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) †Lower
           (Stage) †Ypresian (56.0 - 47.8 Ma)
             1 (Substage) †[upper]
             2 (Substage) †[lower]