Ascocerida

Systematic Paleontology Class Cephalopoda Subclass Nautiloidea Order Ascocerida

The Ascocerida is an order of bizarre nautiloids, confined to the Ordovician and Silurian, that underwent periodic truncation of the shell. Three families are included, shown from earliest to most recent.

Hebetoceratidae, consisting of slender orthocones and exogastric cyrtocones that seem to have undergone periodic truncation. Range, middle and possibly upper Ordovician.

Ascoceratidae, shells consisting of an early, juvenile, deciduous longiconic stage and an inflated breviconic ascoceroid stage. Middle Ordovican -- upper Silurian.

Choanoceratidae, in which shells are slightly curved and septa form deep asymmetrical cones. Upper Silurian.

Refereces W.M. Furnish and Brian F. Glenister, 1964. Nautiloidea - Ascocerida. Treatise on Invertebrate Paleontology, Part K. Charles H. Holland, 1999. The Nautiloid Cephalopod Order Ascocerida in the British Silurian. Palaeontology Vol 42 Part 4. Rousseau H. Flower and Bernhard Kummel Jr, 1950. A Classification of the Nautiloidea. Journal of Paleontology, Vol 24, no. 5.