Hippopotamus
Hippopotamus Temporal range:
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A hippopotamus in Saadani National Park, Tanzania | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Artiodactyla |
Family: | Hippopotamidae |
Genus: | Hippopotamus |
Species: | H. amphibius
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Binomial name | |
Hippopotamus amphibius | |
Current distribution of the hippopotamus |
The hippopotamus (
After
Hippos inhabit rivers, lakes, and
(canine teeth).Etymology
The
Taxonomy and origins
Classification
The modern hippopotamus and the
Five subspecies of hippos have been described based on morphological differences in their skulls as well as differences in geographical range:[8]: 3 [9][10][11]
- H. a. amphibius – (the nominate subspecies) 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 symphysisand 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 – ranged from the southern ; skull characterised by a thicker preorbital region, shorter snout, flatter dorsal surface, reduced mandibular symphysis and smaller chewing teeth.
The suggested subspecies above 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 nonrepresentative samples.[8]: 2 A study examining mitochondrial DNA from skin biopsies taken from 13 sampling locations 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.[10]
Evolution
Until 1909,
Artiodactyla
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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 60 million years ago.[14][16] This hypothesised ancestral group likely split into two branches again around 54 million years ago.[13]
One branch would
A rough evolutionary lineage of the hippo can thus be traced from Eocene and
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, a likely result of the process of insular dwarfism.[24] Fossil evidence indicates many Malagasy hippos were hunted by humans, a factor in their eventual extinction.[24] 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.[25]
Characteristics
The hippopotamus is a megaherbivore and is exceeded in size among land animals only by elephants and some rhinoceros species. The mean adult weight is around 1,480 kg (3,260 lb) for bulls and 1,365 kg (3,009 lb) for cows. Exceptionally large males have been recorded reaching 2,660 kg (5,860 lb).[31] Male hippos appear to continue growing throughout their lives, while females reach maximum weight at around age 25.[32] Hippos measure 2.90 to 5.05 m (9.5 to 16.6 ft) long,[33] including a tail of about 35 to 56 cm (1.15 to 1.84 ft) in length and 1.30 to 1.65 m (4.3 to 5.4 ft) tall at the shoulder,[34][35] with males and females ranging 1.40 to 1.65 m (4.6 to 5.4 ft) and 1.30 to 1.45 m (4.3 to 4.8 ft) tall at the shoulder respectively.[35] The species has a typical head-body length of 3.3–3.45 m (10.8–11.3 ft) and an average standing height of 1.4 m (4.6 ft) at the shoulder.[36]
Hippos have barrel-shaped bodies with short tails and legs, and an hourglass-shaped skull with a long snout.
The hippo's jaw is powered by huge masseter and digastric muscles which give them large, droopy cheeks.[40]: 259 The jaw hinge allows the animal to open its mouth at almost 180°.[8]: 17 A folded orbicularis oris muscle allows the hippo to attain an extreme gape without tearing any tissue.[42] On the lower jaw, the incisors and canines grow continuously, the former reaching 40 cm (1 ft 4 in), while the latter can grow to up to 50 cm (1 ft 8 in). The lower canines are sharpened through contact with the smaller upper canines.[37] The canines and incisors are used mainly for combat instead of feeding. Hippos rely on their flattened, horny lips to grasp and pull grasses which are then ground by the molars.[40]: 259, 263 The hippo is considered to be a pseudoruminant; it has a complex three-chambered stomach, but does not "chew cud".[8]: 22
Hippo skin is 6 cm (2 in) thick across much of its body with little hair.[37][40]: 260 The animal is mostly purplish-grey or blue-black, but brownish-pink on the underside and around the eyes and ears.[40]: 260 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.[43][44] 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.[44] This natural sunscreen cannot prevent the animal's skin from cracking if it stays out of water too long.[45]
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
A hippo's lifespan is typically 40 to 50 years.
