stratigraphic intervals
   (System) †Jurassic (201.3 - 145.0 Ma)
     (Series) †Lower (201.3 - 174.1 Ma)
       (Stage) †Hettangian (201.3 - 199.3 Ma)
         1 (Substage) †liasicus + angulata Zones
         2 (Biozone) †planorbis Zone