Adaptations to cursoriality and digit reduction in the forelimb of the African wild dog ().

Background: The African wild dog (), an endangered canid native to southern and eastern Africa, is distinct among canids in being described as entirely tetradactyl and in its nomadic lifestyle and use of exhaustive predation to capture its prey instead of speed, strength, or stealth. These behavioral and morphological traits suggest a potentially unique set of adaptations.

Methods: Here, we dissected the forelimbs of an adult male specimen and performed detailed descriptions and quantitative analyses of the musculoskeletal anatomy.

Results: Statistical comparisons of muscle masses and volumes revealed that has relatively smaller wrist rotators (mm. pronator teres, pronator quadratus, supinator) than any other included carnivoran taxon, suggesting adaptive pressures for antebrachial stability over rotatory movement in the carpus of . While a complete digit I is absent in , a vestigial first metacarpal was discovered, resulting in changes to insertions of mm. extensor digiti I et II, abductor (et opponens) digiti I and flexor digiti I brevis. Mm. anconeus, brachialis and flexor carpi ulnaris caput ulnare all have more extensive origins in than other canids suggesting an emphasis on posture and elbow stability. M. triceps brachii caput laterale has a larger origin in and m. triceps brachii caput longum has an additional accessory head. Electromyographic studies have shown this muscle is active during the stance phase of trotting and galloping and is important for storing elastic energy during locomotion. We interpret these differences in size and attachments of muscles in as adaptations for long distance running in this highly cursorial species, likely important for exhaustive predation. Absence of a full digit I in may increase speed and stride length; however, the retention of a vestigial digit permits the attachment of reduced pollical muscles which may provide additional stability and proprioception to the carpus.