Hippopotamus

Posted December 22nd, 2007 by Anonymous

The hippopotamus ( Hippopotamus amphibius ), from the Greek ‘ιπποπόταμος ( hippopotamos , hippos meaning "horse" and potamos meaning "river"), often shortened to "hippo", is a large, mostly plant-eating African mammal, one of only two extant species in the family Hippopotamidae (the other being the Pygmy Hippopotamus).

The hippopotamus is semi-aquatic, inhabiting rivers and lakes in sub-Saharan Africa in large groups of up to 40 hippos. During the day they remain cool by staying in the water or mud; reproduction and childbirth both occur in water, where territorial bulls preside over a stretch of river. They emerge at dusk to graze on grass. While hippos rest near each other in territories 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 and the like. The common ancestor of whales and hippos split from other even-toed ungulates around 60 million years ago. The earliest known hippopotamus fossils, belonging to the genus Kenyapotamus in Africa, date to around 16 million years ago.

The hippopotamus is recognizable for its barrel-shaped torso, hairless body, stubby legs and tremendous size. It is similar in size to the White Rhinoceros; only elephants are consistently larger and despite its stocky shape and short legs, it can easily outrun a human. Despite its popularity in zoos and cuddly portrayal as gentle giants in fiction, the hippopotamus is among the most dangerous and aggressive of all mammals. There are an estimated 125,000 to 150,000 hippos remaining throughout Sub-Saharan Africa, of which Zambia (40,000) and Tanzania (20,000-30,000) have the largest populations . They are still threatened by poaching for their meat and ivory canine teeth, and by habitat loss.

Taxonomy and origins

Hippopotamuses (the anomalous plural hippopotami is sometimes used — the correct Greek plural hippopotamodes is never used in English; hippos can be used as a short plural), are gregarious, living in groups of up to 40 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 . They are also known as the Common Hippopotamus or the Nile Hippopotamus.

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 .

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

H. a. amphibius – (the nominate subspecies) which stretched from Egypt, where they are now extinct down 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 in simple variation in non-representative samples. Genetic analyses have tested the existence of three of these putative subspecies. A study using mitochondrial DNA from skin biopsies taken from 13 sampling locations, consider genetic diversity and structure among hippo populations across the continent. They find low but significant genetic differentiation among H. a. amphibius , H. a. capensis , and H. a. kiboko . Neither H.a.constrictus nor H.a.tschadensis have been tested.

Classification

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

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. Evidence, first from blood proteins, then from molecular systematics and DNA and the fossil record, show that their closest living relatives are cetaceans—whales, porpoises and the like. Hippopotamuses have more in common with whales than they do with other Artiodactyls (even-toed ungulates), such as pigs because the common ancestor of hippos and whales branched-off from ruminants and the rest of the even-toed ungulates. Thus, hippos are more closely related to whales than to other members of Artiodactyla. While cetaceans and hippos are each other's closest living relatives, their lineages split soon after their divergence from the rest of the even-toed ungulates.

Evolution

The most recent research into the origins of hippopotamidae suggests that hippos and whales shared a common semi-aquatic ancestor that branched off from other Artiodactyls around 60 million years ago. This hypothesized ancestor likely split into two branches around 54 million years ago. One branch would evolve into cetaceans, possibly beginning with the proto-whale Pakicetus from 52 million years ago and other early whale ancestors, known as Archaeoceti, which eventually underwent aquatic adaptation into the almost completely aquatic cetaceans.

The other branch became the anthracotheres, a large family of four-legged beasts, the earliest of whom in the Late Eocene would have resembled skinny hippopotamuses with comparatively small and narrow heads. All branches of the anthracotheres, except that which evolved into Hippopotamidae, became extinct without leaving any descendants.

A rough evolution can be traced, however, from Eocene and Oligocene species: Anthracotherium and Elomeryx to the Miocene anthracotheres Merycopotamus and Libycosaurus . Merycopotamus , Libycosaurus and all hippopotamids can be considered to form a clade, with Libycosaurus being more closely related to hippos. Their common ancestor would have lived in the Miocene, about 20 million years ago. The last species of anthracotheres became extinct during the pliocene.

Hippopotamids are therefore deeply nested within the family Anthracotheriidae. The oldest known hippopotamid is the genus Kenyapotamus which lived in Africa from 16–8 million years ago. The Hippopotamidae are believed to have evolved in Africa, and while at one point species spread across Asia and Europe, no hippopotamuses have ever been discovered in the Americas, though, various anthracothere genera emigrated into North America during the early Oligocene. From 7.5–1.8 million years ago an ancestor to the modern hippopotamus, the Archaeopotamus lived in Africa and the Middle East.

While the fossil record of hippos is still poorly understood, the two modern genera, Hippopotamus and Choeropsis (sometimes Hexaprotodon ), may have diverged as far back as 8 million years ago. Scientists disagree whether or not the modern Pygmy Hippopotamus is a member of Hexaprotodon —a genus of many Asian Hippopotamuses that is more-closely related to Hippopotamus ; or Choeropsis —an older and basal genus.

Extinct species

As many as three species of Malagasy Hippopotamus became extinct during the Holocene on Madagascar, one of them within the past 1,000 years. The Malagasy Hippos were smaller than the modern hippopotamus, likely through the process of insular dwarfism. There is fossil evidence that many Malagasy Hippos were hunted by humans, a likely factor in their eventual extinction. Isolated members of Malagasy Hippopotamus may have survived in remote pockets; in 1976, villagers described a living animal called the Kilopilopitsofy, which may have been a Malagasy Hippopotamus.

A separate species of Hippopotamus, the European Hippopotamus ( H. antiquus ) and H. gorgops ranged throughout continental Europe and the British Isles. Both species became extinct before the last glaciation. Ancestors of European Hippos, found their way to many

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Hippopotamus - Wikipedia, the free encyclopedia

The hippopotamus ( Hippopotamus amphibius ), from the Greek ‘ιπποπόταμος ( hippopotamos , hippos meaning "horse" and potamos meaning "river"), often shortened to ...

Hippopotamus (Hippopotamus amphibius)

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Hippopotamus Homepage

hippopotamus - definition of hippopotamus by the Free Online ...

Definition of hippopotamus in the Online Dictionary. Meaning of hippopotamus. What does hippopotamus mean? hippopotamus synonyms, hippopotamus antonyms. Information about ...