Distribution and status
Hippopotamus amphibius arrived in Europe around 560-460,000 years ago, during the Middle Pleistocene.
Archaeological evidence exists of its presence in the
Genetic evidence suggests common hippos in Africa experienced a marked population expansion during or after the
As of 2017, the IUCN Red List drawn up by the International Union for Conservation of Nature (IUCN) lists the species as vulnerable, with a stable population estimated between 115,000 and 130,000 animals.[1] The hippo population has declined most dramatically in the Democratic Republic of the Congo.[63] By 2005, the population in Virunga National Park had dropped to 800 or 900 from around 29,000 in the mid-1970s.[64] This decline is attributed to the disruptions caused by the Second Congo War.[64] The poachers are believed to be Mai-Mai rebels, underpaid Congolese soldiers, and local militia groups.[64][65] Reasons for poaching include the belief hippos are harmful to society, as well as financial gain.[66] As of 2016, the Virunga hippo population appears to have increased again, possibly due to better protection from park rangers, who have worked with local fishermen.[67] The sale of hippo meat is illegal, but black-market sales are difficult for Virunga National Park officers to track.[65][66] Hippo meat is highly valued in some areas of central Africa and the teeth may be used as a replacement for elephant ivory.[68]
A population of hippos exists in Colombia, descended from captive individuals that escaped from Pablo Escobar's estate after his death in 1993. Their numbers grew to 100 by the 2020s and ecologists believe the population should be eradicated, as they are breeding rapidly and are an increasing menace to humans and the environment. Attempts to control them include sterilisation and culling.[69]
Behaviour and ecology
Hippos are
Hippos spend most the day in water to stay cool and hydrated. Just before night begins, they leave the water to forage on land. Hippos usually trot to move quickly on land and can gallop at 30 km/h (19 mph) when needed. They are incapable of jumping but can walk up steep banks. A hippo will travel 3–5 km (1.9–3.1 mi) per night, eating around 40 kg (88 lb) of grass. By dawn, they are back in the water.[37] The hippopotamus sleeps with both hemispheres of the brain resting, as in all land mammals, and usually sleeps on land or in water with the nostrils exposed. Despite this, it may be capable of sleeping while submerged, intermittently surfacing to breathe without waking. They appear to transition between different phases of sleep more quickly than other mammals.[71]
Because of their size and their habit of taking the same paths to feed, hippos can have a significant impact on the land across which they walk, keeping the land clear of vegetation and depressing the ground. Over prolonged periods, hippos can divert the paths of swamps and channels.[72] By defecating in the water, the animals also appear to pass on microbes from their gut, affecting the biogeochemical cycle.[73] On occasion, hippos have been filmed eating carrion, usually near the water. There are other reports of meat-eating and even cannibalism and predation.[74] Hippos' stomach anatomy lacks adaptions to carnivory and meat-eating is likely caused by lack of nutrients or just an abnormal behaviour.[8]: 82–84
Social life
It is challenging to study the interaction of bulls and cows because hippos are not sexually dimorphic, so cows and young bulls are almost indistinguishable in the field.[75] Hippo pods fluctuate but can contain over 100 hippos. Although they lie close together, adults develop almost no social bonds. Males establish territories in water but not land, and these may range 250–500 m (270–550 yd) in lakes and 50–100 m (55–109 yd) in rivers. Territories are abandoned when the water dries up. The bull has breeding access to all the cows in his territory. Younger bachelors are allowed to stay as long as they defer to him. A younger male may challenge the old bull for control of the territory. Within the pods, the hippos tend to segregate by sex and status. Bachelor males lounge near other bachelors, females with other females, and the territorial male is on his own. When hippos emerge from the water to graze, they do so individually.[8]: 4–5, 49–50
Hippos engage in "muck-spreading" which involves defecating while spinning their tails to distribute the faeces over a greater area. Muck-spreading occurs both on land and in water and its function is not well understood. It is unlikely to serve a territorial function, as the animals only establish territories in the water. They may be used as trails between the water and grazing areas.[8]: 5, 51–52 "Yawning" serves as a threat display.[37] When fighting, bulls use their incisors to block each other's attacks and their large canines as offensive weapons.[40]: 259–260 When hippos become over-populated or a habitat shrinks, bulls sometimes attempt infanticide, but this behaviour is not common under normal conditions.[76]
The most common hippo vocalisation is the "wheeze honk", which can travel over long distances in air.[77] This call starts as a high-pitched squeal followed by a deeper, resonant call.[8]: 5 The animals can recognise the calls of other individuals. Hippos are more likely to react to the wheeze honks of strangers than to those they are more familiar with.[77] When threatened or alarmed, they produce exhalations,[37] and fighting bulls will bellow loudly.[8]: 5 Hippos are recorded to produce clicks underwater which may have echolocative properties.[78] They have the unique ability to hold their heads partially above the water and send out a cry that travels through both water and air; individuals respond both above and below water.[79]
Reproduction
Cows reach sexual maturity at five to six years of age and have a
Mother hippos are very protective of their young, not allowing others to get too close.
