Differences in molar wear gradient between adult macaques and langurs

Abstract

Interspecific differences in the amount and form of molar wear in nonhuman primates are only beginning to be documented and understood. The purpose of this study was to look at the wear gradient between M1 and M2 in a sample of macaques and langurs to determine if differences in wear gradient could be related to differences in diet. A skeletal collection of wild shot Macaca fascicularis, Presbytis cristata, and Presbytis rubicunda from the Museum of Comparative Zoology at Harvard University was examined using photogrammetric techniques. X, Y, and Z coordinates were used to compute areas of dentin exposure on the buccal occlusal surfaces of M1 and M2. The relationship between these variables was examined using Bartlett’s three-group method and least-squares regression. Interspecific comparisons of the resultant y intercepts indicate that (I) M. fascicularis (as compared with P. cristata or P.) has more dentin exposed on M1 when there is none exposed on M2, and (2) P. cristata (as compared with P. rubicunda) has more dentin exposed on M1 when there is none exposed on M2. Factors that might be responsible for these differences are (a) differences in dentin/enamel structure, (b) differences in molar eruption timing, and (c) differences in behavior. An unusual intercusp sequence of dentin exposure in the langurs makes precise interpretations difficult. However, at the present time, behavioral differences among the species deserve further consideration as a cause of the observed differences in molar wear gradient.