Kingdom Animalia Class Cephalopoda Order Tarphycerida Rank Genus | Phylum Mollusca Subclass Nautiloidea Family Lituitidae | |
Similar Orthocerida, Orthocone, Nautilida, Nautiloid, Orthoceras | ||
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.
References
Rhynchorthoceras Wikipedia(Text) CC BY-SA