The scaling of skeletal microanatomy in non-human primates

The study of scale-correlated changes in the external dimensions and cross-sectional geometry of primate long bones is fundamental to our understanding of primate limb bone structural adaptation. To date, however, there have been no studies of the effects of mechanical loading on patterns of skeletal scaling at the microstructural level. To remedy this, we analysed patterns of microanatomical scaling in the humeri and femora of 107 adult primates belonging to the families Galagonidae and Cercopithecidae. Seven species were included in our analysis. Proximal, midshaft, and distal sections of humeri and femora of each individual were examined and secondary osteonal and cortical area were measured. Secondary osteonal area scales positively allometrically with cortical cross-sectional area and with body mass. This pattern holds generally for humeri and femora—both within and across families. However, there are striking dissimilarities in the relative strengths of the allometric coefficients for humeri and femora measured for different families. These distinctions appear to be related to differences in the ways in which fore- and hindlimbs are loaded. Such differences highlight the promise of microstructural data and the importance of examining the confounding effects of locomotory behaviour in studies of skeletal scaling.