Temporal range: M Ordovician
Gonioceras is an actinocerid with 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. 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 sole representative of the Gonioceratidae. It is found in the Chazy and Blackriveran of the Middle Ordovician in the Champlain region of eastern North America and at the Paquette Rapids of the Ottawa River in Ontario. The genotype, Gonioceras anceps was named by Hall in 1847
Gonioceras was surely a bottom dweller that spent most of its time settled on the sea floor where it may have filled some of the niche filled by modern sting rays. However with its stiff outer shell, Gonioceras would not have been as mobile.
- 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, Vol K; Teichert and Moore, eds; pub GSA & Univ Kansas