In quadrupeds, limb bones are strongly affected by functional constraints linked to weight support, but few studies have addressed the complementary effects of mass, size and body proportions on limb bone shape. During their history, Rhinocerotoidea have displayed a great diversity of body masses and relative size and proportions of limb bones, from small tapir-like forms to giant species. Here, we explore the evolutionary variation of shapes in forelimb bones and its relationship with body mass in Rhinocerotoidea. Our results indicate a general increase in robustness and greater development of muscular insertions in heavier species, counteracting the higher weight loadings induced by an increased body mass. The shape of the humerus changes allometrically and exhibits a strong phylogenetic signal. Shapes of the radius and ulna display a stronger link with body mass repartition than with the absolute mass itself. Congruent shape variation between the humerus and the proximal part of the ulna suggests that the elbow joint is comprised of two strongly covariant structures. In addition, our work confirms the uniqueness of giant Paraceratheriidae among Rhinocerotoidea, whose shape variation is related to both a high body mass and a cursorial forelimb construction.

中文翻译：

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犀牛前肢长骨形状变化：与大小、体重和身体比例的关系

在四足动物中，肢体骨骼受到与重量支撑相关的功能限制的强烈影响，但很少有研究涉及质量、大小和身体比例对肢体骨骼形状的互补影响。在它们的历史中，犀牛科的身体质量和肢体骨骼的相对大小和比例表现出极大的多样性，从小型貘状形式到巨型物种。在这里，我们探讨了犀牛前肢骨骼形状的进化变化及其与体重的关系。我们的研究结果表明，在较重的物种中，健壮性和肌肉插入的更大发展普遍增加，抵消了由体重增加引起的更高的重量负荷。肱骨的形状发生异速变化并表现出强烈的系统发育信号。桡骨和尺骨的形状与体重重新分配的联系比与绝对质量本身的联系更强。肱骨和尺骨近端部分之间的一致形状变化表明肘关节由两个强协变结构组成。此外，我们的工作证实了犀牛科中巨型 Paraceratheriidae 的独特性，其形状变化与高体重和粗略的前肢结构有关。