|Range map of hippopotamus. Historic range is in red while current range is in green.|
The hippopotamus (Hippopotamus amphibius), or hippo, from the ancient Greek for "river horse" (ἱπποπόταμος), is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae (the other is the pygmy hippopotamus). After the elephant and rhinoceros, the 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, their closest living relatives are cetaceans (whales, porpoises, etc.) from which they diverged about . The common ancestor of whales and hippos split from other even-toed ungulates around . The earliest known hippopotamus fossils, belonging to the genus Kenyapotamus in Africa, date to around .
The hippopotamus is semi-aquatic, inhabiting rivers, lakes and mangrove swamps, where territorial bulls preside over a stretch of river and groups of 5 to 30 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 grass. While hippopotamuses rest near each other in the water, grazing is a solitary activity and hippos are not territorial on land. Hippos are recognizable by their barrel-shaped torso, enormous mouth and teeth, nearly hairless body, stubby legs and tremendous size. They are the third largest type of land mammal by weight (between 1½ and 3 tonnes): the only heavier species on average are the white and Indian rhinoceroses, typically 1½ to 3½ tonnes, and the elephants, typically weighing 3 to 9 tonnes. The hippopotamus is one of the largest quadrupeds and, despite its stocky shape and short legs, it can easily outrun a human. Hippos have been clocked at 30 km/h (19 mph) over short distances. The hippopotamus is one of the most aggressive creatures in the world and is regarded as one of the most dangerous animals in Africa. Nevertheless, they are still threatened by habitat loss and poaching for their meat and ivory canine teeth.
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 30 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 Great Lakes region;:256 and Gumarre (Amharic) and Jeer (Somali) in the Horn.
Taxonomy and origins
The hippopotamus is the type genus of the family Hippopotamidae. The pygmy hippopotamus belongs to a different genus in Hippopotamidae, either Choeropsis or Hexaprotodon. Hippopotamidae are sometimes known as Hippopotamids. Sometimes the sub-family Hippopotaminae is used. Further, some taxonomists group hippopotamuses and anthracotheres in the super-family Anthracotheroidea.:39 Hippopotamidae are classified along with other even-toed ungulates in the order Artiodactyla. Other artiodactyls include camels, cows, deer and pigs, although hippopotamuses are not closely related to these groups.
- H. a. amphibius – (the nominate subspecies) which stretched from Egypt, where they are now extinct, south up the Nile River to Tanzania and Mozambique.
- H. a. kiboko – in Kenya in the African Great Lakes region, and in Somalia in the Horn of Africa. Broader nasals and more hollowed interorbital region.
- H. a. capensis – from Zambia to South Africa. Most flattened skull of the subspecies.
- H. a. tschadensis – throughout Western Africa to, as the name suggests, Chad. Slightly shorter and wider face, with prominent orbits.
- H. a. constrictus – in Angola, the southern Democratic Republic of Congo and Namibia. Named for its deeper preorbital constriction.
The suggested subspecies were never widely used or validated by field biologists; the described morphological differences were small enough that they could have resulted from simple variation in non-representative samples.:2 Genetic analyses have tested the existence of three of these putative subspecies. A study examining mitochondrial DNA from skin biopsies taken from 13 sampling locations, considered genetic diversity and structure among hippo populations across the continent. The authors found low, but significant, genetic differentiation among H. a. amphibius, H. a. capensis, and H. a. kiboko. Neither H. a. tschadensis nor H. a. constrictus have been tested.
Until 1909, naturalists grouped hippos with pigs, based on molar patterns. Several lines of evidence, first from blood proteins, then from molecular systematics and DNA  and the fossil record, show that their closest living relatives are cetaceans – whales, dolphins and porpoises. 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 that hippos and whales shared a common semi-aquatic ancestor that branched off from other artiodactyls around  This hypothesized ancestral group likely split into two branches around . One branch would evolve into cetaceans, possibly beginning about with the proto-whale Pakicetus and other early whale ancestors collectively known as Archaeoceti, which 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 whom in the late Eocene would have resembled skinny hippopotamuses with comparatively small and narrow heads. All branches of the anthracotheres, except that which evolved into Hippopotamidae, became extinct during the Pliocene without leaving any descendants..
A rough evolutionary lineage can be traced from Eocene and Oligocene species: Anthracotherium and Elomeryx to the Miocene species Merycopotamus and Libycosaurus and the very latest anthracotheres in the Pliocene. Merycopotamus, Libycosaurus and all hippopotamids can be considered to form a clade, with Libycosaurus being more closely related to hippos. Their common ancestor would have lived in the Miocene, about . Hippopotamids are therefore deeply nested within the family Anthracotheriidae. The Hippopotamidae are believed to have evolved in Africa; the oldest known hippopotamid is the genus Kenyapotamus, which lived in Africa from 16 to . While hippopotamid species spread across Asia and Europe, no hippopotamuses have ever been discovered in the Americas, although various anthracothere genera emigrated into North America during the early Oligocene. From 7.5 to an ancestor to the modern hippopotamus, Archaeopotamus, lived in Africa and the Middle East.
