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?Hippopotamus
Conservation status: Vulnerable[1]
Hippopotamus, Hippopotamus amphibius
Hippopotamus, Hippopotamus amphibius
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Family: Hippopotamidae
Genus: Hippopotamus
Linnaeus, 1758
Species: H. amphibius
Binomial name
Hippopotamus amphibius
Linnaeus, 1758[2]
Range map[1]
Range map[1]

The hippopotamus (Hippopotamus amphibius), or hippo, from the ancient Greek for "river horse" (Ιπποπόταμος), is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae (the other is the Pygmy Hippopotamus.) The hippopotamus is the third largest land animal (after the elephant and the white rhinoceros) and the heaviest extant artiodactyl, despite being considerably shorter than the giraffe.

The hippopotamus is semi-aquatic, inhabiting rivers and lakes where territorial bulls preside over a stretch of river and groups of 5 to 30 females and young. During the day they remain cool by staying in the water or mud; reproduction and childbirth both occur in water. They emerge at dusk to graze on grass. While hippopotamuses rest near each other in the water, grazing is a solitary activity and hippos are not territorial on land.

Despite their physical resemblance to pigs and other terrestrial even-toed ungulates, their closest living relatives are cetaceans (whales, porpoises, etc.) from which they diverged about 55 million years ago}}.[3] The common ancestor of whales and hippos split from other even-toed ungulates around 60million years ago.[4] The earliest known hippopotamus fossils, belonging to the genus Kenyapotamus in Africa, date to around 16 million years ago.

The hippopotamus is recognizable by its barrel-shaped torso, enormous mouth and teeth, nearly hairless body, stubby legs and tremendous size. It is the third-largest land mammal by weight (between 1½ and 3 tonnes), behind the white rhinoceros (1½ to 3½ tonnes) and the three species of elephant (3 to 9 tonnes). Despite its stocky shape and short legs, it can easily outrun a human. Hippos have been clocked at Template:Convert/km/hTemplate:Convert/test/Aon over short distances. The hippopotamus is one of the most aggressive creatures in the world and is often regarded as one of the most dangerous animals in Africa. There are an estimated 125,000 to 150,000 hippos throughout Sub-Saharan Africa; Zambia (40,000) and Tanzania (20,000–30,000) possess the largest populations.[1] They are still threatened by habitat loss and poaching for their meat and ivory canine teeth.

EtymologyEdit

The word "hippopotamus" derives from the ancient Greek ἱπποπόταμος, hippopotamos, from ἵππος, hippos, "horse", and ποταμός, potamos, "river", meaning "horse of the river".[5] In English, the plural is hippopotamuses, but hippopotami is also used;[6] hippos can be used as a short plural. Hippopotamuses are gregarious, living in groups of up to 30 animals; such a group is called a pod, herd, dale or bloat. A male hippopotamus is known as a bull, a female as a cow and a baby as a calf. The species is also known as the Common Hippopotamus or the Nile Hippopotamus.

Taxonomy and originsEdit

ClassificationEdit

The hippopotamus is the type genus of the family Hippopotamidae. The Pygmy Hippopotamus belongs to a different genus in Hippopotamidae, either Choeropsis or Hexaprotodon. Hippopotamidae are sometimes known as Hippopotamids. Sometimes the sub-family Hippopotaminae is used. Further, some taxonomists group hippopotamuses and anthracotheres in the super-family Anthracotheroidea or Hippopotamoidea.

File:Hippo skull dark.jpg
A hippo's skull, showing the large canine teeth used for fighting

Hippopotamidae are classified along with other even-toed ungulates in the order Artiodactyla. Other artiodactyls include camels, cows, deer and pigs, although hippopotamuses are not closely related to these groups.

Five subspecies of hippos have been described based on morphological differences in their skulls and geographical differences:[7]

  • H. a. amphibius – (the nominate subspecies) which stretched from Egypt, where they are now extinct, south up the Nile River to Tanzania and Mozambique.
  • H. a. kiboko – in the Horn of Africa, in Kenya and Somalia. Kiboko is the Swahili word for hippo. Broader nasals and more hollowed interorbital region.
  • H. a. capensis – from Zambia to South Africa. Most flattened skull of the subspecies.
  • H. a. tschadensis – throughout Western Africa to, as the name suggests, Chad. Slightly shorter and wider face, with prominent orbits.
  • H. a. constrictus – in Angola, the southern Democratic Republic of Congo and Namibia. Named for its deeper preorbital constriction.

