Three-dimensional hierarchical structure of female Sprague-Dawley rat tibia cortical bone was characterized as a function of age (3, 12, 32, 42, 60, and 72 wk) using a high-resolution micro-computed tomography. At the whole bone level, 3-wk samples exhibited statistically significant differences in a mean total tissue volume, mean cortical bone volume, mean cortical bone volume density, mean periosteal perimeter, and mean cortical thickness (P < 0.05) compared with all other ages. At the tissue level, there was a statistically significant increase in a mean canal number density and a decrease in a mean canal volume and diameter between 3-wk and 12-wk samples. While no significant variations were found between mean canal lengths, there was a dependence of mean canal orientation on age. At the cell level, there were no statistically significant differences in a lacuna number density and a lacuna volume density, and all lacunae element-based parameters displayed no dependence on age across age. In addition, at the microstructural level, the cannular indexes were reported separately for anterior, posterior, medial, and lateral anatomic regions. From 3 to 32 wk of age, there existed significantly fewer canals per volume of bone in the medial region of the tibia vs. other cross-sectional quadrants. Although there were changes with age, there were no statistically significant differences in the mean canal volume, mean canal diameter, and mean canal length between the four anatomic regions.

To achieve powered flight, bats altered the architecture of their long bones by reducing mineral concentrations and altering cross‐sectional geometries. This study quantifies differences in adult bone architecture of the short‐tailed bat (Carollia) relative to terrestrial rodents (Mus, Peromyscus). By integrating nanoindentation tests with whole bone bending tests, and visualization of cross‐sectional areas, this study documents architectural differences in limb bones of aerial and terrestrial mammals. Nanoindentation tests revealed that metacarpals of bats are 40% as stiff and 36% as hard as that of rodents. Whole bone bending tests revealed that the bat and mouse humerus are roughly equivalent in stiffness, however the bat radius was much more compliant, suggesting a decreased mineral content. Micro‐CT scans showed that the humeral, femoral, and tibial cross‐sectional geometries are equivalent in both bats and mice; however, distal bones of the bat displayed 8–40% larger medullary cavities compared rodents. In comparing rates of long bone ossification, bats delays appositional ossification relative to mice, but begins diaphyseal longitudinal growth earlier. At late fetal stages, bats rapidly elongate the diaphysis. These findings further our understanding of the microstructural properties of chiropteran bone biology.