While the fossil record of hippos is still poorly understood, the two modern genera, Hippopotamus and Choeropsis (sometimes Hexaprotodon), may have diverged as far back as . Taxonomists disagree whether or not the modern pygmy hippopotamus is a member of Hexaprotodon – an apparently paraphyletic genus also embracing many extinct Asian hippopotamuses that is more closely related to Hippopotamus, or Choeropsis – an older and basal genus.
Three species of Malagasy hippopotamus became extinct during the Holocene on Madagascar, one of them within the past 1,000 years. The Malagasy hippos were smaller than the modern hippopotamus, likely through the process of insular dwarfism. There is fossil evidence that many Malagasy hippos were hunted by humans, a likely factor in their eventual extinction. Isolated members of Malagasy hippopotamus may have survived in remote pockets; in 1976, villagers described a living animal called the Kilopilopitsofy, which may have been a Malagasy hippopotamus.
Two species of Hippopotamus, the European hippopotamus (H. antiquus) and H. gorgops, ranged throughout continental Europe and the British Isles. Both species became extinct before the last glaciation. Ancestors of European hippos found their way to many islands of the Mediterranean during the Pleistocene. Both species were larger than the modern hippopotamus, averaging about 1 meter (3.3 feet) longer. The Pleistocene also saw a number of dwarf species evolve on several Mediterranean islands including Crete (H. creutzburgi), Cyprus (H. minor), Malta (H. melitensis) and Sicily (H. pentlandi). Of these, the Cyprus dwarf hippopotamus, survived until the end of the Pleistocene or early Holocene. Evidence from an archaeological site Aetokremnos, continues to cause debate on whether or not the species was encountered, and was driven to extinction, by man.
Hippopotamuses are among the largest living mammals; only elephants and some rhinoceroses and whales are heavier. They are considered megafauna, but unlike all other African megafauna, they have adapted for a semi-aquatic life in freshwater lakes and rivers.:3 Hippos measure 3.3 to 5.2 m (11 to 17 ft) long, including a tail of about 56 cm (22 in) in length and average about 1.5 m (4.9 ft) tall at the shoulder. 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 1,500–1,800 kg (3,300–4,000 lb). Females are smaller than their male counterparts, with average weights measuring between 1,300–1,500 kg (2,900–3,300 lb).:12 Older males can get much larger, reaching at least 3,200 kg (7,100 lb) with a few exceptional specimens exceeding 3,600 kg (7,900 lb). The heaviest known hippopotamus weighed approximately 4,500 kg (9,900 lb). Male hippos appear to continue growing throughout their lives; females reach a maximum weight at around age 25. The range of hippopotamus sizes overlaps broadly with those recorded for the white rhinoceros. While the rhinoceros reportedly is heavier on average, very large male hippopotamus are around the same mass as the largest white rhinos. Compared to a rhinoceros, the hippopotamus has a more elongated body and shorter legs, which result in the hippopotamus having a longer overall length and shorter standing height on average. The Indian rhinoceros also attains weights that can rival those of both hippopotamuses and white rhinoceros, and the three species rank only after elephants in overall body size among extant land animals.
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 water. Their barrel-shaped bodies have graviportal skeletal structures, adapted to carrying the 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. 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. Despite being semi-aquatic 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.:3 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.: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°.:17 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 8100 N (1821 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 (16 in), while the canines reach up to 50 cm (20 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 grass which is then grinded by the molars.:259, 263
Unlike most other semi-aquatic animals, the hippopotamus has very little hair.:260 The skin is 15 cm (5.9 in) thick, providing it great protection against conspecifics and predators. By contrast, its subcutaneous fat layer is thin.:3 The animals's upper parts are purplish-gray to blue-black while the under parts and areas around the eyes and ears can be brownish-pink.:260 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 (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.
A hippo's lifespan is typically 40–50 years.:277 Donna the Hippo, 60, was the oldest living hippo in captivity. She lived at the Mesker Park Zoo in Evansville, Indiana, USA until her death on August 1, 2012. At 58 years old, the oldest living hippo in captivity is currently Blackie, who lives in "retirement" at the Cleveland Metroparks Zoo. The oldest hippo ever recorded was called Tanga; she lived in Munich, Germany, and died in 1995 at the age of 61.
Hippopotamus amphibius was widespread in North Africa and Europe during the Eemian and late Pleistocene until about 30,000 years ago. There is archaeological evidence of its presence in the Levant, dating to less than 3000 years ago. The species was common in Egypt's Nile region during antiquity, but has since been extirpated. Pliny the Elder writes that, in his time, the best location in Egypt for capturing this animal was in the Saite nome; the animal could still be found along the Damietta branch after the Arab Conquest in 639. Hippos are still found in the rivers and lakes of the northern Democratic Republic of the Congo, Uganda, Tanzania and Kenya, north through to Ethiopia, Somalia and Sudan, west to Gambia, and south to South Africa. They inhabit both savanna and forest areas.
