Rhynchorthoceras
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| Rhynchorthoceras Temporal range: MOrdovician | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Subclass: | Nautiloidea |
| Order: | †Tarphycerida |
| Family: | †Lituitidae |
| Genus: | †Rhynchorthoceras |
Rhynchorthoceras is a Middle Ordovician genus characterized by a rapidly expanded, weakly annulate orthocone, like the orthoconic section of Ancistroceras, but with only a curved, cyrtoconic apex instead of juvenile whorls.
Rhynchorthoceras is probably derived from Ancistroceras by a loss of the tarphycerid type apex, although it has been included with the orthocerid Sinoceratidae.