On the relationship between maxillary molar root shape and jaw kinematics in

Area of Science:

• Paleoanthropology
• Biomechanics
• Paleoecology

Background:

• Plio-Pleistocene hominin evolution in South Africa is not well understood.
• Australopithecus africanus and Paranthropus robustus co-existed in South Africa.
• Understanding their environmental exploitation and niche partitioning is crucial.

Purpose of the Study:

• To investigate how Australopithecus africanus and Paranthropus robustus exploited and partitioned their environment.
• To estimate the direction of habitual loads on the chewing surface using first maxillary molar (M1) root orientation as a proxy.
• To compare South African hominins with East African Paranthropus boisei.

Main Methods:

• Landmark-based shape analysis of M1 root reconstructions.
• Analysis included 26 South African hominins and three East African Paranthropus boisei.
• Comparison of M1 root morphology with dento-cranial features, microwear textures, and dietary data (C4 consumption).

Main Results:

• Australopithecus africanus M1 roots suggest adaptation to dissipate a wide range of lateral loads.
• Paranthropus robustus M1 roots indicate adaptation for dissipating antero-posteriorly directed loads.
• Paranthropus robustus and P. boisei showed differences in root morphology, cranio-dental features, and diet, despite overlapping morphologies.

Conclusions:

• South African hominins occupied distinct ecological niches.
• Paranthropus robustus exhibits unique adaptations for specific load dissipation, suggesting niche specialization.
• While Paranthropus monophyly is possible, dietary niche equivalence between P. robustus and P. boisei is unlikely.