Genetic evidence suggests that common hippos in Africa experienced a marked population expansion during or after the Pleistocene Epoch, attributed to an increase in water bodies at the end of the era. These findings have important conservation implications as hippo populations across the continent are currently threatened by loss of access to fresh water. Hippos are also subject to unregulated hunting and poaching. In May 2006, the hippopotamus was identified as a vulnerable species on the IUCN Red List drawn up by the World Conservation Union (IUCN), with an estimated population of between 125,000 and 150,000 hippos, a decline of between 7% and 20% since the IUCN's 1996 study. Zambia (40,000) and Tanzania (20,000–30,000) possess the largest populations.
The hippo population declined most dramatically in the Democratic Republic of the Congo. The population in Virunga National Park had dropped to 800 or 900 from around 29,000 in the mid-1970s. The decline is attributed to the disruptions caused by the Second Congo War. The poachers are believed to be former Hutu rebels, poorly paid Congolese soldiers, and local militia groups. Reasons for poaching include the belief that hippos are harmful to society, and also for money. The sale of hippo meat is illegal, but black-market sales are difficult for Virunga National Park officers to track.
In the late 1980s, Pablo Escobar kept four hippos in a private menagerie at his residence in Hacienda Napoles, 100 km east of Medellín, Colombia, after buying them in New Orleans. They were deemed too difficult to seize and move after Escobar's fall, and hence left on the untended estate. By 2007, the animals had multiplied to 16 and had taken to roaming the area for food in the nearby Magdalena River. In 2009, two adults and one calf escaped the herd and, after attacking humans and killing cattle, one of the adults (called "Pepe") was killed by hunters under authorization of the local authorities.
Hippos spend most of their days wallowing in water or mud with the other members of their pod. This serves to keep their body temperature down, and to keep their skin from drying out or getting sunburned. With the exception of eating, most of hippopotamuses' lives – from childbirth, fighting with other hippos, to reproduction – occur in the water. Hippos leave the water at dusk and travel inland, sometimes up to 8 kilometers (5 mi), to graze on short grass, their main source of food. They spend four to five hours grazing and can consume 68 kilograms (150 lb) of grass each night. Like almost any herbivore, they will consume many other plants if presented with them, but their diet in nature consists almost entirely of grass, with only minimal consumption of aquatic plants. Hippos have (rarely) been filmed eating carrion, usually close to the water. There are other reports of meat-eating, and even cannibalism and predation. The stomach anatomy of a hippo is not suited to carnivory, and meat-eating is likely caused by aberrant behavior or nutritional stress.:84
Hippo defecation creates allochthonous deposits of organic matter along the river beds. These deposits have an unclear ecological function. Because of their size and their habit of taking the same paths to feed, hippos can have a significant impact on the land they walk across, both by keeping the land clear of vegetation and depressing the ground. Over prolonged periods hippos can divert the paths of swamps and channels.
Adult hippos move at speeds up to 8 km/h (5 mph) in water; typically resurfacing to breathe every three to five minutes. The young have to breathe every two to three minutes.:4 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 into the water. As with fish and turtles on a coral reef, hippos occasionally visit cleaning stations and signal, by opening their mouths wide, their readiness for being cleaned of parasites by certain species of fish. This is an example of mutualism in which the hippo benefits from the cleaning, while the fish receive food.
Studying the interaction of male and female hippopotamuses has long been complicated by the fact that hippos are not sexually dimorphic and thus females and young males are almost indistinguishable in the field. Although hippos like to lie close to each other, they do not seem to form social bonds except between mothers and daughters, and are not social animals. The reason they huddle close together is unknown.:49
Hippopotamuses are territorial only in water, where a bull presides over a small stretch of river, on average 250 meters in length, and containing ten females. The largest pods can contain over 100 hippos.:50 Other bachelors are allowed in a bull's stretch, as long as they behave submissively toward the bull. The territories of hippos exist to establish mating rights. Within the pods, the hippos tend to segregate by gender. Bachelors will lounge near other bachelors, females with other females, and the bull on his own. When hippos emerge from the water to graze, they do so individually.:4
Hippopotamuses appear to communicate verbally, through grunts and bellows, and it is thought that they may practice echolocation, but the purpose of these vocalizations is currently unknown. Hippos have the unique ability to hold their head partially above the water and send out a cry that travels through both water and air; individuals above and under water will respond.
