Early Horses

The earliest-known horse fossils come from the Eocene epoch (from 57 to 34 million years ago),and they are so different from the modern version that it was not initially realized that there was any relation.Dawn horse,or Eohippus,as this animal has been called,has been found in both Europe and North America. Eohippus was tiny,about the size of a small dog,and apparently lived in wooded areas.These animals had hooves but,in contrast to modern horses,they had four hoofed toes on the front feet,three on the rear,and the hooves were padded. Eohippus was also pug-nosed by comparison to modern horses,and its teeth reveal that it was a browser that fed on a variety of plants.In fact,although it was completely herbivorous (plant eating),this little horse had canine teeth-a reminder that many of its predecessors were carnivores (meat eaters).

Throughout the Eocene and Oligocene epochs (from 57 to 23 million years ago),the descendants of Eohippus evolved in a fairly straightforward way that is well documented by their fossils.They became gradually larger;the middle toe, eventually to become the single hoof of the modern horses,became stronger and more prominent,and the grinding surfaces of the teeth became larger,with complex,resistant ridges.But the resemblance to Eohippus remained clear.It was only in the Miocene (from 23 to 5 million years ago),coincident with the spread of grassy prairies,that abrupt changes took place,resulting in several different lineages of horse evolution,only one of which is still extant:the modern horse.

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