Horse
Many changes occurred between those little animals and today's horses. These changes are best explained as adaptations. To its changing ecological niche, from a small forest-dweller eating nuts and fruit to a more significant forest browser eating leaves and small branches. Finally, the modern horse is a grazer on open grassland, with different teeth, legs for running, and a much larger size. Significant changes happened in the mid-Miocene when the climate cooled and grassland replaced forests. This change continued, and several groups of mammals changed from browsers to grazers.