The suggested subspecies were never widely used or validated by field biologists; the described morphological differences were small enough that they could have resulted from simple variation in non-representative samples.[8] Genetic analyses have tested the existence of three of these putative subspecies. A study examining mitochondrial DNA from skin biopsies taken from 13 sampling locations, considered genetic diversity and structure among hippo populations across the continent. The authors found low but significant genetic differentiation among H. a. amphibius, H. a. capensis, and H. a. kiboko. Neither H.a.tschadensis nor H.a.constrictus have been tested.[9][10]

DescriptionEdit

File:Hippo zoo Lisbon.JPG
A hippo at the zoo in Lisbon
File:HippoSkelLyd2.png
A drawing of a hippopotamus skeleton
File:Mouth of a hippo.jpg
Inside the mouth of a hippopotamus

Hippopotamuses are the fourth largest mammals in the world (after whales, elephants, and rhinoceroses). They can live in the water or on land. Their specific gravity allows them to sink and walk or run along the bottom of a river. Hippos are considered megafauna, but unlike all other African megafauna, hippos have adapted for a semi-aquatic life in freshwater lakes and rivers.[8]

Because of their enormous size, hippopotamuses are difficult to weigh in the wild. Most estimates of the weight come from culling operations that were carried out in the 1960s. The average weights for adult males ranged between Template:Convert/–Template:Convert/test/Aon. Females are smaller than their male counterparts, with average weights measuring between Template:Convert/–Template:Convert/test/Aon.[8] Older males can get much larger, reaching at least Template:Convert/LoffAonDbSoffTemplate:Convert/test/Aon and occasionally weighing Template:Convert/LoffAonDbSoffTemplate:Convert/test/Aon.[11][12] Male hippos appear to continue growing throughout their lives; females reach a maximum weight at around age 25.[13]


Hippos measure Template:Convert/toTemplate:Convert/test/A long, including a tail of about Template:Convert/cmTemplate:Convert/test/A in length and average about 1.5 meters (5 ft) tall at the shoulder.[14][15] The range of hippopotamus sizes overlaps with the range of the White Rhinoceros; use of different metrics makes it unclear which is the largest land animal after elephants. Even though they are bulky animals, hippopotamuses can run faster than a human on land. Estimates of their running speed vary 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 speeds for only a few hundred meters.[8]

File:Hippo walking.jpg
A bull hippo out of water during daylight, Ngorongoro Crater, Tanzania

A hippo's lifespan is typically 40 to 50 years.[8] Donna the Hippo, 57, is the oldest living hippo in captivity. She lives at the Mesker Park Zoo in Evansville, Indiana.[16][17] The oldest hippo ever recorded was called Tanga; she lived in Munich, Germany, and died in 1995 at the age of 61.[18]

The eyes, ears, and nostrils of hippos are placed high on the roof of the skull. This allows them to be in the water with most of their body submerged in the waters and mud of tropical rivers to stay cool and prevent sunburn. Their skeletal structure is graviportal, adapted to carrying the animals' enormous weight. Hippopotamuses have small legs (relative to other megafauna) because the water in which they live reduces the weight burden. Unlike most other semi-aquatic animals, the hippopotamus has very little hair.[8]

File:Hippo memphis.jpg
A submerged hippo at the Memphis Zoo

Their skin secretes a natural sunscreen substance which is red-colored. The secretion is sometimes referred to as "blood sweat," but is neither blood nor sweat. This secretion is initially colorless and turns red-orange within minutes, eventually becoming brown. Two distinct pigments have been identified in the secretions, one red (hipposudoric acid) and one orange (norhipposudoric acid). The two pigments are highly acidic compounds. Both pigments inhibit the growth of disease-causing bacteria; as well, the light absorption of both pigments peaks in the ultraviolet range, creating a sunscreen effect. All hippos, even those with different diets, 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.[19]

DistributionEdit

Hippopotamus amphibius was widespread in North Africa and Europe during the Eemian[20] and late Pleistocene until about 30,000 years ago, and it can live in colder climates provided the water does not freeze during winter.[citation needed] 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;[21] the animal could still be found along the Damietta branch after the Arab Conquest in 639. Hippos are still found in the rivers and lakes of Uganda, Sudan, Somalia, Kenya, northern Democratic Republic of the Congo and Ethiopia, west through Ghana to Gambia, and also in Southern Africa (Botswana, Republic of South Africa, Zimbabwe, Zambia). A separate population exists in Tanzania and Mozambique. They like to dwell in places with permanent water that isn't too deep.[8]

BehaviorEdit

File:HippoJaw.jpg
An open mouth signals that the hippo feels threatened.
File:Hippo.ogv
Video of hippos in the wild.

Hippos spend most of their days wallowing in the water or the mud, with the other members of their pod. The water serves to keep their body temperature down, and to keep their skin from drying out. With the exception of eating, most of hippopotamuses' lives —from childbirth, fighting with other hippos, and reproduction— occur in the water.

