Behavioral implications of an embedded tyrannosaurid tooth and associated tooth marks on an articulated skull of <i>Edmontosaurus</i> from the Hell Creek Formation, Montana

Because teeth can be taxonomically distinct, particularly for non-mammalian carnivores such as non-avian dinosaurs, teeth that have broken off in the bone of another animal during feeding, predation or antagonism can provide direct information on carnivore behaviour. Here, we report on a semi-complete, articulated adult <i>Edmontosaurus</i> skull (MOR 1627) from the Hell Creek Formation with an embedded theropod tooth in the nasal. To ascertain taxonomic identity of the preserved tooth tip, we compare standardized crown and denticle measurements as well as denticle descriptions of the embedded tooth to known non-avian theropods recovered from the Hell Creek Formation. We also use computed tomography (CT) scans to investigate the full extent and orientation of the embedded tooth. The apicobasal, labiolingual and mesiodistal dimensions of the tip as well as measured denticle densities and observed denticle characteristics indicate the embedded tooth is from a medium to large bodied tyrannosaurid. The curvature and ovoid cross-sectional shape of the tooth further suggests that the tooth is a maxillary tooth from a middle or posterior tooth position. The lack of reactive bone in the region surrounding the tooth suggests the animal died around the time the tooth became embedded in the nasal. Combined, this information suggests the tooth broke off when a tyrannosaurid bit the snout of the <i>Edmontosaurus</i> from the front at or near the time of death of the animal. Comparing observations of hunting and feeding behaviors of modern carnivores specializing in large-bodied prey, the scenario captured by MOR 1627 is most consistent with a bite inflicted during an attempt to control the struggling <i>Edmontosaurus</i> or deliver a killing blow followed by carcass consumption.