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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

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
File:HippoSkelLyd2.png
File:Mouth of a hippo.jpg

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 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

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
File:Hippo.ogv

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

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
File:Hippopotamus @ Barcelona zoo.jpg

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
File:Obaysch 1852.gif
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
  2. ITIS on Hippopotamus amphibius. Integrated Taxonomic Information System. URL accessed on 2007-07-29.
  3. Time Tree. Time Tree. URL accessed on 2010-03-30.
  4. Time Tree. Time Tree. URL accessed on 2010-03-30.
  5. Hippopotamus from Merriam-Webster's Online Dictionary]
  6. Plural of hippopotamus from the OED
  7. Lydekker, R. (1915). Catalogue of the Ungulate Mammals in the British Museum of Natural History, London: British Museum.
  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.
  9. Okello, J.B.A, Nyakaana, S., Masembe, C., Siegismund, H.R. & Arctander, P. (2005). Mitochondrial DNA variation of the common hippopotamus: evidence for a recent population expansion.. Heredity 95 (3): 206–215.
  10. Meijaard, Erik (ed.) (September 2005). Suiform Soundings: The IUCN/SSC Pigs, Peccaries, and Hippos Specialist Group (PPHSG) Newsletter 5 (1).[dead link]
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  12. ADW: Hippopotamus amphibius: Information. Animaldiversity.ummz.umich.edu. URL accessed on 2008-11-03.
  13. Marshall, P.J., Sayer, J.A. (1976). Population ecology and response to cropping of a hippopotamus population in eastern Zambia. The Journal of Applied Ecology 13 (2): 391–403.
  14. Physical Description. URL accessed on 2009-05-08.
  15. Mammals: Hippopotamus. URL accessed on 2009-05-08.
  16. Oldest Hippo Turns 55!. Mesker Park Zoo. URL accessed on 2007-06-21.
  17. includeonly>"Celebrate with Donna", Evansville Courier & Press, 2007-07-12. Retrieved on 2007-07-15.
  18. includeonly>"Old mother hippo dies", Agence France Press, July 12, 1995.
  19. 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).
  20. van Kolfschoten, Th. (2000). The Eemian mammal fauna of central Europe. Netherlands Journal of Geosciences 79 (2/3): 269–281.
  21. 21.0 21.1 Pliny the Elder. "Chapter 15, Book VIII" Naturalis Historia (in Latin original or English translation).
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  23. 23.0 23.1 Grey, J., Harper, D.M. (2002). Using Stable Isotope Analyses To Identify Allochthonous Inputs to Lake Naivasha Mediated Via the Hippopotamus Gut. Isotopes in Environmental Health Studies 38 (4): 245–250.
  24. J.P. Dudley. Reports of carnivory by the common hippo Hippopotamus Amphibius. South African Journal of Wildlife Research 28 (2): 58–59.
  25. McCarthy, T.S., W.N. Ellery, A Bloem (1998). Some observations on the geomorphological impact of hippopotamus (Hippopotamus amphibius L.) in the Okavango Delta, Botswana. African Journal of Ecology 36 (1): 44–56.
  26. Beckwitt, R., Shea, J., Osborne, D., Krueger, S., and Barklow, W. (2002). A PCR-based method for sex identification in Hippopotamus amphibius. African Zoology Journal: 127–130.
  27. William E. Barklow (2004). Low-frequency sounds and amphibious communication in Hippopotamus amphibious. The Journal of the Acoustical Society of America 115 (5).
  28. 28.0 28.1 28.2 Graham L.H., Reid K.; Webster T.; Richards M.; Joseph S. (2002). Endocrine patterns associated with reproduction in the Nile hippopotamus (Hippopotamus amphibius) as assessed by fecal progestagen analysis. General and Comparative Endocrinology 128 (1): 74–81.
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  34. National Geographic exhibit on different animals and their poop.
  35. Nature's World: Africa's Lions and Wildebeests. Discovery HD Theater.
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  37. Hart, George (1986). A Dictionary of Egyptian Gods and Goddesses, Routledge.
  38. Herodotus. "Chapter 71, Book II" The Histories (in English translation).
  39. [1]
  40. 40.0 40.1 Root, N. J. (1993). Victorian England’s Hippomania.. Natural History 103: 34–39.
  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.
  42. Hippoquarium. Toledo Zoo. URL accessed on 2007-03-26.

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