Hippopotamidae
Encyclopedia
Hippopotamuses are the members of the family
Hippopotamidae. They are the only extant artiodactyls which walk on four toes on each foot.
s.
The living species are smooth-skinned and lack both sebaceous gland
s and sweat gland
s. The outer epidermis is relatively thin, so that hippos dehydrate rapidly in dry environments.
Both the incisor
s and canines are large and tusk-like, although the canine tusks are by far the largest. The tusks grow throughout life. The postcanine teeth are large and complex, suited for chewing the plant matter that composes their diet. The number of incisors varies even within the same species, but the general dental formula
is:
, and are popularly thought to have resembled small- or narrow-headed hippos. More specifically, the hippos split off from the anthracotheres some time during the Miocene
. After the appearance of the true hippopotamids, the anthracotheres went into a decline brought about by a combination of climatic change and competition with their descendants, until the last genus, Merycopotamus
, died out in the early Pliocene
of India.
There were once many species of hippopotamid, but only two survive today: Hippopotamus amphibius, and Choeropsis liberiensis. They are the last survivors of two major evolution
ary lineages, the hippos proper and the pygmy hippos, respectively; these lineages could arguably be considered subfamilies but their relationships to each other - apart from being fairly distant relatives - are not well resolved.
The enigmatic Miocene
Kenyapotamus
is insufficiently known to be assigned a place in the hippo phylogeny with any degree of certainty. In addition, the genus
Hexaprotodon
, in a sense now restricted to an extinct group of animals once living around the northern and northeastern Indian Ocean
, which formerly included most ancient hippos, turned out to be paraphyletic.
’s tusks. Hippopotamids and elephants are not closely related, but the lower canine teeth of the hippopotamus and the tusk of the elephant are both long and have a slight curve and both animals use this structure when fighting.
used here mostly follows the review of Boisserie (2005).
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Hippopotamidae. They are the only extant artiodactyls which walk on four toes on each foot.
Characteristics
Hippopotamids are large mammals, with short, stumpy legs, and barrel-shaped bodies. They have large heads, with broad mouths, and nostrils placed at the top of the snout. Like pigs, they have four toes, but unlike pigs, all of the toes are used in walking. Hippopotamids are unguligrade, although, unlike most other such animals, they have no hooves, instead using a pad of tough connective tissue. Their stomach has three chambers, but they are not true ruminantRuminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
s.
The living species are smooth-skinned and lack both sebaceous gland
Sebaceous gland
The sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals...
s and sweat gland
Sweat gland
Sweat glands, or sudoriferous glands, are small tubular structures of the skin that produce sweat. There are two kinds of sweat glands:...
s. The outer epidermis is relatively thin, so that hippos dehydrate rapidly in dry environments.
Both the incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s and canines are large and tusk-like, although the canine tusks are by far the largest. The tusks grow throughout life. The postcanine teeth are large and complex, suited for chewing the plant matter that composes their diet. The number of incisors varies even within the same species, but the general dental formula
Dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...
is:
Evolution
The hippopotamids are descended from the anthracotheres, a family of semi-aquatic artiodactyls that appeared in the late EoceneEocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
, and are popularly thought to have resembled small- or narrow-headed hippos. More specifically, the hippos split off from the anthracotheres some time during the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
. After the appearance of the true hippopotamids, the anthracotheres went into a decline brought about by a combination of climatic change and competition with their descendants, until the last genus, Merycopotamus
Merycopotamus
Merycopotamus is an extinct genus of Asian anthracothere that appeared during the Middle Miocene, and died out in the Late Pliocene. At the height of the genus' influence, species ranged throughout southern Asia. With the extinction of the last species, M. dissimilis, the lineage of...
, died out in the early Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
of India.
There were once many species of hippopotamid, but only two survive today: Hippopotamus amphibius, and Choeropsis liberiensis. They are the last survivors of two major evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary lineages, the hippos proper and the pygmy hippos, respectively; these lineages could arguably be considered subfamilies but their relationships to each other - apart from being fairly distant relatives - are not well resolved.
