Mesohippus was a small, three-toed prehistoric horse that lived during the late Eocene to early Oligocene epoch, around 30 to 40 million years ago. Roughly the size of a medium dog, Mesohippus stood about 2 feet (60 cm) tall at the shoulder and had longer legs and a more developed brain than its predecessors. It lived in forested environments of North America, feeding on soft leaves and vegetation. As one of the key transitional species in horse evolution, Mesohippus offers a clear link between ancient, dog-sized herbivores and the powerful single-toed horses of today.