Cranioceras is a dromomerycid. The dromomerycids were a group of deer-like artiodactyls that lived in North America from the early Miocene, 19 million years ago, to the early Pliocene, 4.5 million years ago. Although related to deer, the group has no known descendents. Dromomerycids typically have a horn over each orbit; in Cranioceras and its relatives there is also a third horn on the back of the skull. Evidence of healed injuries to the orbital horns of some species of dromomerycid suggests that they may have been used for fighting; in Cranioceras, the third horn may have been employed in neck wrestling or butting, such as occurs in present-day giraffes.

Dromomerycids are thought to have been browsers living in subtropical habitats, from open bush through to woodlands. Their extinction in the early Pliocene may have been due to the reduction of these habitats due to increasing aridity.