The enigmatic Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
Kenyapotamus
Kenyapotamus
Kenyapotamus is a possible ancestor of living hippopotamids that lived in Africa roughly 16 million to 8 million years ago during the Miocene epoch...
is insufficiently known to be assigned a place in the hippo phylogeny with any degree of certainty. In addition, the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Hexaprotodon
Hexaprotodon
Hexaprotodon is a genus of Hippopotamidae that is sometimes applied to the pygmy hippopotamus. Pygmy hippos may be classified as either Choeropsis liberiensis or Hexaprotodon liberiensis...
, in a sense now restricted to an extinct group of animals once living around the northern and northeastern Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, which formerly included most ancient hippos, turned out to be paraphyletic.
Analogous structures
An analogous structure that hippopotamids have is the lower canine teeth, which are similar in function and structure to an elephantElephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
’s tusks. Hippopotamids and elephants are not closely related, but the lower canine teeth of the hippopotamus and the tusk of the elephant are both long and have a slight curve and both animals use this structure when fighting.
Species
The systematics and taxonomyTaxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
used here mostly follows the review of Boisserie (2005).
- Genus HippopotamusHippopotamus (genus)Hippopotamus is the name of a genus consisting of one extant species, Hippopotamus amphibius, also known as the Hippopotamus, and several extinct species...
- true hippopotami- Hippopotamus amphibius - Hippopotamus AfricaAfricaAfrica is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
- †Hippopotamus antiquus - mainland EuropeEuropeEurope is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
& British IslesBritish IslesThe British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...
; PleistocenePleistoceneThe Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and .... - †Hippopotamus creutzburgi - CreteCreteCrete is the largest and most populous of the Greek islands, the fifth largest island in the Mediterranean Sea, and one of the thirteen administrative regions of Greece. It forms a significant part of the economy and cultural heritage of Greece while retaining its own local cultural traits...
; Pleistocene - †Hippopotamus minor - CyprusCyprusCyprus , officially the Republic of Cyprus , is a Eurasian island country, member of the European Union, in the Eastern Mediterranean, east of Greece, south of Turkey, west of Syria and north of Egypt. It is the third largest island in the Mediterranean Sea.The earliest known human activity on the...
; Pleistocene to HoloceneHoloceneThe Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"... - †Hippopotamus melitensis - MaltaMaltaMalta , officially known as the Republic of Malta , is a Southern European country consisting of an archipelago situated in the centre of the Mediterranean, south of Sicily, east of Tunisia and north of Libya, with Gibraltar to the west and Alexandria to the east.Malta covers just over in...
; Pleistocene - †Hippopotamus pentlandi - Sicily; Pleistocene
- †Hippopotamus lemerlei - MadagascarMadagascarThe Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
; HoloceneHoloceneThe Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"... - †Hippopotamus laloumena - Madagascar; Holocene
- †Hippopotamus gorgopsHippopotamus gorgopsHippopotamus gorgops is an extinct species of hippopotamus. It first appeared in Africa during the late Miocene, and eventually migrated into Europe during the early Pliocene . It became extinct prior to the Ice Age.With a length of and a shoulder height of H...
- Africa & mainland Europe; Late MioceneLate MioceneThe Late Miocene is a sub-epoch of the Miocene Epoch made up of two stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch....
–Middle PleistoceneMiddle PleistoceneThe Middle Pleistocene, more specifically referred to as the Ionian stage, is a period of geologic time from ca. 781 to 126 thousand years ago....
- Hippopotamus amphibius - Hippopotamus Africa
- Tentatively placed into Hippopotamus:
- †Hippopotamus aethiopicus - Kenya & Ethiopia; Pliocene -Pleistocene
- †Hippopotamus afarensis - formerly genus Trilobophorus
- †Hippopotamus behemoth -
- †Hippopotamus kaisensis - Central Africa; Pliocene
- †Hippopotamus sirensis - MoroccoMoroccoMorocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
& AlgeriaAlgeriaAlgeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...
; Pleistocene
- Genus HexaprotodonHexaprotodonHexaprotodon is a genus of Hippopotamidae that is sometimes applied to the pygmy hippopotamus. Pygmy hippos may be classified as either Choeropsis liberiensis or Hexaprotodon liberiensis...