Female hippos reach sexual maturity at five to six years of age and have a gestation period of 8 months. A study of endocrine systems revealed that female hippopotamuses may begin puberty as early as 3 or 4 years of age. Males reach maturity at around 7.5 years. A study of hippopotamus reproductive behavior in Uganda showed that peak conceptions occurred during the end of the wet season in the summer, and peak births occurred toward the beginning of the wet season in late winter. This is because of the female's estrous cycle; as with most large mammals, male hippopotamus spermatozoa is active year round. Studies of hippos in Zambia and South Africa also showed evidence of births occurring at the start of the wet season.:60–61 After becoming pregnant, a female hippopotamus will typically not begin ovulation again for 17 months.
Mating occurs in the water with the female submerged for most of the encounter,:63 her head emerging periodically to draw breath. Baby hippos are born underwater at a weight between 25 and 45 kg (60–110 lb) and an average length of around 127 cm (50 in) and must swim to the surface to take their first breath. A mother typically gives birth to only one hippo, although twins also occur. The young often rest on their mothers' backs when in water that is too deep for them, and they swim underwater to suckle. They also will suckle on land when the mother leaves the water. Weaning starts between six and eight months after birth and most calves are fully weaned after a year.:64 Like many other large mammals, hippos are described as K-strategists, in this case typically producing just one large, well-developed infant every couple of years (rather than large numbers of small, poorly developed young several times per year as is common among small mammals such as rodents).
Hippopotamuses are by nature very aggressive animals. Hippos involved in attacks on other animals are often either mature bulls, which tend to be very territorial and indiscriminately ill-tempered, or females, which are quite protective of their young calves. Living on the African continent, hippopotamus co-exist with a variety of formidable predators. Nile crocodiles, lions and spotted hyenas are known to prey on young hippos. However, due to their ill temperament and great size, adult hippopotamus are not usually subject to predation by other animals, except humans. Cases where very large lion prides or cooperating groups of Nile crocodiles have successfully predated adult hippopotamus have been reported, but this is typically believed to be exceptionally rare. Crocodiles are particularly frequent targets of hippo aggression, likely due to the fact that they often inhabit the same riparian habitats as hippos. Crocodiles may be either aggressively displaced or killed by hippopotamuses. Hippos are also very aggressive towards humans, whom they commonly attack whether in boats or on land with no apparent provocation. They are widely considered to be one of the most dangerous large animals in Africa.
To mark territory, hippos spin their tails while defecating to distribute their excrement over a greater area. Likely for the same reason, hippos are retromingent – that is, they urinate backwards. "Yawning" serves as a threat display. When in combat, male hippos use their incisors to block each other's attacks, and their canines to inflict damage.:260 Hippos rarely kill each other, even in territorial challenges. Usually a territorial bull and a challenging bachelor will stop fighting when it is clear that one hippo is stronger. When hippos become overpopulated, or when a habitat starts to shrink, bulls will sometimes attempt to kill infants, but this behavior is not common under normal conditions. Some incidents of hippo cannibalism have been documented, but it is believed to be the behavior of distressed or sick hippos, and not healthy behavior.:82–83
Hippos and humans
The earliest evidence of human interaction with hippos comes from butchery cut marks upon hippo bones at Bouri Formation dated around 160,000 years ago. Later rock paintings and engravings showing hippos being hunted have been found in the mountains of the central Sahara dated 4,000–5,000 years ago near Djanet in the Tassili n'Ajjer Mountains.:1 The ancient Egyptians recognized the hippo as a ferocious denizen of the Nile.
The hippopotamus was also known to the Greeks and Romans. The Greek historian Herodotus described the hippopotamus in The Histories (written circa 440 BC) and the Roman Historian Pliny the Elder wrote about the hippopotamus in his encyclopedia Naturalis Historia (written circa 77 AD). Hippopotamus was one of the many exotic animals brought to fight gladiators in Rome by the emperor Philip I the Arab to commemorate Rome's 1000 years anniversary in 248 AD. Silver coins with hippo's image were minted that year.
Zulu warriors preferred to be as brave as a hippopotamus, since even lions were not considered as brave. "In 1888, Captain Baden-Powell was part of a column searching for the Zulu chief Dinizulu, who was leading the Usutu people in revolt against the British colonists. The column was joined by John Dunn, a white Zulu chief, who led an impi (army) of 2,000 Zulu warriors to join the British." 
The words of the Zulu anthem sounded like this:
"Een-gonyama Gonyama! "Invooboo! Yah-bo! Yah-bo! Invooboo!"
"John Dunn was at the head of his impi. [Baden Powell] asked him to translate the Zulu anthem his men had been singing. Dunn laughed and replied: "He is a lion. Yes, he is better than a lion – he is a hippopotamus." 
