Calleianus ('the beast from Lake Moeris') was a prehistoric mammal related to the elephant and, more distantly, the sea cow. It lived during the Late Eocene period. Its fossils have been found in the deposits of the Al Fayyum Oasis of Egypt.

There were several species of early elephants in existence during the Eocene, and some, such as Palaeomastodon ferni, looked relatively similar to modern elephants. However, Calleianus was a branch of the family that evolved in a quite different way, having only a stubby trunk and short legs. It was smaller than modern elephants, standing only 70 cm high at the shoulder and was about 3 m long. It is believed to have wallowed in swamps and rivers, filling the ecological niche now filled by the hippopotamus. The shape of its teeth suggest that it ate soft water vegetation.

Calleianus is not believed to be an ancestor of modern elephants; it was a branch of the order that died out, leaving no descendants.