Meeting Abstract
Mastication is a complex process that involves the use of three dimensional jaw movements to direct precise occlusion between teeth to break down food. Several studies have noted that in mammalian species with a fused mandibular symphysis, late activity of the balancing-side zygomaticomandibularis produces transverse masticatory jaw movement. This is thought to produce lateral transverse bending or “wishboning” forces at the mandibular symphysis, which can be resisted by ossification of this joint. The current study investigates the hypothesis that mammals that have specialized on plant-based diets and have a fused mandibular symphysis will also have a larger, more complex zygomaticomandibularis than their closest animalivorous relatives. In this study, contrast-enhanced microCT scans of representative dietary specialists from orders Chiroptera (bats) and Carnivora (carnivorans) are used to compare size and orientation of the primary jaw adductors, with particular emphasis on the compartments of the masseter (including zygomaticomandibularis). We find that within the carnivoran sample, our hypothesis is supported, but within the chiropteran sample, this signal is somewhat more complicated: while the zygomaticomandibularis does form a larger proportion of the masseter in frugivorous species, the masseter itself is much larger in the animalivorous species. We discuss possible functional explanations for our observations.
