Hippopotamus comes from Greek and means "river horse". The two modern species of hippopotamuses, however, are more closely related to pigs.

The common male hippopotamus weighs up to 4.5 t (5 tn.), but the pygmy hippopotamus weighs only about 160 to 270 kg (350 to 600 lb.).

Unlike the larger, more gregarious hippopotamuses, the pygmy hippo is shy; when one of these small hippos encounters people, it flees at once into the nearest river or swamp.

Although hippos once ranged through Europe and Asia, they are now found only in the African interior and on game reserves. The pygmy hippopotamus, which is the smallest species, occurs in western Africa, living in forests in or near rivers, lakes and swamps. Their life span is about 35 years, and they have adapted well to life in zoological gardens. This is encouraging, as they are threatened with extinction in their natural habitat. The major threats to the pygmy hippopotamus are deforestation and hunting.