The mechanics of food reduction in Tarsius bancanus. Hard-object feeder, soft-object feeder or both?

The high-cusped, almost tritubercular teeth of Bornean tarsiers are used to reduce a wide variety of animal food. Prey is characteristically consumed entire, no parts being discarded. This paper attempts to identify the dental characteristics which permit tarsiers to reduce food substrates with widely varying mechanical properties and to assess whether reduction of some substrates incurs greater costs for tarsiers. Finite elements stress analysis (FESA) modelling is used to compare the effectiveness of tarsier and human teeth in reducing three types of food substrate habitually reduced by both species. Bone is taken as the exemplar of strong, stiff substrates, skin as the exemplar of substrates low in both stiffness and strength, and tendon as the exemplar of low-stiffness but strong substrates. The parameters used to measure performance are the work that must be done to bring tensile stresses to the point where tensile failure will be initiated and the bite-force required to do so. Human molars perform best in reducing bone, and tarsier molars in reducing skin. Neither perform as well in reducing tendon. Blunt, bunodont human molars perform slightly better than the high-cusped molars of tarsiers in reducing bone, but tarsier molars perform much better than human molars in inducing failure in skin and are also considerably better in reducing tendon. While the reduction effectiveness of human molars is greatly affected by substrate properties, the high cusps of tarsier teeth enable them to reduce foodstuffs of widely differing properties reasonably well. Scaling factors undoubtedly influence selection for cusp height, since high cusps are a prerequisite of effective crack propagation in food substrates by small animals. Microwear features do not show a consistent pattern where striations are associated with surface-parallel loads but pitting with surface-normal loads (at least as modelled by FESA). However, FESA modelling of the magnitude of applied forces and relative food/tooth displacement during occlusion suggest that the type of wear found in different regions is governed by the combined influences of relative tooth/food displacement and food/tooth reaction force. Pitting is associated with low levels of food/tooth displacement but high levels of reaction force, striation with high levels of displacement but low levels of force, and stripping or gouging of enamel with high values of both displacement and reaction force.