hippopotamus, herbivorous, river-living mammal of tropical Africa. The large hippopotamus, Hippopotamus amphibius, has a short-legged, broad body with a tough gray or brown hide. The male stands about 5 ft (160 cm) high at the shoulder and weighs about 5 tons (4,500 kg); the female is slightly smaller. The mouth is wide, and the incisors and lower canines are large ivory tusks that grow throughout life. The eyes are near the top of the head, so the animal can see when nearly submerged. Hippopotamuses usually live in herds of about 15 animals. Much of their time is spent standing or swimming underwater, where they feed on aquatic plants; they must rise to breathe every 5 minutes or so. At night groups of animals feed on the shore. The hippopotamus is hunted for meat, and Africans have used the hide for shields and whips. Once widespread in Africa, the animal is now rare except in unsettled areas and reserves. The pygmy hippopotamus, Choeropsis liberiensis, is found in W Africa. It is about 30 in. (75 cm) tall at the shoulder and weighs about 400 lb (180 kg). It tends to be solitary and spends much of its time on the shore, sleeping by day in thickets. Recent DNA studies indicate that whales are most closely related to hippopotamuses. Hippopotamuses are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Artiodactyla, family Hippopotamidae.