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How are the Paleogene, Neogene, and Quaternary periods arranged within the Cenozoic Era?

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Cenozoic migration routes — Cenozoic Era Principal Cenozoic faunal migration routes and barriers.

The Cenozoic Era is currently divided into three distinct geologic time periods, arranged chronologically from oldest to youngest as follows:

Paleogene Period (66 million to 23 million years ago): The oldest division, comprising the Paleocene, Eocene, and Oligocene epochs.123
Neogene Period (23 million to 2.6 million years ago): The middle division, encompassing the Miocene and Pliocene epochs.123
Quaternary Period (2.6 million years ago to the present): The youngest division, which includes the Pleistocene and Holocene epochs.23

While the Cenozoic was traditionally divided into the Tertiary Period and the Quaternary, the International Commission on Stratigraphy now formally recognizes the Paleogene and Neogene as the standard periods that replace the former Tertiary designation.423