Interspecies interactions
Hippos coexist alongside a variety of large predators in their habitats.
Hippos occasionally visit
The parasitic monogenean flatworm Oculotrema hippopotami infests hippopotamus eyes, mainly the nictitating membrane. It is the only monogenean species (which normally live on fish) documented to live on a mammal.[92]
Hippos and humans
Cut marks on bones of H. amphibius found at
The hippo was also known to the
Attacks on humans
The hippo is considered to be extremely aggressive and has frequently been reported charging and attacking boats.[101] Small boats can easily be capsized by hippos and passengers can be injured or killed by the animals, or drown in the water. In one 2014 case in Niger, a boat was capsized by a hippo and 13 people were killed.[102] Hippos will often raid farm crops if the opportunity arises, and humans may come into conflict with them on these occasions. These encounters can be fatal to either humans or hippos.[103]
According to the
In zoos
Hippos have long been popular zoo animals. The first record of hippos taken into captivity for display is dated to 3500 BC in Hierakonpolis, Egypt.[105] The first zoo hippo in modern history was Obaysch, who arrived at the London Zoo on 25 May 1850, where he attracted up to 10,000 visitors a day and inspired a popular song, the "Hippopotamus Polka".[106]
Hippos generally breed well in captivity; birth rates are lower than in the wild, but this can be attributed to zoos' desire to limit births, since hippos are relatively expensive to maintain.
Cultural significance
In
Hippos have been the subjects of various
Hippopotamuses were rarely depicted in European art during the Renaissance and Baroque periods, due to less access to specimens by Europeans. One notable exception is Peter Paul Rubens' The Hippopotamus and Crocodile Hunt (1615–1616).[100]: 122–123 Ever since Obaysch inspired the "Hippopotamus Polka", hippos have been popular animals in Western culture for their rotund appearance, which many consider comical.[106] The Disney film Fantasia featured a ballerina hippo dancing to the opera La Gioconda. The film Hugo the Hippo is set in Tanzania and involves the title character trying to escape being slaughtered with the help of local children. The Madagascar films feature a hippo named Gloria.[100]: 128–129 Hippos even inspired a popular board game, Hungry Hungry Hippos.[114]
Among the most famous poems about the hippo is "The Hippopotamus" by T. S. Eliot, where he uses the animal to represent the Catholic Church. Hippos are 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 featured in the popular "The Hippopotamous Song" by Flanders and Swann.[100]: 128, 136
See also
- American Hippo bill - 1910 bill that proposed the introduction of hippos into Louisiana
- Armley Hippo fossil H. amphibius specimen from England
- Allenton hippopotamus fossil H. amphibius specimen from England
- Owen and Mzee - hippo and tortoise who bonded
- Fiona - hippo born 6 weeks early at the Cincinnati Zoo and Botanical Garden
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