Hominin postcranial remains from Drimolen Main Quarry, South Africa

Overview

This study presents a formal catalog and analysis of 28 isolated postcranial fossil specimens from Drimolen Main Quarry, South Africa, dated to approximately 2 million years ago. The assemblage derives from a paleocave system that has previously yielded abundant craniodental remains, predominantly attributed to Paranthropus robustus alongside more limited evidence of Homo aff. erectus and early Homo. The postcranial collection exhibits a high proportion of juvenile and subadult remains, paralleling the composition of the craniodental assemblage. This work provides paleobiological characterization of the Drimolen hominins through systematic description and comparative analysis of upper limb, lower limb, vertebral, and pelvic elements.

Methods and approach

Isolated postcranial specimens recovered during excavations between 1994 and 2015 were systematically cataloged and formally described. Comparative morphological analysis was conducted on upper limb elements including a distal humerus, ulnar fragment, fetal and perinatal humeri and radii, and manual phalanges. Lower limb material comprising tibiae, metatarsal, and pedal phalanges underwent examination. Vertebral and pelvic specimens were assessed, including an adult lumbar centrum, partial pelvis, and infant neural arches. Functional analyses were applied to infer locomotor capabilities and skeletal morphology. Taxonomic attribution was determined through morphological comparison with known taxa, though attribution challenges resulted from the mixed-species nature of the Drimolen assemblage. Two specimens previously considered possibly hominin were formally excluded from hominin status following reexamination.

Key Findings

Taxonomic assignment was achieved for selected specimens: DNH 32 (distal humerus) and DNH 43 (partial pelvis) attributed to P. robustus with confidence; DNH 150a and b (thoracic and lumbar neural arches) possibly associated with the DNH 134 juvenile cranium assigned to Homo aff. erectus. Remaining specimens, predominantly assessed as likely P. robustus, presented taxonomic attribution challenges. The assemblage demonstrates commitment to terrestrial bipedality based on functional morphology. However, one first metatarsal specimen exhibits atypical tarsometatarsal joint curvature suggesting increased hallucal divergence, representing a departure from expected postcranial morphology in the sample.

Implications

The postcranial evidence supports a pattern of obligate terrestrial bipedality among Drimolen hominins, consistent with established understanding of both P. robustus and early Homo locomotor capabilities. The presence of atypical hallucal morphology in at least one individual raises questions regarding postcranial variation and mosaic evolution within the assemblage. Given the mixed species composition at Drimolen, determining whether this variation reflects taxonomic differences between P. robustus and Homo aff. erectus or intraspecific polymorphism requires further investigation.

Scope and limitations

This summary is based on the study abstract and available metadata. It does not include a full analysis of the complete paper, supplementary materials, or underlying datasets unless explicitly stated. Findings should be interpreted in the context of the original publication.