Differences in molar wear gradient between juvenile macaques and langurs

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 dm₂ 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 Presbytis cristatus and Macaca fascicularis from the Museum of Comparative Zoology at Harvard University was examined using stereophotogrammetric techniques. X, Y, and Z coordinates were used to compute the areas of dentin exposure on the buccal cusps of M₁ and the buccal cusps of dm₂. The relationship between these variables was examined using Bartlett's three group method and least squares regression. Intergeneric comparisons of the resultant y‐intercepts indicate that the macaques have more dentin exposed on dm₂ when there is none exposed on M₁. Factors that might be responsible for this difference include differences in dentin/enamel structure, differences in molar eruption timing, and differences in behavior. At the present time, behavioral differences between the genera appear to be the most likely cause of the difference in wear gradient.