Major climatic changes occurred during the Miocene (Mio - middle; cene - recent). The world became a cooler, drier place. As a result, forests shrunk and grasslands spread.

The animals of the Miocene adapted to this changing world. This epoch is characterized by a major "modernization" of many animals--they began to resemble the animals of the present. Some horses acquired the high-crowned teeth needed to consume abrasive grasses.