Abstract

Excavation from 1992 to 1995 at a site in the Brushy Basin Member of the Morrison Formation near Green River, Utah, yielded approximately 200 elements representing at least five different dinosaur species. Approximately half of these elements have been prepared and of those, nine elements are identified as coming from a single individual theropod (carnivorous dinosaur). Identification of the theropod is the focus of this study.

Prepared theropod elements are: a cervical rib, two sacral vertebrae, sacral rib, two chevrons, scapula, ilium, and pubis. The theropod from the Green River site is Allosaurus Marsh.

Two allosaur morphs are present in the Morrison Formation. One is Allosaurus fragilis known from extensive collections in the Cleveland-Lloyd Dinosaur Quarry, and an unnamed morph, perhaps millions of years younger, from the Dry Mesa Quarry, Colorado. The two morphs differ mainly in the relative size of the appendicular elements and configuration of the lacrimal. Prepared elements from the Green River theropod are similar to the elements of the Cleveland-Lloyd allosaur, except the scapula is approximately 30 percent larger, perhaps indicating large appendicular elements, consistent with the Dry Mesa allosaur. In addition, the Green River Quarry roughly correlates stratigraphically with the Dry Mesa Quarry. From the available specimens, identification to species for the Green River theropod remains undetermined.