Diversity of turtles across the cretaceous/tertiary boundary in Northeastern Montana
Abstract The abundant chelonian faunas of the Hell Creek and Tullock formations of McCone and Garfield counties, Montana, span the Cretaceous/Tertiary boundary and provide a basis for assessing extinction and changes in diversity. Over three thousand specimens were counted on a modified minimum number basis from 510 localities. The Lancian (Maastrichtian) part of the Hell Creek Formation contains at least 19 genera and subgenera of turtles and probably a greater but undetermined number of species and comprises the most diverse fossil turtle fauna known from a single rock unit. At least 15 generic level taxa survive into the Puercan (early Paleocene) part of the overlying Tullock Formation and only one new genus appears. The magnitude of the change in diversity across the Cretaceous/Tertiary boundary is less than or compaable to examples within the Tertiary and is readily explained by moderate ecological changes.