Merychippus was an early ancestor of modern horses that lived around 20 to 10 million years ago during the Miocene epoch. It was a medium-sized animal, about the size of a pony, and had a more horse-like appearance compared to its predecessors. Merychippus had long legs and a single hoof on each foot, adaptations that helped it run faster on open grasslands. This species is significant in the evolution of horses because it represents a transition from earlier multi-toed forms to the single-toed horses we see today. Merychippus also had a more complex tooth structure, allowing it to graze on tougher grasses, which were becoming more common during its time.