CHONDRICHTHYANS FROM THE FAIRPOINT MEMBER OF THE FOX HILLS FORMATION (MAASTRICHTIAN), MEADE COUNTY, SOUTH DAKOTA

The middle part of the Fairpoint Member of the Fox Hills Formation in Meade County, South Dakota consists of marine shoreface deposits and contains a chondrichthyan assemblage which includes both piscivorous and bottom feeding forms. The assemblage consists of 15 genera most of which are widely known from Upper Cretaceous rocks of the Western Interior (e.g., Rhombodus; Carcharias; Serratolamna; Ischyrhiza), and from other parts of North America, Europe, Africa, and Asia. This middle Fairpoint assemblage contains many of the same chondrichthyan genera reported from the lignitic Stoneville lithofacies of the upper part of the Fairpoint Member, and from the Timber Lake Member of the Fox Hills Formation in North Dakota Fairpoint chondrichthyans are probably roughly equivalent in age to the chondrichthyans from the Timber Lake Member, and are probably slightly older than the chondrichthyan assemblage from the Breien Member of the Hell Creek Formation. The Breien, Timber Lake, and Fairpoint chondrichthyans are the youngest transitional marine chondrichthyan assemblages yet recovered from Cretaceous rocks of the Western Interior. The Fairpoint Member assemblage consists of chondrichthyan species different from those of the Paleocene Cannonball Formation of North Dakota. This disparity supports the view that there was a significant turnover among Western Interior chondrichthyans during the Cretaceous/Tertiary transition. The cause of this extinction is not yet clear, nor is it clear that it coincides with the Cretaceous/Tertiary boundary