| Pliocene (plī'ə-sēn') The fifth and last epoch of the Tertiary Period, from about 5 to 2 million years ago. During this time the global climate became cooler and the number and expanse of grasslands and savannas increased greatly. This change in vegetation was accompanied by an increase in long-legged grazers. The land bridge between North America and South America also formed at this time, and massive ice sheets accumulated at the poles. In the later part of the epoch many of the species living in polar regions became extinct. See Chart at geologic time. |