The Eocene EPOCH was a geological period that lasted from 56 to 33.9 million years ago. It was part of the Paleogene Period and was preceded by the Paleocene EPOCH and followed by the Oligocene EPOCH. During this time, the climate was warm and humid, and the continents were beginning to take their modern shapes. The Eocene EPOCH saw the emergence of many modern mammal groups, including primates, whales, horses, and bats.