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William Abler observed in 2001 that Albertosaurus tooth serrations are so thin as to functionally be a crack in the tooth.
However, at the base of this crack is a round void called an ampulla which would have functioned to distribute force over a larger surface area, hindering the ability of the " crack " formed by the serration to propagate through the tooth.
An examination of other ancient predators, a phytosaur and Dimetrodon found similarly crack-like serrations, but no adaptations for preventing crack propagation.
Tyrannosaurid teeth were used as holdfasts for pulling meat off a body, rather than knife-like cutting functions.
Tooth wear patterns hint that complex head shaking behaviours may have been involved in tyrannosaur feeding.
When a tyrannosaur would have pulled back on a piece of meat, the force would tend to push the tip of tooth toward the front of the mouth and the anchored root would experience tension on the posterior side and compression from the front.
This would typically incline the tooth to crack formation on the posterior side of the tooth, but the ampullae at the base of the already crack-like serrations would tend to diffuse potential crack-forming forces.
This form resembles techniques used by guitar makers to " impart alternating regions of flexibility and rigidity to a stick of wood.
" The use of a drill to create an " ampulla " of sorts and prevent the propagation of cracks through an important material is also used to protect airplane surfaces.
Abler demonstrated that a plexiglass bar with kerfs and drilled holes was more than 25 % stronger than one with only regularly placed incisions.
There is some evidence of gregarious behaviour in other tyrannosaurids as well.
Fragmentary remains of smaller individuals were found alongside " Sue ," the Tyrannosaurus mounted in the Field Museum of Natural History in Chicago, and a bonebed in the Two Medicine Formation of Montana contains at least three specimens of Daspletosaurus, preserved alongside several hadrosaurs.
These findings may corroborate the evidence for social behaviour in Albertosaurus, although some or all of the above localities may represent temporary or unnatural aggregations.
Others have speculated that instead of social groups, at least some of these finds represent Komodo dragon-like mobbing of carcasses, where aggressive competition leads to some of the predators being killed and cannibalized.

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