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Equidae in the Eocene

  hyracotherium hyracotherium forelimb
Hyracotherium (left), forelimb of Hyracotherium (right)
Forelimb modified from MacFadden 1992.

        Hyracotherium (popularly known as Eohippus) first appeared 55 million years ago (MacFadden 1994) in North America (Harwood 1996). This genus of small, forest-dwelling animals is generally considered to contain the first members of the family Equidae, and the ancestor of all members of this family (MacFadden 1992).  Hyracotherium was well adapted to its habitat in the
Eocene forests of the northern hemisphere: it was digitigrade, with four hoofed toes on the forelegs and three on the hind legs (Azzaroli 1992).  This helped it to move easily over the soft forest terrain (Draper 1992).  Its small size, 2.2-5hh (Johnson 1967), allowed it to move easily through the dense vegetation and to hide from predators (Benton 2000).  It was also a browser, with low-crowned teeth suitable for eating leaves, fruit, and other soft vegetation (Draper 1996).  Because of Hyracotherium's success as a forest browser, very little evolutionary change occured within the genus during the Eocene (Hunt 1995).

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