Hexaprotodon Temporal range: Latest Miocene to Late Pleistocene | |
---|---|
Hexaprotodon sivalensis skull elements | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Artiodactyla |
Family: | Hippopotamidae |
Subfamily: | Hippopotaminae |
Genus: | † Hexaprotodon Falconer & Cautley, 1836 |
Type species | |
†Hexaprotodon sivalensis | |
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]
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]
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]
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]
The genus Hexaprotodon contains the following species, all from Asia and Africa:
Genus sensu lato:
Genus sensu stricto:
The hippopotamus, also shortened to hippo, further qualified as the common hippopotamus, Nile hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus. Its name comes from the ancient Greek for "river horse" (ἱπποπόταμος).
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 the cetaceans. They are sometimes referred to as hippopotamids.
The pygmy hippopotamus or pygmy hippo 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 been extirpated from Nigeria.
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Rhinoceros is a genus comprising one-horned rhinoceroses. This scientific name was proposed by Swedish taxonomist Carl Linnaeus in 1758. The genus contains two species, the Indian rhinoceros and the Javan rhinoceros. Although both members are threatened, the Javan rhinoceros is one of the most endangered large mammals in the world with only 60 individuals surviving in Java (Indonesia). The word 'rhinoceros' is of Greek origin meaning "nose-horn".
Hippopotamus is a genus of artiodactyl mammals consisting of one extant species, Hippopotamus amphibius, the river hippopotamus, and several extinct species from both recent and prehistoric times. It belongs to the family Hippopotamidae, which also includes the pygmy hippopotamus and a number of extinct genera.
Ratnapura is a major city in Sri Lanka. It is the capital city of Sabaragamuwa Province, as well as the Ratnapura District, and is a traditional centre for the Sri Lankan gem trade. It is located on the Kalu Ganga in south-central Sri Lanka, some 101 km (63 mi) southeast of the country's capital, Colombo. Ratnapura is also spelled as Rathnapura.
The straight-tusked elephant is an extinct species of elephant that inhabited Europe and Western Asia during the Middle and Late Pleistocene. It was larger than any living elephant, with adult males suggested to reach 3.81–4.2 metres (12.5–13.8 ft) in shoulder height, and 11.3–15 tonnes in weight. Like modern elephants, the straight-tusked elephant lived in herds, flourishing during interglacial periods, when its range would extend as far north as Great Britain. Skeletons found in association with stone tools and wooden spears suggest they were scavenged and hunted by early humans, including Neanderthals. It is the ancestral species of most dwarf elephants that inhabited islands in the Mediterranean.
Equus sivalensis is an extinct species of large equid native to the northern Indian subcontinent. Remains date from the beginning of the Pleistocene, c. 2.58 million years ago until around 600,000 years ago, during the Middle Pleistocene. It is considered a "stenonine horse", meaning that it is more closely related to zebras and asses than true horses. Based on isotopes and teeth morphology, it is thought to have been a grazer. The later species Equus namadicus from the same region has sometimes been suggested to be a synonym due to their similar teeth morphology.
Palaeoloxodon namadicus is an extinct species of prehistoric elephant known from the early Middle to Late Pleistocene of the Indian subcontinent, and possibly also elsewhere in Asia. The species grew larger than any living elephant, and some authors have suggested it to have been the largest known land mammal based on extrapolation from fragmentary remains, though these estimates are speculative.
Whippomorpha or Cetancodonta is a group of artiodactyls that contains all living cetaceans and hippopotamuses. All Whippomorphs are descendants of the last common ancestor of Hippopotamus amphibius and Tursiops truncatus. This makes it a crown group. Whippomorpha is a suborder within the order Artiodactyla. The placement of Whippomorpha within Artiodactyla is a matter of some contention, as hippopotamuses were previously considered to be more closely related to Suidae (pigs) and Tayassuidae (peccaries). Most contemporary scientific phylogenetic and morphological research studies link hippopotamuses with cetaceans, and genetic evidence has overwhelmingly supported an evolutionary relationship between Hippopotamidae and Cetacea. Modern Whippomorphs all share a number of behavioural and physiological traits; such as a dense layer of subcutaneous fat and largely hairless bodies. They exhibit amphibious and aquatic behaviors and possess similar auditory structures.
The Cyprus dwarf hippopotamus or Cypriot pygmy hippopotamus is an extinct species of hippopotamus that inhabited the island of Cyprus from the Pleistocene until the early Holocene. The 200-kilogram (440 lb) Cyprus dwarf hippo was roughly the same size as the extant pygmy hippopotamus. Unlike the modern pygmy hippo, the Cyprus dwarf became small through the process of insular dwarfism. H. minor is the smallest hippopotamus of all known insular hippopotamuses. It is estimated to have measured 76 cm (2.5 ft) tall and 121 cm (4.0 ft) long.
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