Distal tibial trabecular architecture of australopiths from South Africa suggests diverse locomotor repertoires

In South African hominins, the externalmorphology of the ankle joint exhibits varyingcombinations of ape-like, human-like, and uniquefeatures. Here we use microtomography toexamine the trabecular structure of the distal tibiaof StW 358, StW 389 from Sterkfontein Member4 (3.4–2 Ma) assigned to Australopithecus afri-canus, StW 567 from Sterkfontein Member 5(1.7–1.4 Ma) assigned to Homo/Paranthropus,U.W. 88-97 from Malapa (1.98 Ma) attributed toAustralopithecus sediba, and SWT1/HR-2c fromSwartkrans Member 1 (2.3–1.7 Ma) assignedto Paranthropus robustus, to determine if thereis evidence for distinctive habitual joint loadingassociated with these various morphotypes.The comparative sample includes 50 extanthominoid distal tibiae. A canonical holisticmorphometric analysis was used to statisticallycompare the distribution patterns of relativetrabecular bone volume (rBV/TV) across taxa.Humans display high rBV/TV at the center ofthe subarticular surface (neutrally loaded ankle),while great apes possess high rBV/TV in theanterior and posterior regions (loading in dorsal/plantar flexion). The distal tibiae from SterkfonteinMember 4 show an intermediate signal, resem-bling humans but also displaying an ape-likeanterior bone concentration. StW 567 presents asimilar pattern but with a central rBV/TV concen-tration that expands more posteriorly, withremnants of the epiphyseal line. Australopithecussediba shows a unique distribution with high rBV/TV laterally, while Paranthropus robustus has agorilla-like rBV/TV pattern. These findings high-light the diverse locomotor repertoires of SouthAfrican hominins, with implications for under-standing their behavioral ecology.