HIPPOPOTAMUS

byname hippo (Hippopotamus amphibius) amphibious African mammal of the family Hippopotamidae (order Artiodactyla). Hippopotamuses are the largest nonruminating, even-toed, hoofed mammals. They formerly occupied lakes and rivers throughout sub-Saharan Africa in historic times but are now restricted to parts of eastern and southeastern Africa, from the upper course of the Nile River in The Sudan southward to South Africa. The animals evolved in the Late Miocene Epoch (11.2 to 5.3 million years ago) and flourished in Asia and Europe as well as Africa during the Pleistocene (1.6 million to 10,000 years ago). Hippopotamuses have barrel-shaped bodies, large mouths, short legs, and four toes on each foot. They may reach a length of 4.6 m (15 feet), a height of 1.5 m at the shoulder, and a weight of 3-4.5 metric tons (3.3-5 tons). The skin is very thick, nearly hairless, and grayish brown above, lighter and pinkish below. The ears and nostrils protrude so that they are above water when the animal is floating with the rest of its body submerged. The mouth is enormous and can open extremely wide; the upper lip is thick and bulging; and the incisor and canine teeth are very large and grow continuously as they are worn away. The lower canines may reach a length of 30 cm (12 inches) above the gumline. The hippopotamus's numerous skin glands release a protective, oily, pinkish secretion that has popularly, but incorrectly, been thought of as "blood sweat" because it appears red in sunlight; this pigment actually serves to protect the animal's skin in both water and dry conditions. Hippopotamuses live in rivers, lakes, swamps, or other permanent bodies of water in groups typically numbering 7-15 animals. During the day they sleep and rest in or near the water, and at night they emerge onto the land to feed on grasses that they crop with their horny lips. In water they can swim fast, can walk along the bottom, and can submerge (with ears and nostrils closed) for 3-5 or as long as 10 minutes at a time. On land hippopotamuses are steady plodders and can gallop for short distances, but they are never found very far from water, and their grazing range extends inland for only about 3 km (2 miles). A single young is born after a gestation period of about eight months and weighs 25-55 kg (55-120 pounds). The baby often rides the mother's back while she swims or floats at the surface. Though gregarious, hippopotamuses tend to be aggressive, and in the breeding season males engage in battles that are sometimes fatal. The hippopotamus's voice is a loud grunt or bellow, and its gaping "yawn" is in fact a threat signal. Hippopotamuses are generally inoffensive to humans but sometimes make unprovoked attacks on small boats, smashing them in their jaws. Their flesh is much esteemed by Africans, and their teeth are of good quality ivory. They can live to the age of 40 years in captivity. The rare pygmy hippopotamus (Choeropsis liberiensis), the other living species of the family Hippopotamidae, is about 1.5 m long, weighs about 190 kg, and is grayish black in colour. It is less gregarious and less aquatic than its larger relative, and it lives alone or in pairs in lowland forests of western Africa from Sierra Leone eastward to Nigeria, where it is found along streams and in wet forests and swamps.