Hippos in zoos
Hippopotamuses have long been popular zoo animals. The first zoo hippo in modern history was Obaysch, who arrived at the London Zoo on May 25, 1850, where he attracted up to 10,000 visitors a day and inspired a popular song, the Hippopotamus Polka. Hippos have remained popular zoo animals since Obaysch, and generally breed well in captivity. Their birth rates are lower than in the wild, but this is attributed to zoos not wanting to breed as many hippos as possible, since hippos are large and relatively expensive animals to maintain.:129
Like many zoo animals, hippos were traditionally displayed in concrete exhibits. In the case of hippos, they usually had a pool of water and patch of grass. In the 1980s, zoo designers increasingly designed exhibits that reflected the animals' native habitats. The best known of these, the Toledo Zoo Hippoquarium, features a 360,000 gallon pool for hippos. In 1987, researchers were able to tape, for the first time, an underwater birth (as in the wild) at the Toledo Zoo. The exhibit was so popular that the hippos became the logo of the Toledo Zoo.
Beginning in 1981, hippos were introduced into Colombia by Pablo Escobar. Managing the hippos, customarily referred to as the "cocaine hippos" because Escobar was a renowned drug lord, has become an issue for the Colombian government since Escobar's death because of their potential as an invasive species. Unlike in Africa, relocation to other Colombian wild habitats is not an option because it would transfer the hippos from one location close to human settlements to other similar locations. Consequently, the Colombian authorities have resorted to a program of moving the hippos to zoos, then sterilizing any remaining hippos in the wild after the zoos have been filled to capacity.
A red hippo represented the Ancient Egyptian god Set; the thigh is the "phallic leg of Set" symbolic of virility. Set's consort Tawaret was also seen as part hippo and was a goddess of protection in pregnancy and childbirth, because ancient Egyptians recognized the protective nature of a female hippopotamus toward her young. The Ijo people wore masks of aquatic animals like the hippo when practicing their water spirit cults. The Behemoth from the Book of Job, 40:15–24 is thought to be based on a hippo.
Hippos have been the subjects of various African folktales. According to a Bushmen story; when the Creator assigned each animal their place in nature, the hippos wanted to live in the water, but were refused out of fear that they might eat all the fish. After begging and pleading, the hippos were finally allowed to live in the water on the conditions that they would eat grass instead of fish and would fling their dung so that it can be inspected for fish bones. In a Ndebele tale, the hippo originally had long, beautiful hair, but was set on fire by a jealous hare and had to jump into a nearby pool. The hippo lost most of his hair and was too embarrassed to leave the water.
Ever since Obaysch inspired the Hippopotamus Polka, hippos have been popular animals in Western culture for their rotund appearance that many consider comical. Stories of hippos like Huberta, who became a celebrity in South Africa in the 1930s for trekking across the country; or the tale of Owen and Mzee, a hippo and tortoise who developed an intimate bond; have amused people who have bought hippo books, merchandise, and many a stuffed hippo toy. Hippos were mentioned in the novelty Christmas song "I Want a Hippopotamus for Christmas" that became a hit for child star Gayla Peevey in 1953. They also feature in the songs "The Hippopotamus" and "Hippo Encore" by Flanders and Swann, with the famous refrain Mud, Mud, Glorious Mud. They even inspired a popular board game, Hungry Hungry Hippos.
Hippos have also been popular cartoon characters, where their rotund frame is used for humorous effect. The Disney film Fantasia featured a ballerina hippopotamus dancing to the opera La Gioconda. Other cartoon hippos have included Hanna-Barbera's Peter Potamus, the book and TV series George and Martha, Flavio and Marita on the Animaniacs, Pat of the French duo Pat et Stanley, The Backyardigan's Tasha, and Gloria and Moto-Moto from the Madagascar franchise. A Sesame Street cartoon from the early 1970s features a hippo who lives in the country and likes it quiet, while being disturbed when the mouse who likes it loud moves in with her.
The hippopotamus characters "Happy Hippos" were created in 1988 by the French designer Andre Roche  based in Munich, to be hidden in the "Kinder Surprise egg" of the Italian chocolate company Ferrero SpA. These characters had such a success that they reappeared several times in different products of this company in the following years, increasing their popularity worldwide each time. The Nintendo Company published Game Boy adventures of them in 2001 and 2007. In the game of chess, the hippopotamus lends its name to the Hippopotamus Defense, an opening system, which is generally considered weak.The River Horse is a popular outdoor sculpture at George Washington University, Washington, D.C.
- Lewison, R. & Oliver, W. (IUCN SSC Hippo Specialist Subgroup) (2008). Hippopotamus amphibius. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 5 April 2009. Database entry includes a range map and justification for why this species is vulnerable.
- "ITIS on Hippopotamus amphibius". Integrated Taxonomic Information System. Retrieved 2007-07-29.
- "Hippopotamus". Merriam-Webster's Online Dictionary. Retrieved 2007-07-18.
- "Plural of hippopotamus". OED. Retrieved 2007-07-18.
- Walker, C. (1997). Signs of the Wild. Struik. p. 140. ISBN 1-86825-896-3.
