Potamotherium ("river beast") is an extinct genus of either mustelid or pinniped from the Miocene of Europe and North America. It physically resembled an otter and, just like an otter, it was a skilled swimmer. It had a good sense of hearing and sight but a terrible sense of smell. It is theorized to have been an early ancestor of seals and sea lions. If it is a pinniped and not a mustelid, as it is currently believed to be, it would be a missing link between the early ancestors of seals and sea lions and their modern descendants.
In The Land Before Time
A Potamotherium appears throughout The Land Before Time Animated Moviebook. In the game, Potamotherium appears in order to help teach the player about shapes, math, and other early learning skills.