Hindlimb bones texture through postnatal ages of Rhea americana (Aves: Palaeognathae).

The bone texture of Rhea americana was evaluated through the examination of a postnatal ontogenetic series. The hind limb bone surfaces of specimens of one, three and five months old, and adults were compared to characterize each stage according to the morphological features generated by their differential ossification. The results suggest a similar process of tissue maturation concerning neognathous birds, although with some differences. A spongy or striated surface with abundant pores in the femur and longitudinal grooves in the tibiotarsus and tarsometatarsus characterizes chicks. Vascularity decreases, and the bone texture gradually changes acquiring a more homogeneous surface, to eventually reach the smooth appearance of adult bones. The establishment of particular textures corresponding to different bones and ontogenetic stages permits the accurate interpretation of remains in ecological, archaeological and paleontological contexts in which bones are fragmented and/or incomplete.

Ontogenetic scaling of the hindlimb muscles of the greater rhea (Rhea americana).

The greater rhea (Rhea americana) is the largest South American bird. It is a cursorial, flightless species with long powerful legs and reduced forelimbs. The goal of this study was to explore how hindlimb muscles scale with body mass during postnatal growth and to analyze whether the specialized locomotion of this species affects the growth of muscle masses. The mass of 19 muscles and body mass were weighed in 21 specimens ranging from 1-month-old individuals to adults. Seventeen muscles scaled with positive allometry with respect to body mass, whereas two muscles scaled isometrically. The predominance of positive allometric growth in hindlimb muscles results in a limb with massive and powerful muscles specialized to support a large body mass and to attain relatively high running speeds. Analysis of muscle mass scaling is a simple and useful way to compare possible differences between locomotor styles, and it is valuable in studies that reconstruct the paleobiology of extinct taxa.

The hindlimb muscles of Rhea americana (Aves, Palaeognathae, Rheidae).

The Greater Rhea is the largest cursorial Ratitae bird native to South America. Due to its increasing importance in farming and therefore in the sustainable use of this species, a comprehensive knowledge of their anatomy is essential. The goal of this study was to provide an anatomical description of the hindlimb muscles of Rhea americana. Six adult birds of both sexes were macroscopically studied analysing the origin and insertion of thigh and shank muscles. The thigh showed the highest number of muscles, whereas the shank showed the lowest number; this feature minimizes inertia and allows achieving high stride frequencies. The muscles of the shank showed long tendons of insertion that reduce the energetic cost during running. The major muscles responsible for extension of the hip and the ankle joints were massive and robust indicating their importance for cursorial locomotion. The pelvic limb muscles of Rhea americana resemble those of other cursorial Ratitae and their features are consistent with specialization for high-speed locomotion.