- Kingdon, J. (1988). East African Mammals: An Atlas of Evolution in Africa, Volume 3, Part B: Large Mammals. University Of Chicago Press. pp. 256–77. ISBN 0-226-43722-1.
- Kane, Thomas Leiper (1990). Amharic-English dictionary: H – N., Volume 1. Otto Harrassowitz Verlag. p. 1909. ISBN 3447028718.
- Saeed, John I. (1999). Somali. John Benjamins Publishing Company. p. 29. ISBN 9027238103.
- Eltringham, S.K. (1999). The Hippos. Poyser Natural History Series. Academic Press. ISBN 0-85661-131-X.
- Okello, J.B.A, Nyakaana, S., Masembe, C., Siegismund, H.R. an Arctander, P. (2005). "Mitochondrial DNA variation of the common hippopotamus: evidence for a recent population expansion.". Heredity 95 (3): 206–215. doi:10.1038/sj.hdy.6800711. PMID 16030528.
- Meijaard, Erik (ed.) (September 2005). "Suiform Soundings: The IUCN/SSC Pigs, Peccaries, and Hippos Specialist Group (PPHSG) Newsletter" (PDF). IUCN 5 (1). Archived from the original on 2008-03-08.
- Ursing, B.M., Arnason U. (1998). "Analyses of mitochondrial genomes strongly support a hippopotamus-whale clade". Proceedings of the Royal Society 265 (1412): 2251–5. doi:10.1098/rspb.1998.0567. PMC 1689531. PMID 9881471.
- Gatesy, J. (1 May 1997). "More DNA support for a Cetacea/Hippopotamidae clade: the blood-clotting protein gene gamma-fibrinogen" (PDF). Molecular Biology and Evolution 14 (5): 537–543. doi:10.1093/oxfordjournals.molbev.a025790. PMID 9159931.
- Geisler, J. H. and Theodor, J. M. (2009). "Hippopotamus and whale phylogeny". Nature 458 (7236): E1–4; discussion E5. doi:10.1038/nature07776. PMID 19295550.
- "Scientists find missing link between the dolphin, whale and its closest relative, the hippo". Science News Daily. 2005-01-25. Retrieved 2011-01-08.
- "National Geographic – Hippo: Africa's River Beast". National Geographic. Retrieved 2007-07-18.
- Boisserie, Jean-Renaud; Lihoreau, Fabrice and Brunet, Michel (2005). "The position of Hippopotamidae within Cetartiodactyla". Proceedings of the National Academy of Sciences 102 (5): 1537–1541. doi:10.1073/pnas.0409518102. PMC 547867. PMID 15677331.
- Boisserie, Jean-Renaud; Fabrice Lihoreau and Michel Brunet (2005). "Origins of Hippopotamidae (Mammalia, Cetartiodactyla): towards resolution". Zoologica Scripta 34 (2): 119–143. doi:10.1111/j.1463-6409.2005.00183.x.
- Boisserie, Jean-Renaud (2005). "The phylogeny and taxonomy of Hippopotamidae (Mammalia: Artiodactyla): a review based on morphology and cladistic analysis". Zoological Journal of the Linnean Society 143: 1–26. doi:10.1111/j.1096-3642.2004.00138.x.
- Stuenes, Solweig (1989). "Taxonomy, habits and relationships of the sub-fossil Madagascan hippopotamuses Hippopotamus lemerlei and H. madagascariensis". Journal of Vertebrate Paleontology 9 (3): 241–268. doi:10.1080/02724634.1989.10011761.
- Burney, David A.; Ramilisonina (1998). "The Kilopilopitsofy, Kidoky, and Bokyboky: Accounts of Strange Animals from Belo-sur-mer, Madagascar, and the Megafaunal "Extinction Window"". American Anthropologist 100 (4): 957–966. doi:10.1525/aa.1922.214.171.1247. JSTOR 681820.
- Petronio, C. (1995). "Note on the taxonomy of Pleistocene hippopotamuses". Ibex 3: 53–55.
- Simmons, A. (2000). "Faunal extinction in an island society: pygmy hippopotamus hunters of Cyprus". Geoarchaeology 15 (4): 379–381. doi:10.1002/(SICI)1520-6548(200004)15:4<379::AID-GEA7>3.0.CO;2-E.
- "Physical Description". Retrieved 2009-05-08.
- "Mammals: Hippopotamus". Retrieved 2009-05-08.
- "Hippopotamus: WhoZoo". Whozoo.org. Retrieved 2008-11-03.
- "ADW: Hippopotamus amphibius: Information". Animal Diversity Web. Regents of the University of Michigan. Retrieved 2008-11-03.
- "San Diego Zoo's Animal Bytes: Hippopotamus". SanDiegoZoo.org. Zoological Society of San Diego. 2009-10-29. Retrieved 2012-08-20.
