Eurohippus prehistoric mammals. Computer illustration of two Eurohippus sp. equid ungulates huddling in a forest around 42 million years ago in what is today France. An ancient ancestor to modern horses, donkeys, and zebras, Eurohippus was about the size of a small dog (about 50 centimetres long and a few kilograms in weight). It possessed three toes instead of a single hoof. While modern equines are adapted to the varying climate of grasslands, Eurohippus lived and foraged in the relative comfort of warm and moist forests.