Hyenas are amazing animals. It takes a single hyena less than two minutes to consume an entire Thompson’s gazelle. A pack of 21 hyenas was able to polish off a 220 kg zebra and a 150 kg foal in about 30 minutes. An extinct species of borophagine dog (Borophagus) was probably able to accomplish similar feats as well. Borophagines, being descended from canids, retained post-carnassial molars. This pushed the carnassials forward in the jaw and they are located in the region of maximum bite force production and is what allowed them to crack bones efficiently using their carnassials (the carnassials are composed of a blade-like upper fourth premolar and a somewhat blade-like lower first molar). In hyenas, however, post-carnassial molars underwent a reduction and hyenas crack bones between their upper and lower third premolars not with the carnassials, which are behind the region of maximum bite.
I bring this up because there is an interesting article in PNAS that looks at the feeding biomechanics of Australopithecus africanus. The article looked at facial morphology that previous research indicated might be a result of premolar loading. The research used finite element analysis in combination with experimental data and comparative morphology to model the strain during simulated bites in the long tailed (or crab eating) macaque and A. africanus (for A. africanus they used a composite of Sts 5 and Sts 52). Bites with molars alone, molars and premolars, and premolars alone were simulated. Overall, results indicated a higher amount of strain in the facial skeleton of A. africanus particularly on the anterior pillars and at the root of the zygoma. Additionally, while both experienced high amounts of strain during premolar biting, in A. africanus this waas dominated by compression while in macaques the strain was a mixture of compression and tension. Significantly, the browridges experienced little strain.
This leads the researchers to suggest that these features of A. africanus were an evolutionary response to eating based on premolar loading – specifically on eating seeds and nuts:
The processing of some large, hard food items may have entailed combining premolar biting with hand-assisted manipulation, as has been observed in extant primates in the wild … and during our in vivo experiments in the laboratory. Premolar-focused biting might also be associated with the ingestion of large, displacement-limited foods. One might hypothesize that the facial features examined here evolved in response to the frequent consumption of such items, but this hypothesis requires that skeletal adaptations to consuming displacement limited foods evolved in australopiths without attendant dental adaptations. Thus, biomechanical considerations do not exclude the possibility that australopiths had a high volume diet or that they consumed smaller and/or displacement-limited items … Indeed, some aspects of australopith craniodental form may be adaptations to such diets … However, these diets do not provide the best explanation for the evolution of craniofacial features functionally related to premolar loading. Thus, large, stress-limited objects are likely to have been a selectively important component of a diet that may have otherwise been quite varied.
Note: The information on carnivores came from the following paper:
Van Valkenburgh 2007 Deja Vu: the evolution of feeding morphologies in the Carnivora. Integrative and Comparitive Biology 47(1):147-163