Below the crown: examining interspecies variation in postcanine enamel thickness, EDJ, and root form in the Paranthropus clade

Although there is considerable evidence of shared craniodental morphology within the Paranthropus clade, microwear and isotopic studies suggest that this shared morphology may be linked to different dietary behaviour in eastern and southern Africa. Recently, it has been demonstrated that detailed morphological analyses of the internal structure of tooth crowns (specifically, enamel thickness, enamel-dentine junction morphology and root/pulp canal form), assessed using high resolution microtomography, can reveal previously undetected differences in tooth structure that can have systematic and functional implications In this study, we generate high-resolution surface models of the EDJ surface, external root surface, and pulp canal form of Paranthropus specimens from Kromdraai, Swartkrans, Drimolen, Koobi Fora, West Turkana, and the Omo. We assess enamel thickness in 2D mesial planes of section, root/canal form through an expanded qualitative typology for the hominin clade, and EDJ morphology through landmark-based 3D geometric morphometrics. Our results indicate that 1) the generally accepted derived nature of P. boisei relative to P. robustus is matched by detailed morphological features of the crown (increased enamel thickness and very low dentine horns) and roots (increased root volumes and increasing distal pulp canal size); 2) there is evidence for population differences between sites preserving P. robustus; and 3) there is evidence at Gondolin (South Africa) for morphological similarity in molar form with P. boisei from Koobi Fora. The implications of these findings for the systematics, functional morphology, and paleogeography of Paranthropus are discussed