Dental macrowear analysis in Great Apes

Abstract

Chimpanzees ('Pan troglodytes'), orangutans ('Pongo pygmaeus') and gorillas ('Gorilla gorilla') rely on different food. The dietary diversity is reflected in their dental morphology, with differences in size and shape of teeth. However, while morphology can suggest what a tooth is capable of processing, tooth wear can tell us how a tooth is used. In this study we apply the Occlusal Fingerprint Analysis (OFA) method using 3D digital models of teeth, to quantitatively compare wear facet patterns in great apes. Unlike microwear, dental macrowear is a cumulative process that occurs throughout the individual's lifetime and thus reflect long-term diet. The results show significant differences between the three groups analyzed: in Pongo the occlusal surface is characterized by large and flat phase II facets, while in Gorilla there is a minimal development of buccal phase I facets and a steep wear facets inclination. Pan is somehow in between, with large lingual phase I facets and moderately steep wear planes. This macrowear pattern variation can be explained with the use of different food sources. In fact, while orangutans rely on hard food objects more than any other apes, showing thus a larger proportion of crushing wear, gorillas exhibit an increase in shearing wear, which is interpreted as an adaptation to a folivorous diet. Finally, the "intermediate" tooth macrowear found in chimpanzees, mirrors their highly variable diet. The OFA method demonstrates to be a powerful tool for better understanding the relationship between food items, mastication and tooth wear processes in living primates.