UC Berkeley

Proboscideans exhibit limb morphologies specialised for supporting extreme body masses under predominantly compressive loading. These graviportal adaptations include repositioning of the limb bones closer to the trunk, resulting in a columnar stance. Among proboscideans, two humeral morphotypes have been proposed (slender and robust), yet their functional significance under compressive loading remains poorly understood. Finite element analysis (FEA) is applied to evaluate biomechanical performances of proboscidean humeri subject to axial compression, simulating conditions associated with a columnar stance and deviations from it. Our results reveal clear differences between morphotypes, with slender humeri performing worse than the robust morphotype and functioning optimally under near-axial loading. Robust humeri consistently exhibit lower peak stress under both neutral and off-axis loading and show considerable resistance to mediolateral stresses. Across all taxa, stress magnitudes generally increase when deviating from a neutral orientation, especially during posterior loading orientations, highlighting the mechanical importance of maintaining columnar limb posture. These findings support the hypothesis that robust morphologies are better adapted to resist multidirectional stresses, while slender morphologies favour energetic and locomotor efficiency. This study demonstrates the applicability of FEA in assessing compressive performance in postcranial elements and provides a novel framework for investigating biomechanical adaptations in graviportal taxa.