First record of Lancian (Late Cretaceous) mammals from the Hell Creek Formation of southwestern North Dakota, USA

Abstract

First records of fossil mammals from the Hell Creek Formation of southwestern North Dakota, USA, are described. The assemblage is similar to local faunas from the Lance Formation type area, Wyoming, and the Hell Creek Formation type area, Montana. One species absent from the Lance ( Gypsonictops illuminatus), however, occurs both in the Hell Creek Formation of North Dakota and the Scollard Formation of Alberta. These findings suggest a Lancian age for the part of the Hell Creek in which these fossils occur and imply that Lancian local faunas in the Western Interior of North America sample a coherent latest Cretaceous biogeographic realm. Megafloral zonation of the Hell Creek Formation and correlation to the standard ammonite zonation suggest that future research efforts at the base of the Hell Creek in eastern Montana and southwestern North Dakota may help to elucidate mammalian faunal turnover across the ‘Edmontonian’-Lancian boundary.