Functional Morphology of the Thoracic Limb in the Silky Anteater ( Cyclopes didactylus ): A Comparative Study With Tamandua tetradactyla

The order Xenarthra presents unique morphophysiological adaptations related to its specialized ecological niches. This study investigates the functional morphology and comparative myology of the thoracic limb in Cyclopes didactylus (silky anteater) and Tamandua tetradactyla (southern tamandua) to elucidate how muscle arrangements support digging and climbing activities. Two C. didactylus and four T. tetradactyla specimens were dissected following standard anatomical procedures. The results revealed that although both species share a similar muscular structure, C. didactylus exhibits marked muscle hypertrophy, particularly in the intrinsic muscles of the arm and forearm, reflecting its strictly arboreal lifestyle. Comparative dissections demonstrated that C. didactylus shares the characteristic continuity between the medial head of the triceps brachii muscle and the flexor digitorum profundus muscle, previously described for T. tetradactyla , thereby providing a modern comparative description of its forelimb musculature. This configuration, alongside the significant development of the M. brachioradialis and extensor muscles, enhances digit flexion and grip strength. We conclude that the observed myological variations represent specific ecomorphological specializations: while T. tetradactyla maintains a balance for terrestrial digging and climbing, C. didactylus presents a specialized apparatus for sustained suspension and locomotion in the canopy.