Middle Ordovician – Late Ordovician
Gonioceratidae is an extinct family of nektobenthic carnivores
Description of the Family
- Straight shell, strongly depressed in cross section
- Dorsal and ventral sides are flat
- Sinuous sutures
- Small siphuncles, subventral to subcentral
- Of Ordovician cephalopods, only the actinocerid family Gonioceratidae surpass this group in the degree of flattening of the conch cross-section. The nature of the siphuncle and the siphonal deposits in the Gonioceratidae indicate that any direct relationship between the two families is unlikely.
- Certainly, a similar trend (in terms of shell shape) may be seen in some actinocerids, where genera such as Gonioceras and Lambeoceras show extreme depression of the conch and others such as Leurorthoceras show moderate depression combined with flattening of the venter and a submarginal siphuncle.
Treatise on Invertebrate Paleontology, Part K, Vol. 3 (1964):
- Large, straight shells, strongly depressed in cross section, with flat ventral and dorsal sides and angular flanks; sutures sinuous. Siphuncles comparatively small, subventral to subcentral.
Flower and Kummel (1950):
- Siphuncles as in Armenoceratidae. Shell strongly flattened, sides acutely angled in cross section. Ordovician.