stratigraphic intervals
   (System) †Jurassic (201.3 - 145.0 Ma)
     (Series) †Middle (174.1 - 163.5 Ma)
       (Stage) †Bathonian (168.3 - 166.1 Ma)
         1 (Substage) †upper
         2 (Substage) †middle
         3 (Substage) †lower