Ontogenetic shape changes in the pelvis of the Greater rhea (Aves, Palaeognathae) 2 and their relationships with cursorial locomotion: a geometric morphometric 3 approach

PICASSO, MARIANA BEATRIZ JULIETA; MONTI AILÌN; MOSTO, MARÍA CLELIA; MORGAN CECILIA CLARA

JOURNAL OF ANATOMY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2020 vol. 236 p. 1137 - 1145

0021-8782

Knowledge of the ontogenetic pattern of morphological features is essential to improve 3 biological interpretations. The study of morphological features of the pelvic girdle and 4 hind limb apparatus throughout growth is an excellent pproach to understand how the 5 skeletal morphology and muscles are interrelated during growth in a bird with a 6 specialized mode of locomotion. The Greater Rhea (Rhea americana) is a large 7 cursorial palaeognathous bird with long legs and powerful musculature. The postnatal 8 shape changes of the pelvis of this bird were studied with geometric morphometric 9 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 pelvis of sixteen specimens of Rhea americana from one-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- andpost-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, there was only a clear differentiation between young and adult birds. Shape differences were influenced by body mass and pelvic muscles, specially the post-acetabular muscle mass explained the highest percentage of the variation. The specialized locomotion of greater rhea is reflected on 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 propels the body forward during locomotion. Bone morphology is affected by the forces produced by body mass and the muscle activity, demonstrating he presence of common growth mechanisms, which are primordial to give rise to a unctional and properly proportioned adult