The Eocene refers to the second of the five epochs in the Tertiary Period. It is the second of the three epochs in the Paleogene. The Eocene Epoch witnessed the substitution of older mammalian orders by modern ones.
The first emergent were the hoofed animals, involving the famous dawn horse (Eohippus) and ancestral tapirs and rhinoceroses. Early rabbits, bats, mice, rats, whales, and carnivorous mammals, beavers, also originated at the time of Eocene Epoch.