The Hell Creek Formation records one of the most complete terrestrial sequences of the uppermost Cretaceous in the world. The exposures that occur along the tributaries of the Missouri River in northeastern Montana offer a near complete section of the Hell Creek and overlying Paleocene Tullock Formations. The goal of this study is to collect both surface and screened samples of microvertebrate fossils from a series of localities in different facies and stratigraphic levels of the Hell Creek Formation in an effort to analyze trends in faunal diversity. Our hypothesis is that an analysis of these microfossils will provide new information on faunal diversity and change within the latest Cretaceous ecosystem of the Western Interior.

At present, sites from channel/point bar, floodplain, and crevasse splay deposits have been wet-screened for microvertebrate remains. Floodplain deposits have initially yielded greater numbers of specimens and taxonomic diversity. Mammals, theropod dinosaurs, and salamanders are the most common faunal elements, followed by bony fish and lizards. Snakes and frogs are scarce, and juvenile or embryonic dinosaurs and champsosaurs are also present.