Hippopotamus
The hippopotamus, often shortened to hippo, further qualified as the common hippopotamus, Nile hippopotamus and river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus. Its name comes from the Ancient Greek for "river horse".
After elephants and rhinoceroses, the hippopotamus is the next largest land mammal. It is also the largest extant land artiodactyl. Despite their physical resemblance to pigs and other terrestrial even-toed ungulates, the closest living relatives of the hippopotamids are cetaceans, from which they diverged about 55 million years ago. Hippos are recognisable for their barrel-shaped torsos, wide-opening mouths with large canine tusks, nearly hairless bodies, short legs, and large size: adults average for bulls and for cows.
Hippos inhabit rivers, lakes, and mangrove swamps. Territorial bulls each preside over a stretch of water and a group of five to thirty cows and calves. Mating and birth both occur in the water. During the day, hippos remain cool by staying in water or mud, emerging at dusk to graze on grasses. While hippos rest near each other in the water, grazing is a solitary activity and hippos typically do not display territorial behaviour on land. Hippos are among the most dangerous animals in the world due to their aggressive and unpredictable nature. They are threatened by habitat loss and poaching for their meat and ivory.
Etymology
The Latin word hippopotamus is derived from the ancient Greek ἱπποπόταμος, from ἵππος and ποταμός , together meaning. In English, the usual plural is "hippopotamuses".Taxonomy and origins
Classification
The modern hippopotamus and the pygmy hippopotamus are the only living members of the family Hippopotamidae. Some taxonomists place hippos and anthracotheres in the superfamily Anthracotheroidea. Hippopotamidae are classified along with other even-toed ungulates in the order Artiodactyla.Five subspecies of hippos have been described based on morphological differences in their skulls as well as differences in geographical range:
- H. a. amphibius – ranges from Gambia east to Ethiopia and then south to Mozambique and historically ranged as far north as Egypt; its skull is distinguished by a moderately reduced preorbital region, a bulging dorsal surface, elongated mandibular symphysis and larger chewing teeth.
- H. a. kiboko – found in Kenya and Somalia; was noted to be smaller and more lightly coloured than other hippos with wider nostrils, somewhat longer snout and more rounded and relatively raised orbits with the space between them being incurved.
- H. a. capensis – found in Zambia and South Africa; distinguished by wider orbits.
- H. a. tschadensis – ranges between Chad and Niger; featured a slightly shorter but broader face, and pronounced, forward-facing orbits.
- H. a. constrictus – ranges from the southern Democratic Republic of Congo to Angola and Namibia; skull characterised by a thicker preorbital region, shorter snout, flatter dorsal surface, reduced mandibular symphysis and smaller chewing teeth.
Evolution
Until 1909, naturalists classified hippos together with pigs based on molar patterns. Several lines of evidence, first from blood proteins, then from molecular systematics, DNA and the fossil record, show their closest living relatives are cetaceans. The common ancestor of hippos and whales branched off from Ruminantia and the rest of the even-toed ungulates; the cetacean and hippo lineages split soon afterwards.The most recent theory of the origins of Hippopotamidae suggests hippos and whales shared a common semiaquatic ancestor that branched off from other artiodactyls around. This hypothesised ancestral group likely split into two branches again around.
One branch would evolve into cetaceans, possibly beginning about, with the protowhale Pakicetus and other early whale ancestors collectively known as Archaeoceti. This group eventually underwent aquatic adaptation into the completely aquatic cetaceans. The other branch became the anthracotheres, a large family of four-legged beasts, the earliest of which in the late Eocene would have resembled skinny hippos with comparatively smaller, narrower heads. All branches of the anthracotheres, except that which evolved into Hippopotamidae, became extinct during the Pliocene, leaving no descendants.
A rough evolutionary lineage of the hippo can thus be traced from Eocene and Oligocene species: from Anthracotherium and Elomeryx to the Miocene species Merycopotamus and Libycosaurus and finally the very latest anthracotheres in the Pliocene. These groups lived across Eurasia and Africa. The discovery of Epirigenys in East Africa, which was likely a descent of Asian anthracotheres and a sister taxon to Hippopotamidae, suggests that hippo ancestors entered Africa from Asia around. An early hippopotamid is the genus Kenyapotamus, which lived in Africa from 15 to. Hippopotamid species would spread across Africa and Eurasia, including the modern pygmy hippo. From 7.5 to, a possible ancestor to the modern hippo, Archaeopotamus, lived in Africa and the Middle East. The oldest records of the genus Hippopotamus date to the Pliocene. The oldest unambiguous records of the modern H. amphibius date to the Middle Pleistocene, though there are possible Early Pleistocene records.
