Tertiary (period of Cenozoic) en

First period of the Cenozoic, comprising the major portion of the era. It extends from 65.8 million to 2.6 million years ago. The Tertiary is subdivided into five epochs: Paleocene, Eocene, Oligocene, Miocene, and Pliocene. Some authorities, chiefly European, have lately replaced the Tertiary with two new time divisions: Paleogene (comprising the earlier three epochs of the period) and Neogene (covering the final two).