles, atlas axis, five cervical vertebrae, three cervical ribs, three dorsal vertebrae, dorsal ribs, several gastralia, synsacrum (23.4 mm), caudal vertebra, scapulae (39.3, ~34.6 mm), coracoids (one incomplete; 26.2 mm), furcula (28.9 mm), partial sternum (~28.8 mm), sternal ribs, humeri (one proximal; 46.6, 43 mm), radii (one incomplete; 45.8, 39.6 mm), ulnae (46.8, 44.8 mm), proximal carpal, semilunate carpal, distal carpal III, metacarpals I (4.5, ~4.1 mm), phalanges I-1 (10 mm), manual unguals I (5.9, ~4 mm), metacarpals II (21.7, ~16.8 mm), phalanges II-1 (11.1, 10.1 mm), phalanges II-2 (8.7, 8.4 mm), manual unguals II (5.5, 4.7 mm), metacarpals III (20.7, ~18.4 mm), phalanx III-1 (6.9, ~4.4 mm), ?phalanx III-2, partial ilia (~27 mm), pubes (33.4, 35 mm), ischia (17.5, 18 mm), incomplete femur (~38.8 mm), incomplete tibia, astragalocalcaneum, distal tarsal, metatarsal I (7 mm), phalanx I-1 (7 mm), tarsometatarsi (~24.8, 25 mm; mtII ~22.4, mtIII 25, mtIV 22.8 mm), phalanx II-1 (5.6 mm), phalanx II-2 (~7.8 mm), phalanx III-1 (~8.4 mm), phalanx IV-1 (4.1 mm), phalanx IV-2, phalanx IV-3, pedal phalanx, two pedal unguals, body feathers, two remiges
Diagnosis- (after Wang et al., 2010) narrow nasal lacking subnarial process; postorbital with elongate, straight ventral process; robust teeth with circular sections and slightly recurved apices; omal tips of furcula expanded; distal third of coracoid laterally convex; posterolateral sternal process expanded distally and fan-shaped; unreduced and unfused manus with unguals on digits I and II; dorsally projecting tubercle on posterodorsal surface of semilunate carpal; pubic boot present; strap-like ischium without obturator process; J-shaped metatarsal I lacking lateral compression, with lateral facet for metatarsal II and posterior facet for phalanx I-1.
Comments- This specimen was discovered before 2009 and used in O'Connor's (2009) thesis. O'Connor et al. (2011) listed it as "Dalianornis mengi" in their data matrix, though as Shenquiornis is used in the main article and cladogram, the matrix was probably created before it was officially named and mistakenly made it through publication. Many of the characters listed in the diagnosis are common in enantiornithines, and the unfused carpometacarpus is probably ontogenetic.
References- O'Connor, 2009. A systematic review of Enantiornithes (Aves: Ornithothoraces). PhD Thesis. University of Southern California. 586 pp.
Wang, O'Connor, Zhao, Chiappe, Gao and Cheng, 2010. New species of Enantiornithes (Aves: Ornithothoraces) from the Qiaotau Formation in Northern Hebei, China. Acta Geologica Sinica. 84(2), 247-256.
O'Connor, Chiappe and Bell, 2011. Pre-modern birds: Avian divergences in the Mesozoic. in Dyke and Kaiser (eds.). Living Dinosaurs: The Evolutionary History of Modern Birds. 39-114.
O'Connor, Zhang, Chiappe, Meng, Li and Liu, 2013. A new enantiornithine from the Yixian Formation with the first recognized avian enamel specialization. Journal of Vertebrate Paleontology. 33(1), 1-12.

