The hindlimb myology of the South American eagle Geranoaetus melanoleucus (Accipitridae, Aves)

Geranoaetus melanoleucus is a widely distributed accipitrid across South America. Like other accipitrids, it employs powerful hindlimb muscles to capture and immobilize prey. Whereas previous research has focused predominantly on the grip muscles of diurnal raptorial birds, detailed myological descriptions of the entire hindlimb are lacking. This study offers a comprehensive overview of the hindlimb musculature of G. melanoleucus, comparing it with existing information on other raptors. Several features are shared with other accipitrids, including the absence of m. flexor cruris lateralis, the fusion of m. iliotrochantericus cranialis and medialis, and a vinculum connecting distally m. flexor hallucis longus and m. flexor digitorum longus, among others. However, G. melanoleucus exhibits distinctive characteristics, such as a smaller origin area for m. tibialis cranialis and a distal trifurcated tendon of m. flexor perforatus digiti IV, among others. Similar to other diurnal raptorial birds, digit flexors constitute the majority of the muscle mass, aligning with their primary role in grip force generation. In summary, accipitrids appear to demonstrate a conservative muscular anatomy pattern, but the study of different species is crucial for detecting specific features and taxonomic differences. Moreover, detailed myological descriptions provide essential information for morphofunctional analyses.