Conclusions

Comparison and statistical analysis of measurements of about 1800 fossilized bones of Pleistocene mammals show mixed results. In many cases (e.g., nearly all the measurements of Smilodon fatalis, Bison antiquus, Equus occidentalis, and some dimensions of Panthera atrox, Paramylodon harlani, and Camelops hesternus), there is significantly higher variability in intermembranous bones than in endochondral bones. In others (one dimension of Panthera atrox, two of Paramylodon harlani, and Camelops hesternus astragali and patellae, and some the sesamoids of Paramylodon harlani), the trend is reversed or equivocal. In general (in the CV data set, 21 out of 27 dimensions of all the taxa combined), most of these findings agree with the hypothesis that intermembranous bones are more variable than endochondral bones because they are not as tightly constrained by articular surfaces with other bones, joints, or tendons. The results of these analyses suggest that movement and growth play less of an important role in constraining the growth of intermembranous bones than previously suggested in anatomical literature.