Belongs within: Maniraptora.
Contains: Ornithothoraces.
Though the specific definition has varied from author to author, the clade Avialae has always effectively referred to the total group of all ‘birds’, i. e. the union of living birds with other flying fossil dinosaurs. Basal members of the clade such as Archaeopteryx and Jeholornis retained a long skeletal tail. Eleven specimens of Archaeopterygidae are known from the Late Jurassic of Europe; some authors have assigned all these specimens to a single species Archaeopteryx lithographica whereas others have recognised multiple species.
More derived avialans in the clade Pygostylia had the tail reduced as in modern birds. This clade includes the Confuciusornithidae from the lower Cretaceous Yixian Formation of China, which are characterised by toothless jaws with a hooked rostrum (Padian 2004).
Synapomorphies (from Holtz 1998): Vertebral foramen to cranial articular facet ratio of dorsals 0.4 or greater; less than 25 caudal vertebrae present; glenoid oriented laterally; proximal ulnar shaft arched; preacetabular portion of ilium significantly longer than postacetabular portion; ischial proximodorsal process just distal to iliac process; ischiadic terminal processes separate; proximal region of fibular medial face flat; metatarsal IV subequal in length to metatarsal II; metatarsal I completely reverted.
<==Avialae [Archaeornithes, Palaeoaves, Sauriurae] |--Aurornis Godefroit, Cau et al. 2013GC13 | `--*A. xui Godefroit, Cau et al. 2013GC13 `--+--Anchiornis huxleyiGC13 `--+--Archaeopterygidae [Archaeopterygiformes, Archaeopteryginae, Archaeornithidae]P04 | |--Wellnhoferia Elżanowski 2001P04 | | `--W. grandis Elżanowski 2001P04 | `--Archaeopteryx von Meyer 1861GC13, P04 (see below for synonymy) | |--A. bavarica Wellnhofer 1993P04 | `--A. lithographica von Meyer 1861 (see below for synonymy)P04 `--+--Xiaotingia Xu, You et al. 2011GC13, XY11 | `--*X. zhengi Xu, You et al. 2011XY11 `--+--+--Rahonavis Forster, Sampson et al. 1998GC13, P04 (see below for synonymy) | | `--R. ostromi (Forster, Sampson et al. 1998) [=Rahona ostromi Forster, Sampson et al. 1998]P04 | `--Shenzhouraptor Zhou & Zhang 2002GC13, D07 | `--S. sinensisD07 `--+--Balaur Csiki, Vremir et al. 2010GC13, CV10 | `--*B. bondoc Csiki, Vremir et al. 2010CV10 |--Jeholornis Zhou & Zhang 2002 [Jeholornithiformes]ZZ02 | `--*J. prima Zhou & Zhang 2002ZZ02 `--PygostyliaP04 |--+--JinguofortisidaeWSZ18 | | |--Chongmingia zhengi Wang et al. 2016WSZ18 | | `--Jinguofortis Wang, Stidham & Zhou 2018WSZ18 | | `--*J. perplexus Wang, Stidham & Zhou 2018WSZ18 | `--+--OrnithothoracesWSZ18 | `--Sapeornis Zhou & Zhang 2002P04 [SapeornithiformesWSZ18] | `--S. chaoyangensis Zhou & Zhang 2002P04 (see below for synonymy) `--ConfuciusornithiformesWSZ18 |--EoconfuciusornisWSZ18 `--ConfuciusornithidaeP04 |--YangavisWSZ18 |--Changchengornis Ji, Chiappe & Ji 1999P04 | `--C. hengdaoziensis Hi, Chiappe & Ji 1999P04 `--Confuciusornis Hou, Zhou et al. 1995GC13, P04 |--C. dui Hou, Martin et al. 1999P04 `--C. sanctus Hou, Zhou et al. 1995 (see below for synonymy)P04 Avialae incertae sedis: Jibeinia Hou 2000P04 `--J. luahera Hou 2000P04 Wileyia valdensis Harrison & Walker 1973 (n. d.)P04 Ilerdopteryx viai Lacasa-Ruiz 1991 (n. d.)P04 ‘Ornithomimus’ minutus Marsh 1892P04 Platannavis nana Nessov 1992 (n. d.)P04 Protoavis [Protoavidae]P04 `--P. texensis Chatterjee 1991 (n. d.)P04 Cuspirostrisornis Hou 1997D07 `--C. houiD07 Yandangornis Cai & Zhao 1999D07 `--Y. longicaudatusD07 Eurolimnornis [Limnornithidae]U93 `--E. corneti Kessler & Jurcsák 1984U93 Asiavis phosphatica Nessov 1986U93 Zhongjianornis yangiMWL11
Archaeopteryx von Meyer 1861GC13, P04 [incl. Archaeornis Petronievics in Petronievics & Woodward 1917P04, Griphosaurus Wagner 1861P04, Jurapteryx Howgate 1985P04]
Archaeopteryx lithographica von Meyer 1861 [incl. Pterodactylus crassipes von Meyer 1857, Archaeopteryx crassipes, Rhamphorhynchus crassipes, Scaphognathus crassipes, Griphornis longicaudatus Woodward 1862, Griphosaurus longicaudatus, Archaeopteryx macrura Owen 1862, Archaeopteryx oweni Petronievics 1921, Griphosaurus problematicus Woodward 1862, Archaeopteryx recurva Howgate 1984, Jurapteryx recurva, Archaeopteryx siemensii Dames 1897, Archaeornis siemensi]P04
Confuciusornis sanctus Hou, Zhou et al. 1995 [incl. C. chuonzhous Hou 1997, C. suniae Hou 1997]P04
Rahonavis Forster, Sampson et al. 1998GC13, P04 [incl. Rahona Forster, Sampson et al. 1998P04; Rahonavidae, Rahonaviformes]
Sapeornis chaoyangensis Zhou & Zhang 2002P04 [incl. Didactylornis jiiP10, Omnivoropteryx sinousaorumP10]
*Type species of generic name indicated
References
[CV06] Csiki, Z., M. Vremir, S. L. Brusatte & M. A. Norell. 2010. An aberrant island-dwelling theropod dinosaur from the Late Cretaceous of Romania. Proceedings of the National Academy of Sciences of the USA 107 (35): 15357–15361.
[D07] Dixon, D. 2007. The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. Hermes House: London.
[GC13] Godefroit, P., A. Cau, Hu D.-Y., F. Escuillié, Wu W. & G. Dyke. 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature 498: 359–362.
[MWL11] Meng, J., Y. Wang & C. Li. 2011. Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont. Nature 472: 181–185.
[P04] Padian, K. 2004. Basal Avialae. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 210–231. University of California Press: Berkeley.
[P10] Paul, G. S. 2010. Dinosaurs: A Field Guide. A & C Black.
[U93] Unwin, D. M. 1993. Aves. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 717–737. Chapman & Hall: London.
[WSZ18] Wang, M., T. A. Stidham & Z. Zhou. 2018. A new clade of basal Early Cretaceous pygostylian birds and developmental plasticity of the avian shoulder girdle. Proceedings of the National Academy of Sciences of the USA 115 (42): 10708–10713.
[XY11] Xu, X., H. You, K. Du & F. Han. 2011. An Archaeopteryx-like theropod from China and the origin of Avialae. Nature 475: 465–470.
[ZZ02] Zhou, Z., & F. Zhang. 2002. A long-tailed, seed-eating bird from the Early Cretaceous of China. Nature 418: 405–409.