''Hexaprotodon'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

hippopotamid Hippopotamidae is a family of stout, naked-skinned, and semiaquatic artiodactyl mammals, possessing three-chambered stomachs and walking on four toes on each foot. While they resemble pigs physiologically, their closest living relatives are t ...

known from

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

. The name ''Hexaprotodon'' means "six front teeth" as some of the fossil forms have three pairs of

incisors Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wh ...

.''Hexaprotodon''
The Paleobiology Database, läst 19 mars 2013. The name ''Hexaprotodon'' was often applied to the

pygmy hippopotamus The pygmy hippopotamus or pygmy hippo (''Choeropsis liberiensis'') is a small hippopotamid which is native to the forests and swamps of West Africa, primarily in Liberia, with small populations in Sierra Leone, Guinea, and Ivory Coast. It has bee ...

before its reclassification into the genus ''

Choeropsis The pygmy hippopotamus or pygmy hippo (''Choeropsis liberiensis'') is a small Hippopotamidae, hippopotamid which is native to the forests and swamps of West Africa, primarily in Liberia, with small populations in Sierra Leone, Guinea, and Ivory C ...

''. The genus ''

sensu lato ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular co ...

'', including African taxa, has been suggested to be

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

with respect to both species of living hippopotamus. The uncontroversial, core Asian members of the genus most closely related to the type ''H. sivalensis'' were widespread throughout the Late

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

and

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

South South is one of the cardinal directions or Points of the compass, compass points. The direction is the opposite of north and is perpendicular to both east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Pro ...

and

Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...

, with the oldest records coming from the Late

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

Siwalik Hills The Sivalik Hills, also known as the Shivalik Hills and Churia Hills, are a mountain range of the outer Himalayas that stretches over about from the Indus River eastwards close to the Brahmaputra River, spanning the northern parts of the India ...

. They were mostly extinct by the Late

Middle Pleistocene The Chibanian, widely known by its previous designation of Middle Pleistocene, is an age in the international geologic timescale or a stage in chronostratigraphy, being a division of the Pleistocene Epoch within the ongoing Quaternary Period. The ...

in Southeast Asia but survived in

Sumatra Sumatra is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the sixth-largest island in the world at 473,481 km2 (182,812 mi.2), not including adjacent i ...

into the early Late Pleistocene. The last known populations survived on the

Indian Subcontinent The Indian subcontinent is a list of the physiographic regions of the world, physiographical region in United Nations geoscheme for Asia#Southern Asia, Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian O ...

to the very end of the Pleistocene. ''Hexaprotodon'' survived in

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

until the terminal Pleistocene, with the latest dates being around 16,467–15,660 cal years

Before Present Before Present (BP) years, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Becaus ...

from bones found in the Narmada River valley in central India. Fossil evidence from a late-surviving Indian ''Hexaprotodon'' indicates that it lived during a catastrophic

drought A drought is defined as drier than normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, an ...

caused by the latest

Heinrich event A Heinrich event is a natural phenomenon in which large groups of icebergs break off from glaciers and traverse the North Atlantic. First described by marine geologist Hartmut Heinrich (Heinrich, H., 1988), they occurred during five of the last s ...

, leading to an extremely weak

Indian monsoon The Monsoon of South Asia is among several geographically distributed global monsoons. It affects the Indian subcontinent, where it is one of the oldest and most anticipated weather phenomena and an economically important pattern every year fro ...

. It is thought that these drought conditions led to a heavy

habitat fragmentation Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological processes ...

due to ''Hexaprotodon'' depending on aquatic habitats, prompting an

extinction vortex Extinction vortices are a class of models through which conservation biologists, geneticists and ecologists can understand the dynamics of and categorize extinctions in the context of their causes. This model shows the events that ultimately lead ...

. Humans may have also facilitated the extinction by hunting the hippopotamuses during this vulnerable state, although no evidence of hippopotamus butchery is known from the Indian subcontinent.

Species

The genus ''Hexaprotodon'' contains the following species, all from Asia: *'' Hexaprotodon bruneti'' (Boisserie and White, 2004) *''

Hexaprotodon crusafonti ''Hexaprotodon'' is an extinct genus of Hippopotamidae, hippopotamid known from Asia. The name ''Hexaprotodon'' means "six front teeth" as some of the fossil forms have three pairs of incisors.

'' (Aguirre, 1963) *'' Hexaprotodon hipponensis'' (Gaudry, 1867) *'' Hexaprotodon imagunculus'' (Hopwood, 1926) *'' Hexaprotodon iravticus'' (Falconer and Cautley, 1847) *'' Hexaprotodon karumensis'' (Coryndon, 1977) *'' Hexaprotodon mingoz'' (Boisserie et al., 2003) *'' Hexaprotodon namadicus'' (Falconer and Cautley, 1847 - possibly same as ''H. palaeindicus'') *'' Hexaprotodon palaeindicus'' (Falconer and Cautley, 1847) *'' Hexaprotodon pantanellii'' (Joleaud, 1920) *'' Hexaprotodon primaevus'' (Crusafont et al., 1964) *'' Hexaprotodon protamphibius'' (Arambourg, 1944) *'' Hexaprotodon siculus'' (Hooijer, 1946) *'' Hexaprotodon sinhaleyus'' (Deraniyagala) *'' Hexaprotodon sivajavanicus'' (Hooijer, 1950) *'' Hexaprotodon sivalensis'' (Falconer and Cautley, 1836) *''Hexaprotodon'' sp. - Myanmar hippopotamus (

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

)

References

Hippopotamuses Prehistoric even-toed ungulate genera Extinct mammals of Asia Pleistocene even-toed ungulates Fossil taxa described in 1836 {{Paleo-eventoedungulate-stub