Hippos leave the water at dusk and travel inland, sometimes up to 8 kilometers (5 mi), to graze on short grass, their main source of food. They spend four to five hours grazing and can consume 68 kilograms (150 lb) of grass each night.[22] Like almost any herbivore, they will consume many other plants if presented with them, but their diet in nature consists almost entirely of grass, with only minimal consumption of aquatic plants.[23] Hippos have (rarely) been filmed eating carrion, usually close to the water. There are other reports of meat-eating, and even cannibalism and predation.[24] The stomach anatomy of a hippo is not suited to carnivory, and meat-eating is likely caused by aberrant behavior or nutritional stress.[8]

The diet of hippos consists mostly of terrestrial grasses, but they spend most of their time in the water. Most of their defecation occurs in the water, creating allochthonous deposits of organic matter along the river beds. These deposits have an unclear ecological function.[23] Because of their size and their habit of taking the same paths to feed, hippos can have a significant impact on the land they walk across, both by keeping the land clear of vegetation and depressing the ground. Over prolonged periods hippos can divert the paths of swamps and channels.[25]

File:Lightmatter hippo.jpg
A submerged hippo at the San Diego Zoo. Adult hippos typically resurface to breathe every 3–5 minutes.

Adult hippos cannot swim and are not buoyant. When in deep water, they usually propel themselves by leaps, pushing off from the bottom. They move at speeds up to 8 km/h (5 mph) in water. Young hippos are buoyant and more often move by swimming —propelling themselves with kicks of their hind legs. Adult hippos typically resurface to breathe every 3–5 minutes. The young have to breathe every two to three minutes.[8] The process of surfacing and breathing is automatic, and even a hippo sleeping underwater will rise and breathe without waking. A hippo closes its nostrils when it submerges.

Social lifeEdit

Studying the interaction of male and female hippopotamuses has long been complicated by the fact that hippos are not sexually dimorphic and thus females and young males are almost indistinguishable in the field.[26] Although hippos like to lie close to each other, they do not seem to form social bonds except between mothers and daughters, and are not social animals. The reason they huddle close together is unknown.[8]

File:Hippo pod edit.jpg
It is difficult to identify the gender of hippos in the field, because all researchers can usually see are their backs, like with this pod in Zambia.
File:Hippopotamus @ Barcelona zoo.jpg
Hippopotamus fighting at Barcelona Zoo

Hippopotamuses are territorial only in water, where a bull presides over a small stretch of river, on average 250 meters in length, and containing ten females. The largest pods can contain up to 100 hippos. Other bachelors are allowed in a bull's stretch, as long as they behave submissively toward the bull. The territories of hippos exist to establish mating rights. Within the pods, the hippos tend to segregate by gender. Bachelors will lounge near other bachelors, females with other females, and the bull on his own. When hippos emerge from the water to graze, they do so individually.[8]

Hippopotamuses appear to communicate verbally, through grunts and bellows, and it is thought that they may practice echolocation, but the purpose of these vocalizations is currently unknown. Hippos have the unique ability to hold their head partially above the water and send out a cry that travels through both water and air; hippos above and under water will respond.[27]

ReproductionEdit

Female hippos reach sexual maturity at five to six years of age and have a gestation period of 8 months. A study of endocrine systems revealed that female hippopotamuses may begin puberty as early as 3 or 4 years of age.[28] Males reach maturity at around 7.5 years.

A study of hippopotamus reproductive behavior in Uganda showed that peak conceptions occurred during the end of the wet season in the summer, and peak births occurred toward the beginning of the wet season in late winter. This is because of the female's estrous cycle; as with most large mammals, male hippopotamus spermatozoa is active year round. Studies of hippos in Zambia and South Africa also showed evidence of births occurring at the start of the wet season.[8] After becoming pregnant, a female hippopotamus will typically not begin ovulation again for 17 months.[28]

File:Beware of hippopotamus.jpg
Hippos can be dangerous to humans, as this sign from Kruger National Park notes. Mating occurs in the water with the female submerged for most of the encounter, her head emerging periodically to draw breath. Hippos are one of the few mammals that give birth under water, along with Cetaceans and Sirenians (manatees and dugongs). Baby hippos are born underwater at a weight between 25 and 45 kg (60–110 lb) and an average length of around 127 cm (50 in) and must swim to the surface to take their first breath. A mother typically gives birth to only one hippo, although twins also occur. The young often rest on their mothers' backs when in water that is too deep for them, and they swim underwater to suckle. They also will suckle on land when the mother leaves the water. Weaning starts between six and eight months after birth and most calves are fully weaned after a year.[8] Like many other large mammals, hippos are described as K-strategists, in this case typically producing just one large, well-developed infant every couple of years (rather than large numbers of small, poorly developed young several times per year as is common among small mammals such as rodents).[8][28][29]