Sulcavis O'Connor, Zhang, Chiappe, Meng, Li and Liu, 2013
S. geeorum O'Connor, Zhang, Chiappe, Meng, Li and Liu, 2013
Barremian-Aptian, Early Cretaceous
Yixian Formation, Liaoning, China
Holotype- (BMNHC Ph 000805) (171 g) incomplete skull, sclerotic plates, partial mandibles, incomplete hyoids, seven cervical vertebrae, posterior cervical ribs, about ten fragmentary dorsal vertrebrae, incomplete dorsal ribs, gastralial fragments, synsacrum (19.3 mm), six caudal vertebrae, pygostyle (19.6 mm), chevrons, incomplete scapulae (34.9 mm), incomplete coracoids (24.8 mm), incomplete furcula, sternla? fragments, sternal ribs, humeri (46.5 mm), radii (one incomplete; 47.7 mm), ulnae (one incomplete; 51.1 mm), scapholunare, pisiform, metacarpals I (one partial), phalanges I-1 (one partial), manual ungual I, carpometacapri (one incomplete), phalanx II-1, phalanx II-2, manual ungual II, manual claw sheaths, phalanx III-1, manual fragments, ilia (one partial; 26.5 mm), partial pubis, ischial fragment, femora (41.3 mm), tibiae (47.3 mm), incomplete fibulae (18.9 mm), astragalocalcanea, metatarsals I (5 mm), phalanges I-1, pedal unguals I, tarsometatarsi (24.85 mm- II 21.6 mm, III 24.3 mm, IV 22.6 mm), phalanges II-1, phalanges II-2, pedal unguals II, phalanx III-1, phalanx III-2, pahlanx III-3, pedal ungual III, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, pedal claw sheaths, feathers
Diagnosis- (after O'Connor et al., 2012) broad nasal with short, tapered, anteriorly directed maxillary process; robust teeth with caudally recurved apices, D-shaped cross-section with flat lingual margin, and lingual face with longitudinal grooves radiating from the occlusal tip; posteriormost transverse processes of synsacrum extending far beyond the posterior articular surface of their respective centra; scapula with long and delicate acromion process; convex lateral margin of the coracoid; medial angle of coracoid expanded; Y-shaped furcula with blunt omal apices; alular claw larger than that of the major digit; pedal digit II hypertrophied; deep pits for the collateral ligament and lateral ridges present on pedal unguals.
Reference- O'Connor, Zhang, Chiappe, Meng, Li and Liu, 2013. A new enantiornithine from the Yixian Formation with the first recognized avian enamel specialization. Journal of Vertebrate Paleontology. 33(1), 1-12.

Zhouornis Zhang, Chiappe, Han and Chinsamy, 2013
Z. hani Zhang, Chiappe, Han and Chinsamy, 2013
Barremian-Albian, Early Cretaceous
Jehol Group, Liaoning, China
Holotype- (CNUVB-0903) (227 g, subadult) skull (~35 mm), partial mandible, altas, axis, third cervical vertebra, fourth cervical vertebra, fifth cervical vertebra, sixth cervical vertebra, seventh cervical vertebra, eighth cervical vertebra, cervical ribs, nine dorsal vertebrae, dorsal ribs, gastralia, synsacrum, caudal vertebrae, pygostyle (17.3 mm), scapulae (40.7, 40.4 mm), coracoids (28.4, 28.3 mm), furcula, sternum, sternal ribs, humeri (50.6, 50.6 mm), radii, ulnae (53.5, 54 mm), scapholunares, pisiforms, carpometacarpi (mcI 4.1, 3.7 mm; 23.6, 24.4 mm), phalanges I-1 (9.1, 9.1 mm), manual unguals I (4.6, 5.0 mm), phalanges II-1 (10.8, 10.6 mm), phalanges II-2 (8.1, 7.5 mm), manual unguals II (4.9, 3.7 mm), phalanges III-1 (5.6, 5.6 mm), manual claw sheaths, partial ilia, pubes, femora (44.5, 43.5 mm), tibiotarsi (52.1, 51.2 mm), fibulae, metatarsals I, phalanges I-1 (6.3, 6.5 mm), pedal unguals I (8, 8.8 mm), tarsometatarsi (26.1, 25.8 mm), phalanges II-1 (6.3, 7.2 mm), phalanges II-2 (8.3, 8.8 mm), pedal unguals II (10.1, 11.2 mm), phalanges III-1 (7.7 mm), phalanges III-2 (7.1, 6.9 mm), phalanges III-3 (7.1, 6.8 mm), pedal unguals III (10.1, 10.2 mm), phalanx IV-1 (4.2 mm), phalanx IV-2 (4 mm), phalanx IV-3 (3.3 mm), phalanges IV-4 (4.3 mm), pedal unguals IV (7, 7.2 mm), pedal claw sheaths, body feathers remiges
