Eric Snively and Andrew Cox

Pachycephalosaurian dinosaurs have dorsally thickened crania and uniquely shaped frontoparietal domes in some genera, suggested as evidence for head- or flank-butting behavior. Trabeculae thought to have resisted impact compression are present as only one histological zone of some pachycephalosaur domes, and are surrounded superficially or replaced by thick compacta in adults. The capabilities of pachycephalosaurian crania for head-butting are testable by finite element analysis (FEA). FEA of 2- and 3-D dorsal skull shapes of adult Homalocephale and Pachycephalosaurus reveal that the domes could withstand considerable impact force at certain closing speeds, and that stress and strain would dissipate efficiently throughout the dorsal portion of the skull before reaching the brain. Greater vaulting of the dome permitted higher impact forces. An analysis restricted to the frontoparietal dome of a subadult pachycephalosaurine, with material properties corresponding to histological zones, shows higher compressive strain (not less) in the trabecular region. The trabecular zone, if present, would not have rigidly resisted compression but rather have allowed slight elastic compression and rebound. Modeled keratinous coverings of varying depth indicate reductions in force and energy transmission to underlying bone. FEA therefore leaves open the possibility of head-butting in both flat- and dome-headed pachycephalosaurs, especially at low collision speeds.

Eric Snively. Department of Biological Sciences. CW 405, Biological Sciences Centre. University of Alberta. Edmonton, Alberta, T6G 2E9, Canada
Andrew Cox. 561 Woodland Drive. Radnor, PA, 19087, USA

KEY WORDS: Pachycephalosauria, Dinosauria, behavior, finite element analysis, biomechanics, sexual selection

PE Article Number: 11.1.3A
Copyright: Palaeontological Association March 2008
Submission: 18 September 2007. Acceptance: 18 January 2008