A model for comparison of masticatory effectiveness in primates.

A model is presented to express how effectively animals increase the exposed surface area of their food by chewing. It includes a coefficient of masticatory effectiveness (E) the value of which increases with effectiveness of exposing new food surface area with each chew. Humans and other species of primates differ significantly in their values of E; among the nonhuman primates studied, Lemur catta has a higher coefficient than Lemur fulvus, and both have higher coefficients than either Varecia variegatus or Galago crassicaudatus argentatus. The differences among the coefficients of these prosimians are correlated with variations in specific features of the molar morphology. Of six lower molar shearing crests considered, the relative length of the postmetacristid correlates most highly with the coefficient of masticatory effectiveness for the prosimian species. Also, among comparable-sized prosimians, E correlates significantly with the absolute postmetacristid length. Both these findings indicate that the relative size of molar shearing crests is related significantly to how effectively an animal chews its food. These are also implications for an adaptation to a high-fiber diet.