Variation in a population of Theropoda (Dinosauria): Allosaurus from the Cleveland-Lloyd Quarry (Upper Jurassic), Utah, USA

Ontogenetic and individual variation in a population of the large theropod Allosaurus cf. A. fragilis was examined using the Bjork superimposition method on the premaxillae, maxillae, lachrymal, postorbital, and jugal. This method allows utilization of incomplete specimens without having to estimate (fabricate) missing data. In addition, it visually shows regions of ontogenetic change and variation. Comparison of these results with other morphometric studies of the same specimens show that most allometric trends are not supported. Instead, ontogenetic change is mostly isometric. In addition, the wide range of individual variation in all the skull elements analyzed makes some autapomorphic characters used to define other theropod taxa suspect.