Potamotherium (Greek for "river beast"); pronounced POT-ah-moe-THEE-ree-um
Rivers of Europe and North America
Miocene (23-5 million years ago)
Size and Weight:
About 5 feet long and 20-30 pounds
Slender body; short legs
When its fossils were first discovered, way back in 1833, no one was quite sure what to make of Potamotherium, though the preponderance of the evidence pointed to its being a prehistoric weasel (a logical conclusion, given this megafauna mammal's sleek, weasel-like body). However, further studies have relocated Potamotherium on the evolutionary tree as a distant ancestor of modern pinnipeds, a family of marine reptiles that includes seals and walruses. The recent discovery of Puijila, the "walking seal," has sealed the deal, so to speak: these two mammals of the Miocene epoch were clearly closely related to each other.