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Referred- (BMNHC Ph 756) (137 g, subadult) skull, mandibles, hyoids, six or seven cervical vertebrae, cervical ribs, three dorsal vertebrae, dorsal ribs, uncinate process, gastralia, synsacrum, four or five caudal vertebrae, pygostyle (22.4 mm), scapulae (32.4, 36 mm), coracoids (20.9, 23.1 mm), partial furcula, sternum, sternal ribs, incomplete humeri (38.3, 40.5 mm), incomplete radii, ulnae (one incomplete; 36.9, 41.5 mm), scapholunares, pisiforms, (carpometacarpi 19.3, 19.5 mm) semilunate carpals, metacarpals I, phalanges I-1 (one partial), manual unguals I (one fragmentary), metacarpals II, phalanges II-1, phalanges II-2, manual unguals II, manual claw sheaths, metacarpals III, phalanges III-1, incomplete ilium, incomplete pubes, ischium, femora (31.4, 26.4 mm), tibiotarsi (one partial; 39.3, 41.7 mm), partial fibulae, metatarsals I, phalanges I-1, pedal unguals I, tarsometatarsi (22.5, 20 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 (one partial), phalanx IV-4, pedal unguals IV, pedal claw sheaths, feathers (Zhang et al., 2014)
Diagnosis- (after Zhang et al., 2013) bifurcated posterior end of maxillary process of premaxilla; oval maxillary fenestra; large paraoccipital processes; long basipterygoid processes; axis with short epipophyses; scapula with curved blade; coracoid displaying longitudinal dorsal trough that extends through omal half of bone; sternum bearing pair of long, robust lateral processes with triangular, posteromedially slanting distal end, and angular anterolateral corners; humeral head proximally flat.
Comments- The holotype was acquired from a farmer, making locality information uncertain.
References- Zhang, Chiappe, Han and Chinsamy, 2013. A large bird from the Early Cretaceous of China: New information on the skull of enantiornithines. Journal of Vertebrate Paleontology. 33(5), 1176-1189.
Zhang, O'Connor, Liu, Meng, Sigurdsen and Chiappe, 2014. New information on the anatomy of the Chinese Early Cretaceous Bohaiornithidae (Aves: Enantiornithes) from a subadult specimen of Zhouornis hani. PeerJ. 2, e407.

Longusunguis Wang, Zhou, O'Connor and Zelenkov, 2014
L. kurochkini Wang, Zhou, O'Connor and Zelenkov, 2014
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V17964) (130 g, subadult) partial skull (~33.9 mm), mandibles, partial hyoids, six cervical vertebrae, elevan dorsal vertebrae, partial dorsal ribs, synsacrum, seven caudal vertebrae, chevrons, pygostyle (22.8 mm), scapulae (34.7 mm), coracoid (24.2 mm), furcula, sternum (31.1 mm), furcula, humeri (40.3 mm), radii (40.5 mm), ulnae (one incomplete; 43.6 mm), scapholunares, pisiforms, semilunate carpals, metacarpals I (3.6 mm), incomplete phalanges I-1 (7.1 mm), manual ungual I (4.5 mm), metacarpals II (16.8 mm), phalnges II-1 (one fragmentary; 10.5 mm), phalanx II-2 (6.9 mm), manual ungual II (~3.4 mm), metacarpals III (18 mm), phalanges III-1 (one partial; 5.2 mm), partial ilia, pubes (one partial; 29.1 mm), ischia (one partial; 17 mm), femora (one incomplete; 35.8 mm), tibiae (one incomplete; 41.8 mm), fibula, astragalocalcanea, distal tarsal IV, metatarsal I, phalanx I-1 (5.4 mm), metatarsals II (19.6 mm), phalanges II-1 (5.4 mm), phalanges II-2 (7.2 mm), pedal unguals II, metatarsals III (21.4 mm), phalanges III-1 (7 mm), phalanges III-2 (6.4 mm), phalanx III-3 (6.7 mm), pedal ungual III (12 mm), metatarsal IV (20.2 mm), phalanx IV-1 (3.7 mm), phalanx IV-2 (2.9 mm), phalanx IV-3 (3.4 mm), phalanx IV-4 (4.6 mm), body feathers, retrices or leg remiges
Diagnosis- (after Wang et al., 2014) maxilla with fenestra on posterior process; ventral process of lacrimal with elongate excavation on posterior margin; pygostyle longer than tarsometatarsus; lateral margin of coracoid more convex than other bohaiornithids; acromion strongly projecting dorsally.
