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Shonisaurus
''Shonisaurus'' is a genus of ichthyosaur. At least 37 incomplete fossil specimens of the marine reptile have been found in the Luning Formation of Nevada, USA. This formation dates to the late Carnian age of the late Triassic period, about 215 million years ago.
==Description==
''Shonisaurus'' lived during the Norian stage of the late Triassic period. ''S. popularis'' measured around long. A second species from British Columbia was named ''Shastasaurus sikanniensis'' in 2004. ''S. sikkanniensis'' was one of the largest marine reptiles of all time, measuring . However, phylogenetic studies later showed ''S. sikanniensis'' to be a species of ''Shastasaurus'' rather than ''Shonisaurus''.
''Shonisaurus'' had a long snout, and its flippers were much longer and narrower than in other ichthyosaurs. While ''Shonisaurus'' was initially reported to have had socketed teeth (rather than teeth set in a groove as in more advanced forms), these were present only at the jaw tips, and only in the very smallest, juvenile specimens. All of these features suggest that ''Shonisaurus'' may be a relatively specialised offshoot of the main ichthyosaur evolutionary line. It was historically depicted with a rather rotund body, but studies of its body shape since the early 1990s have shown that the body was much more slender than traditionally thought. ''S. popularis'' had a relatively deep body compared with related marine reptiles.〔
''Shonisaurus'' was also traditionally depicted with a dorsal fin, a feature found in more advanced ichthyosaurs. However, other shastasaurids likely lacked dorsal fins, and there is no evidence to support the presence of such a fin in ''Shonisaurus''. The upper fluke of the tail was probably also much less developed than flukes found in later species.〔Wallace, D.R. (2008). ''Neptune's Ark: From Ichthyosaurs to Orcas''. University of California Press, 282pp.〕
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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