HIPPOPOAMUS

The hippopotamus (Hippopotamus amphibius), from the Greek ἱπποπόταμος (hippopotamos, ιππος hippos meaning "horse" and πόταμος potamus 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 groups of 5-30 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, porpoise, etc.). 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, enormous mouth and teeth, hairless body, stubby legs and tremendous size. It is similar in size to the White Rhinoceros; only elephants are consistently heavier. Despite its stocky shape and short legs, it can easily outrun a human. Hippos have been clocked at 30 mph (48 km/h) while running short distances, faster than an Olympic sprinter. The hippopotamus is one of the most aggressive animals in the world, and are often regarded as the most dangerous animal in Africa. 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 [1]. They are still threatened by poaching for their meat and ivory canine teeth, and by habitat loss.Hippopotamuses are one of the largest mammals. They can live in the water, or go 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.[5]

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 1500–1800 kg (3,300–4,000 lbs). Females are smaller than their male counterparts, with average weights measuring between 1300–1,500 kg (2,900–3,300 lbs).[5] Older males can get much larger, reaching at least 3,200 kg (7,100 lbs) and occasionally weighing 4500 kg (9900 lbs)[20][21]. Male hippos appear to continue growing throughout their lives; females reach a maximum weight at around age 25.[22]

On the National Geographic Channel television program, "Dangerous Encounters with Brady Barr", Dr. Brady Barr measured the bite pressure of an adult female hippo at 1,821 lb (826 kg) after abandoning an attempt to measure the bite of an adult male due to its aggressiveness.[23]

Hippos average 3.5 meters (11 ft) long, 1.5 meters (5 ft) tall at the shoulder. 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.[5]
A bull hippo out of water during daylight, Ngorongoro Crater, Tanzania.
A bull hippo out of water during daylight, Ngorongoro Crater, Tanzania.

A hippo's lifespan is typically 40 to 50 years.[5] Donna the Hippo, 56, is the oldest living hippo in captivity. She lives at the Mesker Park Zoo in Evansville, Indiana.[24][25] The oldest hippo ever was called Tanga; she lived in Munich, Germany, and died in 1995 at the age of 61.[26]
A drawing of a hippopotamus skeleton.
A drawing of a hippopotamus skeleton.

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 legs that are small, relative to other megafauna, because the water in which they live reduces the weight burden. Like other aquatic mammals, the hippopotamus has very little hair.[5]
Eye of a hippo in San Francisco Zoo
Eye of a hippo in San Francisco Zoo

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 and one orange. The two pigments are highly acidic compounds. They are known as red pigment hipposudoric acid and orange pigment norhipposudoric acid. The red pigment was found to inhibit the growth of disease-causing bacteria. 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. [27]