RESUMO
Knowledge of the ontogenetic pattern of morphological features is essential to improve biological interpretations. The study of morphological features of the pelvic girdle and hind limb apparatus throughout growth is an excellent approach to understand how the skeletal morphology and muscles are interrelated during growth in a bird with a specialized mode of locomotion. The Greater Rhea (Rhea americana) is a large cursorial palaeognathous bird with long legs and powerful musculature. The postnatal shape changes of the pelvis of this bird were studied with geometric morphometric techniques, using landmarks and semilandmarks. In addition, regression analyses were used to explore the association between pelvic shape changes with muscle and body mass. The pelvises of 16 specimens of Rhea americana from 1 month old to adulthood were studied in dorsal and lateral views. Noticeable differences in pelvic shape were noted between ages, particularly in lateral view. In young birds, the pre- and post-acetabular ilium was subequal in length, whereas in adults the pre-acetabular ilium became shorter. In dorsal view, the main shape changes observed were the progressive thinning of both ilium portions and the elongation of the vertex craniolateralis ilii from chicks to adulthood. In this view, the only clear differentiation was between young and adult birds. Shape differences were influenced by body mass and pelvic muscles; the post-acetabular muscle mass explained the highest percentage of the variation. The specialized locomotion of Greater Rhea is reflected in their pelvic musculoskeletal system, in which the change to a longer post-acetabular ilium correlates with the growth of the powerful post-acetabular muscles. The actions of these muscles provide the necessary strength to support the body mass, minimize the body swinging movements and propel the body forward during locomotion. Bone morphology is affected by the forces produced by body mass and the muscle activity, demonstrating the presence of common growth mechanisms, which are primordial and gave rise to a functional and properly proportioned adult.
Assuntos
Evolução Biológica , Membro Posterior/anatomia & histologia , Locomoção/fisiologia , Pelve/anatomia & histologia , Corrida/fisiologia , Animais , Feminino , Membro Posterior/fisiologia , Masculino , Pelve/fisiologia , ReiformesRESUMO
We studied the hindlimb myology of the monk parakeet (Myiopsitta monachus). Like all parrots, it has zygodactyl feet enabling perching, climbing, hanging, moving easily among trees, and handling food. Muscles were described and weighed, and physiological cross-sectional area (PCSA) of four flexors and one extensor was calculated. In comparison to other muscles, the M. tibialis cranialis and the M. fibularis brevis show increased development and high PCSA values, and therefore, large potential force production. Also, a large proportion of muscle mass was involved in flexing the digits. We hypothesize that these muscle traits are associated with the arboreal locomotion and food manipulation habits. In the monk parakeet, the M. extensor digitorum longus sends a branch to the hallux, and the connection between the M. flexor digitorum longus and the M. flexor hallucis longus is type I (Gadow's classification). We reaffirm the presence of the M. ambiens as a plesiomorphic condition that disappears in most members of the order. Among Psittaciformes, the M. fibularis brevis is stronger and the M. fibularis weaker in arboreal species than in basal terrestrial ones (e.g., Strigops).