Evolution of posture in amniotes–Diving into the trabecular architecture of the femoral head.

This article investigates the relationship between femoral posture and the microanatomical architecture of trabecular bone in the femoral head across a diverse sample of extant amniotes, including mammals and reptiles. Using phylogenetic generalized least squares and ancestral state reconstruction methods, the study finds that microanatomical parameters—such as bone volume fraction, trabecular thickness, and degree of anisotropy—are significantly correlated with body mass but not with femoral posture or lifestyle. Ancestral reconstructions suggest a sprawling posture for the common ancestor of archosaurs and a crouched posture for early mammals and therians, although microanatomical data yield conflicting results regarding the timing of postural transitions in synapsids. Overall, the trabecular architecture of the femoral head does not reliably indicate limb posture, but the authors highlight the potential of ancestral state reconstruction methods to enhance understanding of postural evolution in amniotes, especially when incorporating fossil taxa with known postures.