Reference- Wang, Zhou, O'Connor and Zelenkov, 2014. A new diverse enantiornithine family (Bohaiornithidae fam. nov.) from the Lower Cretaceous of China with information from two new species. Vertebrata PalAsiatica. 52(1), 31-76.

Parabohaiornis Wang, Zhou, O'Connor and Zelenkov, 2014
P. martini Wang, Zhou, O'Connor and Zelenkov, 2014
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (IVPP V18691) (subadult) incomplete skull (42.5 mm), incomplete mandibles, partial hyoids, eight cervical vertebrae, eleven dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, synsacrum, four caudal vertebrae, pygostyle (18 mm), scapula (33.3 mm), coracoid (21.9 mm), furcula, partial sternum, sternal ribs, humeri (43.4 mm), radii (40.3 mm), ulnae (43.8 mm), scapholunares, pisiforms, semilunate carpals, metacarpals I (3.9 mm), phalanges I-1 (8.1 mm), manual unguals I (3.5 mm), metacarpals II (16.5 mm), phalanges II-1 (10.2 mm), phalanges II-2 (7.4 mm), manual unguals II (3.2 mm), metacarpals III (17.6 mm), phalanges III-1 (5.5 mm), ilia (23.7 mm), pubes (31 mm), ischia (one partial; 20.3 mm), femora (36 mm), tibiae (40 mm), fibulae, astragalocalcaneum, distal tarsal III, metatarsals I, phalanges I-1 (5.4 mm), pedal unguals I (6 mm), metatarsals II (17.1 mm), phalanges II-1 (4.5 mm), phalanges II-2 (6.8 mm), pedal unguals II (8.7 mm), metatarsals III (19.5 mm), phalanges III-1 (6.4 mm), phalanges III-2 (5.4 mm), phalanges III-3 (5.3 mm), pedal unguals III (8.8 mm), metatarsals IV (18.1 mm), phalanges IV-1 (2.9 mm), phalanges IV-2 (2.6 mm), phalanges IV-3 (2.9 mm), phalanges IV-4 (4.1 mm), pedal unguals IV (~4.7 mm)
Paratype- (IVPP V18690) (subadult) few cervical vertebrae, seven dorsal vertebrae, dorsal ribs, uncinate processes, gastralia, synsacrum, six caudal vertebrae, pygostyle (21.8 mm), scapulae (one partial; one incomplete), coracoids (one incomplete; 25.6 mm), incomplete furcula, incomplete sternum, sternal ribs, humeri (one incomplete; 46.7 mm), incomplete ilia (24.4 mm), pubes (32 mm), ischia (20.8 mm), femora (37.5 mm), tibiotarsi (45 mm), fibulae, distal tarsal III, metatarsals I, phalanges I-1 (6.1 mm), pedal unguals I (~6.3 mm), metatarsals II (20.4 mm), phalanges II-1 (5.8 mm), phalanges II-2 (7.6 mm), pedal unguals II (10 mm), metatarsals III (22 mm), phalanges III-1 (7.8 mm), phalanges III-2 (6.5 mm), phalanges III-3 (6.6 mm), pedal unguals III (11.5 mm), metatarsals IV (20.6 mm), phalanges IV-1 (2.9 mm), phalanges IV-2 (2.6 mm), phalanges IV-3 (2.9 mm), phalanges IV-4 (4.4 mm), pedal unguals IV (7 mm), pedal claw sheaths
Diagnosis- (after Wang et al., 2014) three premaxillary teeth; four maxillary teeth; nasal without anteroventral process; intercondylar incisure absent on tibiotarsus; acromion parallel to scapular shaft; length ratio of pygostyle to metatarsal III 0.92-0.99; pedal phalanx IV-1 <70% length of IV-4.
Reference- Wang, Zhou, O'Connor and Zelenkov, 2014. A new diverse enantiornithine family (Bohaiornithidae fam. nov.) from the Lower Cretaceous of China with information from two new species. Vertebrata PalAsiatica. 52(1), 31-76.

