Part of the Cenozoic era, the Tertiary
period is divided into five epochs: Paleocene, Eocene, Oligocene,
Miocene, and Pliocene. During this time mammals diversified
quickly. Some examples are marsupials, insectivores, bears,
hyenas, dogs, cats, seals, walruses, whales, dolphins, early
mastodons, hoofed mammals, horses, rhinoceroses, hippopotamuses,
oreodonts, rodents, rabbits, monkeys, lemurs, apes, and humans (Australopithecus).