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(suborder Hippomorpha, family Equidae)

Known formerly as Eohippus (the ‘dawn horse’), the earliest known perissodactyl, an animal that was only 27 cm high, the size of a fox terrier. It was short-faced with low-crowned cheek teeth, and had four toes on the fore feet and three on the hind. Abundant in the early Eocene of N. America and Europe, it was also discovered in Palaeocene deposits in Mongolia. It was a browser dwelling in forest glades, and the likely ancestor for all the horses. Because of its small size, when the fossils were first found they were mistakenly associated with the African hyraxes, hence the name. In America the fossils were identified correctly and the name Eohippus was adopted, but according to the rules of taxonomic nomenclature, which require that the first name to be accepted must stand, Hyracotherium takes precedence. The modern tendency is to break up Hyracotherium into two or more genera, of which Protorohippus might be the ancestor of Equidae, while Cymbalophus would be close to the ancestry of the entire Perissodactyla.

Subjects: Zoology and Animal Sciences.

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