Enamel Prism Angle Variation and Hard-Object Feeding in Cercopithecoids With Known Diets

To examine relationships between enamel prism angles relative to wear surfaces and dietary hardness in three cercopithecoid genera. We hypothesized that the hard-object feeding (durophagous) Cercocebus atys and Lophocebus albigena would have higher prism angles, making their enamel in this region stiffer and stronger in this region, than the soft-object feeding Cercopithecus. We further investigated whether the habitually durophagous Cercocebus atys and the fallback hard-object feeding Lophocebus albigena had similarly high prism angles.

Molars were sectioned using standard protocols and imaged with a Motic BA 310 Microscope with a Moticam camera. ImageJ FIJI was used to measure prism and wear angles. Measurements were made on 13 Cercocebus atys, 13 Lophocebus albigena, and 11 Cercopithecus molars, though sample sizes varied for different comparisons.

Repeated measures regressions of upper functional and non-functional cusps were used to test for the effects of tooth, genus, tooth-genus interaction, and wear angle on prism angle. Genus and wear angle were found to be statistically significant predictors. Pairwise comparisons revealed significantly higher prism angles in Cercocebus atys vs. both Lophocebus albigena and Cercopithecus. There was no significant difference between Lophocebus albigena and Cercopithecus in prism angles.

Our finding that the prism angles of a fallback hard-object feeder (Lophocebus albigena) are more similar to those of a soft-object feeder (Cercopithecus) than to a habitual hard-object feeder (Cercocebus atys) suggests that the correspondence between durophagy and enamel microstructure is not straightforward, complicating our ability to infer durophagy in the fossil record.