ASSESSING THE IDENTITY OF A NEW ALLOSAURUS SKELETON FROM THE JURASSIC MORRISON FORMATION OF WYOMING

Allosaurus fragilis is one of the best known theropod dinosaurs, with numerous skeletons described from Utah, Wyoming, and Montana. However, relatively complete skeletons of Allosaurus remain rare, in part because they are often found in disarticulated bone beds. We provide a preliminary description of a new specimen, comprised of 65 cranial and postcranial elements, found near Shell in the Jurassic Morrison Formation in north-central Wyoming. The specimen exhibits a unique combination of large body size with sub-adult characteristics. We interpret the remains as belonging to a sub-adult individual due to the majority of the dorsal vertebrae remaining unfused, the pubes being unfused, the coracoid not being fused to the scapula, and elements within the skull remaining unfused. Additionally, the number of alveoli is high compared to agreed-upon "adult" individuals of Allosaurus. Whereas previously described adult specimens of Allosaurus exhibit 14–17 alveoli in the maxilla and dentary, the new specimen exhibits 19–21 alveoli in each jaw element. Despite these indications that the individual was not fully grown, it was comparable in body size to other "adult" Allosaurus specimens. For example, the new partial femur has a mid-shaft circumference of 28cm, and other "adult" Allosaurus femora exhibit mid-shaft circumferences of up to 30cm. Similarly, the dentary tooth rows are 32.6cm and 33.2cm in anteroposterior length in the new specimen, and other "adult" Allosaurus dentaries exhibit tooth row lengths of up to 33cm. The dorsally-projecting lacrimal horn of the new specimen is comparatively pronounced and the anterior edge of its descending process exhibits a more prominent projection into the antorbital fenestra relative to many other specimens of Allosaurus. Further comparison to other specimens is needed, and we are making arrangements to examine the histology of the femur of the new specimen to independently assess the ontogenetic age of this individual.