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''Tienoceras''is an orthoceratoid genus from the Permian of China (Hunan). Orthoceratoids are slender conical or near cylindrial, orthoconic, nautiloid cephalopods from the Paleozoic. Nautiloids, which include a number of different extinct orders, were far more diverse and numerous in the past, but are represented today by only two closely related genera. ''Teinoceras'' is represented by a smooth orthocone that enlarges slightly with growth and that has a lenticular (i.e. "lens-shaped") cross section. The middle of the dorsum and venter (top and bottom) are flattened or depressed and the dorsolateral and ventrolateral areas have longitudinal depressions. Sutures, formed where septa join the outer wall, have mid-dorsal, mid-ventral, and sharp lateral lobes separated by narrow ventrolateral and dorsolateral saddles. The siphuncle, which is small, runs through the middle. The exact relationship of ''Tienoceras'' within the orthoceratoids is unknown. ==References== * Sweet, W.C. 1964; Nautiloidea --Orthocerida, in the Treatise on Invertebrate Paleontology, Part K Nautiloidea; Geological Society of America and University of Kansas press * Sepkoski, J.J. Jr. 2002. A compendium of fossil marine animal genera. ''Bulletins of American Paleontology'' 363: 1–560. () 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「Tienoceras」の詳細全文を読む スポンサード リンク
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