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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.


  • Flower, R. H. 1950. A Classification of the Nautiloidia. Jour Paleontology, V.24, N.5, pp 604–616, Sept.
  • Furnish & Glenister, 1964. Nautiloidea -Tarphycerida. Treatise on Invertebrate Paleontology Part K, Mollusca 3 ...Nautiloidea