Dietary adaptation in Paranthropus robustus postcanine teeth

Objectives: Recent studies of Paranthropus robustus crania identified temporal trends in features associated with increased bite force production, coinciding with environmental shifts toward more arid conditions. To test whether the evolution of postcanine teeth also reflects increasing mechanical demands associated with hard food consumption, we analyzed trends in the architecture of P. robustus postcanine teeth, including crown area, tooth shape, and average (AET) and relative (RET) enamel thickness.

Materials and Methods: 2D mesial sections were created from microCT scans of upper premolars (n=24), upper molars (n=14), and lower molars (n=16) from multiple South African sites. Descriptive statistics, Mann-Whitney U tests, and Jonckheere-Terpstra tests were used to identify significant differences over time, with Holm-Bonferroni corrections applied for multiple comparisons.

Results: Significant temporal trends existed in premolar morphology with increased crown area (CA), absolute crown strength (ACS), overall enamel thickness (AET and RET), and increased enamel thickness over the occlusal half of the tooth. Upper molars increased in CA, but no other measured variable. Lower molars showed no significant temporal trends in any measured variable.

Discussion: These results suggest rapid dental evolution in response to dietary pressures, with varying and independent rates of change between different tooth types. These findings support the hypothesis that selection resulted in shifts to P. robustus dental morphology to increases in mechanical resistance, consistent with an expanding dietary niche that incorporated increasingly challenging foods.