''Chilotherium'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

rhinoceros A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant taxon, extant species (or numerous extinct species) of odd-toed ungulates in the family (biology), family Rhinocerotidae. (It can also refer to a member ...

endemic to

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelag ...

during the

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 recent" ...

through

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58mya Mya may refer to: Brands and product names * Mya (program), an intelligent personal assistant created by Motorola * Mya (TV channel), an Italian Television channel * Midwest Young Artists, a comprehensive youth music program Codes * Burmese ...

, existing for approximately .. Retrieved 19 May 2013.

Description

It was a large, robust animal reaching 1.5-1.8 m in height and a weight between 1 and 2.5 tons, depending on the species. Both sexes are hornless. The lower jaw has a widened symphysial part and large tusk-like second incisors separated by a broad diastema. The dental formula is . The limbs are very short and the body stout; the feet are tridactyl with diverging metapodials. Studying ''C. wimani'', found a significant

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

in the tusks and mandible, most notably the length of the tusks in males. argued that some features in ''Chilotherium'', such as second incisors, mandible, cheek-teeth and other cranial features, are

plesiomorphic In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, an ...

, while some features in the tusks are

apomorphic In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

: the dorsal surface of the tusks in primitive species is turned latero-dorsally in more derived species while the medial edge has become very sharp and sickle-like and rotated dorsally, and thus a more effective cutting tool. ''Chilotherium'' were a group of

grazing In agriculture, grazing is a method of animal husbandry whereby domestic livestock are allowed outdoors to roam around and consume wild vegetations in order to convert the otherwise indigestible (by human gut) cellulose within grass and other ...

animals that radiated into several subgenera and species. Their feet were tridactyl and their legs shorter than in related groups. A few of them remained browsers, but most of them were adapted to a grass-based diet, hence the short legs. Their heads were horn-less but equipped with tusk-like lower incisors and were held in a horizontal position, in contrast to modern rhinos. They inhabited the so-called sub- Paratethyan or Greek-Iranian province during the late Miocene when this region was invaded by advanced rhinos from Africa, such as '' Ceratotherium'' (modern white rhinos). Like them, ''Chilotherium'' gradually evolved into specialised grazers, including

hypsodont Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on grit ...

teeth and shortened

metapodial Metapodials are long bone The long bones are those that are longer than they are wide. They are one of five types of bones: long, short, flat, irregular and sesamoid. Long bones, especially the femur and tibia, are subjected to most of the load d ...

Taxonomy

''Chilotherium'' was named by . It was assigned to ''Rhinocerotidae'' by Carroll (1988); to '' Aceratheriini'' by Antoine and Saraç (2005); and to '' Chilotheriini'' by Deng (2005).

Species

Twelve species of ''Chilotherium'' have been described and 19 other species have been assigned the genus. Nine are considered valid: four from Europe, one from Iran, and four from China. '' Aprotodon'' differs from ''Chilotherium'' in its proportionally larger and wider symphysis; the horizontal mandibular ramus is curved both in side view and in dorsal view, unlike most rhinocerotids; and the premolars are semi-molariform, unlike the fully molariform premolars in ''Chilotherium''. In '' Subchilotherium'' the mandibular symphysis is much more narrow than in ''Chilotherium''. '' Acerorhinus'' has a strongly constricted nasal base and a mandibular symphysis that is narrow compared to that in ''Chilotherium''.

Pathology

A female ''Chilotherium'' skull bears the distinctive bite marks of '' Dinocrocuta gigantea'' on the forehead. Based on the regrowth of bone around the injury, the rhinoceros escaped the predator's attack and later recovered.

Notes

References

* * * * * * * {{Taxonbar, from=Q19389 Miocene rhinoceroses Pliocene extinctions Prehistoric mammals of Asia Prehistoric mammals of Europe Pliocene rhinoceroses Fossil taxa described in 1924