''Curtoceras'' is a genus in the tarphycerid family

Trocholitidae The Trocholitidae are Tarphycerida with whorls in close contact as with the Tarphyceratidae, but in which the siphuncle, similar in structure, becomes dorsal. The Trocholitidae are derived from the Tarphyceratidae, perhaps from different tarphyc ...

found widespread in the late

Early Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...

and

Middle Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The ...

of North America and northern Europe. ''Curtoceras'' has a shell that is gradually expanded, with half the fully mature body chamber divergent from the preceding volution. Whorl sections are near equidimentional with the inner margin (dosum) moderately impressed. The surface may be smooth or weakly ribbed. The

siphuncle The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and ...

is ventral in the initial chamber and becomes dorsal after one volution. With the exception of the dorsal siphuncle, ''Curtoceras'' is somewhat similar to the tarphyceratid '' Campbelloceras''

References

*Furnish, W.M. and Glenister, Brian F 1964; Nautiloidea -Tarphycerida, in

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and co ...

, Part K, Nautiloidea; Geological Society of America and University of Kansas press. {{Taxonbar, from=Q5196016 Tarphycerida Early Ordovician first appearances Middle Ordovician extinctions Paleozoic life of Quebec Prehistoric nautiloid genera

See also

References