Cyrtonybyoceras

Cyrtonybyoceras is a genus of slightly exogastric members of the Wutinoceratidae, a family of actinocerids and probably derived from an earlier Wutinoceras . The shell of Cyrtonybyoceras is curved slightly upwardly and is slightly compressed. Sutures slope toward the aperture, from the dorsum to the venter. The siphuncle is ventral but not marginal, in general form like that of Nybyoceras. Upper and lower septal necks are recumbent or narrowly free. The canal system is reticular, characteristic of the Wutinoceratidae.[1]

Cyrtonybyoceras
Temporal range: eM Ordovician
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order: †Actinocerida
Family: †Wutinoceratidae
Genus: †Cyrtonybyoceras
Teichert, 1933

Cyrtonybyoceras and Wutinoceras are similar, except for Cyrtonybyoceras being slightly cyrtoconic, and almost intergrade.

Cyrtonybyoceras is so far known only from the Whiterock Stage in North America. The genotype, Cyrtonybyoceras haesitans, was named by Teichert in 1933, based on Orthoceras haesitans Billings 1865, from the Tablehead formation in Newfoundland. It has also been found in the Antelope Valley Limestone in the Toquima Range in Nevada.

References
  1. Flower R.H.,1968;The First Great Expansion of the Actinoceroids, New Mexico Bureau of Mines and Mineral Resources, Memoir 19 Part I, Socorro NM

Further reading
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