School of Anatomy Physiology and Human Biology, University of Western Australia, Crawley, Western Australia 6009, Australia.
Proc Biol Sci. 2012 Sep 7;279(1742):3449-56. doi: 10.1098/rspb.2012.0593. Epub 2012 Jun 6.
How animals cope with increases in body size is a key issue in biology. Here, we consider scaling of xenarthrans, particularly how femoral form and function varies to accommodate the size range between the 3 kg armadillo and its giant relative the 300 kg glyptodont. It has already been noted that femoral morphology differs between these animals and suggested that this reflects a novel adaptation to size increase in glyptodont. We test this idea by applying a finite element analysis of coronal plane forces to femoral models of these animals, simulating the stance phase in the hind limb; where the femur is subject to bending owing to longitudinal compressive as well as abduction loads on the greater trochanter. We use these models to examine the hypothesis that muscles attaching on the third trochanter (T3) can reduce this bending in the loaded femur and that the T3 forces are more effective at reducing bending in glyptodont where the T3 is situated at the level of the knee. The analysis uses traditional finite element methods to produce strain maps and examine strains at 200 points on the femur. The coordinates of these points before and after loading are also used to carry out geometric morphometric (GM) analyses of the gross deformation of the model in different loading scenarios. The results show that longitudinal compressive and abductor muscle loading increases bending in the coronal plane, and that loads applied to the T3 reduce that bending. In the glyptodont model, the T3 loads are more effective and can more readily compensate for the bending owing to longitudinal and abductor loads. This study also demonstrates the usefulness of GM methods in interpreting the results of finite element analyses.
动物如何应对体型的增加是生物学中的一个关键问题。在这里，我们考虑了异关节动物的比例关系，特别是股骨的形态和功能如何变化以适应 3 公斤重的犰狳和 300 公斤重的雕齿兽之间的体型范围。人们已经注意到这些动物的股骨形态不同，并提出这反映了雕齿兽体型增大的一种新的适应。我们通过对这些动物的股骨模型进行冠状面力的有限元分析来检验这一观点，模拟后肢的站立阶段；此时股骨由于大转子上的纵向压缩和外展负荷而受到弯曲。我们使用这些模型来检验以下假设：附着在第三转子（T3）上的肌肉可以减少受载股骨的弯曲，并且 T3 力在 T3 位于膝关节水平的雕齿兽中更有效地减少弯曲。分析使用传统的有限元方法生成应变图，并检查股骨上 200 个点的应变。在加载前后，这些点的坐标也用于在不同的加载情况下对模型的总变形进行几何形态测量（GM）分析。结果表明，纵向压缩和外展肌的加载增加了冠状面的弯曲，而 T3 的加载减少了这种弯曲。在雕齿兽模型中，T3 的负荷更有效，并且可以更容易地补偿由于纵向和外展负荷引起的弯曲。本研究还展示了 GM 方法在解释有限元分析结果方面的有用性。
