The Paleocene (pronunciation: /ˈpæliəˌsiːn, ˈpæ-, -lioʊ-/) or Palaeocene, the "old recent", is a geologic epoch that lasted from about 66 to 56 million years ago. It is the first epoch of the Paleogene Period in the modern Cenozoic Era. As with many geologic periods, the strata that define the epoch's beginning and end are well identified, but the exact ages remain uncertain. The Paleocene also is the last time in earths history that Reptiles were semi dominant before the Mammals took over in the Eocene.