Age of Mammals, Cenozoic, Cenozoic era - approximately the last 63 million years

Pliocene, Pliocene epoch - from 13 million to 2 million years ago; growth of mountains; cooling of climate; more and larger mammals

Miocene, Miocene epoch - from 25 million to 13 million years ago; appearance of grazing mammals

Oligocene, Oligocene epoch - from 40 million to 25 million years ago; appearance of sabertoothed cats

Eocene, Eocene epoch - from 58 million to 40 million years ago; presence of modern mammals

Paleocene, Paleocene epoch - from 63 million to 58 million years ago; appearance of birds and earliest mammals

geological period, period - a unit of geological time during which a system of rocks formed; "ganoid fishes swarmed during the earlier geological periods"

ordinal - being or denoting a numerical order in a series; "ordinal numbers"; "held an ordinal rank of seventh"