A tiny, two-feet tall horse-like animal scampers through a forest, nibbling on leaves. This isn't a fairy tale, but a look back in time at Hyracotherium, an ancient member of the horse family. For millions of years, many horse species in all shapes and sizes roamed Earth's forests and grasslands. But only a very few that were adapted to the grasslands survived. All domestic horses belong to a single species, Equus caballus.

Image credits: main image, © AMNH; Sandra Olsen: courtesy of Sandra Olsen; Sandra Olsen: courtesy of Sandra Olsen.