Ormoceras

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Ormoceras Fossil range: M Ordovician - Devonian
Scientific classification
Kingdom: Animalia Phylum: Mollusca Class: Cephalopoda Subclass: Nautiloidea Order: Actinoceratida Family: Ormoceratidae Genus: Ormoceras Stokes, 1840
species
†Ormoceras boreale †Ormoceras centrale †Ormoceras dobrovljanensis †Ormoceras ferecentricum †Ormoceras koraiense †Ormoceras langskawiense †Ormoceras manchuriense †Ormoceras nanumforme †Ormoceras pollacki †Ormoceras schohariae †Ormoceras tenuifilum †Ormoceras yokoyamai

Ormoceras is an actinocerid genus of the family Ormoceratidae which is found in North America from the late Chazyan though the early Cincinnatian of the Middle and Upper Ordovician, but continued through the Devonian worldwide.

Ormoceras is a fairly wide spread genus representative of the Ormoceratidae with a straight shell, more or less circular in cross section , and a relatively narrow subcentral siphuncle composed of globular segments in which the radial canals in the endosiphuncular canal system are straight and normal to the central canal. Septal necks are short, narrowly rounded or sharply recurved, but never recumbent. As with most actinocerids, cameral deposits are common.

Ormoceras is derived from Adamsoceras which has a siphuncle with the same general form but in which the canal system is reticulate as in Wutinoceras. Ormoceras gave rise to Deiroceras early on during the Mohawkian (Middle Ordovician) and slightly later to Troedssonoceras. Ormoceras also gave rise to later genera such as Metarmenoceras from the Lower Devonian of Quebec, either directly or through Cyrtactinoceras of the Silurian which may also have given rise to the Carbactinoceratidae of the Carboniferous.

[edit] References

• Flower, R.H, 1957, Studies of the Actinoceratida, New Mexico Bureau of Mines and Mineral Resources, Memoir 2.
• Teichert, C, 1964, Actinoceratoidea, in the Treatise on Invertebrate Paleontology, pub Univ of Kansas and the GSA, Vol K, p K210-213