- Marshall, P.J., Sayer, J.A. (1976). "Population ecology and response to cropping of a hippopotamus population in eastern Zambia". The Journal of Applied Ecology 13 (2): 391–403. doi:10.2307/2401788. JSTOR 2401788.
- Novak, R. M. 1999. Walker's Mammals of the World. 6th edition. Johns Hopkins University Press, Baltimore. ISBN 0-8018-5789-9
- Laurie, W.A.; Lang, E. M., Groves, C.P. (1983). "Rhinoceros unicornis". Mammalian Species (American Society of Mammalogists) (211): 1–6. doi:10.2307/3504002. JSTOR 3504002.
- Boitani, L. (1984) Simon & Schuster's Guide to Mammals. Simon & Schuster, Touchstone Books. ISBN 978-0-671-42805-1
- Barr, Brady. "Undercover Hippo," Dangerous Encounters, National Geographic Channel, January 20, 2008.
- Estes, R. (1992). The Behavior Guide to African Mammals: including hoofed mammals, carnivores, primates. University of California Press. pp. 222–26. ISBN 0-520-08085-8.
- Saikawa Y, Hashimoto K, Nakata M, Yoshihara M, Nagai K, Ida M, Komiya T (2004). "Pigment chemistry: the red sweat of the hippopotamus". Nature 429 (6990): 363. doi:10.1038/429363a. PMID 15164051.
- "Oldest Hippo Turns 55!". Mesker Park Zoo. 2006-06-12. Archived from the original on 2007-09-27. Retrieved 2007-06-21.
- "Celebrate with Donna". Evansville Courier & Press. 2007-07-12. Retrieved 2007-07-15.
- "Blackie the hippo at Cleveland Metroparks Zoo: Whatever happened to ...?". Cleveland.com. 2012-05-07.
- "Old mother hippo dies". Agence France Press. July 12, 1995.
- van Kolfschoten, Th. (2000). "The Eemian mammal fauna of central Europe". Netherlands Journal of Geosciences 79 (2/3): 269–281.
- Horwitz, Liora Kolska; Eitan Tchernov (1990). "Cultural and Environmental Implications of Hippopotamus Bone Remains in Archaeological Contexts in the Levant". Bulletin of the American Schools of Oriental Research 280: 67–76.
- Haas, Georg (1953). "On the Occurrence of Hippopotamus in the Iron Age of the Coastal Area of Israel". Bulletin of the American Schools of Oriental Research 132: 30–34.
- Pliny the Elder. "Chapter 15, Book VIII". Naturalis Historia (in Latin original or English translation). ISBN 3-519-01652-4.
- "Hippo Haven". Smithsonian Magazine. 2006-01-01. Retrieved 2007-01-23.
- "DR Congo's hippos face extinction.". BBC. 2005-09-13. Retrieved 2005-11-14.
- Sundaram, Anjan (2005-09-12). "Congo's Hippos Fast Disappearing". Toronto Star.
- Kraul C. (December 20, 2006). "A hippo critical situation". Los Angeles Times. Retrieved 2008-03-27.
- "Colombia kills drug baron hippo". BBC News. 2009-07-11. Retrieved 2009-07-11.
- "Crece controversia en el país por decisión de cazar a hipopótamos de Pablo Escobar". El Tiempo. Retrieved 2009-07-11.
- "Hippopotamus". Kruger National Park. Retrieved 2007-06-18.
- Grey, J., Harper, D.M. (2002). "Using Stable Isotope Analyses To Identify Allochthonous Inputs to Lake Naivasha Mediated Via the Hippopotamus Gut". Isotopes in Environmental Health Studies 38 (4): 245–250. doi:10.1080/10256010208033269.
- Dudley, J.P. "Reports of carnivory by the common hippo Hippopotamus Amphibius". South African Journal of Wildlife Research 28 (2): 58–59.
- McCarthy, T.S., Ellery, W. N., Bloem, A (1998). "Some observations on the geomorphological impact of hippopotamus (Hippopotamus amphibius L.) in the Okavango Delta, Botswana". African Journal of Ecology 36 (1): 44–56. doi:10.1046/j.1365-2028.1998.89-89089.x.
- "Hippopotamuses". Kids National Geographic. Retrieved 4 November 2011.
- Beckwitt, R., Shea, J., Osborne, D., Krueger, S., and Barklow, W. (2002). "A PCR-based method for sex identification in Hippopotamus amphibius". African Zoology Journal: 127–130.
- William E. Barklow (2004). "Low-frequency sounds and amphibious communication in Hippopotamus amphibious". The Journal of the Acoustical Society of America 115 (5): 2555.
- Graham L.H., Reid K.; Webster T.; Richards M.; Joseph S. (2002). "Endocrine patterns associated with reproduction in the Nile hippopotamus (Hippopotamus amphibius) as assessed by fecal progestagen analysis". General and Comparative Endocrinology 128 (1): 74–81. doi:10.1016/S0016-6480(02)00066-7. PMID 12270790.