Bohaiornis Hu, Li, Hou and Xu, 2011
= "Bohaiornis" Hu, Hou and Xu, 2009
B. guoi Hu, Li, Hou and Xu, 2011
= "Bohaiornis guoi" Hu, Hou and Xu, 2009
Early Albian, Early Cretaceous
Jiufotang Formation, Liaoning, China
Holotype- (LPM B00167) (296 mm; subadult) incomplete skull (~47 mm), sclerotic plates, mandibles (38 mm), hyoid, 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, cervical ribs, seven dorsal vertebrae, dorsal ribs, gastralia, synsacrum, six caudal vertebrae, pygostyle, scapulae, coracoids (23 mm), furcula (24 mm), sternum (36.4 mm), sternal ribs, humerus (47 mm), radii (45.4 mm), ulnae (48 mm), scapholunare, pisiforms, semilunate carpals, metacarpals I (8 mm), phalanges I-1 (9.5 mm), manual unguals I (4.5 mm), metacarpals II (21.3 mm), phalanges II-1 (10.8 mm), phalanges II-2 (7.5 mm), manual unguals II (3.6 mm), metacarpals III (22.7 mm), phalanx III-1 (5.5 mm), ilium (25.6 mm), pubes (33 mm), ischia (21 mm), femora (39 mm), tibiae (46 mm), fibulae (23 mm), astragalocalcaneum, distal tarsal, metatarsals I (5.7 mm), phalanges I-1 (6 mm), pedal unguals I (9 mm), metatarsals II (20.8 mm), phalanges II-1 (5 mm), phalanges II-2 (7 mm), pedal unguals II (12 mm), metatarsals III (one partial; 22.5 mm), phalanges III-1 (7.6 mm), phalanges III-2 (7.2 mm), phalanges III-3 (6.5 mm), pedal unguals III (10.3 mm), metatarsals IV (one distal; 21.8 mm), phalanges IV-1 (4 mm), phalanges IV-2 (3.3 mm), phalanges IV-3 (3.5 mm), phalanges IV-4 (4.2 mm), pedal unguals IV (7.5 mm), remiges, retrices
Referred- (IVPP V17963) (adult) skull (45.3 mm), sclerotic plates, mandibles, seven cervical vertebrae, four dorsal vertebrae, dorsal ribs, gastralia, synsacrum, six caudal vertebrae, pygostyle (19.2 mm), scapulae (one partial; ~33.9 mm), coracoids (25.9, ~22.6 mm), furcula, incomplete sternum (36.2 mm), sternal ribs, humeri (50.3 mm), radii (48.8 mm), ulnae (53mm), scapholunare, pisiform, carpometacarpi (~23.3; mcI 4, mcII 22.8, mcIII ~21 mm), phalanges I-1 (9.3 mm), manual unguals I (5.1 mm), phalanges II-1 (11.1 mm), phalanges II-2 (7 mm), manual unguals II (3.4 mm), phalanges III-1 (6.7 mm), incomplete ilium (24.2 mm), proximal pubes, proximal ischium, femora (42.6 mm), tibiotarsi (49.4 mm), metatarsals I, phalanges I-1, pedal ungual I, tarsometatarsi (~22.7 mm), phalanx II-1 (6.1 mm), phalanx II-2 (8.1 mm), pedal unguals II (10.2 mm), phalanx III-1, phalanges III-2 (6.5 mm), phalanges III-3 (6.6 mm), pedal unguals III (one fragmentary; 10.5 mm), phalanges IV-1 (3.8 mm), phalanges IV-2 (3.5 mm), phalanges IV-3 (3.2 mm), phalanges IV-4 (4.4 mm), pedal unguals IV (8.7 mm), pedal claw sheaths, gastroliths (Li et al., 2014)
Diagnosis- (after Hu et al., 2009) sacral centra strongly compressed transversely; clavicular ramus of furcula straight; clavicular facet with a transversely expanded proximal end; prominent ridge along medioventral margin of clavicular ramus of furcula.
(after Hu et al., 2011) posterior end of the articular pointed posteroventrally.
(after Li et al., 2014) strap-like and faintly ventrally recurved jugal bar; reduced maxillary and dentary dentition; robust teeth; broad scleral ossicles; acromion developed as a rectangular process with a broadly expanded tip; slightly medially hooked acrocoracoid; glenoid facet on coracoid positioned at approximately the same level as acrocoracoid process; flat to sub-concave lateral margin of the coracoid with small lateral process; sternal midline with slightly developed T-shaped terminus approximately equal in posterior extent to posterolateral process; elongate, strongly recurved pedal unguals; third pedal ungual larger but less recurved than other pedal unguals.
