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Hippopotamus

2007 Schools Wikipedia Selection. Related subjects: Mammals

                  iHippopotamus
   Pod of hippos, Luangwa Valley, Zambia
   Pod of hippos, Luangwa Valley, Zambia

                             Conservation status

   Vulnerable (VU)
            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), from the Greek ‘ιπποπόταμος
   (hippopotamos, hippos meaning "horse" and potamos meaning "river"), is
   a large, plant-eating African mammal, one of only two extant, and three
   or four recently extinct, species in the family Hippopotamidae.

Characteristics

   Hippopotamuses (hippopotami is also accepted as a plural form by the
   OED), also sometimes called hippos, are gregarious, living in groups of
   up to 40 animals, called a pod, herd, school or bloat. A male
   hippopotamus is known as bull, a female as cow, and a baby as calf. A
   hippo's lifespan is typically 40 to 50 years. Female hippos will reach
   sexual maturity at 5 to 6 years, and have a gestation period of 8
   months.

   Hippos average 3.5 metres (11 ft) long, 1.5 m (5 ft) tall at the
   shoulder, and weigh from 1500 kg to 3200 kg (3,300 to 7,000 lb). They
   are approximately the same size as the White Rhinoceros, and experts
   are split on which is the next largest land animal after the elephant.
   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 as being the
   upper limit of weight for a male hippo. However, larger specimens than
   this have been documented, including one which weighed about 10,000 lb
   (4,500 kg) and measured about 16 feet (5 m) long. Even though they are
   bulky animals, hippopotamuses can run faster than a human on land.
   There are estimates of their running speed varying from 30 km/h (18
   mph) to 40 km/h (25 mph), or even 50 km/h (30 mph). The hippo can
   maintain these higher estimates for only a few hundred metres or yards.
   A hippopotamus
   Enlarge
   A hippopotamus

   The eyes, ears, and nostrils of the hippo are placed high on the roof
   of the skull. This allows them to spend most of the day with the
   majority of their body submerged in the waters of tropical rivers to
   stay cool and prevent 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 and
   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 does not 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)

   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 . Hippopotami have more in common with
   whales than they do with other artiodactyls (even-toed ungulates), such
   as pigs. Thus, the common ancestor of hippos and whales existed after
   the branch-off from ruminants, which occurred after the divergence from
   the rest of the even-toed ungulates, including pigs. While the whale
   and hippo are each other's closest living relatives, their lineages
   split very soon after their divergence from the rest of the even-toed
   ungulates.

Range

   Before the last Ice Age, the hippo was wide-spread in North Africa and
   Europe, and it can live in colder climates on the condition that the
   water does not freeze during winter. The species was common in Egypt's
   Nile region until historic times but has since been extirpated. 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 on the island of Malta, at Għar Dalam (the Cave
   of Darkness), bone remains of hippopotamuses have been found, dated to
   about 180,000 years old. Hippos are still found in the rivers and lakes
   of Uganda, Sudan, Kenya, 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.

Behaviour

   A submerged Hippopotamus
   Enlarge
   A submerged Hippopotamus

   Hippos are highly 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. Their canine teeth are 50 cm (20 inches) long,
   and it uses its head as a battering ram, especially against rival males
   while fighting over territory. Since their habitat is often encroached
   upon by farmers and tourists, and because they are so territorial, the
   hippopotamus is considered the most dangerous animal in Africa. They
   kill crocodiles and lions, and are even responsible for more human
   deaths than any other African animal. The hippo does not hunt humans,
   but defends its own territory vigorously.

   Hippos are usually found in shallow water, and rarely come out of that
   depth. Most hippos that look as though they are floating are standing
   or lying on the bottom. They come on to land to feed, mostly at night,
   consuming as much as 50 kg (110 lb) of vegetation per day. They have
   been known to occasionally scavenge meat from animals found near their
   range, but hippos are not significantly carnivorous.
   Three hippopotamuses at Flamingo Land Theme Park and Zoo, England
   Enlarge
   Three hippopotamuses at Flamingo Land Theme Park and Zoo, England

   Adult hippos are not generally buoyant. When in deep water, they
   usually propel themselves by leaps, pushing off from the bottom. They
   move at speeds upto 8 km/h in water. Young hippos are buoyant and more
   often move by swimming, propelling themselves with kicks of their back
   legs. One hippo calf survived after being pushed out to sea during the
   tsunami generated by the 2004 Indian Ocean earthquake and was rescued
   on a nearby island.

