Adaptive wear-based changes in dental topography associated with atelid (Mammalia: Primates) diets

Primates are generally characterized by low-crowned, brachydont molars relative to many other groups of mammals. This conservative architecture may create special challenges for maintaining dental functionality in the case of a diet requiring proficient shearing ability (e.g. folivory). One recent hypothesis, the 'dental sculpting hypothesis', suggests that some folivorous primates have dentitions that functionally harness macrowear in maintaining occlusal sharpness. We examined the relationships between four dental topography metrics [Dirichlet normal energy (DNE), orientation patch count rotated (OPCR), relief index (RFI) and occlusal relief (OR)] against macrowear [as measured by the dentine exposure ratio (DER)] in lower first molars of Ateles and Alouatta, which are two closely related platyrrhines with different diets (Alouatta is a folivore and Ateles a frugivore). We find support for the dental sculpting hypothesis, in that DNE increases with macrowear in the folivorous Alouatta but not in the frugivorous Ateles. Multiple contradictions between OPCR and the other variables suggest that this metric is a poor reflection of the molar form-function relationship in these primates. Distributions of relief measures (RFI and OR) confound expectations and prior observations, in that Ateles shows higher values than Alouatta, because these measures are thought to be correlated with dental shearing ability. We discuss the role that the relatively thicker enamel caps of Ateles might play in the distributions of these metrics.