The Hippopotamus, also shortened to a hippo, further qualified as the common hippopotamus, Nile hippopotamus or River hippopotamus (Hippopotamus Amphibius), is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus (Choeropsis liberiensis or Hexaprotodon liberiensis). Its name comes from the ancient Greek for "river horse" (ἱπποπόταμος). After the elephant and rhinoceros, the hippopotamus is the next largest land mammal. It is also the largest extant land artiodactyl. Despite their physical resemblance to pigs and other terrestrial even-toed ungulates, the closest living relatives of the hippopotamids are cetaceans (whales, dolphins, porpoises, etc.), from which they diverged about 55 million years ago. Hippos are recognisable for their barrel-shaped torsos, wide-opening mouths with large canine tusks, nearly hairless bodies, pillar-like legs, and large size: adults average 1,500 kg (3,300 lb) for bulls (males) and 1,300 kg (2,900 lb) for cows (females). Despite its stocky shape and short legs, it is capable of running 30 km/h (19 mph) over short distances.