Sagittal long bone curvature in birds

The maximum sagittal curvature of the long bones (humeras, radius, ulna, femur, tibiotarsus and tarsometatarsus) of 45 specimens of birds, belonging to 36 species, was measured and regressed to the corresponding body mass. Mathematical results show a tendency of curvature to scale with strong positive allometry. Within the species studied, those with more characteristic flapping flight tend to show relatively low values of curvature in the wing bones. To check the agreement of the present results with current hypotheses on the origin of long bone curvature, previous results on scaling of myological and cross-sectional parameters in birds are considered. Indirect evidence suggests that curvature tends to increase bone stresses. Hypotheses that consider curvature as a consequence of the mechanical action of muscle allocation and optimization of functional strains are discussed at length. The possible double genetic-epigenetic determinism of the curvature character is evoked.