Many tetrapod lineages show extreme increases in body mass in their evolutionary history, associated with important osteological changes. The ankle joint, essential for foot movement, is assumed to be particularly affected in this regard. We investigated the morphological adaptations of the astragalus and the calcaneus in Rhinocerotidae, and analysed them in light of a comparative analysis with other Perissodactyla. We performed 3D geometric morphometrics and correlated shape with centroid size of the bone and body mass of the species. Our results show that mass has an influence on bone shape in Rhinocerotidae and in Perissodactyla, but this is not as strong as expected. In heavy animals the astragalus has a flatter trochlea, orientated more proximally, associated with a more upright posture of the limb. The calcaneus is more robust, possibly to sustain the greater tension force exerted by the muscles during plantarflexion. Both bones show wider articular facets, providing greater cohesion and better dissipation of the loading forces. The body plan of the animals also has an influence. Short-legged Teleoceratina have a flatter astragalus than the other rhinocerotids. Paraceratherium has a thinner calcaneus than expected. This study clarifies adaptations to high body weight among Rhinocerotidae and calls for similar investigations in other groups with massive forms.

中文翻译：

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质量对架形状变化的影响：犀牛科（哺乳动物：Perissodactyla）的形态计量学研究

许多四足动物谱系在其进化史中显示出体重的极端增加，这与重要的骨学改变有关。在这方面，脚运动必不可少的踝关节被认为受到特别的影响。我们调查了犀牛科中黄芪和跟骨的形态适应，并根据与其他Perissodactyla的比较分析对它们进行了分析。我们执行了3D几何形态计量学，并将形状与骨骼的质心大小和物种的体重相关联。我们的研究结果表明，质量对犀牛科和Perissodactyla中的骨形状有影响，但这并不像预期的那样强烈。在较重的动物中，黄芪的扁平滑车朝向更近端，与肢体的更直立姿势相关。跟骨更坚固 可能会在plant屈期间维持肌肉施加的更大拉力。两根骨头都显示出较宽的关节面，从而提供了更大的内聚力和更好的负载力消散。动物的身体计划也有影响。短腿Teleoceratina的黄芪比其他犀牛更扁平。跟骨旁骨膜的跟骨比预期的薄。这项研究阐明了犀牛科对高体重的适应性，并呼吁其他具有大量体型的群体进行类似的研究。