AggressionEdit

Hippopotamuses are by nature very aggressive animals, especially when young calves are present. Frequent targets of their aggression include crocodiles, which often inhabit the same river habitat as hippos. Nile crocodiles, lions, and spotted hyenas are known to prey on young hippos.[30] Hippos are very aggressive towards humans, whom they commonly attack whether in boats or on land with no apparent provocation.[31] They are widely considered to be one of the most dangerous large animals in Africa.[32][33] To mark territory, hippos spin their tails while defecating to distribute their excrement over the greatest possible area.[34] Hippos are retromingent, likely for the same reason.[35] Hippos rarely kill each other, even in territorial challenges. Usually a territorial bull and a challenging bachelor will stop fighting when it is clear that one hippo is stronger. When hippos become overpopulated, or when a habitat starts to shrink, bulls will sometimes attempt to kill infants, but this behavior is not common under normal conditions.[29] Some incidents of hippo cannibalism have been documented, but it is believed to be the behavior of distressed or sick hippos, and not healthy behavior.[8]

Hippos and humansEdit

File:Hippopotamus Egypt fayence Berlin.jpg
A faience sculpture, from the New Kingdom of Egypt, 18th/19th dynasty, c. 1500–1300 BC, when hippos were still widespread along the Nile
File:Obaysch 1852.gif
Obaysch lounging at the London Zoo in 1852 The earliest evidence of human interaction with hippos comes from butchery cut marks upon hippo bones at Bouri Formation dated around 160,000 years ago.[36] Later rock paintings and engravings showing hippos being hunted have been found in the mountains of the central Sahara dated 4,000–5,000 years ago near Djanet in the Tassili n'Ajjer Mountains. Hippos were also well-known to the ancient Egyptians, where the hippo was recognized as a ferocious denizen of the Nile.[8] In Ancient Egyptian Religion, the hippopotamus-headed Tawaret was a goddess of protection in pregnancy and childbirth, because ancient Egyptians recognized the protective nature of a female hippopotamus toward her young.[37] The hippopotamus has been known to historians since classical antiquity. The Greek historian Herodotus described the hippopotamus in The Histories (written circa 440 BC) and the Roman Historian Pliny the Elder wrote about the hippopotamus in his encyclopedia Naturalis Historia (written circa 77 AD).[21][38] "John Dunn was at the head of his impi. [Baden Powell] asked him to translate the Zulu anthem his men had been singing. Dunn laughed and replied: "He is a lion. Yes, he is better than a lion—he is a hippopotamus." [39]

Hippos in zoosEdit

Hippopotamuses have long been popular zoo animals. The first zoo hippo in modern history was Obaysch
who arrived at the London Zoo on May 25, 1850, where he attracted up to 10,000 visitors a day and inspired a popular song, the Hippopotamus Polka.[40] Hippos have remained popular zoo animals since Obaysch, and generally breed well in captivity. Their birth rates are lower than in the wild, but this is attributed to zoos not wanting to breed as many hippos as possible, since hippos are large and relatively expensive animals to maintain.[8][40]

Most hippos in zoos were born in captivity. There are enough hippos in the international zoo system that introducing further animals from the wild will be unnecessary if zoos cooperate to maintain the genetic diversity of the breeding stock.[8]

Like many zoo animals, hippos were traditionally displayed in concrete exhibits. In the case of hippos, they usually had a pool of water and patch of grass. In the 1980s, zoo designers increasingly designed exhibits that reflected the animals' native habitats. The best known of these, the Toledo Zoo Hippoquarium, features a 360,000 gallon pool for hippos.[41] In 1987, researchers were able to tape, for the first time, an underwater birth (as in the wild) at the Toledo Zoo. The exhibit was so popular that the hippos became the logo of the Toledo Zoo.[42]


ReferencesEdit

  1. Cite error: Invalid <ref> tag; no text was provided for refs named Redlist
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  8. 8.00 8.01 8.02 8.03 8.04 8.05 8.06 8.07 8.08 8.09 8.10 8.11 8.12 8.13 8.14 8.15 8.16 8.17 Eltringham, S.K. (1999). The Hippos, London: Academic Press.
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  41. includeonly>Melissa Greene. "No rms, jungle vu: a new group of "landscape-immersion" zoo designers are trying to break down visitors' sense of security by reminding them that wild animals really are wild.", The Atlantic Monthly, December 1987.
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