The common hippopotamus Hippopotamus amphibius, or hippo, is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus Choeropsis liberiensis or Hexaprotodon liberiensis. The name comes from the ancient Greek for "river horse". After the elephant and rhinoceros, the common hippopotamus is the third-largest type of land mammal and the heaviest extant artiodactyl. Despite their physical resemblance to pigs and other terrestrial even-toed ungulates, their closest living relatives are cetaceans whales, porpoises, etc. from which they diverged about 55 million years ago. The common ancestor of whales and hippos split from other even-toed ungulates around 60 million years ago. The earliest known hippopotamus fossils, belonging to the genus Kenyapotamus in Africa, date to around 16 million years ago.
Common hippos are recognizable by their barrel-shaped torsos, wide-opening mouths revealing large canine tusks, nearly hairless bodies, columnar-like legs and large size.
They are the third-largest type of land mammal by weight between 1½ and 3 tonnes: the only heavier species on average are the white and Indian rhinoceroses, and the elephants.
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