Avialae

{{Short description|Clade including all birds and their ancestors}} {{Automatic taxobox | name = Avialans | fossil_range = Middle Jurassic–Present, {{Fossil range|150.8|0|earliest=165|ref=<ref>{{Cite journal |last=Schweigert |first=G. |year=2007 |title=Ammonite biostratigraphy as a tool for dating Upper Jurassic lithographic limestones from South Germany – first results and open questions |journal=Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen |volume=245 |issue=1 |pages=117–125 |doi=10.1127/0077-7749/2007/0245-0117|bibcode=2007NJGPA.245..117S |s2cid=140597349 |url=http://doc.rero.ch/record/13825/files/PAL_E722.pdf }}</ref>}}<small>Earliest 165 Ma if Anchiornithidae are members<ref>{{cite journal | last1 = Zhang | first1 = H. | last2 = Wang | first2 = M. | last3 = Liu | first3 = X. | year = 2008 | title = Constraints on the upper boundary age of the Tiaojishan Formation volcanic rocks in West Liaoning-North Hebei by LA-ICP-MS dating | journal = Chinese Science Bulletin | volume = 53 | issue = 22| pages = 3574–3584 | doi = 10.1007/s11434-008-0287-4| bibcode = 2008SciBu..53.3574Z }}</ref></small> | image = Jeholornis prima NMNS.jpg | image_caption = Fossil specimen of ''Jeholornis prima'' | image2 = A special composite of birds.jpg | image2_caption = Collage of four extant birds. Clockwise from top-left: Spanish imperial eagle (''Aquila adalberti''), common ostrich (''Struthio camelus''), mallard (''Anas platyrhynchos''), and common kingfisher (''Alcedo atthis'') | taxon = Avialae | display_parents = 2 | authority = Gauthier, 1986 | subdivision_ranks = Subgroups | subdivision = *{{extinct}}''Alcmonavis'' *{{extinct}}''Baminornis''<ref>{{cite journal |last1=Chen |first1=Runsheng |last2=Wang |first2=Min |last3=Dong |first3=Liping |last4=Zhou |first4=Guowu |last5=Xu |first5=Xing |last6=Deng |first6=Ke |last7=Xu |first7=Liming |last8=Zhang |first8=Chi |last9=Wang |first9=Linchang |last10=Du |first10=Honggang |last11=Lin |first11=Ganmin |last12=Lin |first12=Min |last13=Zhou |first13=Zhonghe |title=Earliest short-tailed bird from the Late Jurassic of China |journal=Nature |date=February 2025 |volume=638 |issue=8050 |pages=441–448 |doi=10.1038/s41586-024-08410-z |pmid=39939791 |bibcode=2025Natur.638..441C |url=https://www.nature.com/articles/s41586-024-08410-z |language=en |issn=1476-4687|url-access=subscription }}</ref> *{{extinct}}''Cretaaviculus'' *{{extinct}}''Dalianraptor'' *{{extinct}}''Fukuipteryx'' *{{extinct}}''Gargantuavis''? *{{extinct}}''Jixiangornis'' *{{extinct}}''Tingmiatornis''? *{{extinct}}''Yandangornis'' *{{extinct}}''Zhongornis'' *{{extinct}}'''Jeholornithidae''' *'''Avebrevicauda''' <small>Paul, 2002</small> **{{extinct}}'''Omnivoropterygidae'''? **'''Pygostylia''' {{Collapse top|title=Possible avialans |left=yes|padding=0|border=0|border2=0|bg=clear|bg2=clear}} *{{extinct}}''Archaeopteryx'' *{{extinct}}''Balaur'' *{{extinct}}''Hesperonychus'' *{{extinct}}''Overoraptor'' *{{extinct}}''Rahonavis'' *{{extinct}}''Wellnhoferia'' *{{extinct}}''Yixianosaurus'' *{{extinct}}'''Anchiornithidae''' *{{extinct}}'''Scansoriopterygidae''' *{{extinct}}'''Unenlagiinia'''<ref name="Motta2025">{{cite journal |last1=Motta |first1=Matías J. |last2=Agnolína |first2=Federico L. |last3=Eglia |first3=Federico Brissón |last4=Rozadillaa |first4=Sebastián |last5=Novas |first5=Fernando E. |title=Phylogenetic relationships of Unenlagiidae among Paraves (Dinosauria) |journal=Journal of Systematic Palaeontology |date=22 Aug 2025 |volume=23 |issue=1 |article-number=2529608 |doi=10.1080/14772019.2025.2529608 |bibcode=2025JSPal..2329608M |url=https://www.tandfonline.com/doi/full/10.1080/14772019.2025.2529608 |access-date=22 August 2025|url-access=subscription }}</ref> {{Collapse bottom}} }}

'''Avialae''' ("bird wings") is a clade containing the only living dinosaurs, the birds, and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used (see below).

