Three-dimensional (3D) models of fossil bones are increasingly available, thus opening a novel frontier in the study of organismal size and shape evolution. We provide an example of how photogrammetry can be combined with Geometric Morphometrics (GMM) techniques to study patterns of morphological convergence in the mammalian group of Xenarthra. Xenarthrans are currently represented by armadillos, sloths, and anteaters. However, this clade shows an incredibly diverse array of species and ecomorphotypes in the fossil record, including gigantic ground sloths and glyptodonts. Since the humerus is a weight-bearing bone in quadrupedal mammals and its morphology correlates with locomotor behavior, it provides an ideal bone to gain insight into adaptations of fossil species. A 3D sample of humerii belonging to extant and fossil Xenarthra allowed us to identify a significant phylogenetic signal and a strong allometric component in the humerus shape. Although no rate shift in the evolution of the humerus shape was recorded for any clade, fossorial and arboreal species humerii did evolve at significantly slower and faster paces, respectively, than the rest of the Xenarthran species. Significant evidence for morphological convergence found among the fossorial species and between the two tree sloth genera explains these patterns. These results suggest that the highly specialized morphologies of digging taxa and tree sloths represent major deviations from the plesiomorphic Xenarthran body plan, evolved several times during the history of the group.

中文翻译：

---

Xenarthra 肱骨 3D 几何中的运动适应：收敛性测试

骨骼化石的三维 (3D) 模型越来越可用，从而开辟了生物体大小和形状演化研究的新前沿。我们提供了一个示例，说明如何将摄影测量与几何形态测量 (GMM) 技术结合起来研究 Xenarthra 哺乳动物群中的形态收敛模式。Xenarthrans 目前以犰狳、树懒和食蚁兽为代表。然而，这个进化枝在化石记录中显示出极其多样化的物种和生态形态，包括巨大的地懒和雕齿兽。由于肱骨是四足哺乳动物的承重骨，其形态与运动行为相关，因此它提供了一种理想的骨骼，可以深入了解化石物种的适应性。属于现存和化石 Xenarthra 的肱骨 3D 样本使我们能够识别出显着的系统发育信号和肱骨形状中的强异速生长成分。尽管没有记录到任何进化枝的肱骨形状进化速度发生变化，但与其他 Xenarthran 物种相比，化石和树栖物种 humerii 确实分别以明显更慢和更快的速度进化。在化石物种和两个树懒属之间发现的形态趋同的重要证据解释了这些模式。这些结果表明，挖掘类群和树懒的高度特化形态代表了与拟异形 Xenarthran 身体计划的主要偏差，在该群体的历史中进化了几次。