The earliest known fossils of the horse family, called Hyracotherium, were found in North America and date back to the early Eocene epoch, approximately 56 million years ago.

Hyracotherium was a small, four-toed creature that lived in forests and ate leaves and fruit. It was about the size of a fox and had a short, deep skull with small teeth. While not a horse in the modern sense, it shared key characteristics that would evolve into the modern horse, such as its relatively long legs and single toe on each foot.

It's important to note that the term "Hyracotherium" is not commonly used anymore, with paleontologists now preferring the term Eohippus for this early ancestor.