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A reconstruction of Albertosaurus at the Royal Tyrrell Museum in Canada. Image from Wikipedia.

When I was in elementary school, I was told that mammals and reptiles could easily be told apart by their teeth. Mammals had a full, enamel-covered toolkit in their mouths—incisors, canines, premolars, and molars suited to different tasks—while reptiles had only one kind of tooth. The dental differences were presented as one of the ways in which mammals were superior to reptiles, but like a number of other things I was taught in grade school, this wasn’t quite right.

Not all mammals have differentiated sets of teeth. Dolphins, for example, have jaws full of nearly identical, conical teeth. Among reptiles, on the other hand, multiple species have been found with a variety of tooth shapes in their jaws. Pakasuchus, an extinct cousin of modern crocodiles found in the 105-million-year-old rock of Tanzania, had three different types of teeth in its jaws, and even the mighty Tyrannosaurus and Albertosaurus possessed differentiated teeth. What this meant for how the tyrant dinosaurs ate was addressed in a Canadian Journal of Earth Sciences paper by Miriam Reichel last year.

Although the teeth of Albertosaurus and Tyrannosaurus may seem to be all the same, these dinosaurs actually had three different tooth classes. The teeth at the front of the jaw are small and closely packed; those in the middle of the jaw are exceptionally long and curved and those at the back of the jaw are smaller and only slightly recurved. (The differences between the teeth can perhaps best be seen in the skull of the juvenile Tyrannosaurus “Jane“.) What Reichel wanted to know was how these various teeth functioned, and so she created computerized, 3-D models of Albertosaurus and Tyrannosaurus teeth to test how they would have held up to the stresses and strains created by biting.

As might be expected for large predators, the teeth of both tyrant dinosaurs were suited to different tasks. The small and stout front teeth were likely used for pulling large pieces of meat from carcasses, the much larger teeth in the middle of the jaw were adapted to coping with the stresses of struggling prey, and the teeth at the rear of the jaw were positioned to deliver heavy, crushing forces in an arrangement Reichel likened to a clamp.

There was one notable way in which Albertosaurus and Tyrannosaurus differed, though. Albertosaurus had a matching set of upper and lower teeth—their functions were consistent from front-to-back along the jaw—but in Tyrannosaurus the patterns of the upper and lower teeth differed. Specifically, the teeth at the front of the lower jaw in Tyrannosaurus were not adapted to pulling off chunks of flesh, but were instead suited to withstanding forces associated with capturing prey. Perhaps, Reichel suggests, this is because Tyrannosaurus had a slight overbite in which the teeth at the front of the lower jaw were closest to the large, prey-capturing teeth near the middle of the upper jaw, meaning that they changed in function to compensate for the alteration in jaw position.

Lacking live tyrannosaurs to study, paleontologists will surely continue to find ways to model the bites of these famous dinosaurs. It is not an easy task. Teeth, bones, muscles, ligaments, and other aspects of the living animal must all be accounted for and combined to create a picture of the entire dinosaur. We do not have a fully comprehensive understanding of tyrannosaur bites just yet, but the more we discover about their jaws, they more terrifying the tyrants become.

References:

Reichel, M. (2010). The heterodonty of Albertosaurus sarcophagus and Tyrannosaurus rex: biomechanical implications inferred through 3-D models Canadian Journal of Earth Sciences, 47 (9), 1253-1261 DOI: 10.1139/E10-063

SMITH, J. (2005). HETERODONTY IN TYRANNOSAURUS REX: IMPLICATIONS FOR THE TAXONOMIC AND SYSTEMATIC UTILITY OF THEROPOD DENTITIONS Journal of Vertebrate Paleontology, 25 (4), 865-887 DOI: 10.1671/0272-4634(2005)025[0865:HITRIF]2.0.CO;2