- hexaprotodons or Asian hippopotami- †Hexaprotodon bruneti - EthiopiaEthiopiaEthiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2...
; Pliocene - †Hexaprotodon coryndoni - Ethiopia; Pliocene
- †Hexaprotodon crusafonti - SpainSpainSpain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
; Late Miocene (syn. Hexaprotodon primaevus) - †Hexaprotodon hipponensis - AlgeriaAlgeriaAlgeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...
- †Hexaprotodon imagunculus - UgandaUgandaUganda , officially the Republic of Uganda, is a landlocked country in East Africa. Uganda is also known as the "Pearl of Africa". It is bordered on the east by Kenya, on the north by South Sudan, on the west by the Democratic Republic of the Congo, on the southwest by Rwanda, and on the south by...
& CongoCongo BasinThe Congo Basin is the sedimentary basin that is the drainage of the Congo River of west equatorial Africa. The basin begins in the highlands of the East African Rift system with input from the Chambeshi River, the Uele and Ubangi Rivers in the upper reaches and the Lualaba River draining wetlands...
; Pliocene - †Hexaprotodon iravaticus - MyanmarMyanmarBurma , officially the Republic of the Union of Myanmar , is a country in Southeast Asia. Burma is bordered by China on the northeast, Laos on the east, Thailand on the southeast, Bangladesh on the west, India on the northwest, the Bay of Bengal to the southwest, and the Andaman Sea on the south....
; Pliocene - Pleistocene - †Hexaprotodon karumensis - Kenya & EritreaEritreaEritrea , officially the State of Eritrea, is a country in the Horn of Africa. Eritrea derives it's name from the Greek word Erethria, meaning 'red land'. The capital is Asmara. It is bordered by Sudan in the west, Ethiopia in the south, and Djibouti in the southeast...
; Pleistocene - †Hexaprotodon madagascariensis - Madagascar; Holocene
- †Hexaprotodon namadicus - IndiaIndiaIndia , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
; (possibly same as Hex. palaeindicus) - †Hexaprotodon palaeindicus - India;
- †Hexaprotodon pantanellii - ItalyItalyItaly , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
; Pliocene - †Hexaprotodon protamphibius - Kenya & Chad; Pliocene
- †Hexaprotodon siculus -
- †Hexaprotodon sivalensis - India
- †Hexaprotodon sp. (undescribed) - Myanmar
- †Undescribed IndonesiaIndonesiaIndonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
n species; PleistocenePleistoceneThe Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
- †Hexaprotodon bruneti - Ethiopia
- Genus ArchaeopotamusArchaeopotamusArchaeopotamus is an extinct genus of Hippopotamidae that lived between 7.5 and 1.8 million years ago in Africa and the Middle East. The genus was described in 2005 to encompass species of hippos that were previously grouped in Hexaprotodon....
- formerly included in Hexaprotodon- †Archaeopotamus harvardi - Arabian PeninsulaArabian PeninsulaThe Arabian Peninsula is a land mass situated north-east of Africa. Also known as Arabia or the Arabian subcontinent, it is the world's largest peninsula and covers 3,237,500 km2...
& Central Africa; MioceneMioceneThe Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
- PliocenePlioceneThe Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch... - †Archaeopotamus lothagamensis - KenyaKenyaKenya , officially known as the Republic of Kenya, is a country in East Africa that lies on the equator, with the Indian Ocean to its south-east...
; Miocene
- †Archaeopotamus harvardi - Arabian Peninsula
- 1-2 undescribed species
- Genus Choeropsis - pygmy hippopotamus
- Choeropsis liberiensis - Pygmy HippopotamusPygmy HippopotamusThe pygmy hippopotamus is a large mammal native to the forests and swamps of western Africa . The pygmy hippo is reclusive and nocturnal...
- Choeropsis liberiensis - Pygmy Hippopotamus
- Genus Saotherium - formerly included in Hexaprotodon
- Saotherium mingoz ChadChadChad , officially known as the Republic of Chad, is a landlocked country in Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west...
; Pliocene
- Saotherium mingoz Chad