''Charactoceras'' is a tarphycerid genus

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

which lived during the

Late Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The ...

. ''Charactoceras'' has a closely coiled, rapidly expanding evolute shell, dorsally impressed, with a flattened venter and rounded sides. Sutures are close spaced laterally, but with broad ventral and dorsal lobes. Hyponomic sinus is well developed. The siphuncle is cyrtochoanitic and empty, located between the center and venter; segments expanded slightly into the chambers. The genus '' Charactocerina'' from the Late Orovician is similar but has costae on the dorsolateral region of the shell. Both are included in the family

Aspidoceratidae The Aspidoceratidae comprise a family of middle and upper Jurassic ammonites that make up part of the superfamily Perisphinctoidea, characterized by evolute shells, commonly stocky, that tend to develop tubercles. The Aspidoceratidae are thought ...

. Also somewhat similar to ''Charactoceras'' in external form are '' Uranoceras'' and '' Cumingsoceras'' from the Middle

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

, but both differ in detail.

References

* Walter C. Sweet, 1964. Nautiloidea- Barrandeocerida; Treatise on Invertebrate Paleontology. Geological Society of America and University of Kansas Press. {{Taxonbar, from=Q18346133 Prehistoric nautiloid genera Paleozoic life of Manitoba Paleozoic life of the Northwest Territories Paleozoic life of Nunavut Paleozoic life of Quebec