Postnatal ontogeny of the locomotor skeleton of a cursorial bird: greater rhea

The greater rhea (Rhea americana) is the largest flightless bird of South America and has a cursorial locomotion style. The objective of this study was to explore how the leg configuration of this species changes from juveniles to adult, and the possible implications of these changes for the locomotor style of this bird. In this regard, it is interesting to study the presence of allometries during growth (ontogenetic allometry), because it may provide information about morpho-functional aspects. Growth of femur, tibiotarsus and tarsometatarsus were studied in individuals of different ages, ranging from 1 month to adulthood. Allometric analysis was performed on a total of 21 measurements of limb bones to evaluate ontogenetic changes. Ten measurements were allometric, correlating positively and negatively with body mass. Some of them, like the positive allometry of the tarsometatarsus length, the negative allometry of the distal region of the tibiotarsus and the proximal segment of the tarsometatarsus, seem to be associated with cursoriality. On the other hand, the positive allometric growth of the distal segment of the femur may be related to the large body size of these birds.