Английская Википедия:Hipparion

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Шаблон:Short description Шаблон:Automatic taxobox Hipparion is an extinct genus of three-toed equine belonging to the extinct tribe Hipparionini. While the genus formerly included most hipparionines, the genus is now more narrowly defined as hipparionines from Eurasia spanning the Late Miocene.

Taxonomy

The genus "Hipparion" was used for over a century as a form classification to describe over a hundred species of Holartic hipparionines from the Pliocene and Miocene eras that had three toes and isolated protocones. Since then, groups such as the genera Cormohipparion and Neohipparion were proposed to further sort these species, typically based on differences in skull morphology. As a result, these species are now known as "Hipparion" in sensu lato (s.l.), or a broad sense.

Hipparion in sensu stricto (s.s.), or a strict sense, describes the genus of Old World hipparionines from remains found in Eurasia from the Late Miocene era (~10-5 Ma, or million years ago). The assignment of remains from elsewhere to the genus, such as North America and Africa, is uncertain.

Morphology

Файл:Hipparion forcei NT.jpg

Life reconstruction of H. forcei

Skull of H. gracile against a black background

H. gracile skull

Fossil of three-toed Hipparion lower hind leg, held up on a stand and against a brown cloth background

Three-toed Hipparion hind leg fossil

Hipparion resembled the modern horse, but was tridactyl, or three-toed. It had two vestigial outer toes in addition to its hoof. In some species, these outer toes were functional. Hipparion was typically medium in size, at about Шаблон:Convert tall at the shoulder. Hipparion had hypsodont dentition (high-crowned teeth) for its premolars and molars. Hipparion had isolated protocones in the upper molars, meaning a cusp of the teeth called a protocone was not connected to a tooth crest called a protoloph. Hipparion is also characterized by its facial fossa, or depression in the skull, located high on the head.

Evolution and Extinction

Evolution

Hipparion likely evolved from a species of Cormohipparion during the Late Miocene, about 11.4-11.0 Ma. This species, C. occidentale, came to Eurasia and Africa from North America. The last common ancestor of Hipparion and the modern horse was Merychippus.

Extinction

In the Old World, Hipparion experienced population decline and extinction down a North to South gradient, as did many other Miocene vertebrates. This trend is believed to be due to environmental changes caused by global cooling and decreasing carbon dioxide levels in the atmosphere.