The Oligocene epoch is a geologic period that extends from about 34 million to 23 million years before the present. As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly uncertain. The name Oligocene comes from the Greek ὀλίγος (oligos, few) and καινός (kainos, new), and refers to the sparsity of additional modern mammalian faunas after a burst of evolution during the Eocene. The Oligocene follows the Eocene epoch and is followed by the Miocene epoch. The Oligocene is the third and final epoch of the Palaeogene period.
ecosystems of the Miocene."(Haines)
The start of the Oligocene is marked by a major extinction event that may be related to the impact of a large extraterrestrial object in Siberia and/or one near Chesapeake Bay. The Oligocene-Miocene boundary is not set at an easily identified worldwide event but rather at regional boundaries between the warmer Oligocene and the relatively cooler Miocene.