TAPHONOMY AND RARE EARTH ELEMENT GEOCHEMISTRY OF THE STEGOSAURUS SP. AT THE CLEVELAND LLOYD DINOSAUR QUARRY

The Cleveland Lloyd Dinosaur Quarry in Emery County, Utah is the site of the mass death of a large number of Jurassic-aged dinosaurs, including Allosaurus fragilis and Stegosaurus sp. The deposit of bones is unique in that it contains the largest collection of Allosaurus fragilis specimens in the world (forty-seven). Recent studies have shown that the deposit of dinosaur bones at the Cleveland Lloyd Dinosaur Quarry is the result of a catastrophic drought event (Gates, 2002). By looking at the taphonomy of the Stegosaurus sp. it can be compared to the overall taphonomy recently described by Gates (2002). Rare earth element analysis is used to determine the environment of deposition and to aid in the investigation of taphonomy. Bones excavated from the quarry deposit, as well as bones in the collections of the University of Utah and the College of Eastern Utah, were used to determine the number of individual Stegosaurs represented in the quarry deposit.

Three-dimensional mapping, excavation and taphonomic analysis of bones were used to determine that the biostratigraphy and taphonomy represented in the study area. Results show that the Stegosaurus bones are above the Allosaurus bones and have more occurrences of teeth marks and abrasion. Further analysis shows that the bones were not greatly transported (autochthonous) but appear slightly orientated due to fluvial action. The population surveyed showed that there are six individuals of Stegosaurus currently found at Cleveland Lloyd Dinosaur Quarry. Bone samples of Allosaurus and Stegosaurus were collected for rare earth element analysis to determine the environment of deposition at the time the dinosaurs died. Rare earth element compositions show that both the Allosaurus bones and the Stegosaurus bones were deposited in a very similar environment. They show enrichment in light rare earth elements which is indicative of a dry, aeolian-influenced depositional environment. This evidence supports the drought-induced scenario concluded by Gates (2002).