Other diagnoses- Hu et al. (2009) state the presence of cervical centra with strong ventral keels is unique, but this is shared with most other enantiornithines except Pengornis. The long acromion is also present in Eoalulavis.
Comments- Hu et al. (2009) briefly describe this new taxon in their SVP abstract, which made it a nomen nudum according to ICZN Article 9.9. They later described it officially in 2011.
Although Hu et al. believed the holotype to be from the Yixian Formation, Li et al. (2014) described a specimen from near the same village which was found in the Jiufotang Formation. As their fieldwork found most of the exposures there to be Jiufotang, so believe the holotype was from that formation too.
While the authors state Bohaiornis strongly resembles Eoenantiornis in several characters (short and deep skull with six to seven teeth on each side of upper and lower jaws; forelimbs subequal to hindlimbs in length; manual digit I with robust and curved ungual extending distally to the level of the distal end of metacarpal II), only the short and deep skull is potentially synapomorphic. Their 2009 phylogenetic analysis found Bohaiornis to be more derived than Protopteryx, but more basal than most other enantiornithines including Eoenantiornis. Their 2011 phylogenetic analysis is a version of the Elsornis analysis with eight added characters and finds Bohaiornis in a polytomy with other non-longipterygid enantiornithines. Li et al. (2014) used a version of Clarke's analysis to find Bohaiornis more derived than Protopteryx, but outside Longipterygidae and a clade of Cathayornis, Concornis, Gobipteryx and Neuquenornis.
References- Hu, Hou and Xu, 2009. A new enantiornithine bird from the Lower Cretaceous of Western Liaoning, China. Journal of Vertebrate Paleontology. 29(3), 118A.
Hu, Li, Hou and Xu, 2011. A new enantiornithine bird from the Lower Cretaceous of Western Liaoning, China. Journal of Vertebrate Paleontology. 31(1), 154-161.
Li, Zhou and Clarke, 2012. A large-bodied basal enantiornithine bird from the Early Cretaceous of China with a proposed raptorial feeding ecology. Journal of Vertebrate Paleontology. Program and Abstracts 2012, 127.
Li, Zhou, Wang and Clarke, 2014. A new specimen of large-bodied basal enantiornithine Bohaiornis from the Early Cretaceous of China and the inference of feeding ecology in Mesozoic birds. Journal of Paleontology. 88(1), 99-108.
Wang, Zhou, O'Connor and Zelenkov, 2014. A new diverse enantiornithine family (Bohaiornithidae fam. nov.) from the Lower Cretaceous of China with information from two new species. Vertebrata PalAsiatica. 52(1), 31-76.

Liaoningornithiformes Hou, 1996
Liaoningornithidae Hou, 1996
Diagnosis- (proposed) sternum elongate (unknown in Vorona); posteromedial sternal processes absent (also in taxa less derived than Longipteryx; unknown in Vorona); posterolateral sternal processes absent (unknown in Vorona); posteromedian process of sternum extremely expanded (unknown in Vorona); metatarsals at least partially fused distally (also in Changchengornis, Avisaurus gloriae and Euornithes; unknown in Eoalulavis); trochlea of metatarsal II subequal in width to III (also in non-enantiornithines and Longipterygidae; unknown in Eoalulavis); metatarsal IV not reduced in width compared to II and III (also in non-enantiornithines and those more basal than Longipteryx; unknown in Eoalulavis).
Reference- Hou, 1996. The discovery of a Jurassic carinate bird in China. Chinese Science Bulletin. 41(2), 1861-1864.

