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Avialae ("bird wings") is a clade of dinosaurs containing their only living representatives, the birds. It is usually defined as all theropod dinosaurs more closely related to modern birds (Aves) than to deinonychosaurs, though alternate definitions are occasionally used (see below). ''Archaeopteryx lithographica'', from the late Jurassic Period Solnhofen Formation of Germany, is the earliest known avialan which may have had the capability of powered flight.〔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. . (PDF fulltext ) (Supplementary info )〕 However, several older avialans are known from the late Jurassic Tiaojishan Formation of China, dated to about 160 million years ago. == 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''."〔Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.) (2004). ''The Dinosauria'', Second Edition. University of California Press., 861 pp.〕〔Senter, P. (2007). "A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda)." ''Journal of Systematic Palaeontology'', ().〕 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. 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. Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier, who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight, and the birds that descended from them.〔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.)〕〔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.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Avialae」の詳細全文を読む スポンサード リンク
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