<P> The Miohippus population that remained on the steppes is believed to be ancestral to Parahippus, a North American animal about the size of a small pony, with a prolonged skull and a facial structure resembling the horses of today . Its third toe was stronger and larger, and carried the main weight of the body . Its four premolars resembled the molar teeth; the first were small and almost nonexistent . The incisor teeth, like those of its predecessors, had a crown (like human incisors); however, the top incisors had a trace of a shallow crease marking the beginning of the core / cup . </P> <P> In the middle of the Miocene epoch, the grazer Merychippus flourished . It had wider molars than its predecessors, which are believed to have been used for crunching the hard grasses of the steppes . The hind legs, which were relatively short, had side toes equipped with small hooves, but they probably only touched the ground when running . Merychippus radiated into at least 19 additional grassland species . </P> <P> Three lineages within Equidae are believed to be descended from the numerous varieties of Merychippus: Hipparion, Protohippus and Pliohippus . The most different from Merychippus was Hipparion, mainly in the structure of tooth enamel: in comparison with other Equidae, the inside, or tongue side, had a completely isolated parapet . A complete and well - preserved skeleton of the North American Hipparion shows an animal the size of a small pony . They were very slim, rather like antelopes, and were adapted to life on dry prairies . On its slim legs, Hipparion had three toes equipped with small hooves, but the side toes did not touch the ground . </P> <P> In North America, Hipparion and its relatives (Cormohipparion, Nannippus, Neohipparion, and Pseudhipparion), proliferated into many kinds of equids, at least one of which managed to migrate to Asia and Europe during the Miocene epoch . (European Hipparion differs from American Hipparion in its smaller body size--the best - known discovery of these fossils was near Athens .) </P>

The four-toed ancestor of the modern horse would have been well suited to life in the