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''Shastasaurus'' ("Mt. Shasta lizard") is an extinct genus of ichthyosaur from the middle and late Triassic, and is the largest marine reptile that has yet been found.〔Hilton, Richard P., ''Dinosaurs and Other Mesozoic Animals of California'', University of California Press, Berkeley 2003 ISBN 0-520-23315-8, at pages 90-91.〕 Specimens have been reported from the United States, Canada, and China. ==Description== ''Shastasaurus'' lived during the late Triassic period. The type species ''Shastasaurus pacificus'' is known from California. A second possible species of ''Shastasaurus'', ''S. sikanniensis'', is known from the Pardonet Formation British Columbia, dating to the middle Norian age (about 210 million years ago). If ''S. sikkanniensis'' belongs to ''Shastasaurus'', it would be the largest species, measuring up to . ''Shastasaurus'' was highly specialized, and differed considerably from other ichthyosaurs. It was very slender in profile. The largest specimens had a ribcage slightly less than deep despite a distance of over between its flippers.〔 Due to its unusually short, toothless snout (compared to the long, toothed, dolphin-like snouts of most ichthyosaurs) it was proposed that ''Shastasaurus'' was thought to be a suction feeder, feeding primarily on soft-bodied cephalopods〔 although current research indicates ichthyosaur jaws do not fit the suction-feeding profile. In ''S. liangae'', the only species with several well preserved skulls, the skull measures only 8.3% of the total body length (9.3% in a juvenile specimen). Unlike the related ''Shonisaurus'', even juvenile ''Shastasaurus'' completely lacked teeth. The snout was highly compressed via a unique arrangement of skull bones. Unlike almost all other reptiles, the nasal bone, which usually forms the mid part of the skull, extended to the very tip of the snout, and all bones of the snout tapered to abrupt points.〔 ''Shastasaurus'' 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 any species. The upper fluke of the tail was probably also much less developed than the shark-like tails 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）』 ■ウィキペディアで「Shastasaurus」の詳細全文を読む スポンサード リンク
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