The eohippus, or Dawn Horse, is an extinct species that is thought to be the oldest known horse. They lived in Europe, Asia, and North America in the early Eocene Epoch. Living about 50 million years ago, this dog sized creature was about two feet long, weighing 55 pounds. The eohippus was an herbivore that ate plants and nuts. Fossils of these small horses were found by Richard Owen in England. He named it the Hyracotherium, or eohippus.