Meeting Abstract

P2.118  Tuesday, Jan. 5  A biomechanical comparison between three large theropod dinosaurs: relative roles of functional and phylogenetic constraints FERRER, E.A.; Univ. of California, Berkeley eferrer@berkeley.edu

Understanding differences in cranial anatomy and biomechanics can help elucidate the causes and modes by which carnivorous dinosaurs (Theropoda) evolved large size. Comparisons of basic cranial anatomy and stress strain ratios generated by Finite Element Analysis were conducted to determine what aspects of cranial anatomy of Tyrannosaurus rex, Allosaurus fragilis, and Majungasaurus crenatissimus (encompassing three major clades of large theropods) were influenced by the functional consequences of allometry as opposed to phylogenetic constraints of trait complexes retained from their small-bodied ancestors. The main assumption, that large-bodied theropods function more similarly to each other than to small-bodied ancestors or relatives, proved false. Large size in theropods, which evolved independently in separate groups, does not seem to come with specific prescribed adaptations. Tyrannosaurus showed more differences in cranial traits (relating to function) compared to Dilong, its basal relative, than to Majungasaurus, and Allosaurus exhibited disparities with other large theropods. Differences in feeding function influence cranial adaptation more than large size or inherited traits do, which is further supported by the observation that the cranial anatomy of Majungasaurus is more similar to large sister taxa than to small-bodied ancestors, yet it likely fed in a completely independent fashion. The stress distributions from this and previous studies show relatedness by exhibiting a general pattern of stress dispersal through the skull during biting that large and small theropods share, which suggests an inherited theropod condition. However, slight discrepancies in distribution support the idea that there were differences in feeding habits among the three taxa.