Abstract
Plio-Pleistocene hominins from South Africa remain poorly understood. Here, we focus on how Australopithecus africanus and Paranthropus robustus exploited and—in part—partitioned their environment. Specifically, we explore the extent to which first maxillary molar roots (M1) are oriented and thus, by proxy, estimate the direction of loads habitually exerted on the chewing surface. Landmark-based shape analysis of M1 root reconstructions of 26 South African hominins and three East African Paranthropus boisei suggest that A. africanus may have been able to dissipate the widest range of laterally directed loads. Paranthropus robustus and P. boisei, despite having overlapping morphologies, differ in aspects of root shape/size, dento-cranial morphologies, microwear textures and C4 food consumption. Hence, while Paranthropus monophyly cannot be excluded, equivalence of dietary niche can. The South African hominins occupied distinct ecological niches, whereby P. robustus appears uniquely adapted to dissipate antero-posteriorly directed loads.
Highlights
A century ago, Australopithecus africanus was first announced from South Africa [1]
This study aimed to explore whether differences in craniodental morphologies between the PlioPleistocene hominins from South Africa A. africanus and P. robustus could initially have been driven by niche partitioning or may—perhaps—be due to phylogenetic constraints in the latter taxon
We focused on tooth root form and—in particular—tooth root splay, a functionally important trait that may inform whether a species habitually consumes foods that need to be broken down in crush or in shear
Summary
Australopithecus africanus was first announced from South Africa [1]. Discoveries since South African hominins have remained enigmatic. It is unclear whether the 2 morphological variability within the A. africanus hypodigm indicates the presence of multiple species [2] or should be expected in a long-lived, eurybiomic taxon [3]. Nor do we know the phylogenetic relationship(s) of South and East African hominins [4,5]. To understand the evolutionary pathway(s) of the South African Plio-Pleistocene hominins and their role in human evolution, it is imperative to resolve issues concerning their diversity and specializations, with regard to feeding ecology. We investigate an understudied functional – morphological aspect of the masticatory apparatus, namely tooth root splay and its bearing on mandibular kinematics
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