   Baby hippos are born underwater at a weight between 25 and 45 kg
   (60−110 pounds) and must swim to the surface in order to take their
   first breath. The young often rest on their mothers' backs when in
   water that is too deep for them, and swim underwater in order to
   suckle.

   Adult hippos typically resurface to breathe every 3–5 minutes. The
   young have to breathe every two to three minutes. The process of
   surfacing and breathing is automatic, and even a hippo sleeping
   underwater will rise and breathe without waking. Hippos have been
   documented staying submerged for up to thirty minutes. A hippo closes
   its nostrils when it submerges.

   Adult hippos are extremely hostile toward crocodiles, which often live
   in the same pools and rivers as hippopotami. This is especially so when
   hippo calves are around. Hippos also seem to empathize with the prey of
   crocodiles and have been known to stand guard over dead and dying
   antelope on river banks.

Extinction

   A hippo's skull, showing the large canine teeth used for fighting
   Enlarge
   A hippo's skull, showing the large canine teeth used for fighting

   Three species of hippos (family Hippopotamidae) became extinct within
   the Holocene on Madagascar, one of them as recently as about a thousand
   years ago. A 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 population of hippos in Democratic Republic of the Congo's
   Virunga National Park had dropped to 800 or 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. The poachers are believed to be former Hutu rebels,
   poorly paid Congolese soldiers and local militia groups. Reasons for
   poaching include the belief that hippos are unintelligent, that they
   are a harm to society, and also for money—a three-tonne hippo is worth
   thousands of dollars. The sale of hippo meat is illegal, but
   black-market sales are difficult for WWF officers to track.

Conservation status and research

   The Hippopotamus Hunt (1616), by Peter Paul Rubens
   Enlarge
   The Hippopotamus Hunt (1616), by Peter Paul Rubens

   Five subspecies of hippos have been described based on morphological
   differences (H. a. amphibius, H. a. kiboko, H. a. capensis, H. a.
   tschadensis, H. a. constrictus; Lydekker 1915). However, the existence
   of these putative subspecies had not been tested by genetic analyses. A
   recent paper by Okello et al. (2005) does just that. Using
   mitochondrial DNA from skin biopsies taken from 13 sampling locations,
   the authors consider genetic diversity and structure among hippo
   populations across the continent. They find low but significant genetic
   differentiation among 3 of the 5 putative groups - H. a. amphibius, H.
   a. capensis, H. a. kiboko. If these findings are accurate, that would
   mean that common hippos in Kenya and Somalia (kiboko), southern Africa
   (capensis from Zambia to South Africa), and the rest of sub-Saharan
   African countries (amphibius) represent three distinct subspecies, with
   H. a. amphibus as the ancestral group. Okello et al. also find evidence
   that common hippos in Africa experienced a marked population expansion
   during or after the Pleistocene Epoch, which they attribute to an
   increase in water bodies at the end of this era. These findings have
   important conservation implications. Hippo populations across the
   continent are threatened by habitat loss and unregulated hunting. In
   addition to addressing these common threats, the genetic diversity of
   these three distinct subspecies will need to be preserved. The
   hippopotamus has been moved on to the IUCN Red List drawn up by the
   World Conservation Union (IUCN) in May 2006. This signifies that the
   common hippopotamus is now in serious danger of extinction.

Miscellanea

   Tami the Hippo having lunch in the Jerusalem Biblical Zoo
   Enlarge
   Tami the Hippo having lunch in the Jerusalem Biblical Zoo
     * Hippo seem to be aware of the presence of large bodies of water
       from some distance away. After the construction of the Blyde Canyon
       Dam in South Africa, a group of hippo walked up an access road for
       about 15 km and settled in the water of the new dam.
     * Donna the Hippo, 55, is the oldest known hippo in captivity. Donna
       can be found at the Mesker Park Zoo in Evansville, IN.

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