Worn T. rex tooth (annotated)

Not the prettiest tooth, but I very much enjoy fossils like this that demonstrate behavior and tell a story.

T. rex and other Tyrannosaurs were unusual among theropods in that they consumed the entire carcass of an animal - bones and all. Most theropod dinosaurs have ziphodont teeth, thin and knife-like, good for cutting muscle from bone. The thick and robust teeth of adult Tyrannosaurs, coupled with their incredible bite force, allowed them to shatter and pulverize bone - even those of the large, formidable herbivores they hunted. Despite the robustness of their teeth, Tyrannosaurs often broke them in the process of biting. It may have been a while before the broken tooth was replaced by a new one, so in the meantime, the broken tooth would continue to accumulate wear. This is one such tooth, a large portion of the tooth was broken off when the animal bit into another dinosaur, and it was still used afterwards for some time before it was replaced. Based on the placement and extension of the carinae to the base of the tooth, and the size, this was an anterior tooth (at the front of the mouth, probably the first dentary tooth) of an adult individual.

See Schubert & Ungar (2005) for a discussion on Tyrannosaur tooth wear features (open-access).