Eoalulavis Sanz, Chiappe, Perez-Moreno, Buscalioni, Moratalla, Ortega and Poyato-Ariza, 1996
E. hoyasi Sanz, Chiappe, Perez-Moreno, Buscalioni, Moratalla, Ortega and Poyato-Ariza, 1996
Late Barremian, Early Cretaceous
Calizas de La Huerguina Formation, Spain
Holotype- (LH-13500) (~150 mm; 45 g, adult) five posterior cervical vertebrae, ten dorsal vertebrae, several dorsal ribs, scapulae, coracoids (17 mm), furcula, sternum, humeri (27 mm), radii, ulnae (31 mm), pisiform, metacarpal I, phalanx I-1, manual ungual I, metacarpal II, phalanx II-1, phalanx II-2, manual ungual II, metacarpal III, phalanx III-1, ilium, proximal femur, feather impressions
References- Sanz, Chiappe, Perez-Moreno, Buscalioni, Moratalla, Ortega and Poyato-Ariza, 1996. An Early Cretaceous bird from Spain and its implications for the evolution of avian flight. Nature. 382, 442-445.
Sanz, Pérez-Moreno, Chiappe and Buscalioni, 2002. The Birds from the Lower Cretaceous of Las Hoyas (Privince of Cuenca, Spain). pp 209-229. in Chiappe and Witmer (eds.). Mesozoic Birds: Above the Heads of Dinosaurs. University of California Press, Berkeley, Los Angeles, London.

Liaoningornis Hou, 1996
L. longidigitus Hou, 1996
Late Barremian-Early Aptian, Early Cretaceous
Jianshangou Beds of Yixian Formation, Liaoning, China
Holotype- (IVPP V11303) (~150 mm) several partial dorsal ribs, gastralia, partial scapula or pubis, partial coracoid, sternum, few sternal ribs, partial furcula, distal humerus, incomplete radius, incomplete ulna, femur, tibiotarsus, fibula, 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, phalanx IV-1, phalanx IV-2, phalanx IV-3, phalanx IV-4, pedal ungual IV, body feathers
Diagnosis- (after O'Connor, 2012) small, imperforate sternum without posterolateral or posteromedial processes; T-shaped posteromedian process; anteriorly forked, ventrally projecting sternal keel that does no extend to anterior margin; sternal keel low distally and continuous with posteromedian process; femorotibiotarsal ratio 82%; metatarsal I P-shaped with nearly parallel articular surfaces; large, curved pedal unguals.
Comments- This specimen has a number of controversial element identifications. An element identified as a scapula by Hou (1997) was identified as a pubis by Zhou and Hou (2002) and later as two dorsal ribs by O'Connor (2012). Another pubis identified by Zhou and Hou was unlabeled in Hou (1997), and identified as more dorsal ribs by O'Connor. The coracoid is interpreted as laying with its lateral edge against the sternum by Hou, but with its distal edge against the sternum in articulation by Zhou and Hou and O'Connor. Finally, an elongate bone was identified as a hypocleidium by Hou, but as part of the sternal keel by Zhou and Hou. Clarke (2002) and O'Connor agree with the former identification.
While initially identified as an euornithine (hiss Ornithurae) by Hou (1996) and most later non-cladistic studies, Clarke (2002), O'Connor et al. (2010) and O'Connor (2012) found it to be enantiornithine, the latter emphasizing the similarity of its sternum to Eoalulavis.
References- Hou, 1996. The discovery of a Jurassic carinate bird in China. Chinese Science Bulletin. 41(2), 1861-1864.
Hou, Martin, Zhou and Feduccia, 1996. Early adaptive radiation of birds: Evidence from fossils from northeastern China. Science. 274, 1164-1167.
Hou, 1997. A carinate bird from the Upper Jurassic of western Liaoning, China. Chinese Science Bulletin. 42(5), 413-417.
Hou, 1997. Mesozoic Birds of China. Phoenix Valley Bird Park. 221 pp.
Clarke, 2002. The morphology and systematic position of Ichthyornis Marsh and the phylogenetic relationships of basal Ornithurae. PhD thesis. 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, Berkeley, Los Angeles, London. 160-183.
O'Connor, Zhou and Zhang, 2010. A new look at 'old' birds from the Jehol fauna. Journal of Vertebrate Paleontology. Program and Abstracts 2010, 141A.
O'Connor, 2012. A revised look at Liaoningornis longidigitrus (Aves). Vertebrata PalAsiatica. 50(1), 25-37.

Vorones Zelenkov in Zelenkov and Kurochkin, 2015
Definition- (Vorona berivotrensis <- Gobipteryx minuta, Passer domesticus) (Zelenkov and Kurochkin, 2015)
Voroniformes Zelenkov in Zelenkov and Kurochkin, 2015
Comments- Vorones was named by Zelenkov in a Russian book chapter by Zelenkov and Kurochkin (2015) as a parvclass of euornithines (their Ornithurae) including Vorona, Mystiornis, Hollanda and Patagopteryx, each given their own order and family. Their definition of (translated) "birds that are more related to Vorona berivotrensis Forster et al., 1996 than Passer domesticus (Linnaeus, 1758) or Gobipteryx minuta Elzanowski, 1974". Given a placement of Vorona deeply nested within Enantiornithes as on this site, that definition could cover a large number of enantiornithine genera depending on the position of Gobipteryx.
Reference- 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.
Vorona Forster, Chiappe, Krause and Sampson, 1996
V. berivotrensis Forster, Chiappe, Krause and Sampson, 1996
Maastrichtian, Late Cretaceous
Maevarano Formation, Madagascar
Holotype- (UA 8651) (~510 mm) distal tibiotarsus, tarsometatarsus (60.9 mm; metatarsal II 53.8 mm, metatarsal III 61 mm, metatarsal IV 58.4 mm, metatarsal V 16.4 mm)
Paratype- (FMNH PA 715) (~540 mm) incomplete femur (93.7 mm), tibiotarsus (165.8 mm), incomplete fibula
Referred- (FMNH PA 717) incomplete femur (94.1 mm) (Forster et al., 2002)
?(FMNH PA 743) proximal humerus (Forster and O'Connor, 2000; described by O'Connor and Forster, 2010)
?(FMNH PA 744) partial humerus (~120 mm) (Forster and O'Connor, 2000; described by O'Connor and Forster, 2010)
?(FMNH PA 745) distal humerus (O'Connor and Forster, 2010)
?(FMNH PA 750) incomplete ulna (Forster and O'Connor, 2000; described by O'Connor and Forster, 2010)
(FMNH PA 782) tarsometatarsus (41.9 mm) (O'Connor and Forster, 2009; described by O'Connor and Forster, 2010)
(UA 9609) distal tibiotarsus (O'Connor and Forster, 2010)
?(UA 9749) partial humerus (O'Connor and Forster, 2010)
?(UA 9750) incomplete humerus (~79.4 mm) (O'Connor and Forster, 2010)
?(UA 9751) ulna (93.3 mm) (O'Connor and Forster, 2010)
(UA 9752) proximal tibiotarsus (O'Connor and Forster, 2009; described by O'Connor and Forster, 2010)
Comments- Using the tibiotarsus to estimate gives a length of 690 mm, while using the metatarsus gives a length of 460 mm. I decided to use tibial diameter, figuring this would remain more constant in different taxa. This gives the 540 mm estimate above, which seems appropriate. This is based off the referred specimen, the holotype was about 6% smaller, or about 510 mm long.
Two of the humeri were stated by Forster and O'Connor (2000) to belong to Vorona, probably FMNH PA 743 and 744 which were stated to correspond in size to Vorona by O'Connor and Forster (2010). The three other humeri are ~80% the size, but match in morphology. All of these are termed Humeral Taxon A by O'Connor and Forster and show a mix of enantiornithine and euornithine anatomy as Vorona does, so are tentatively referred to the taxon by those authors. The ulna speculated to belong to Vorona by Forster and O'Connor (2010) is probably FMNH PA 750 due to its large size, while O'Connor and Forster added UA 9751 which is 72% the size. Finally, O'Connor and Forster (2009) noted a small tibiotarsus and tarsometatarsus referrable to Vorona, which are UA 9752 (based on the reference to proximal details) and FMNH PA 782 respectively, described by O'Connor and Forster (2010) as Vorona in addition to distal tibiotarsus UA 9609.
References- Forster, Chiappe, Krause and Sampson, 1996. The first Cretaceous bird from Madagascar. Nature. 382, 532-534.
Forster and O'Connor, 2000. The avifauna of the Upper Cretaceous Maevarano Formation, Madagascar. Journal of Vertebrate Paleontology. 20(3), 41A-42A.
Forster, Chiappe, Krause and Sampson, 2002. Vorona berivotrensis, a primitive bird from the Late Cretaceous of Madagascar. In Chiappe and Witmer (eds.). Mesozoic Birds: Above the Heads of Dinosaurs. University of California Press. 268-280.
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.