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''Campbelloceras'' is a tarphyceratid nautiloid known from the Lower Ordovician, Upper Canadian Epoch of North America, where it is widespread. ''Campbelloceras'' was named by Ulrich and Foerste in 1936. The shell of ''Campbelloceras'' has a circular whorl section, only slightly impressed, and a siphuncle that is close to the venter in all growth stages. ''Campbelloceras'' differs from ''Tarphyceras'' in that the rate of expansion is greater, the siphuncle is proportionally largers, and an impression is shallower. ''Campbelloceras'' may have given rise to the barrandeocerid ''Plectoceras'' (Plectoceratidae) through simplification of the connecting rings, and to ''Tarphyceras'' through tighter coiling, development of a deeper impression, and reduction in the size of the siphuncle. ''Campbelloceras'' may be conceivably derived from ''Estonioceras'' (Estonioceratidae). The cross section of ''Campbelloceras'' and that of the outer whorl of ''Estonioceras'' are similar, except for ''Campbelloceras'' being slightly impressed. Both have proportionally large siphuncles, near the venter. ==References== * Flower, R.H 1984; Bodeiceras A New Mohawkian Oxycone, with revision of the Older Barrandeocerida and Discussion of the Status of the Order; Journal of Paleontology V 58, no.6, pp1372–1379, Nov 1984 * Furnish and Glenister 1964; Nautiloidea - Tarphycerida;K355 in the Treatise on Invertebrate Paleontology Vol K; Teichert and Moore, (eds) GSA and U of Kansas Press 1964 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「Campbelloceras」の詳細全文を読む スポンサード リンク
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