USING COMPUTED TOMOGRAPHY TO ANALYZE THE BRAINCASE OF A NEW ALLOSAURUS SPECIMEN FROM THE JURASSIC MORRISON FORMATION OF WYOMING

This Allosaurus fragilis specimen was found in 2004 near Shell, Wyoming, in the Jurassic Morrison Formation, and is comprised of 65 cranial and postcranial elements (seven of these are attributed to the braincase). The recent use of computed tomography (CT) scanning to study the soft tissue spaces of fossil specimens has created a unique avenue of study in paleo-anatomy. Capitalizing on this technology, we collected CT scans of the braincase elements of this specimen and digitally reconstructed its braincase for further anatomical study. Here, we provide a preliminary description of the endocranial space of this new specimen of Allosaurus established from this digital reconstruction and articulation of braincase elements – the majority of which are well preserved, except for the middle portion of the basisphenoid. While A. fragilis is one of the most well-known theropod species, detailed studies of individual Allosaurus specimens remain rare as most specimens have been unearthed from disarticulated, multi-individual bonebeds. CT results provide the resolution necessary to distinguish foramina on all of the scanned braincase elements (basisphenoid, basioccipital, otoccipital, prootic), as well as significant intracranial space in the basioccipital/basisphenoid region of the braincase, indicative of this region housing brain matter and other soft-tissues. We have identified the foramina for cranial nerves VII and IX-XII in the lateral braincase elements in posterior view, and the foramina for cranial nerves V and VII in right lateral view. Our cranial nerve reconstructions are similar in placement to those in digitally-reconstructed endocasts of Acrocanthosaurus and Giganotosaurus, indicating conserved endocranial morphology amongst members of Allosauroidea. Overall, analysis of the braincase material of our new specimen of Allosaurus provides the opportunity to directly connect its endocast morphology to its skeletal morphology, which has not previously been discerned for this phylogenetically important taxon. Continued study of non-avian theropod cranial anatomy through digital reconstruction methods holds the potential to not only yield phylogenetic insights, but also clues into the paleobiology of extinct theropod dinosaurs.