RIDGELY, RC*; WITMER, LM; Ohio University; Ohio University: Braincase morphology in tyrannosaurs using computed tomography and 3D visualization, with special reference to the cerebral endocast and ear region

The morphology of the ear region, cerebral endocast, and pneumatic sinuses in the braincases of tyrannosaurid dinosaurs was investigated using CT and 3D visualization. Several adult specimens of Tyrannosaurus rex (AMNH 5029, 5117; FMNH 2081) and a subadult Gorgosaurus braincase were scanned along with the skull of a contentious juvenile specimen which has been regarded as representing either a juvenile T. rex or a separate taxon, Nanotyrannus lancensis. The inner ear of tyrannosaurids is generally comparable to that of other coelurosaurian theropods, with long, thin semicircular canals, suggesting a well developed vestibulo-ocular reflex. Orientation of the horizontal canal indicates that �alert posture� of the head was down-turned in all taxa, most strongly in Nanotyrannus. The lagena, while elongate in all specimens, is somewhat shorter in Gorgosaurus and longer in T. rex and Nanotyrannus, potentially suggesting a difference in auditory abilities within the group. The cerebral endocast is similar in some aspects to other large bodied theropods, yet still reflects its coelurosaurian ancestry. The braincase in all studied taxa is highly pneumatized by diverticula arising from tympanic, pharyngeal, and subcondylar recesses. The rostral tympanic recess occupies most of the rostral portion of the basicranium. The caudal tympanic recess excavates both the paroccipital processes and supraoccipital. Medial and lateral subcondylar recesses pneumatize the crista tuberalis and occipital condyle, and may derive from cervical air sacs. Pharyngeal recesses include the subsellar, which invades the cultriform process, and a median pharyngeal recess which extensively pneumatizes the basicranium. Both Nanotyrannus and Gorgosaurus share derived pneumatic features not found in Tyrannosaurus.