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Eutrephoceras
''Eutrephoceras'' is an extinct genus of nautilus from the Late Jurassic to the Miocene (around 161 to 5 million years ago). They are characterized by a highly rounded involute shell with slightly sinuous suture patterns.
==Description==
''Eutrephoceras'' typically possess nearly globular conchs (shells). The whorls are reniform (kidney-shaped) in cross section and broadly rounded on the sides and lower edge. On the upper edge it is only slightly curved. The surface of the shell is usually smooth, but can sometimes be sculptured. The suture patterns are slightly sinuous, though it can be more or less straight in some species. The umbilicus is small and barely noticeable, sometimes hidden altogether. The septa are averagely convex towards the tip. The siphuncle is small and circular in cross section. It can vary in position considerably and its placement is important in identifying different species under the genus, but it is never marginal.
Puncture marks made by teeth on several ''Eutrephoceras'' fossils (such as ''E. campbelli'', of the Trent River Formation in Vancouver) are cited as evidence of mososaur predation on this genus. 〔Ludvigsen, Rolf & Beard, Graham. 1997. West Coast Fossils: A Guide to the Ancient Life of Vancouver Island. pg. 117 〕
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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