Experiments were performed to examine the relationship between the particle size of chitin and its digestibility in the small insectivorous prosimian Galago senegalensis. In the first set of experiments, four animals were fed a 25% chitin diet with the chitin particles less than or equal to 60mesh (0.250 mm maximum diameter). On average, the animals digested 22.5 -+ 2.2 percent of the ingested chitin. In the second set of experiments, the four animals were fed a 25% chitin diet with the chitin particles ground to S 4 0 -and 245-mesh (between 0.425 and 0.325 mm). On average, the animals digested 2.75 -t 1.38 percent of the ingested chitin. There was no significant variation between the performance of any of the animals on either the 60-or 40-45-mesh trials. In all instances, however, each animal digested significantly more of the 60-mesh chitin and the 40-45-mesh chitin.These experiments demonstrate the importance of masticatory efficiency among small mammals for improving the digestibility of foods such as insects which contain high proportions of chitin. They also suggest why insectivorous and folivorous primates have certain convergent dental specializations for finely grinding their foods. Both leaves and insects contain relatively indigestible structural carbohydrates. These substances are much more completely digested when the surface area to volume ratio of the swallowed material is increased. The masticatory efficiency of frugivorous primates is much lower since the constituents of these foods are relatively completely digested irrespective of the fineness of grinding.Recently, it has been shown that insectivorous primates masticate their foods more efficiently than do comparable sized frugivorous species (Sheine and Kay, '77). It was suggested that this provided more surface area for the action of digestive enzymes and enhanced the assimilation of chitin, a major component of insect exoskeletons. To confirm this hypothesis there must be evidence that there are chitinolytic enzymes in these species and that the digestibility of chitin increases as its surface-area to volume ratio is increased. The first of these requirements has been met. Beerton-Joly e t al. ('74) showed that there is a strong chitinolytic activity in the AM. J. PHYS, ANTHROP. (1979) 50: 301-308

The chewed food particle size and shearing capacity of the lower molars of two primate species, the fat-tailed dwarf lemur, Cheirogaleus medius and the bushbaby Galago senegalensis, and an insectivoran, the tree shrew, Tupaia glk, were compared. Differences in the shearing design of the lower molars correlate strongly with the chewed food particle size in these species: the greater the shearing capacity, the smaller the chewed food particles.These three species are of comparable size but differ greatly in diet in the wild.C. medius primarily eats fruit and nectar, while G. senegalensis and T. glis are largely insect-eaters. The lower molars of G. senegalensisand T! glisshow a much greater shearing capacity than do those of C. medius. The average length of chewed food particles of C. medius is significantly larger than that of G. senegalensis, while that of T. glis is intermediate between the two primates but iscloser to that of G. senegalensis.Our findings that insect-eating species grind their food more finely than do fruit-and resin-eating species can be correlated with digestibility of foods: finely chewing foods such as fruits which are low in relatively undigestible cell wall components would not greatly improve their digestibility, so a highly efficient food processing apparatus would be less important to the animal's survival. Insect-eaters much more finely chew their foods, implying that there is some constituent of insect bodies difficult to digest, and that grinding increases its digestibility. We suggest that this constituent is chitin.Considerable attention has recently 'been given to differences in the functional organization of the primate dentition and its relevance to feeding behavior (e.g., Kay, '73, '75, in press; Kay and Hylander, in press; Hylander, '75; Zingeser, '73; Rosenberger and Kinzey, '76). However only Walker and Murray ('72, '75) actually attempted to establish some link between molar structure and size of chewed food particles in primate species with different diets. In this paper we attempt to refine and extend their analyses on the assumption that the most meaningful way to characterize the biological role of the denti-AM. J. PHYS. ANTHROP., 47: 15-20. tion, and particularly the triturition mechanism, is to determine the particle size of chewed foods. Of particular concern here is identifying dental parameters which can be correlated with particle size or shape so that one can assign a "triturition efficiency" rating to a particular molar shape or construction.(Kay ('73, '75) and Kay and Hylander (in press) showed that there are major differences between the molar shapes of insectivorous and frugivorous mammals and inferred that these differences are related to the efficiency of digestion. We present evidence to support this notion. 15

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.