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The Piloceratidae are a compressed, rapidly expanding, cyrtoconic brevicones with holochoanitic ventral siphuncles and simple endocones. Most likely evolved from ''Clitendoceras'', a narrow, slightly endogastric genus intermediate in form between straight shelled ''Proendoceras'' and the bulkier Piloceratidae. Found in shallow carbonate marine sediments of Demingian through the Cassinian age, (essentially Arenigian, = early Middle -Upper Canadian) . Pilocerids split off from the Proterocameroceratidae very shortly after their inception and are the first family which the proterocamerocerids gave rise to. With the exception of Humeoceras, found in the middle Silurian, pilocerid genera are limited to the Lower Ordovician (Canadian in North America). The general shape of the pilocerid shell precludes an ambush predator lying in wait on the sea floor, or a stealthful hunter drifting through the water. Rather, they probably crawled over the sea floor, head down with the shell off the bottom, searching for prey. Nothing is known of their soft part anatomy, other than what can be surmised from the fact they are cephalopods. They likely possessed tentacles of some sort, but were they numerous like those of modern Nautilus, limited to eight or ten as with octopus or squid, or of some other arrangement. Pilocerid genera include the strongly curved ''Piloceras'', ''Bisonoceras'' with its hooked bison horn shape, nearly straight ''Allopiloceras'', ''Dartonoceras'', and internally complex ''Cassinoceras''. Ecologically the Piloceratidae were replaced in the Middle Ordovician by the Cyrtendoceradae,which may have evolved early from the Endoceratidae rather than being direct pilocerid descendents. == References == *Flower 1950 in Flower and Kümmel; A Classification of the Nautiloidea; Jour Paleon V.24, n 5, pp 604–616, 1 text-fig, Sept 1950. *– – 1955, Status of Endoceroid Classification; Jour. Paleon. V 29. n.3, pp 327–370, May 1955 *– – 1976, Ordovician Cephalopod Faunas and Their Role in Correlation, pp 531–537 in The Ordovician System: Proceedings of a Paleontological Association Symposium; Univ of Wales and Welsh Nat’l Mus Press. 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「Piloceratidae」の詳細全文を読む スポンサード リンク
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