stratigraphic intervals
   (System) †Devonian (419.2 - 358.9 Ma)
     (Series) †Middle (393.3 - 382.7 Ma)
       (Stage) †Givetian (387.7 - 382.7 Ma)
         1 (Substage) †varcus-cristatus Zones
         2 (Biozone) †ensensis Zone