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''Rangeroceras'' is an extinct nautiloid cephalopod genus that lived in what is now western North America during the latter part of the Early Ordovician. Shells of ''Rangeroceras'' are smooth, slightly depressed, rod-bearing orthocones with moderately large submarginal siphuncles. The siphuncular rods, which lie along the lower (ventral) side of the siphuncle interiors show thin, slightly undulating, growth lamellae in vertical longitudinal section, a somewhat unique feature. Dorsal annuli only begin to form when the rod has almost filled the entire siphncle toward to apical end. Connecting rings are thin, but layered. Cameral deposits are known from the dorsal side, the ventral side of the type specimen lost from erosion. Hook and Flower (1977) originally placed ''Rangeroceras'' in the Baltoceratidae because of the siphunclular rod and thin connecting rings. Evans (2005) proposed the family Rangeroceratidae for ''Rangeroceras'' and a somewhat similar genus ''Cyclorangeroceras'' from Great Britain and included them in the Dissidocerida. ''Rangeroceras'' is named for one of the characters, the range ranger, in the Tajar stories by Jane Shaw Ward. Other Tajar story based genera include ''Tajaroceras'', ''Wardoceras'', and ''Veneficoceras'' The type, ''Rangeroceras hintzei'' came from the Wahwah Limestone in the Ibex area in Western Utah. ==References== * Stephen C. Hook and Rousseau H. Flower 1977. Late Canadian (Zones J,K) Cephalopod Faunas from Southwestern United States. Memoir 32, New Mexico Bureau of Mines and Mineral Resources. 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「Rangeroceras」の詳細全文を読む スポンサード リンク
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