MACROFOSSILS AND MICROFOSSILS FOUND AT A DINOSAUR SITE IN THE BIGHORN BASIN, WYOMING

Paleoenvironments were analyzed for a Jurassic dinosaur site in the Bighorn Basin near Shell, Wyoming, for an NSF REU (Research Experiences for Undergraduates) project. Several different aspects were considered, including dinosaur macrofossils and the microfaunal content of the bone-bearing layers and quarry walls. Microfossils were collected by a screen-washing process in a nearby stream. Four different locales in the quarry walls consisting of intraformational conglomerates of mudstone rip-up clasts were sampled, along with two bone-bearing siltstone layers. After an initial drying cycle, the sediments were placed into nested 18 and 30 mesh screens for two washing and two drying cycles, each at least four hours long. Samples were transported back to the laboratory for macroscopic and microscopic examination. Findings consisted of several tooth fragments, including one from a sauropod; Jurassic bone fragments; an internal mold of a gastropod; and nonmarine ostracodes. The presence of ostracodes at all four quarry wall locations has helped determine the initial location of the mudstone as a calm, aquatic environment. Identification of the species will provide more detail as to specific environmental conditions. The microfaunal material of this dinosaur site can provide vital information to the overall interpretation of the environment of deposition.