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Microraptor
''Microraptor'' (Greek, μίκρος, ''mīkros'': "small"; Latin, ''raptor'': "one who seizes") was a genus of small, four-winged paravian (possibly dromaeosaurid) dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. They date from the early Cretaceous Jiufotang Formation (Aptian stage), 125 to 120 million years ago. Three species have been named (''M. zhaoianus'', ''M. gui'', and ''M. hanqingi''), though further study has suggested that all of them represent variation in a single species, which is properly called ''M. zhaoianus''. ''Cryptovolans'', initially described as another four-winged dinosaur, is usually considered to be a synonym of ''Microraptor''.〔Senter, P., Barsold, R., Britt, B.B., and Burnham, D.A. (2004). "Systematics and evolution of Dromaeosauridae (Dinosauria, Theropoda)." ''Bulletin of the Gunma Museum of Natural History'', 8: 1-20.〕
Like ''Archaeopteryx'', well-preserved fossils of ''Microraptor'' provide important evidence about the evolutionary relationship between birds and dinosaurs. ''Microraptor'' had long pennaceous feathers that formed aerodynamic surfaces on the arms and tail but also on the legs. This led paleontologist Xu Xing in 2003 to describe the first specimen to preserve this feature as a "four-winged dinosaur" and to speculate that it may have glided using all four limbs for lift. Subsequent studies have suggested that it is possible ''Microraptor'' were capable of powered flight as well.
''Microraptor'' were among the most abundant non-avian dinosaurs in their ecosystem, and the genus is represented by more fossils than any other dromaeosaurid, with possibly over 300 fossil specimens represented across various museum collections.〔
==Description==
With adult specimens ranging ) and with a weight estimated up to , ''Microraptor'' was among the smallest known non-avian dinosaurs.〔 Holtz estimated it longer at .〔Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'' (Winter 2010 Appendix. )〕 An even longer estimate, made by Benson ''et al.'' in 2012 found that ''Microraptor'' had a maximum length of .〔 Aside from their extremely small size, ''Microraptor'' were among the first non-avialan dinosaurs discovered with the impressions of feathers and wings. Seven specimens of ''M. zhaoianus'' have been described in detail, from which most feather impressions are known. Unusual even among early birds and feathered dinosaurs, ''Microraptor'' is one of the few known bird precursors to sport long flight feathers on the legs as well as the wings. Their bodies had a thick covering of feathers, with a diamond-shaped fan on the end of the tail (possibly for added stability during flight). Xu ''et al.'' (2003) compared the longer plumes on ''Microraptors head to those of the Philippine eagle. Bands of dark and light present on some specimens may indicate color patterns present in life,〔 though at least some individuals almost certainly possessed an iridescent black coloration.〔 Several anatomical features found in ''Microraptor'', such as a combination of unserrated and partially serrated teeth with constricted 'waists', and unusually long upper arm bones, are shared with both primitive avians and primitive troodontids. ''Microraptor'' is particularly similar to the basal troodontid ''Sinovenator''; in their 2002 description of two ''M. zhaoianus'' specimens, Hwang ''et al.'' note that this is not particularly surprising, given that both ''Microraptor'' and ''Sinovenator'' are very primitive members of two closely related groups, and both are close to the deinonychosaurian split between dromaeosaurids and troodontids.〔Hwang, S.H., Norell, M.A., Ji, Q., and Gao, K. (2002). "New Specimens of ''Microraptor zhaoianus'' (Theropoda: Dromaeosauridae) from Northeastern China." ''American Museum Novitates'', 3381: 44pp.〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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