Extinct species
Three species of Malagasy hippopotamus became extinct during the Holocene on Madagascar, the last of them within the past 1,000 years. The Malagasy hippos were smaller than the modern hippo, likely a result of the process of insular dwarfism. Fossil evidence indicates many Malagasy hippos were hunted by humans, a factor in their eventual extinction. Isolated individual Malagasy hippos may have survived in remote pockets; in 1976, villagers described a living animal called the kilopilopitsofy, which may have been a Malagasy hippo.Hippopotamus gorgops from the Early Pleistocene to the early Middle Pleistocene of Africa and West Asia grew considerably larger than the living hippopotamus, with an estimated body mass of over. Hippopotamus antiquus ranged throughout Europe, extending as far north as Britain during the Early and Middle Pleistocene epochs, before being replaced by the modern H. amphibius in Europe during the latter part of the Middle Pleistocene. The Pleistocene also saw a number of dwarf species evolve on several Mediterranean islands, including Crete, Cyprus, Malta, and Sicily. Of these, the Cyprus dwarf hippo survived until the end of the Pleistocene or early Holocene. Evidence from the archaeological site Aetokremnos continues to cause debate on whether or not the species was driven to extinction or even encountered by humans.
Characteristics
The hippopotamus is a megaherbivore and is the third largest land mammal after elephants and some rhinoceros species. The mean adult weight is around for bulls and for cows. Exceptionally large males have been recorded reaching. Male hippos appear to continue growing throughout their lives, while females reach maximum weight at around age 25. It is long, including a tail of about in length and tall at the shoulder, with males and females ranging and tall at the shoulder respectively. The species has a typical head–body length of and an average standing height of at the shoulder.Hippos have barrel-shaped bodies with short tails and legs, and an hourglass-shaped skull with a long snout. Their skeletal structures are graviportal, adapted to carrying their enormous weight, and their dense bones and low centre of gravity allows them to sink and move along the bottom of the water. Hippopotamuses have small legs because the water in which they live reduces the weight burden. The toes are webbed and the pelvis rests at an angle of 45 degrees. Though chubby-looking, hippos have little fat. 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 is submerged. The nostrils and ears can close when underwater while nictitating membranes cover the eyes. The vocal folds of the hippo are more horizontally positioned, much like baleen whales. Underneath are throat tissues, where vibrations are transmitted to produce underwater calls.
The hippo's jaw powered by huge masseter and digastric muscles, and the hinge is located far back enough so that they can open their mouths at 100–110 degrees. Extensions at the back of the jaw create more surface area for muscle attachment, which gives them large, droopy cheeks This allows them to achieve their gape without tearing any tissue. On the lower jaw, the incisors and canines grow continuously, the former reaching, while the latter can grow to up to. The lower canines are sharpened through contact with the smaller upper canines. The canines and incisors are used mainly for combat instead of feeding, and the jaws are too rigid for side to side motion, making them less efficient for chewing. Hippos rely on their flattened, horny lips to grasp and pull grasses which are then passed to the molars, which have complex enamel folds on their chewing surface. The hippo is considered to be a pseudoruminant; it has a complex three-chambered stomach, but does not "chew cud".
Hippo skin is thick across much of its body with little hair. The animal is mostly purplish-grey or blue-black, but brownish-pink on the underside and around the eyes and ears. Their skin secretes a natural, red-coloured sunscreen substance that 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 highly acidic pigments have been identified in the secretions; one red hipposudoric acid and one orange norhipposudoric acid, which inhibit the growth of disease-causing bacteria and their light-absorption profile peaks in the ultraviolet range, creating a sunscreen effect. Regardless of diet, all hippos secrete these pigments so food does not appear to be their source; rather, they may be synthesised from precursors such as the amino acid tyrosine. This natural sunscreen cannot prevent the animal's skin from cracking if it stays out of water too long.
The testes of the males do not fully descend 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 the vulval vestibule has two large, protruding diverticula. Both of these have an unknown function.
A hippo's lifespan is typically 40 to 50 years. Donna the Hippo was one of the oldest living hippos 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. Two hippos share the record for the oldest hippo ever recorded at 65 years. Bertha, a female Hippo, who lived in the Manila Zoo in the Philippines since it first opened in 1959 until her death in July 2017, and male Hippo Lu, from the Ellie Schiller Homosassa Springs Wildlife State Park, who was born at the San Diego Zoo on January 26th, 1960, and died at Homosassa, where he died in June 2025, also at the age of 65. Two other notably long-lived hippos were the female Tanga at the Hellabrunn Zoo in Munich, Germany and male Blackie at the Cleveland Metroparks Zoo. Currently, the oldest hippo in captivity is believed to be Mae Mali at the Khao Kheow Open Zoo in Thailand, who will turn 60 in September 2025.