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Fig. 1 | BMC Evolutionary Biology

Fig. 1

From: Morphological diversification of biomechanical traits: mustelid locomotor specializations and the macroevolution of long bone cross-sectional morphology

Fig. 1

Cross-sectional traits and example loading regimes. In A, a humerus showing the orientation of anatomical axes about which SMA was measured: cranio-caudal (Cr-Ca) and medio-lateral (M-L). The total bone tissue (dark grey) within the cross-section determines the bone’s cross-sectional area (CSA), whereas the distribution of bone tissue about specified axes determines the bone’s second moment of area (SMA). CSA and SMA withstand specific forms of mechanical loads (B). CSA determines resistance to forces causing axial compression along the length of the bone, whereas SMA determines resistance to bending moments that cause a bone to flex about a given axis. SMAML is associated with bending about the M-L axis (i.e., bending in the Cr-Ca plane), whereas SMACC is associated with bending about the Cr-Ca axis (i.e., bending in the M-L plane). Notably the farther bone tissue is from an axis of bending, the greater the resistance to bending. Thus in A, SMAML is greater than SMACC. Note that the example of bending in B is exaggerated for illustrative purposes, and all cross-sectional traits were measured with BoneJ 1.4.2 [17]

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