ROSS, C.F.; BADEN, A.L.; GEORGI, J.; SIPLA, J.; WOLFF, M.; University of Chicago; Stony Brook University; Stony Brook University; Stony Brook University; Stony Brook University: Jaw kinematics in two species of primates

Jaw kinematics were studied in two vervet monkeys and three eulemurs to evaluate the influence of species, food type and cycle type on the relative durations of the phases of the chewing cycle. Videofluoroscopic data were gathered in lateral view and bone strain data were gathered from the mandibular corpus while the animals chewed a range of food types. To control for differences in chewing frequency, phase durations were expressed as a percentage of overall cycle time. The results reveal similar effects of cycle type in both species: swallow cycles exhibit shorter fast and slow close phases, and longer slow open phases than do puncture crushing and mastication cycles. Intercuspal phase duration and fast open are unaffected by cycle type. There is no consistent cycle effect on power stroke duration (as measured by corpus bone strain). There is no species effect on fast close, slow close, or fast open duration, but there is a significant species effect on intercuspal phase and slow open duration, with eulemur having longer intercuspal and shorter slow open phases and vervets the reverse. There is no consistent species effect on power stroke duration. Slow close duration is affected by food type, being shorter during grape chews, and overall closing duration is longer during hard prune chews. These results suggest that eulemurs and vervets share common jaw kinematic patterns during swallowing and mastication, despite morphological differences in the masticatory apparatus. Both species shorten relative duration of the closing phases to make time for the swallow that occurs during slow open. Also, in both species, intercuspal phase duration is probably determined by occlusal morphology, with eulemurs having relatively narrow lower teeth, increasing the time it takes to traverse the uppers.