AN INVESTIGATION OF MICROVERTEBRATES IN THE MORRISON FORMATION NEAR SHELL, WYOMING

In this study Upper Jurassic microvertebrate specimens were recovered from a Morrison Formation dinosaur site in the vicinity of Shell, Wyoming. Sediments including mudstones and rip-up clast conglomerates from low to moderate energy environments were dried and screen washed through nested 18 and 30 mesh sieves. The selection of samples for screen washing was based on the presence of larger vertebrate fossils, plant fossils, and the texture of the sediment. We also sampled anthills since the biological sorting that results in their construction may exhume microfossils.

Preliminary processing has recovered small fragmentary bones from several sampled units at the site. Some of these specimens resemble mammal limb bones, whereas others appear to be fish elements. A unit of interbedded sandstones and rip up clast conglomerate low in the site's stratigraphic section has yielded a partial tooth of a small theropod dinosaur. Furthermore, a mudstone unit in the site's dinosaur-bearing Upper Quarry has yielded a single, 0.77 mm wide, partial mammal tooth preserving three high, triangularly-arrayed cusps.

More processing of sediment samples is required since the material recovered to date is difficult to classify to low taxonomic levels. However, the fragmentary microvertebrate fossils found so far provide a glimpse of the small vertebrate fauna that shared the site with the larger dinosaurs (Allosaurus, Torvosaurus, Stegosaurus, and Camarasaurus and other sauropods) that frequented the area.