The relationship between form and function of the carnivore mandible.

Abstract

Dietary morphology diversified extensively in Carnivoraformes (living Carnivora and their stem relatives) during the Cenozoic (the last 66 million years) as they evolved to capture, handle, and process new animal and plant diets. We used 3D geometric morphometrics, mechanical advantage, and finite element analysis to test the evolutionary relationship between mandibular form and biomechanical function as subclades independently made the transition from mesocarnivorous diets (50%-70% animal matter) to hypercarnivorous (>70% animal matter) and osteophagous ones (substantial bone processing). We found that mandible shape is correlated with these dietary categories, with mechanical advantage estimates, and with stress and strain caused by the interaction between canine loading and the position of the temporalis relative to the carnassial. The separation of dietary categories is likely related to differences in mandible shape regarding condyle shape, muscle attachment shape, carnassial length, and the length and curvature of the horizontal ramus. This is in turn related to mechanical advantage estimates as the most strongly associated are related to the lengthening of the temporalis lever arm and the shortening of the mandible and the bite point lever arm. The stress and strain differences are likely related to the variation in the distal (or rostral) part of the mandible associated with prey of different sizes (mesocarnivores usually take prey smaller than their own body size, whereas hypercarnivores take prey equal to or larger than themselves). Mesocarnivorous taxa, on average, have higher stress and strain on the mandible than the other diet groups.