- Lewison, R (1998). "Infanticide in the hippopotamus: evidence for polygynous ungulates". Ethology, Ecology & Evolution 10 (3): 277–286. doi:10.1080/08927014.1998.9522857.
- "Hippopotamus". Pocanticohills.org. Retrieved 2008-11-03.
- Carnivores of the World by Dr. Luke Hunter. Princeton University Press (2011), ISBN 9780691152288
- Crocodiles and Alligators edited by S Charles A. Ross & Stephen Garnett. Checkmark Books (1989), ISBN 978-0816021741.
- "Are hippos the most dangerous animal?". 2006-12-06. Retrieved 2008-08-09.
- "Dangerous Encounters: Undercover Hippo". National Geographic Channel. Retrieved 2008-11-04.
- Hippo Specialist Group, World Conservation Union. (June 2008). In the News. Duke University. Retrieved 2009-9-04.
- National Geographic exhibit on different animals and their poop. News.nationalgeographic.com (October 28, 2010). Retrieved on 2012-05-12.
- Nature's World: Africa's Lions and Wildebeests. Discovery HD Theater. June 17, 2002. Archived from the original on 2011-07-16. http://web.archive.org/web/20110716031728/http://dhd.discovery.com/schedule/bestof/nature.html.
- Clark, JD; Beyene, Y; WoldeGabriel, G; Hart, WK; Renne, PR; Gilbert, H; Defleur, A; Suwa, G et al. (2003). "Stratigraphic, chronological and behavioural contexts of Pleistocene Homo sapiens from Middle Awash, Ethiopia". Nature 423 (6941): 747–52. doi:10.1038/nature01670. PMID 12802333.
- Herodotus. "Chapter 71, Book II". The Histories (in English translation). ISBN 0-19-521974-0.
- Ingonyama – he is a lion!. Scouting.org.za. Retrieved on 2011-03-29.
- Orans, Lewis P. (June 17, 1997). "Dinizulu". Pinetreeweb.com. Retrieved 2011-03-29.
- Root, N. J. (1993). "Victorian England's Hippomania". Natural History 103: 34–39.
- Melissa Greene (December 1987). "No rms, jungle vu: a new group of "landscape-immersion" zoo designers are trying to break down visitors' sense of security by reminding them that wild animals really are wild.". The Atlantic Monthly.
- "Hippoquarium". Toledo Zoo. Archived from the original on February 11, 2007. Retrieved 2007-03-26.
- "Colombia Confronts Drug Lord’s Legacy: Hippos". Retrieved 2013-01-30.
- "The invaders". NatGeo Wild. October 9, 2012.
- Cooper, J.C. (1992). Symbolic and Mythological Animals. London: Aquarian Press. p. 129. ISBN 1-85538-118-4.
- Hart, George (1986). A Dictionary of Egyptian Gods and Goddesses. Routledge. ISBN 0-415-05909-7.
- Hamilton, Janice (2003). Nigeria in Pictures. Twenty-First Century Books. p. 49. ISBN 0-8225-0373-5.
- Metzeger, Bruce M., Coogan, Michael D. f, ed. (1993). The Oxford Companion to the Bible. Oxford, UK: Oxford University Press. p. 76. ISBN 0-19-504645-5.
- Greaves, N.; Clement, R. (2000). When Hippo Was Hairy: And Other Tales from Africa. Struik. pp. 67–71. ISBN 1-86872-456-5.
- Chilvers, H.A. (1931). Huberta Goes South, a Record of the Lone Trek of the Celebrated Zululand Hippopotamus. London: Gordon & Gotch.
- "A hippo and tortoise tale". NPR. July 17, 2005. Retrieved 2007-06-18.
- Hatkoff, Isabella; Hatkoff, Craig and Kahumbu, Paula (2006). Owen & Mzee; The True Story of a Remarkable Friendship. New York: Scholastic Press. ISBN 0-439-82973-9.
- "I Want A Hippopotamus For Christmas Lyrics". Christmas-lyrics.org. Retrieved 2007-12-20.
- "Childhood Trauma: Hungry Hungry Hippos". Newcastle Herald (Australia). May 2, 2006.
- "Fred Kroll, of Trouble and Hungry Hungry Hippos games, dead at 82". Associated Press. August 5, 2003.
- Andre Roche at Kindest Illustrations. Retrieved on 14 August 2008.
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- "Hippos: Wildlife summary". African Wildlife Foundation. Archived from the original on 2010-11-19.
- IUCN Hippo Specialist Group
- Hippos of Lake Edward a blog about the last significant group of Hippos in Virunga National Park, DRC
- Pablo Escobar's Fugitive Hippo Shot Dead by The Telegraph
- Section 8. King Tut may have been killed by a hippopotamus Ancient History Encyclopedia