Orthoceratidae
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Kionoceras |
Orthoceratidae are a family of extinct nautiloid cephalopods. It is also known as Michelinoceratidae. Members are characterised by long, slender, usually orthoconic (straight) but sometimes slightly-curved shells, a central or subcentral orthochoanitic siphuncle that is free of deposits, a long body chamber, and cylindrical or only slightly-inflated connecting rings. Ornamentation may be in the form of longitudinal or transverse ribs and/or lirae, or the shell surface may be smooth.
Orthoceratids first appeared in the early Ordovician and continued through to either the end of the Permian or the end of the Triassic (there is some question as to whether or not the Triassic forms attributed to the genus Michelinoceras belong here). They are most common from the Ordovician to the Devonian, and many fine specimens are known from Europe and North America, although specimens are also known from Asia and Australia.
The family is sometimes called Michelinoceratidae, but Orthoceratidae is the more correct name.
[edit] References
- Dzik, Jerzy (1984) Phylogeny of the Nautiloidea, Palaeontologica Polonica, no. 43
- Sweet, Walter C., (1964), Nautiloidea -- Orthocerida, in Treatise on Invertebrate Paleontology. Part K. Mollusca 3. (Geological Society of America, and University of Kansas Press, New York, New York and Lawrence, Kansas)
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