First Primate Clavicles From Swartkrans Cave: Further Indications of Habitual Arboreal Behavior in Some Early Pleistocene South African Hominins.

OBJECTIVES

We provide descriptions and taphonomic and functional interpretations of two hominin clavicles, SWT1/HR-5 and SWT1/HR-6, from Swartkrans Member 1. We explore the possibility that one of the clavicles derives from the same Paranthropus robustus individual as SWT1/HR-2, an articulating os coxae and partial lower limb from Swartkrans Member 1.

MATERIALS AND

METHODS

We employed taphonomic methods to describe damage on SWT1/HR-5 and SWT1/HR-6. Complementing the qualitative descriptions, we used osteometric tools and micro-CT scanning to generate quantitative data on external shape, cross-sectional geometry, and trabecular structure of the fossils. Observations were interpreted through comparative analyses. To explore a possible individual association of one of the new Swartkrans clavicles with the SWT1/HR-2 fossil-set, we developed linear regression models, fitted to extant hominoid samples. We then applied these models to each of the Swartkrans clavicles and to the SWT1/HR-2b femur.

RESULTS

Periosteal surfaces of the Swartkrans clavicles retain important anatomical and taphonomic details. Their external shapes do not ally them exclusively with the clavicles of any comparative hominoid taxon. However, their cross-sectional geometries and trabecular structures are ultimately consistent with apelike arboreality. Results fail to clarify whether the SWT1/HR-5 and SWT1/HR-6 individuals derived from the same taxon. Association of SWT1/HR-2 with either clavicle could not be reliably determined, although such an association is more likely with SWT1/HR-6.

DISCUSSION: The finding that SWT1/HR-5 and SWT1/HR-6 derived from arboreally active individuals concords with analyses of the SWT1/HR-2 fossil-set, strengthening the idea that arborealism was an important adaptation for some South African Pleistocene hominins.