The earlier of the two periods which comprise the Cenozoic era, preceded by the Cretaceous, followed by the Neogene, and dated at 65.5–23.03 Ma ago (Int. Commission on Stratigraphy, 2004). The Palaeogene period is subdivided into the Palaeocene, Eocene, and Oligocene epochs.
http://www.geologypage.com/2014/04/paleogene-period.html The Palaeogene Period.