Paleogene Period
Paleogene Period, the name of the earlier (less recent) of two periods into which some geologists divide the Cenozoic Era. The Paleogene began about 65,000,000 years ago and ended around 23,000,000 years ago with the beginning of the Neogene Period. The Paleogene Period consists of the Paleocene, Eocene, and Oligocene Epochs. (Using a different classification scheme, some geologists consider these epochs part of a period they call the Tertiary Period.)