3.4" Ordovician, Oncoceratid (Cyrtorizoceras) Fossil - Wisconsin

This is a 3.4" long example of Cyrtorizoceras sp. This fossil is part of a collection from the Grand Detour Formation in Rock County, Wisconsin. Cyrtorizoceras was an oncoceratid, a curve-shelled nautiloid cephalopod. This specimen is a partial shell found embedded in stone. Cyrtorizoceras is a nautiloid and related to Onioceras, commonly found in the Grand Detour formation.

The cephalopod shell fossil is removable from the surrounding stone.