Molar form, enamel growth, and durophagy in Cercocebus and Lophocebus

Objectives: To test the hypothesis that differences in crown structure, enamel

growth, and crown geometry in Cercocebus and Lophocebus molars covary with differences

in the feeding strategies (habitual vs. fallback durophagy, respectively) of these

two genera. Relative to Lophocebus molars, Cercocebus molars are predicted to possess

features associated with greater fracture resistance and to differ in enamel

growth parameters related to these features.

Materials and Methods: Sample proveniences are as follows: Cercocebus atys molars

are from the Taï Forest, Ivory Coast; Lophocebus albigena molars are from a site north

of Makoua, Republic of Congo; and a Lophocebus atterimus molar is from the Lomako

Forest, Democratic Republic of Congo. For μCT scans on which aspects of molar

form were measured, sample sizes ranged from 5 to 35 for Cercocebus and 3 to

12 for Lophocebus. A subsample of upper molars was physically sectioned to measure

enamel growth variables.

Results: Partly as a function of their larger size, Cercocebus molars had significantly

greater absolute crown strength (ACS) than Lophocebus molars, supporting the

hypothesis. Greater crown heights in Cercocebus are achieved through faster enamel

extension rates. Also supporting the hypothesis, molar flare and proportional occlusal

basin enamel thickness were significantly greater in Cercocebus. Relative enamel

thickness (RET), however, was significantly greater in Lophocebus.

Discussion: If ACS is a better predictor of fracture resistance than RET, then Cercocebus

molars may be more fracture resistant than those of Lophocebus. Greater molar

flare and proportional occlusal basin thickness might also afford Cercocebus molars

greater fracture resistance.