''Archaeopteryx lithographica'', from the late Jurassic Period Solnhofen Formation of Germany, is usually considered the earliest known avialan which may have had the capability of powered flight;<ref name="Alonso">{{cite journal|last1=Alonso |first1=P. D. |last2=Milner |first2=A. C. |last3=Ketcham |first3=R. A. |last4=Cookson |first4=M. J. |last5=Rowe |first5=T. B. |year=2004 |title=The avian nature of the brain and inner ear of ''Archaeopteryx'' |url=http://www.ucm.es/info/paleo/personal/patricio/DMKCR-2004.pdf |journal=Nature |volume=430 |issue=7000 |pages=666–669 |doi=10.1038/nature02706 |pmid=15295597 |archive-url=https://web.archive.org/web/20060209193641/http://www.ucm.es/info/paleo/personal/patricio/DMKCR-2004.pdf |archive-date=2006-02-09 |bibcode=2004Natur.430..666A |s2cid=4391019 }} [http://www.nature.com/nature/journal/v430/n7000/suppinfo/nature02706.html Supplementary info]</ref> a minority of studies have suggested that it might have been a deinonychosaur instead.<ref name=":0">{{Cite journal|last1=Hartman|first1=Scott|last2=Mortimer|first2=Mickey|last3=Wahl|first3=William R.|last4=Lomax|first4=Dean R.|last5=Lippincott|first5=Jessica|last6=Lovelace|first6=David M.|date=2019-07-10|title=A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight|journal=PeerJ|volume=7|article-number=e7247|doi=10.7717/peerj.7247|issn=2167-8359|pmc=6626525|pmid=31333906 |doi-access=free }}</ref> Several older (but non flight-capable) possible avialans are known from the late Jurassic Tiaojishan Formation of China, dated to about 160 million years ago.<ref name="Hu et al.2009">{{cite journal |last1=Hu |first1=D. |last2=Hou |first2=L. |last3=Zhang |first3=L. |last4=Xu |first4=X. |name-list-style=amp |year=2009 |title=A pre-''Archaeopteryx'' troodontid theropod from China with long feathers on the metatarsus |journal=Nature |volume=461 |issue=7264 |pages=640–643 |doi=10.1038/nature08322|pmid=19794491|bibcode=2009Natur.461..640H |s2cid=205218015 }}</ref><ref name=daohugouage2012>{{cite journal |author1=Liu Y.-Q. |author2=Kuang H.-W. |author3=Jiang X.-J. |author4=Peng N. |author5=Xu H. |author6=Sun H.-Y. |year=2012 |title=Timing of the earliest known feathered dinosaurs and transitional pterosaurs older than the Jehol Biota |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=323–325 |pages=1–12 |doi=10.1016/j.palaeo.2012.01.017 |bibcode=2012PPP...323....1L }}</ref>

== Definition == Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used a definition similar to "all theropods closer to birds than to ''Deinonychus''."<ref name="weishampel2004">Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.) (2004). ''The Dinosauria'', Second Edition. University of California Press., 861 pp.</ref><ref name="senter2007">{{cite journal | last1 = Senter | first1 = P | year = 2007 | title = A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda) | journal = Journal of Systematic Palaeontology | volume = 5| issue = 4| pages = 429–463| doi = 10.1017/S1477201907002143 | bibcode = 2007JSPal...5..429S | s2cid = 83726237 }}</ref> A nearly identical definition, "the theropod group that includes all taxa closer to ''Passer'' than to ''Dromaeosaurus''", was used by Agnolín and Novas (2013) for their clade Averaptora, operating under the assumption that troodontids and birds were more closely related to each other than to dromaeosaurs. They also redefine Avialae as the smallest clade containing ''Archaeopteryx'' and modern birds.<ref name=avianancestry>{{cite book|author1=Federico L. Agnolín |author2=Fernando E. Novas |name-list-style=amp |year=2013 |title=Avian ancestors. A review of the phylogenetic relationships of the theropods Unenlagiidae, Microraptoria, ''Anchiornis'' and Scansoriopterygidae |pages=1–96 |doi=10.1007/978-94-007-5637-3 |series=SpringerBriefs in Earth System Sciences |isbn=978-94-007-5636-6 |s2cid=199493087 }}</ref>

