Hexaprotodon

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Hexaprotodon
Temporal range: Latest Miocene to Late Pleistocene 6–0.015  Ma
Skull of the Hexaprotodon sivalensis.png
Hexaprotodon sivalensis.jpg
Hexaprotodon sivalensis skull elements
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Family: Hippopotamidae
Subfamily: Hippopotaminae
Genus: Hexaprotodon
Falconer & Cautley, 1836
Type species
Hexaprotodon sivalensis
Falconer & Cautley, 1836
Species

See text

Synonyms

Hexoprotodon [sic] [1]

Hexaprotodon is an extinct genus of hippopotamid known from Asia and possibly Africa and Europe. The name Hexaprotodon means "six front teeth" as some of the fossil forms have three pairs of incisors. [2] [3]

Contents

Taxonomy

The name Hexaprotodon was often applied to the pygmy hippopotamus before its reclassification into the genus Choeropsis . The genus has been historically applied to numerous fossil hippopotamus species spanning Asia, Africa and Europe. The genus sensu lato , has been suggested to be paraphyletic with respect to both species of living hippopotamus. [2] The uncontroversial, core Asian members of the genus most closely related to the type species H. sivalensis first appeared around 6 million years ago, during the latest Miocene and were widespread throughout South and Southeast Asia, with the oldest records coming from the Siwalik Hills. [4] [5] The African species Hexaprotodon bruneti from the Early Pleistocene of Ethiopia may be closely related to the Asian Hexaprotodon species, and thus belong in the genus in its more narrow sense. If so, it likely originates from a migration from Asia. [2]

Description

The Asian species of Hexaprotodon, like the living hippopotamus (Hippopotamus amphibius), but unlike the pygmy hippoptamus are thought to have had a semiaquatic ecology, with their skull shape greatly resembling that of H. amphibius, with elevated orbits that allowed them to see above water while submerged. This lifestyle likely evolved independently in both Hexaprotodon and the genus Hippopotamus. In comparison to Hippopotamus, the mandibular symphysis is much more robust, the canine processes do not extend laterally outwards, and the molar teeth are lower crowned. The more slender and less massive postcranial skeleton compared to H. amphibius also suggests that Hexaprotodon was less adapted to walking in mud. [6] Dental microwear suggests a grazing diet for Asian Hexaprotodon species, similar to H. amphibius. [7]

Extinction

Hexaprotodon was largely extinct by the Late Middle Pleistocene in Southeast Asia [4] but survived in Sumatra into the early Late Pleistocene, with one tooth dated to around 70,000 years ago. [5] The last known populations survived on the Indian Subcontinent to the very end of the Pleistocene, [4] with among the latest dates being around 16,467–15,660 cal years Before Present 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 caused by the latest Heinrich event, leading to an extremely weak Indian monsoon. It is thought that these drought conditions led to a heavy habitat fragmentation due to Hexaprotodon depending on aquatic habitats, prompting an extinction vortex. 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. [4]

Species

The genus Hexaprotodon contains the following species, all from Asia and Africa:

Life Restoration of Hexaprotodon sivalensis Hexaprotodon Sivalensis.png
Life Restoration of Hexaprotodon sivalensis

Genus sensu lato:

Genus sensu stricto:

H. imagunculus Hippopotamus imagunculus.JPG
H. imagunculus

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References

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