An ecomorphological study of the raptorial digital tendon locking mechanism

Extensive adaptive radiation in hindlimb design among raptors is well known. However, the degree of variation in the structure and expression of the digital tendon locking mechanism (TLM) and its adaptive significance have received little attention. This comparative morphological study of 12 raptor and three non-raptor species revealed a distinct raptorial design, characterized by a distally located TLM that is densely packed with locking elements of increased robustness and height. Although the Falconiformes and Strigiformes converged upon this pattern, unique design features were identified among the nocturnal birds of prey. Variation in TLM structure was often consistent with phylogeny, although interfamily similarities were revealed among a number of species with the same dietary habit. The evolutionary factors that may have led to the observed variation, as well as the biomechanical implications of varying designs, are discussed.