WHETHER tyrannosaurs occupied predatory or scavenging niches has been debated for nearly a century(1-5). Palaeontologists have turned to the study of dental morphology to address this question, but the results have been highly disparate. Some contend that the tyrannosaur dentition was very strong and well suited for engaging and killing herbivorous dinosaurs(6,7). Others posit that tyrannosaurs ate carrion, because their teeth and/or jaws would fail during struggles with prey(2,3). The discovery of skeletal remains with bite marks from Tyrannosaurus rex(8) makes it possible to estimate, through indentation simulations on bovine ilia, the bite forces produced by T. rex during feeding. The estimates (6,410 to 13,400 N) rival the largest bite forces determined for any taxon to date and suggest that T. rex had very strong, impact-resistant teeth, Although these data do not prove that T, rex was predominantly predacious, they indicate that its dentition could probably withstand the stresses associated with prey capture.