common name of either of two species of artiodactylous (even-toed, hoofed) mammals that constitute the family Hippopotamidae, found only in Africa. Hippopotamuses (also called river horses) are heavy-bodied, short-legged, short-tailed animals, resembling pigs more than horses. They have large heads with small eyes and small ears; their nostrils, surrounded by sparse, bristly hairs, are equipped with special flaps that close down when the animal goes underwater. The eyes and the ears are located on the top of the head. The mouth is huge and contains long, pointed incisor and canine teeth; the common adult hippopotamus has tusklike canine teeth in the lower jaw. They are about 61 cm (about 24 in) long, weigh almost 3 kg (6 lb), and are valued as ivory. The bare skin becomes 5 cm (2 in) thick and is used to make leather whips known as sjamboks. The feet are four-toed. The meat of the hippopotamus is edible, and soup is made from the hide.

The common brown or gray hippopotamus, Hippopotamus amphibius, once widely distributed throughout Africa and now found south of lat 17° N, is one of the largest four-footed animals. It reaches a length of 4 m (14 ft) and weighs more than 3.6 metric tons; because of its short legs it stands no higher than 1.5 m (5 ft) at the shoulder. Its stomach is more than 3 m (more than 10 ft) long.

The hippopotamus is semiaquatic, spending most of the day with only its eyes, ears, and nostrils above the surface of a river, and it is capable of remaining underwater for as long as 25 minutes. During the day it feeds on aquatic vegetation and often swims more than 40 km (25 mi) in search of food, emerging at night to feed on land plants. It is fond of sugarcane and corn and sometimes enters plantations, where it does more damage by trampling the plants than it does by feeding. Hippopotamuses have occasionally been seen in mountain rivers at heights of more than 1500 m (5000 ft) above sea level and at temperatures near freezing.

Common hippopotamuses travel in herds of about 40 animals. The cow bears one young at a time and fights ferociously if the calf is attacked. Old bulls, like old elephants, sometimes go berserk and attack other hippopotamuses or humans. The species is widely hunted, traditionally by harpooning, or by digging pitfalls, or by fencing it in and starving it to death.

The pygmy hippopotamus, Choeropsis liberiensis, is about half the size of the common hippopotamus. It is found only in western Africa, especially in Liberia. It is black on top, with a greenish sheen; below, it is yellowish-green. It is less aquatic than the common hippopotamus and is found in cool forests and in marshlands. Pygmy hippopotamuses almost always travel in pairs, rarely forming a herd.

Remains of many fossil hippopotamuses have been found in European and Indian deposits of the Pliocene epoch and Quaternary period; fossils in England seem to be of the same species as the present-day common hippopotamus.

For further information on this topic, see the Bibliography, sections 462. Animal behavior, 475. Mammal, 478. Hoofed mammals.