Potamotherium

Potamotherium ('river beast') is an extinct genus of mustelids or early pinniped that existed during the Miocene period.

The genus was first described in 1833. In 1988 it was assigned to the family Mustelidae and the subfamily Oligobuninae. One species has been identified in the genus: P. miocenicum.

Finds range from the mid-latitudes of Europe and North America, dated from Oligocene/Miocene boundary and surviving through to the end of the Miocene. It has been interpreted as a basal, non-marine ancestor of seals and sea lions, suggesting a freshwater phase in the evolutionary transition of pinnipeds from land to sea. The relatives of Potamotherium was possibly early bears (whose ancestors at the time where small and generally weasel-like).

Physically, Potamotherium resembled a modern otter, and was 1.5 meters (5 ft) long, with an elongated, slender body and short legs. With a flexible backbone and a streamlined shape, it was probably a good swimmer. Analysis of fossils suggests that Potamotherium had a poor sense of smell, but made up for this with good vision and hearing.