iPhoneOgraphy – 25 Oct 2016 (Day 299/366)
The common hippopotamus (Hippopotamus amphibius), or hippo, is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus (Choeropsis liberiensis or Hexaprotodon liberiensis). The name comes from the Ancient Greek for “river horse” (ἱπποπόταμος). After the elephant and rhinoceros, the common hippopotamus is the third-largest type of land mammal and the heaviest extant artiodactyl. Despite their physical resemblance to pigs and other terrestrial even-toed ungulates, the closest living relatives of the Hippopotamidae are cetaceans (whales, porpoises, etc.) from which they diverged about 55 million years ago. 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.
Common hippos are recognisable by their barrel-shaped torsos, wide-opening mouths revealing large canine tusks, nearly hairless bodies, columnar-like legs and large size; adults average 1,500 kg (3,300 lb) and 1,300 kg (2,900 lb) for males and females respectively, making them the largest species of land mammal after the three species of elephants and the white and Indian rhinoceros. Despite its stocky shape and short legs, it is capable of running 30 km/h (19 mph) over short distances. The hippopotamus is a highly aggressive and unpredictable animal and is ranked among the most dangerous animals in Africa. Nevertheless, they are still threatened by habitat loss and poaching for their meat and ivory canine teeth.
The common hippopotamus is semiaquatic, inhabiting rivers, lakes and mangrove swamps, where territorial bulls preside over a stretch of river and groups of five to thirty females and young. 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 hippopotamuses rest near each other in the water, grazing is a solitary activity and hippos are not territorial on land.
The word “hippopotamus” is derived from the Ancient Greek ἱπποπόταμος, hippopotamos, from ἵππος, hippos, “horse”, and ποταμός, potamos, “river”, meaning “horse of the river”. In English, the plural is hippopotamuses, but “hippopotami” is also used; “hippos” can be used as a short plural. Hippopotamuses are gregarious, living in groups of up to thirty animals. A group is called a pod, herd, dale, or bloat.
In Africa, the hippo is known by various names, including seekoei (Afrikaans), mvuvu (Venda), kubu (Lozi) and mvubu (Xhosa, Siswati and Zulu) in the south; kiboko (Swahili), ensherre (Nkore), tomondo (Turu), nvubu (Luganda), ifuru (Luhya), emiria (Ateso), magawit (Sebei), kibei (Kalenjin) and olmakau (Maasai) in the African Great Lakes region; and gumarre (Amharic) and jeer (Somali) in the Horn of Africa.
Hippopotamuses are among the largest living land mammals, being only smaller than elephants and some rhinoceroses. Mean adult weight is around 1,500 kg (3,300 lb) and 1,300 kg (2,900 lb) for males and females respectively, very large males can reach 2,000 kg (4,400 lb) and an exceptional male weighing almost 2,700 kg (6,000 lb) has been reported. Male hippos appear to continue growing throughout their lives while females reach maximum weight at around age 25.
Different from all other large land mammals, hippos are of semiaquatic habits, spending the day in lakes and rivers. 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. Their barrel-shaped bodies have graviportal skeletal structures, 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, hippopotamuses 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. 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 are unusual in that the vagina is ridged and two large diverticula protrude from the vulval vestibule. The function of these is unknown.
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. The jaw hinge is located far back enough to allow the animal to open its mouth at almost 180°. A moderate folding of the orbicularis oris muscle allows the hippo to achieve such a gape without tearing any tissue. On the National Geographic Channel television program, “Dangerous Encounters with Brady Barr”, Dr. Brady Barr measured the bite force of an adult female hippo at 8,100 newtons (1,800 lbf); Barr also attempted to measure the bite pressure of an adult male hippo, but had to abandon the attempt due to the male’s aggressiveness. Hippopotamus 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 (1.3 ft), while the canines reach up to 50 cm (1.6 ft). 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. The hippo is considered to be a pseudo ruminant; it has a complex three-chambered stomach but does not “chew cud”.
Unlike most other semiaquatic animals, the hippopotamus has very little hair. The skin is 6 cm (2 in) thick, providing it great protection against conspecifics and predators. By contrast, its subcutaneous fat layer is thin. The animals’ upper parts are purplish-gray to blue-black, while the under parts and areas around the eyes and ears can be brownish-pink. 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. Both pigments inhibit the growth of disease-causing bacteria; as well, 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. Nevertheless, this natural sunscreen cannot prevent the animal’s skin from cracking if it stays out of water too long.
A hippo’s lifespan is typically 40–50 years. Donna the Hippo was the oldest living hippo in captivity. She lived at the Mesker Park Zoo in Evansville, Indiana in the US until her death in 2012 at the age of 61. The oldest hippo ever recorded was called Tanga; she lived in Munich, Germany, and died in 1995 at the age of 61.