The Hippopotamus averages 3.5 metres (11 feet) in length, 1.5 metres (5 feet) tall at the shoulder and weigh from 1500 kilograms to 3200 kilograms (3,300 to 7,000 pounds). Baby hippos weigh 60 – 110 pounds (28 – 50 kilograms) at birth. Hippos have an almost hairless body which is covered in thin skin that dries easily in the sun, that is why hippos are found wallowing in mud ponds and lakes.
Hippopotamuses have a huge muzzle and mouth and canine teeth that measure 28 inches (72 centimetres) long. Their enormous mouth can open 4 feet (1.2 metres) wide. Hippos have unusual pores on their body which excretes a thick, oily, red sweat. The secretion is sometimes referred to as ‘blood sweat’ but is neither blood nor sweat. This secretion is initially colourless and turns red-orange within minutes, eventually becoming brown. Two distinct pigments have been identified in the secretions, one red and one orange. The two pigments are highly acidic compounds.
Here is a basic anatomy diagram of a River Hippopotamus.
River hippos unlike pygmy hippos have a number of special adaptations to life in the water. Their eyes are on the tops of their heads and are set in sockets that bulge upward, keeping the eyes above the waterline when the body is afloat.
Hippos nostrils also face upward and can be sealed completely during a dive. Adult hippos are not generally buoyant. When in deep water, they usually propel themselves by leaps, pushing off from the bottom. Hippos move at speeds up to 8 kilometres per hour (5 miles per hour) in water. Young hippos are buoyant and more often move by swimming, propelling themselves with kicks of their back legs. Adult hippos typically resurface to breathe every 4 to 6 minutes. The young have to breathe every 2 to 3 minutes. 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.
Male and female hippos have similar bodies, however, male hippos are larger and have larger tusks than female hippos. This is most clearly demonstrated when male river hippos aggressively fight each other over territory.
Both male and female hippos have two pairs of tusks set in the lower jaw. Among pygmy hippos, the size difference between males and female hippos is not as great or as easily visible.
Hippos live relatively long lives. In the wild, river hippos live about 40 years, however, in captivity they have survived into their early 60s. The normal life span of pygmy hippos is unknown, however, in captivity some pygmy hippos have lived more than 40 years.