Hippo

Hippos or hippopotamus are recognisable harmony land animals by their barrel-shaped torsos, wide-opening mouths revealing large canine tusks, nearly hairless bodies, columnar legs and large size; adults average 1,500 kg (3,310 lb) and 1,300 kg (2,870 lb) for males and females respectively. 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, where territorial males preside over a stretch of river and groups of five to thirty females and young hippos. During the day, they remain cool by staying in the water or mud; reproduction and childbirth both occur in water. They emerge at dusk to graze on grasses. While hippos rest near each other in the water, grazing is a solitary activity and hippos are not territorial on land. The hippo is among the most dangerous animals in the world as it is highly aggressive and unpredictable. They are threatened by habitat loss and poaching for their meat and ivory canine teeth.

Hippos are among the largest living land mammals, being only smaller than elephants and some rhinoceroses. Among the extant African megafauna, behind the two African elephant species, they average smaller than the white rhinoceros but are larger by body mass than the black rhinoceros and the giraffe. Mean adult weight is around 1,500 kg (3,310 lb) and 1,300 kg (2,870 lb) for males and females respectively, very large males can reach 2,000 kg (4,410 lb) and exceptional males weighing 2,660 kg (5,860 lb), 3,200 kg (7,050 lb) and 4,500 kg (9,920 lb) (in captivity)[26] have been reported. Male hippos appear to continue growing throughout their lives while females reach maximum weight at around age 25.

Hippos have barrel-shaped bodies with short legs and long muzzles. Their skeletal structures are graviportal,[8]:8 adapted to carrying their enormous weight, and their specific gravity allows them to sink and move along the bottom of a river. Hippopotamuses have small legs (relative to other megafauna) because the water in which they live reduces the weight burden. Though they are bulky animals, hippos can gallop at 30 km/h (19 mph) on land but normally trot. They are incapable of jumping but do climb up steep banks. Despite being semiaquatic and having webbed feet, an adult hippo is not a particularly good swimmer nor can it float. It is rarely found in deep water; when it is, the animal moves by porpoise-like leaps from the bottom.[8]:3 The eyes, ears, and nostrils of hippos are placed high on the roof of their skulls. This allows these organs to remain above the surface while the rest of the body submerges.:259 The testes of the males descend only partially and a scrotum is not present. In addition, the penis retracts into the body when not erect. The genitals of the female hippos are unusual in that the vagina is ridged and two large diverticula protrude from the vulval vestibule. The function of these is unknown.[8]:28–29

The hippo's jaw is powered by a large masseter and a well-developed digastric; the latter loops up behind the

former to the hyoid.:259 The jaw hinge is located far back enough to allow the animal to open its mouth at almost 180°.[8]:17 A moderate folding of the orbicularis oris muscle allows the hippo to achieve such a gape without tearing any tissue. The bite force of an adult female hippo has been measured as 8,100 newtons (1,800 lbf). Hippo teeth sharpen themselves as they grind together. The lower canines and lower incisors are enlarged, especially in males, and grow continuously. The incisors can reach 40 cm (1 ft 4 in), while the canines reach up to 50 cm (1 ft 8 in). The canines and incisors are used for combat and play no role in feeding. Hippos rely on their broad horny lips to grasp and pull grasses which are then ground by the molars.[31]:259, 263 The hippo is considered to be a pseudoruminant; it has a complex three-chambered stomach but does not "chew cud".[8]:22

Unlike most other semiaquatic animals, hippos have very little hair.:260 The skin is 6 cm (2 in) thick, providing it great protection against conspecifics and predators. By contrast, its subcutaneous fat layer is thin.[8]:3 The animals' upper parts are purplish-grey to blue-black, while the under parts and areas around the eyes and ears can be brownish-pink.[31]:260 Their skin secretes a natural sunscreen substance which is red-coloured. 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 (hipposudoric acid) and one orange (norhipposudoric acid). The two pigments are highly acidic compounds. They inhibit the growth of disease-causing bacteria, and their light absorption 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 synthesise the pigments from precursors such as the amino acid tyrosine. Nevertheless, this natural sunscreen cannot prevent the animal's skin from cracking if it stays out of water too long. The secretion does help regulate the body temperature of the hippo and acts an antibiotic source.

Hippos differ from all other large land mammals, being of semiaquatic habits, and spending their days in lakes and rivers.[8]:3 They can be found in both savannah and forest areas. Proper habitat requires enough water to submerge in and grass nearby.[28] Larger densities of the animals inhabit quiet waters with mostly firm, smooth sloping beaches. Male hippos may be found in very small numbers in rapid waters in rocky gorges.:264 Hippos mostly live in freshwater habitats, however populations in West Africa mostly inhabit estuarine waters and may even be found at sea. With the exception of eating, most of a hippo's life occurs in the water. Hippos leave the water at dusk and travel inland, sometimes up to 15 km (9 mi), to graze on short grasses, their main source of food. They spend four to five hours grazing and can consume 68 kg (150 lb) of grass each night.

Like most herbivores, hippos consume other plants if presented with them, but their diet in nature consists almost entirely of grass, with only minimal consumption of aquatic plants. Hippos are born with sterile intestines, and require bacteria obtained from their mothers' feces to digest vegetation. On occasion, hippos have been filmed eating carrion, usually near the water. There are other reports of meat-eating, and even cannibalism and predation.[69] The stomach anatomy of a hippo is not suited to carnivory, and meat-eating is likely caused by aberrant behaviour or nutritional stress.