Additionally, beginning in the late 2000s and early 2010s, several groups of researchers began adding the genus ''Troodon'' as an additional specifier in the definition of Avialae. ''Troodon'' had long been considered a close relative of the dromaeosaurids in the larger group Deinonychosauria, though some contemporary studies found it and other troodontids more closely related to modern birds, and so it has been specifically excluded from Avialae in more recent studies.<ref name=Nature>{{cite journal|author1=Pascal Godefroit |author2=Andrea Cau |author3=Hu Dong-Yu |author4=François Escuillié |author5=Wu Wenhao |author6=Gareth Dyke |year=2013 |title=A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds |journal=Nature |volume= 498|issue= 7454|pages= 359–62|doi=10.1038/nature12168 |bibcode = 2013Natur.498..359G |pmid=23719374|s2cid=4364892 }}</ref>

Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on derived characteristics that were not present among lineage predecessors). Jacques Gauthier, who named Avialae in 1986, redefined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight, and the birds that descended from them.<ref name="gauthier1986">Gauthier, J. (1986). "Saurischian monophyly and the origin of birds." In: K. Padian, ed. ''The origin of birds and the evolution of flight.'' San Francisco: California, Acad.Sci. pp.1–55. (Mem.Calif.Acad.Sci.8.)</ref><ref name="gauthier&dequeiroz2001">Gauthier, J., and de Queiroz, K. (2001). "[https://repository.si.edu/bitstream/handle/10088/4690/2001Gau_deQOst.pdf Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and the name Aves]." Pp. 7-41 in ''New perspectives on the origin and early evolution of birds: proceedings of the International Symposium in Honor of John H. Ostrom'' (J. A. Gauthier and L. F. Gall, eds.). Peabody Museum of Natural History, Yale University, New Haven, Connecticut, U.S.A.</ref> The clade '''Avialae''' was given a formal phylogenetic definition in the ''PhyloCode'' by Juan Benito and colleagues in 2022 as "the largest clade containing ''Vultur gryphus'', but not ''Dromaeosaurus albertensis'' and ''Saurornithoides mongoliensis''".<ref name="benitoetal2022">{{cite journal |last1=Benito |first1=J. |last2=Chen |first2=A. |last3=Wilson |first3=L.E. |last4=Bhullar |first4=B.S. |last5=Burnham |first5=D. |last6=Field |first6=D.J. |title=Forty new specimens of ''Ichthyornis'' provide unprecedented insight into the postcranial morphology of crownward stem group birds |journal=PeerJ |date=2022 |volume=10 |article-number=e13919 |doi=10.7717/peerj.13919|doi-access=free |pmid=36545383 |pmc=9762251}}</ref> This definition ensures that both dromaeosaurids and troodontids are excluded from '''Avialae'''.<ref name="benitoetal2022"/>

Most members of Avialae, in contrast to other theropods, have lost the proatlas bones of the neck,<ref name="Korneisel2025">{{Cite journal|doi=10.1111/brv.70053|last1=Korneisel|first1=Dana E.|last2=Maddin|first2=Hillary C.|title=Review of the tetrapod skull–neck boundary: implications for the evolution of the atlas–axis complex|journal=Biological Reviews|date=2025-07-22|pmc=12586291}}</ref> though they are present in ''Archaeopteryx''.<ref>{{Cite journal |last=O’Connor |first=Jingmai |last2=Clark |first2=Alexander |last3=Kuo |first3=Pei-Chen |last4=Kiat |first4=Yosef |last5=Fabbri |first5=Matteo |last6=Shinya |first6=Akiko |last7=Van Beek |first7=Constance |last8=Lu |first8=Jing |last9=Wang |first9=Min |last10=Hu |first10=Han |date=2025-05-29 |title=Chicago Archaeopteryx informs on the early evolution of the avian bauplan |url=https://www.nature.com/articles/s41586-025-08912-4 |journal=Nature |language=en |volume=641 |issue=8065 |pages=1201–1207 |doi=10.1038/s41586-025-08912-4 |issn=0028-0836|url-access=subscription }}</ref>

=== Differentiation from Aves === Gauthier and de Queiroz<ref name="gauthier&dequeiroz2001" /> (page 34) identified four conflicting ways of defining the term "Aves", which is a problem since the same biological name is being used four different ways. They proposed a solution, number 4 below, which is to reserve the term '''Aves''' only for the crown group, the last common ancestor of all living birds and all of its descendants. Other definitions of Aves found in literature were reassigned to other clade names.

