FREQUENCY OF CRANIOFACIAL PATHOLOGIES IN TYRANNOSAURIDAE

Craniofacial pathologies in Tyrannosauridae are commonly reported in literature as a relative metric on intraspecific tyrannosaurid behavior. While genera within Tyrannosauridae vary considerably in paleogeographic distribution and body size, no direct comparison of craniofacial pathology frequencies between taxa or tyrannosaurid subfamilies (Albertosaurinae + Tyrannosaurinae) has been conducted. In order to conduct such a comparison, eight genera of tyrannosaurids were observed for the presence of craniofacial pathologies in the forms of trauma from bites and secondary infection resulting from injury. A total of 66 tyrannosaurid specimens were examined, including 32 albertosaurines (Albertosaurus and Gorgosaurus) and 34 tyrannosaurines (Daspletosaurus, Teratophoneus, Bistahierversor, Lythronax, Tarbosaurus, and Tyrannosaurus). A chi-square test was performed using data from both subfamilies to determine whether the differences in the frequencies of pathologic and non-pathologic tyrannosaurids were statistically significant. Results indicate that tyrannosaurines are considerably more likely to possess craniofacial pathologies; of the 34 specimens examined, 11 specimens possessed injuries (32%) while only three of the 32 albertosaurines showed injuries (9%). These differences were found to be statistically significant (p < 0.05). While prior research has suggested trends of increased body size in Late Cretaceous tyrannosaurids, the high frequency of craniofacial pathologies in Tyrannosaurus, Daspletosaurus, and Tarbosaurus may suggest changes in tyrannosaurine behavior in the Late Cretaceous. As body size increased, it is likely that intraspecific aggression also increased, resulting in craniofacial injuries and subsequent infections. Increased sample sizes from each genera within Albertosaurinae and Tyrannosaurinae may yield further insight in to Tyrannosaurid behavior and paleoecology in the Late Cretaceous.