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Bite me: Biomechanical models of theropod mandibles and implications for feeding behavior
A biomechanical approach is used to study feeding behavior in non-avian theropods. Mandibles can be modeled as beams undergoing bending loads during food ingestion. The bite force applied at any given point along the mandible should be proportional to the external dimensions of the mandibular ramus at that location. Thus, patterns of variation in these dimensions reflect the adaptation of the jaw to specific loads, which are related to the method of killing prey. These beam models were compared to those of the extant varanids Varanus komodoensis (Komodo dragon, an ambush predator with a slashing bite) and Varanus niloticus (Nile monitor, molluscivorous) to gain insight into the feeding behavior of theropods. On the basis of our results, we identified five distinct theropod feeding categories: (1) the allosauroid "Antrodemus valens" and the abelisaurids Majungatholus atopus and Carnotaurus sastrei share the mandibular properties of the Komodo dragon, and these shared properties, combined with the similarity between the craniodental morphology of "Antrodemus" and Majungatholus and that of the varanid, suggest that they were probably large-prey hunters delivering slashing bites; (2) dromaeosaurids have mandibular properties reminiscent of those of V. komodoensis for slashing bites, but differences can be identified between Dromaeosaurus and velociraptorines, the former having a stronger bite than the latter, suggesting that it possibly relied more on its jaws to capture and kill prey; (3) Suchomimus tenerensis and Dilophosaurus wetherilli exhibit mandibular adaptations related to the capture of prey smaller than themselves, the former probably practicing a bite-and-hold strategy and the latter finishing its prey with slashing bites; (4) Ceratosaurus nasicornis, Allosaurus fragilis, Acrocanthosaurus atokensis, and Giganotosaurus carolinii demonstrate adaptations of the anterior extremity of the mandible for capturing prey and delivering powerful bites to bring down prey or deliver the final blow; and (5) tyrannosaurids, unlike other theropods, exhibit mandibular adaptations to resist high torsional stresses at the anterior of the mandible induced during prey capture, bone crushing, or both. The mandibular models were also used to infer relative bite force in theropods. Velociraptorines appear to have had a maximum bite force similar to that of V. komodoensis, whereas that of Dromaeosaurus was three times as great. Suchomimus, Allosaurus, "Antrodemus," and Ceratosaurus were capable of exerting maximum bite forces as great as A. mississippiensis, and those of abelisaurids and Albertosaurus were twice as powerful. Among the largest theropods, Acrocanthosaurus and Giganotosaurus were surpassed by Daspletosaurus and Tyrannosaurus. The high estimates obtained for tyrannosaurids are consistent with previously published values that suggest bone-cracking abilities. Growth series for Allosaurus fragilis, Albertosaurus sarcophagus, Gorgosaurus libratus, and Tyrannosaurus rex were also studied in order to determine whether mandibular properties changed during ontogeny. Significant changes were observed in Allosaurus, especially in bending rigidity, indicating that juveniles did not feed the same way as adults; juveniles probably delivered simple slashing bites. Unfortunately, the question of parental care in Allosaurus cannot be resolved in light of our results. The mandibular properties of tyrannosaurids were not found to vary significantly during ontogeny, other than in terms of bite force. This finding strongly suggests that juveniles were apt predators, capable of subduing their own prey rather than relying on carrion or parental care to survive.