"global chronostratigraphic units"
   (Eon) Phanerozoic Eon (541.0 Ma - present)
     (Era) Cenozoic Era (66.0 Ma - present)
       (Sub-era) †Tertiary Sub-era (66.0 - 2.58 Ma) see Period Tertiary Period (66.0 - 2.58 Ma)
         (Period) †Paleogene Period (66.0 - 23.03 Ma)
           (Epoch) †Oligocene Epoch (33.9 - 23.03 Ma)
             (Stage) †Chattian Stage (27.82 - 23.03 Ma)