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).
The last few million years of the Tertiary Period saw a gradual change in climate. Temperatures dropped steadily, leading into the severe freezing conditions of the Ice Age to come.
This period also called the Age of birds.
The North America was dominated by carnivorous birds like Diatryma; after the land bridge formed between North and South America, they cannot complete with mammals from South America, and became extinct.