stratigraphic intervals
   (System) †Tertiary (66.0 - 2.58 Ma)
     (Subsystem) †Paleogene (66.0 - 23.03 Ma) see System Paleogene System (66.0 - 23.03 Ma)
       1 (Series) †Oligocene (33.9 - 23.03 Ma)
       2 (Series) †Eocene (56.0 - 33.9 Ma)
       3 (Series) †Paleocene (66.0 - 56.0 Ma)