A species
Common hippopotamus
Hippopotamus amphibius
The river giant that walks underwater.
You and the common hippopotamus last shared an ancestor about 95 million years ago (on 23 December, if life's history were one year).
The common hippo cannot really swim. It sinks and gallops along the riverbed in slow motion, walking on the bottom instead of floating. Surprisingly, its closest living relatives are whales, dolphins and porpoises, not horses.
It is one of the largest land animals alive, about 3 to 5 metres long, with large males as heavy as a small truck. It has a big barrel-shaped body, short legs and grey to purple-grey skin with almost no hair. Its small eyes, ears and nostrils sit high on top of its head, so they stay above water while the rest of it hides below.
By day it often rests in shallow water about 2 metres deep, crowded close with other hippos. At dusk it leaves the water to graze on short grasses near the bank.
Natural sunscreen
Hippos make a fluid often called blood sweat that starts clear and turns red. It is not blood or true sweat, and it keeps skin moist while guarding against sunburn and germs.
Teeth that never stop
Its long tusks keep growing all through life, reaching about 50 centimetres long. Hippos use them mainly for fighting and defence.
Fast on land
On land it can run up to about 35 kilometres per hour over short distances.