Ontogenetic scaling of foot musculoskeletal anatomy in elephants

This study quantifies the shape change in elephant manus and pes anatomy with increasing body mass, using computed tomographic scanning. Most manus and pes bones, and manus tendons, maintain their shape, or become more gracile, through ontogeny. Contrary to this, tendons of the pes become significantly more robust, suggesting functional adaptation to increasingly high loads. Ankle tendon cross-sectional area (CSA) scales the highest in the long digital extensor, proportional to body mass^1.08±0.21, significantly greater than the highest-scaling wrist tendon (extensor carpi ulnaris, body mass^0.69±0.09). These patterns of shape change relate to the marked anatomical differences between the pillar-like manus and tripod-like pes, consistent with differences in fore- and hindlimb locomotor function. The cartilaginous predigits (prepollux and prehallux) of the manus and pes also become relatively more robust through ontogeny, and their pattern of shape change does not resemble that seen in any of the 10 metacarpals and metatarsals. Their CSAs scale above isometry proportional to body mass ^0.73±0.09 and body mass^0.82±0.07 respectively. We infer a supportive function for these structures, preventing collapse of the foot pad during locomotion.