ROSS, CF; University of Chicago: How do primates chew harder?

Mammalian mastication is a rhythmic activity used to break down foods with a variety of material properties. How do mammals chew harder foods? Do they chew faster or slower? How do they modulate bite force? Corpus bone strain data were collected from seven species of primates (four anthropoids and three strepsirrhines) during mastication of a variety of foods. Chewing frequency, power stroke duration, strain magnitude and strain rate were calculated and the relationships between them were assessed. Chewing frequency did not vary consistently with food type, strain magnitude or strain rate. Strain magnitude varies as a function of strain rate. Chewing duty factor (percentage of cycle time taken up by power stroke) increases with chew frequency, but absolute power stroke duration does not vary with chew frequency. These data suggest that primates chew at species-specific frequencies governed largely by size, although there is variation. Increases in chewing frequency within a species are achieved by reducing the amount of time in opening and closing, while keeping power stroke duration relatively constant. Increases in corpus strain�i.e., bite force�are achieved by increasing the rate at which bite force is exerted. These data suggest that the masticatory central pattern generator maintains a relatively constant chewing frequency and that bite force must be modulated within this framework by increasing the rate at which force is exerted. The strepsirrhines in this study were provided by the Duke University Primate Center.