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Acaroceratidae is family of Upper Cambrian (Trempealeauan) nautiloid cephalopods included in the Ellesmerocerida that contains two known genera, ''Acaroceras'' and ''Weishanuceras'', both found in northern China. Acaroceratidae represent some of the earliest Ellesmeroderida, which have their origin in the Plectronoceratidae, either in ''Plectronoceras'' or some related genus. ''Acaroceras'' is known from the lower and middle Trempealeauan, upper Yenchou and overlying Wanwankou members of the Fengshan Formation. ''Weishanuceras'' is so far limited to the Wanwankou. The Acaroceratidae are characterized by small, slightly expanded, laterally compressed shells with a slight downward,(endogastric), curvature. Siphuncles are tubular, located along the ventral margin; composed of straight segments. In general conformation ''Acaroceras'' and ''Weishanuceras'' are rather similar, but differ in the details of the siphuncle. ''Acaroceras'', the earlier of the two, has a siphuncle composed of short straight septal necks and thin straight connecting rings, and is empty of internal calcarous deposits. Rather thin, slightly concave diaphragms are present in the early, adapical, portion. ''Weishanuceras'', which came later, also has short straight septal necks, but connecting rings are moderately thick as well as straight, and the siphuncle contains internal, ring-like deposits. Neither of the Acaroceratidae appears to have left any descendants. Early ''Acaroceras'', from the upper Yenchou, are contemporary with later ''Plectronoceras'', early ''Paraplectronoceras'', ''Hunyuanoceras'', and a few others. Later ''Acaroceras'' and ''Weishanuceras'' are part of the entire suite of early cephalopods that lived during the Late Cambrian. ''Acaroceras'' lends its name to the ''Acaroceras-Sinoceremoceras'' Zone which is contained by the Wanwankou member of the Fengshan Formation. ==References== *Chen Jun-yuan and Curt Teichert, 1983. Cambrian Cephalopods. Geology V.11, p 647-650, Nov 1983 *Chen Jun-yuan Zou Xi-ping & Chen Ting-en, 1979 Late Cambrian Ellesmerocerida (Cephalopoda) of North China. Acta Paleontologica Sinica 1979-02 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「Acaroceratidae」の詳細全文を読む スポンサード リンク
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