Science Fair Project Encyclopedia
The Hippopotamus (Hippopotamus amphibius) or Greek "ἵππόποταμος" ("river horse") is a large, plant-eating African mammal, one of only two living and three (or four) recently extinct species in the family Hippopotamidae.
Hippopotamuses ('hippopotami' is also accepted as a plural form by the OED), also called hippos, are gregarious, living in groups of up to 40 animals. They spend most of the day up to their nostrils in the waters of tropical rivers, as they are highly susceptible to sunburn. For additional protection from the sun their skin secretes a natural sunscreen substance which is red colored. This secretion is sometimes referred to as "blood sweat," but it is not actually blood. Hippos can close their nostrils and remain completely submerged for more than ten minutes. Eyes, ears, and nostrils are placed high on the roof of the skull. They are buoyant and very skilled and graceful in water, and have been videotaped swimming in surf on the coast of East Africa. Hippos are good swimmers, and are born underwater able to swim almost immediately. They feed on land mostly at night, consuming as much as 50 kg (110 lb) of vegetation a day. Hippos are territorial; a male hippo often marks his territory along a riverbank from which to draw in a harem of females while defending it against other males. Male hippos challenge one another with threatening gapes.
The hippo is now extinct in Egypt but was a familiar animal of the Nile into historic times. Pliny the Elder writes that in his time the best location in Egypt for capturing this animal was in the Saite nome (N.H. 28.121); and the animal could still be found along the Damietta branch after the Arab Conquest (639). Even in the island of Malta, at Għar Dalam (the Cave of Darkness) bone remains of hippopotamuses were found, being about 180,000 years old. Hippos are still found in the rivers of Sudan, northern Democratic Republic of the Congo and Ethiopia, west to Gambia as well as in Southern Africa (Botswana, Republic of South Africa, Zimbabwe, Zambia). A separate population is in Tanzania and Mozambique.
Despite the popular image of the animal being easygoing and peaceful, the hippopotamus is actually one of the most dangerous African animals, said to account for more human deaths than any other mammal. This is not because they are more aggressive than other African mammals but rather because they are highly territorial and their space often conflicts with that of farmers and tourists. In other words, the hippos are protecting their own territory and do not hunt humans. Its canine teeth are 50 cm (20 inches) long, and it uses its head as a battering ram, especially against rival males fighting over territory. The animals are 1.5 metres (5 ft) tall at the shoulder and weigh 1,500 kg up to 3,200 kg (3300 up to 7040 lb). They are approximately the same size as the White Rhinoceros and one or the other is the next-largest land animal after the species of elephants. While it is accepted that a hippo can run faster than a human on land, there are various estimates of its actual running speed. Some web-sites claim 18 mph (30 km/h), while others record 40 km/h (25 mph) or even 30 mph (48 km/h). The higher values probably refer to short bursts. They can move at 8 km/h in water.
The less familiar dwarf hippopotamus of West Africa, Hexaprotodon (Choeropsis) liberiensis is less specialized. It has longer legs and the orbits of its eyes are not raised above the roof of its skull. The pigmy hippo exists in two populations. One ranges in Guinea, Sierra Leone, Liberia and Côte d'Ivoire. The other population, with a different shape to the skull, ranged until recently in the Niger Delta but may now be extinct.
Three more species became extinct within the Holocene on Madagascar, one of them as recently as about a thousand years ago. Another dwarf species, Phanourios minutis , existed on the island of Cyprus but became extinct at the end of the Pleistocene. Whether this was caused by human intervention is debated (see Aetokremnos).
As indicated by the name, ancient Greeks considered the hippopotamus to be related to the horse. Until 1985 naturalists grouped hippos with pigs, based on molar patterns. However evidence, first from blood proteins, then from molecular systematics, and more recently from the fossil record, show that their closest living relatives are cetaceans – whales, porpoises and the like. 
- ITIS listing
- as of 2004-08-11
- IUCN Pigs, Peccaries and Hippopotamus Specialist group
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