Hyracotherium (Eohippus) - "dawn horse".
Earliest of known ancestors of a horse is Eohippus (Hyracotherium), or the dawn horse who lived in Northern America during an epoch Eocene (54 - 38 million years ago).
The Eohippus was the size of a fox or small to medium sized dog. Actually its head and body looked more like a deer and it had 5 toes on each of it's two front feet and three on his two hinds. The toes ended in a strong, thick, horny type nail and their tips. In the Middle of the bottom of the foot the toes were supported by a callous like pad. The Eohippus had little or no lateral vision and it's teeth were similar to a pig, short and crowned for eating plants. Eohippus probably stood about 14 inches high at his shoulder and weighed around 12 lbs!
Try riding that!