TAPHONOMY AND SEDIMENTOLOGY OF A TYRANNOSAURID LOCALITY FROM THE LATE CRETACEOUS (MAASTRICHTIAN) HELL CREEK FORMATION OF EASTERN MONTANA

The C-rex quarry, located in eastern Montana, has yielded a diverse terrestrial fossil assemblage from the late Cretaceous (Maastrichtian) Hell Creek Formation. The fossil assemblage consists of more than 10 species, including Tyrannosaurus rex, freshwater molluscs, as well as plant material. The fossils are found 85 feet above the base of the Hell Creek Formation in a mudstone. The mudstone is a coarsening upward, organic rich sediment with evidence of bioturbation. The dinosaur specimen is a partially articulated adult Tyrannosaurus rex lying on its left side. The disarticulated components of the skeleton are found in the general area that they would be were the animal articulated. Skeletal elements show little or no weathering, while the only bone modifications are attributed to modern weathering or lithostatic loading. The invertebrate fauna is composed entirely of freshwater gastropods and clams. They are dominated by the genera Sphaerium and Campaloma. All of the molluscs in the assemblage are interpreted to be from quiet water settings. Both articulated as well as fragmented shells are found. The plant material occurs in both organic mats of small fragmentary leaves or isolated, nearly complete specimens. The Crex quarry is interpreted to be a lacustrine setting where autochthonous molluscs were preserved with allochthonous vertebrate and floral material.