Fig. 4. Arrangement of mineral (structure) in a cartilaginous matrix contributes more to the material properties of elasmobranch vertebral cartilage than the amount of mineral. (A) Strength increases with both mineral amount (blue; R²=0.112; P<0.001) in M. californicus vertebrae and mineral arrangement (red; R²=0.580; P<0.001) in eight elasmobranch species. Increasing mineral from 40% to 50% will increase strength over a range of morphologies 44% (red) but only 32% over the range of mineral amount (blue). (B) Stiffness only increases with respect to mineral arrangement (red) within the vertebral cartilage (R²=0.604; P<0.001). The natural variation (blue) of mineral contents found in M. californicus vertebrae are presented this regression. Mineral morphology (red) is shown as mean mineral content and strength or stiffness for M. californicus and for each of seven species previously examined (Porter et al., 2006). Regression statistics were calculated using all data points from each species rather than the mean value shown in the figure.