Pliohippus
"more recent horse"
The first single-hoofed horse was Pliohippus, which evolved about ten million years ago. This was the prototype for today's modern horse, Equus caballus, which was established a million years ago. Pliohippus was about the height of a donkey. Its mane was stiff and upright. In addition, the head and neck lengthened even more and the eyes were set even wider apart. This gave it the ability to see both in front and behind itself.
Although Pliohippus was related to Equus, it probably did not give rise to our modern horse. Pliohippus had deep facial fossae, whereas Equus has none. Also Pliohippus's teeth are very curved, but those of Equus are straight.