DUFEAU, D.L.*; WITMER, L.M.; Ohio University; Ohio University: Tympanic pneumaticity in theropod dinosaurs: Recognizing patterns of organization and homology.

The tympanic cavity of theropod dinosaurs (including birds) gives rise to a variety of epithelial diverticula that pnuematize the bones of the braincase and suspensorium. Theropod pneumaticity is not very well understood with regard to its morphological variability and phylogenetic distribution. We present here a preliminary survey of the tympanic cavity of several members of Theropoda and comment upon the possible homologies and organization of the associated pneumatic recesses. Of particular interest are the similarities in the pattern of tympanic pneumaticity between theropod dinosaurs and extant archosaurs, particularly avian taxa. Focal theropod taxa include the abelisaurid Majungatholus, the allosauroids Acrocanthosaurus and Allosaurus, as well as nonavian coelurosaurs such as tyrannosaurids, oviraptorosaurs, ornithomimids, troodontids, and dromaeosaurids. Analysis of the alvarezsaurid Shuvuuia is of special importance because the phylogenetic status of alvarezsaurids is controversial, having been linked variably with ornithomimids, troodontids, and birds. The main methods include computed X-ray tomography (CT) and 3D visualization of the CT scan data, providing a detailed examination of the pneumatic recesses relative to the tympanic recess, otic labyrinth and brain cavity. Additionally, CT scans of extant taxa allow us insight into soft-tissue associations within and surrounding the pneumatic recesses. Similarities in organization between examined fossils and extant taxa allow us to make statements about the homologies of these pneumatic recesses in a phylogenetic context, and test hypotheses regarding their potential functional role. The rostral tympanic recess is the most widely distributed of the paratympanic sinuses whereas the dorsal tympanic recess may be restricted to coelurosaurian clades.