# Aves can mean all reptiles closer to birds than to crocodiles (alternatively Avemetatarsalia [=Panaves]) # Aves can mean those advanced archosaurs with feathers (alternatively Avifilopluma) # Aves can mean those feathered dinosaurs that can fly (alternately Avialae) # Aves can mean the last common ancestor of all the currently living birds and all of its descendants (a "crown group"). (alternatively Neornithes)

Under the fourth definition ''Archaeopteryx'' is an avialan, and not a member of Aves. Gauthier's proposals have been adopted by many researchers in the field of paleontology and bird evolution, though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is sometimes used synonymously with the vernacular term "bird" by these researchers.<ref name=Nature />

== Evolution == {{See also|Origin of birds|List of fossil bird genera}} {{Cladogram|caption=Cladogram following the results of a phylogenetic study by Wang ''et al.'', 2016.<ref name=wangetal2016>{{cite journal | last1 = Wang | first1 = M. | last2 = Wang | first2 = X. | last3 = Wang | first3 = Y. | last4 = Zhou | first4 = Z. | year = 2016 | title = A new basal bird from China with implications for morphological diversity in early birds | journal = Scientific Reports | volume = 6 | article-number = 19700 | doi = 10.1038/srep19700 | pmid=26806355 | pmc=4726217| bibcode = 2016NatSR...619700W }}</ref>|clades= {{clade| style=font-size:80%;line-height:80% |label1='''Avialae''' |1={{clade |1=†''Anchiornis'' |2={{clade |1=†''Archaeopteryx'' |2={{clade |1=†''Rahonavis'' |2={{clade |1={{clade |1=†''Jixiangornis'' |2=†''Jeholornis'' 50 px}} |label2=Avebrevicauda |2={{clade |1=†''Sapeornis'' |2={{clade |1=†''Confuciusornis'' 50 px |2={{clade |1=†''Chongmingia'' |2=Ornithothoraces 20 px }} }} }} }} }} }} }} }} }} The earliest known avialans come from the Tiaojishan Formation of China, which has been dated to the late Jurassic period (Oxfordian stage), about 160 million years ago.<ref name="Nature" /> The avialan species from this time period include ''Anchiornis huxleyi'' and ''Aurornis xui''. ''Xiaotingia zhengi'' used to be considered a member, but was later classified within the clade Dromaeosauridae. The well-known ''Archaeopteryx'' dates from slightly later Jurassic rocks (about 155 million years old) from Germany. Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds, but were later lost during bird evolution. These features include enlarged claws on the second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering.<ref name="zhengetal2013">{{cite journal | last1 = Zheng | first1 = X. | last2 = Zhou | first2 = Z. | last3 = Wang | first3 = X. | last4 = Zhang | first4 = F. | last5 = Zhang | first5 = X. | last6 = Wang | first6 = Y. | last7 = Wei | first7 = G. | last8 = Wang | first8 = S. | last9 = Xu | first9 = X. | year = 2013 | title = Hind Wings in Basal Birds and the Evolution of Leg Feathers | journal = Science | volume = 339 | issue = 6125| pages = 1309–1312 | doi = 10.1126/science.1228753 | pmid = 23493711 |bibcode = 2013Sci...339.1309Z | citeseerx = 10.1.1.1031.5732 | s2cid = 206544531 }}</ref> It is also thought that early avialans were either cranially akinetic or had otherwise limited cranial kinesis.<ref name="wang2021">{{cite journal | title = Cretaceous bird with dinosaur skull sheds light on avian cranial evolution | last1 = Wang | first1 = M. | last2 = Stidham | first2 = T.A. | last3 = Li | first3 = Z. | last4 = Xu | first4 = X. | last5 = Zhou | first5 = Z. | journal = Nature Communications | date = 2021 | volume = 12 | issue = 1 | page = 3890 | pmid=34162868 | doi = 10.1038/s41467-021-24147-z |pmc=8222284| bibcode = 2021NatCo..12.3890W }}</ref><ref name="hu2019">{{cite journal | title = Evolution of the vomer and its implications for cranial kinesis in Paraves | date = 2019 | first1 = H. | last1 = Hu | first2 = G. | last2 = Sansalone | first3 = S. | last3 = Wroe | first4 = P.G. | last4 = McDonald | first5 = J.K. | last5 = O'Connor | first6 = Z. | last6 = Li | first7 = X | last7 = Xu | first8 = Z. | last8 = Zhou | journal = PNAS | volume = 116 | issue = 39 | pages = 19571–19578 | doi = 10.1073/pnas.1907754116| pmid = 31501339 | pmc=6765239 | bibcode = 2019PNAS..11619571H | doi-access = free }}</ref>

