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

Trocholitidae The Trocholitidae are Tarphycerida with Whorl (botany), 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 di ...

of mollusks found widespread in the late

Early Early may refer to: Places in the United States * Early, Iowa, a city * Early, Texas, a city * Early Branch, a stream in Missouri * Early County, Georgia * Fort Early, Georgia, an early 19th century fort Music * Early B, stage name of Jamaican d ...

and

Middle Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era, and the second of twelve periods of the Phanerozoic Eon. The Ordovician spans 41.6 million years from the end of the Cambrian Period Ma (milli ...

of North America and northern Europe (all species in the genus are

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

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

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

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,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

, 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