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 us ed to reduce a wide variety of animal food. Prey is characteristically consumed entire, no parts being discarded. This paper attempts to ide ntify the dental characteristics which per mit tarsiers to reduce food substrates with widely varying mechanical properties and to assess wh ether reduction of some substrates incurs greater costs for tarsiers. Finite elements stress analysis (FESA) modelling is used to compare th e effectiveness of tarsier and human teeth in reducing three types of food substrate habitually reduced by both species. Bone is taken as th e exemplar of strong, stiff substrates, skin as the exemplar of substr ates low in both stiffness and strength, and tendon as the exemplar of law-stiffness but strong substrates. The parameters used to measure p erformance 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 tar sier molars in reducing skin. Neither perform as well in reducing tend on. Blunt, bunodont human molars perform slightly better than the high -cusped molars of tarsiers in reducing bones but tarsier molars perfor m much better than human molars in inducing failure in skin and are al so considerably better in reducing tendon. While the reduction effecti veness of human molars is greatly affected by substrate properties, th e high cusps of tarsier teeth enable them to reduce foodstuffs of wide ly differing properties reasonably well. Scaling factors undoubtedly i nfluence selection for cusp height, since high cusps are a prerequisit e of effective crack propagation in food substrates by small animals. Microwear features do not show a consistent pattern where striations a re associated with surface-parallel loads but pitting with surface-nor mal loads (at least as modelled by FESA). However, FESA modelling of t he magnitude of applied forces and relative food/tooth displacement du ring occlusion suggest that the type of wear found in different region s is governed by the combined influences of relative tooth/food displa cement and food/tooth reaction force. Pitting is associated with low l evels of food/tooth displacement but high levels of reaction force, st riation with high levels of displacement but low levels of force, and stripping or gouging of enamel with high values of both displacement a nd reaction force.