Avialans diversified into a wide variety of forms during the Cretaceous Period.<ref name="chiappe2007">{{cite book|last=Chiappe |first=Luis M. |year=2007 |title=Glorified Dinosaurs: The Origin and Early Evolution of Birds |location=Sydney |publisher=University of New South Wales Press |isbn=978-0-86840-413-4}}</ref> Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves). While the earliest forms, such as ''Archaeopteryx'' and ''Shenzhouraptor'', retained the long bony tails of their ancestors,<ref name="chiappe2007" /> the tails of more advanced avialans were shortened with the advent of the pygostyle bone in the group Pygostylia. In the late Cretaceous, around 95 million years ago, the ancestor of all modern birds also evolved a better sense of smell.<ref>{{cite web|url=http://archive.cosmosmagazine.com/news/birds-survived-dino-extinction-with-keen-senses/ |title=Birds survived dino extinction with keen senses |access-date=11 June 2012 |author=Agency France-Presse |date=13 April 2011 |publisher=Cosmos Magazine |archive-url=https://web.archive.org/web/20150402124421/http://archive.cosmosmagazine.com/news/birds-survived-dino-extinction-with-keen-senses/ |archive-date=2 April 2015 }}</ref>

The following cladogram is based on the analysis by Hartman ''et al''. (2019), which found flight likely evolved five separate times among paravian dinosaurs, two of those among Avialae (in Scansoriopterygids and other avialans). ''Archaeopteryx'' and "anchiornithids" were placed in Deinonychosauria, Avialae's sister group.<ref name=":0" />

{{clade |label1=Paraves |1={{clade |label1=†Deinonychosauria |1={{clade |1=†Archaeopterygidae |2={{clade |1=†Unenlagiidae |2={{clade |1=†Dromaeosauridae |2=†Troodontidae }} }} }} |label2='''Avialae''' |2={{clade |1=†Scansoriopterygidae |2={{clade |1=†''Yandangornis'' |2={{clade |1={{clade |1=†''Bauxitornis'' |2=†''Balaur'' }} |2={{clade |1=†''Shenzhouraptor'' |2={{clade |1=†''Jixiangornis'' |2={{clade |1={{clade |1=†''Zhongornis'' |2=†''Sapeornis'' }} |2={{clade |1=†Confuciusornithidae |2={{clade |1=†''Changchengornis'' |2={{clade |1=†''Chongmingia'' |2={{clade |1=†''Jinguofortis'' |2={{clade |1=†''Zhongjianornis'' |2=Ornithothoraces }} }} }} }} }} }} }} }} }} }} }} }} }}

In a study conducted in 2020, ''Archaeopteryx'' was recovered as an avialan.<ref name=Cau2020>{{Cite journal|last=Cau|first=Andrea|date=2020-02-25|title=The body plan of Halszkaraptor escuilliei (Dinosauria, Theropoda) is not a transitional form along the evolution of dromaeosaurid hypercarnivory|journal=PeerJ|language=en|volume=8|article-number=e8672|doi=10.7717/peerj.8672|issn=2167-8359|pmid=32140312|pmc=7047864 |doi-access=free }}</ref>

== See also == {{Portal|Dinosaurs}} * Bird flight * Feathered dinosaur

==References==<!-- ActaPalaeontolPol47:97. --> {{Reflist|30em}}

{{Paraves|A.}} {{Taxonbar|from=Q782930}}

Category:Avialae Category:Bird clades