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)
       (Series) †Eocene (56.0 - 33.9 Ma)
         (Subseries) †Middle
           1 (Stage) †Bartonian (41.2 - 37.71 Ma)
           2 (Stage) †Lutetian (47.8 - 41.2 Ma)