Most previous studies examining tetrapod skeletal form in relation to mechanical function have only been concerned with adult phenotype. However, adult bone form is the result of interactions between mechanical, hormonal, nutritional, and phylogenetic influences throughout an animal’s life. To be able to fully interpret skeletal morphology in adult animals, the influence of these different factors during ontogenetic growth must also be accounted for. The goal of this dissertation was to examine the ontogenetic relationships between in vivo skeletal mechanics and morphology at the gross and microstructural levels in select limb bones of representative tetrapod taxa:​ domestic goats and emu. To achieve this goal, in vivo bone strains in the goat radius and emu femur and tibiotarsus were measured throughout ontogeny during steady locomotion. Bone strains were related to limb loads and ontogenetic scaling patterns of the bone mid-shaft crosssectional geometry, curvature, and mineral content. Subsequently, for each taxon, detailed cross-sectional strain distributions for each bone’s mid-shaft were related to regional histomorphological measurements of cortical bone growth, bone porosity and remodeling, and collagen fiber orientation.

Although the distribution of strains remained similar in the bones of both taxa throughout ontogeny, strain magnitudes generally increased despite similar relative limb loads and locomotor kinematics during growth, and significant decreases and increases in bone curvature and mineral content, respectively. The likely reasons for these increases in strain were strong negative allometry and general isometry of the cross-sectional geometries in the bones of the goats and emu, respectively. The goat radii were loaded in axial bending throughout ontogeny, while the emu femora and tibiotarsi experienced torsional shear strains. These differences in loading were reflected in the regional cortical growth rates. Relatively high bending strains in the medial and lateral cortices of the goat radii corresponded to thicker bone cortices and higher growth rates, resulting in asymmetrically shaped bone cross-sections. Shear strains in the emu femora and tibiotarsi resulted in more uniform regional growth patterns and nearly circular bone cross-sections. Regional or inter-bone variation in porosity, remodeling, and collagen fiber orientation did not correspond closely to differences in mechanical strain environment.