Sixty million years ago, in the Eocene epoch, the doglike eohippus flourished in swampy forests where it browsed on leaves. The Eohippus had little or no lateral vision and had a coat similar to a deer in texture and in color right down to fawn like spots to help to camouflage them. It had molars with small grinding surfaces to chew the succulent leaves of its forest habitat. Eohippus was about the size of a fox, had four toes on its forefeet and three on its hind feet which were padded like those of a dog and allowed easy movement over wet ground. These toes and pads are now the ergots and splint bones found on the legs of the modern horse. Eohippus was a browsing animal that lived on soft leaves growing on low shrubs.
By the Oligocene period, about 38 million years ago, Eohippus had evolved into Mesohippus and had achieved the size of a German Shepherd. This evolution was taller and heavier, with teeth that allowed them to eat a wider variety of plants. They were still browsers living in forests and swamps. Their front feet were reduced to three toes, still padded, but the middle toe carried most of the weight. Mesohippus lived in this more open country where it ran and trotted. It was adapted for running in open country. .
With the spread of Miocene grasslands 25 million years ago, only the descendants whose teeth had adapted to grinding survived. The drying climate produced harder ground, and the middle digit of Merychippus, expanded to bear the strain of its increased weight. As it adapted to changing conditions, the neck and head became longer, the incisors moved forward in the skull and the form and position of the eyes altered to allow the horse to view the horizon while grazing. The Merychippus began to develop defenses and a heightened sense of smell. The teeth changed to those more like today's horses. These 3 toed grazers were believed to be quick, speedy and surefooted to escape from predators.