Tyrannosaurid theropods display several unusual adaptations of the skulls and teeth. Their nasals are fused and vaulted, suggesting that these elements braced the cranium against high feeding forces. Exceptionally high strengths of maxillary teeth in Tyrannosaurus rex indicate that it could exert relatively greater feeding forces than other tyrannosaurids. Areas and second moments of area of the nasals, calculated from CT cross-sections, show higher nasal strengths for large tyrannosaurids than for Allosaurus fragilis. Cross-sectional geometry of theropod crania reveals high second moments of area in tyrannosaurids, with resulting high strengths in bending and torsion, when compared with the crania of similarly sized theropods. In tyrannosaurids trends of strength increase are positively allomeric and have similar allometric exponents, indicating correlated progression towards unusually high strengths of the feeding apparatus. Fused, arched nasals and broad crania of tyrannosaurids are consistent with deep bites that impacted bone and powerful lateral movements of the head for dismembering prey.

Key words: : Theropoda, Carnosauria, Tyrannosauridae, biomechanics, feeding mechanics, computer modeling, computed tomography.

Eric Snively esnively@ucalgary.ca, Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada; Donald M. Henderson don.henderson@gov.ab.ca, Royal Tyrrell Museum of Palaeontology, Box 7500, Drumheller, Alberta T0J 0Y0, Canada; Doug S. Phillips phillips@ucalgary.ca, Department of Information Technologies, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada.