The Hippopotamus (Hippopotamus amphibius), also known as the common hippopotamus or simply hippo, is a large, mostly herbivorous, semiaquatic mammal and ungulate 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). The name comes from the ancient Greek for "river horse" (ἱπποπόταμος). 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, the closest living relatives of the Hippopotamidae are cetaceans (whales, dolphins, porpoises, etc.) from which they diverged about 55 million years ago.
Common hippos are recognizable by their barrel-shaped torsos, wide-opening mouths revealing large canine tusks, nearly hairless bodies, columnar legs and large size; adults average 1,500 kg (3,310 lb) and 1,300 kg (2,870 lb) for males and females respectively. Despite its stocky shape and short legs, it is capable of running 30 km/h (19 mph) over short distances. They are fast in water.
The common hippo inhabits rivers, lakes and mangrove swamps, where territorial bulls preside over a stretch of river and groups of five to thirty females and young. During the day, they remain cool by staying in the water or mud; reproduction and childbirth both occur in water. They emerge at dusk to graze on grasses. While hippos rest near each other in the water, grazing is a solitary activity and hippos are not territorial on land. The hippo is among the most dangerous animals in the world as it is highly aggressive and unpredictable.
Like almost any herbivore, they consume other plants if presented with them, but their diet in nature consists almost entirely of grass, with only minimal consumption of aquatic plants. Hippos are born with sterile intestines, and require bacteria obtained from their mothers to digest vegetation.
Despite its herbivorous nature, it is extremely dangerous, as its teeth are strong enough to bite a twelve-foot crocodile in half. They are threatened by habitat loss and poaching for their meat and ivory canine teeth.