Most recent forms of mammals evolved during the Pleistocene (Pleisto - most; cene - recent) Epoch. A dramatic "event" of this time period was the last "Ice Age." The Pleistocene Epoch also was the last time that a great diversity of mammals lived in North America, including mammoths, mastodons, giant sloths, several llama-like camels, and tapirs. And it was the last epoch native horses lived in North America. The horses were both abundant and diverse.