''Gonioceras'' is an extinct genus of actinocerid

nautiloidea Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s typified by a broad, low shell; flattened ventrally, convexly rounded dorsally; top and bottom meeting at an acute angle along the sides. In most the shell is rather thin, especially along the lateral portion. The aperture is contracted. Sutures from broad ventral and dorsal lobes, more narrowly rounded ventro-lateral and dorso-lateral saddles, and sharp pointed lateral lobes; more complex than in later ''

Lambeoceras ''Lambeoceras'' is a genus of large actinocerids with a convexly lenticular cross section from the Upper Ordovician of North America and the sole representative of the family Lambeoceratidae. Morphological description ''Lambeoceras'' is of med ...

''. The siphuncle is typically subcentral but may be closer to the venter; armenocerid in form with short segments and very short brims and containing a straight endosiphuncular canal system. ''Gonioceras'' is derived from '' Armenoceras'' and is the type genus of Gonioceratidae. Fossils are found in marine strata of the Chazy and Blackriveran of the Middle

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

in the Champlain region of eastern North America and at the Paquette Rapids of the Ottawa River in Ontario. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

, ''Gonioceras anceps'' was named by Hall in 1847. The flattened shell suggests that the living animal was a benthic organism.

References

* Flower R.H. 1957. Studies of the Actinoceratida, New Mexico Bureau of Mines and Mineral Resources Memoir 2, Socorro NM . * Teichert, C, 1964; Actinoceratoidea in the

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

, Vol K; Teichert and Moore, eds; pub GSA & Univ Kansas {{Taxonbar, from=Q5581915 Ordovician cephalopods of North America Nautiloids Fossils of Georgia (U.S. state) Paleozoic life of Ontario Paleozoic life of Newfoundland and Labrador Paleozoic life of the Northwest Territories Paleozoic life of Nunavut