Hippopotamus

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Hippopotamus

Image:Hippo pod.jpg
Pod of hippos, Luangwa Valley, Zambia

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Family:	Hippopotamidae
Genus:	Hippopotamus
Species:	H. amphibius

Binomial name

Hippopotamus amphibius
Linnaeus, 1758

The Hippopotamus (Hippopotamus amphibius) or Greek "ίππόποταμος" ("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.

Eyes, ears, and nostrils are placed high on the roof of the skull. Hippos can close their nostrils and remain completely submerged for more than ten minutes. They are buoyant and very skilled and graceful in water, but for the most part do not swim. They can swim if need be (a hippo calf was recently rescued out at sea after being swept there by a river flood). They generally walk on the bottom in water. They feed on land mostly at night, consuming as much as 50 kg (110 lb) of vegetation a day. They have been known to occasionally scavenge meat from animals found near their range, but hippos are not carnivorous in any realistic sense. 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.

Before the last Ice Age, the hippo was wide-spread in North Africa and Europe[1], and it can live in colder climates on the condition that the water does not freeze during winter. It is now extinct also in Egypt where it 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.

Image:Lightmatter hippo.jpg

Despite the popular image of the animal being easygoing and peaceful, the hippopotamus is actually one of the most dangerous animals in Africa, and is said to account for more human deaths than any other African mammals. This is not because they are more aggressive than other African mammals but rather because they are highly territorial and their spaces often conflict with those of farmers and tourists. Thus, the hippos do not hunt humans, but rather protect their own territory. 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. Male hippos appear to continue growing throughout their lives, whereas the females reach a maximum weight at around the age of 25. Females are smaller than their male counterparts, and normally weigh no more than 1500 kg. The value given above of 3200 kg is often quoted for the upper limit of weight for a male hippo. However, larger specimens than this have been documented, one of which weighed almost five tonnes.

While it is accepted that a hippo can run faster than a human on land, there are various estimates of its actual running speed. These vary from 30 km/h (18 mph) to 40 km/h (25 mph) or even 48 km/h (30 mph). The higher values probably refer to short bursts of speed. While underwater, hippos can move at 8 km/h. It is often claimed that a hippo cannot swim, but this is untrue. They are in fact excellent swimmers, propelling themselves by kicking their back legs. Given that they are born underwater, baby hippos begin swimming almost immediately after their birth. They often rest on their mothers' backs and swim underwater in order to suckle. Adult hippos can stay submerged for much longer - usually for 5-10 minutes. Some have even been documented as being able to stay underwater for up to 25 minutes. The process of surfacing and breathing is automatic, and even a hippo sleeping underwater will rise and breathe without waking.

Hippos 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, nor sweat. This secretion starts out colorless, turns red-orange within minutes, eventually becoming brown.

There are two distinct pigments that have been identified in the secretions, red and orange. The two pigments are highly acidic compounds. They are known as red pigment hipposudoric acid and orange one norhipposudoric acid. The red pigment was found to inhibit the growth of disease-causing bacteria, lending credence to the theory that the secretion has an antibiotic effect. The light absorption of both pigments peaks in the ultraviolet range, creating a sunscreen effect. Hippos all over the world secrete the pigments so it doesn't appear that food is the source of the pigments. Instead, the animals may synthesize the pigments from precursors such as the amino acid tyrosine. (Saikawa, et al., 2004)

The word hippopotamus comes, by way of Latin, from the ancient Greek ῾ίππος ποταμός (hippos potamos), which means river horse. A male hippo is known as a bull; the female, a cow; a baby, a calf; and a group of hippopotami, a pod, herd, school or a bloat.

Image:Hippo skull dark.jpg

The less familiar pygmy 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). In 2005, the BBC reported that the population of hippos in Democratic Republic of the Congo's Virunga National Park had dropped to 900 individuals from around 29,000 in the mid 1970s, raising concerns about the viability of that population. This decline is attributed to the disruptions caused by the Second Congo War [2].

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. [3]

References

Saikawa Y, Hashimoto K, Nakata M, Yoshihara M, Nagai K, Ida M, Komiya T (2004). Pigment chemistry: the red sweat of the hippopotamus. Nature 429 (6990): 363. PMID 15164051