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Avialans
Temporal range: Late JurassicPresent, 160–0 Ma
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Fossil specimen of Archaeopteryx lithographica
Scientific classification Red Pencil Icon
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauria
Clade: Eumaniraptora
Clade: Avialae
Gauthier, 1986
Subgroups


Avialae ("bird wings") is a clade of dinosaurs containing their only living representatives, birds (Aves), and the most immediate extinct relatives of birds.

Competing definitions

Systematic studies of the Avialae have produced different results depending on the specimens included and the definitions used. Including or excluding Archaeopteryx from the group Aves has a large effect on the subgroups of Avialae. Archaeopteryx, from the late Jurassic Period, may be the earliest known theropod dinosaur which may have had the capability of powered flight.[1] If Archaeopteryx is defined as an avian, then there are few non-avian avialans.

Character-based definition

Avialae is traditionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier named Avialae in 1986, and first defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight, and the birds that descended from them.[2][3]

Avialae vs. Aves

Gauthier[3] (page 34) identified four conflicting ways of defining the term "Aves", which is a problem because the same biological name is being used four different ways. Gauthier 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. He assigned other names to the other groups.

  1. Aves can mean those advanced archosaurs with feathers (alternately Avifilopluma)
  2. Aves can mean those that fly (alternately Avialae)
  3. Aves can mean all reptiles closer to birds than to crocodiles (alternately Panaves)
  4. Aves can mean the last common ancestor of all the currently living birds and all of its descendants (a "crown group"). (alternately Neornithes)

Under the fourth definition Archaeopteryx is an avialan, and not a member of Aves.

Branch-based definition

Several authors have use a similar, but branch-based, definition; "all theropods closer to birds than to Deinonychus."[4][5]

The cladogram below follows the results of a phylogenetic study by Gao and colleagues in 2002. Note that these authors used the more inclusive, node-based definition of Aves.[6] The placement of scansoriopterygids follows Zhang et al., 2008.[7]

Avialae


Scansoriopterygidae


Aves


Archaeopteryx




Jeholornis




Zhongornis


Pygostylia


Confuciusornithidae




Sapeornis


Ornithothoraces


Enantiornithes



Ornithuromorpha









Non-Avian Avialans

There are three taxa that are not members of Aves, but are avialans, in any definition of Avialae listed above.

Senter (2007) placed Scansoriopteryx as a sister group to Archaeopteryx within Avialae.[8] The age of the Daohugou Beds where Scansoriopteryx was collected may be Middle Jurassic; older than Archaeopteryx. A study by Zhang et al. (2008) confirmed that Scansoriopteryx was within Avialae and also added a new taxon, Epidexipteryx.[7]

References

  1. ^ Alonso, P. D., Milner, A. C., Ketcham, R. A., Cookson, M. J. & Rowe, T. B. (2004). The avian nature of the brain and inner ear of Archaeopteryx. Nature. 430(7000): 666–669. PMID 15295597. doi:10.1038/nature02706. PDF fulltext Supplementary info
  2. ^ 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.)
  3. ^ a b Gauthier, J., and de Queiroz, K. (2001). "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.
  4. ^ Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.) (2004). The Dinosauria, Second Edition. University of California Press., 861 pp.
  5. ^ Senter, P. (2007). "A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda)." Journal of Systematic Palaeontology, (doi:10.1017/S1477201907002143).
  6. ^ Gao, C.; Chiappe, L.; Meng, Q.; O'Connor, J.K.; Wang, X.; Cheng, X.; Liu, J. (2008). "A new basal lineage of Early Cretaceous birds from China and its implications on the evolution of the avian tail". Palaeontology. 51 (4): 755–791. 
  7. ^ a b Zhang, F.; Zhou, Z.; Xu, X.; Wang, X.; Sullivan, C. (2008). "A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers". Nature. 455 (7216): 1105–1108. Bibcode:2008Natur.455.1105Z. PMID 18948955. doi:10.1038/nature07447. 
  8. ^ Senter, Phil (2007). "A new look at the phylogeny of Coelurosauria (Dinosauria, Theropoda)". Journal of Systematic Palaeontology. 5 (4): 429–463. doi:10.1017/S1477201907002143. 

See also

Hemipus picatus This article is part of Project Bird Taxonomy, a All Birds project that aims to write comprehensive articles on every order, family and other taxonomic rank related to birds.
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