Eohippus

Eohippus is small fossil proto-horse. It is an extinct genus of small equid ungulates. The only species is "E. angustidens", which was long considered a species of "Hyracotherium". Its remains have been found in North America and date to the early Eocene (4856 million years ago).
Much of the evolution of the horse took place in North America. That is where horses originated, but became extinct there about 10,000 years ago.