**Taxonomy and Evolution**:
– The modern hippopotamus and the pygmy hippopotamus are the only living members of the family Hippopotamidae.
– Some taxonomists place hippos and anthracotheres in the superfamily Anthracotheroidea.
– Hippopotamidae are classified along with other even-toed ungulates in the order Artiodactyla.
– Evolutionary relationships show that hippos’ closest living relatives are cetaceans.
– Hippos and whales shared a common semiaquatic ancestor around 60 million years ago.
– Ancestral group likely split into two branches around 54 million years ago, one evolving into cetaceans and the other into anthracotheres.
**Extinct Species**:
– Three species of Malagasy hippos became extinct during the Holocene.
– Fossil evidence indicates hunting by humans contributed to their extinction.
– Hippopotamus gorgops grew larger than living hippos.
– Hippopotamus antiquus ranged throughout Europe, extending to Britain.
– Isolated individual Malagasy hippos may have survived in remote pockets.
**Conservation Status**:
– Hippos are listed as Vulnerable on the IUCN Red List.
– They are among the most dangerous animals due to their aggressive nature.
– Threatened by habitat loss and poaching for meat and ivory.
– Inhabit rivers, lakes, and mangrove swamps.
– Remain cool during the day in water or mud, grazing on grasses at dusk.
**Physical Characteristics**:
– Hippos are megaherbivores, surpassed in size on land by elephants and some rhinoceros species.
– Adult weight for bulls is around 1,480kg (3,260lb), with exceptionally large males reaching 2,660kg (5,860lb).
– Females reach maximum weight around age 25.
– Length ranges from 2.90 to 5.05m (9.5 to 16.6ft) with a shoulder height of 1.30 to 1.65m (4.3 to 5.4ft).
– Barrel-shaped bodies, hourglass-shaped skulls, and small legs adapted to living in water.
**Adaptations and Physiology**:
– Hippos have dense bones and a low center of gravity for underwater movement.
– Webbed toes and a 45-degree pelvis angle aid in swimming.
– Nostrils, ears, and eyes are adapted to aquatic life.
– Powerful jaw muscles and unique vocal features.
– Characteristic yawn, large droopy cheeks, and unique skeletal adaptations.
The hippopotamus (/ˌhɪpəˈpɒtəməs/; pl.: hippopotamuses or hippopotami), also shortened to hippo (pl.: hippos; Hippopotamus amphibius), further qualified as the common hippopotamus, Nile hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus (Choeropsis liberiensis or Hexaprotodon liberiensis). Its name comes from the ancient Greek for "river horse" (ἱπποπόταμος).
| Hippopotamus Temporal range:
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|---|---|
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| A hippopotamus in Saadani National Park, Tanzania | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Family: | Hippopotamidae |
| Genus: | Hippopotamus |
| Species: | H. amphibius
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| Binomial name | |
| Hippopotamus amphibius | |
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| Current distribution of the hippopotamus | |
After elephants and rhinoceroses, the hippopotamus is the next largest land mammal. It is also the largest extant land artiodactyl. Despite their physical resemblance to pigs and other terrestrial even-toed ungulates, the closest living relatives of the hippopotamids are cetaceans (whales, dolphins, porpoises, etc.), from which they diverged about 55 million years ago. Hippos are recognisable for their barrel-shaped torsos, wide-opening mouths with large canine tusks, nearly hairless bodies, pillar-like legs, and large size: adults average 1,500 kg (3,300 lb) for bulls (males) and 1,300 kg (2,900 lb) for cows (females). Despite its stocky shape and short legs, it is capable of running 30 km/h (19 mph) over short distances.
Hippos inhabit rivers, lakes, and mangrove swamps. Territorial bulls each preside over a stretch of water and a group of five to thirty cows and calves. Mating and birth both occur in the water. During the day, hippos remain cool by staying in water or mud, emerging at dusk to graze on grasses. While hippos rest near each other in the water, grazing is a solitary activity and hippos typically do not display territorial behaviour on land. Hippos are among the most dangerous animals in the world due to their aggressive and unpredictable nature. They are threatened by habitat loss and poaching for their meat and ivory (canine teeth).