Xenarthra, one of the major clades of placentals, comprises two different lineages (sloths and anteaters, and armadillos) with extant representatives showing strongly different morphologies and life habits. Sloths are arboreal herbivores, anteaters are insectivores with digging/climbing abilities, and armadillos are terrestrial diggers with varied diets. The ulna is one of the forelimb elements that exhibits distinct morphological specializations for different abilities (e.g., digging and climbing). A sample of xenarthrans was analyzed in this work from a functional and ecological perspective, using 2-D geometric morphometry. The analyses performed were a Principal Components Analysis (PCA), a regression of the shape on the centroid size, and a PCA with the residuals from the regression. The first PCA shows that the morphospace is strongly influenced by differences in length of the olecranon with respect to the shaft between the three clades. Allometry was detected for the whole sample. In the residual PCA, the allometry-free morphospace allows the differentiation between the ecological categories of substrate preference: armadillos and giant anteaters (terrestrial) are located towards the negative side of PC1, while sloths and silky anteaters (arboreal) are located near the positive end, with collared anteaters (semiarboreal) placed near the center. The terrestrial taxa present a more robust diaphysis, and a comparatively long, diaphysis-aligned olecranon, while the arboreal taxa show a relatively long ulna with an anteriorly curved shaft and an anteriorly deflected carpal facet. The ulnar curvature has biomechanical implications in relation to the bone response to different loadings produced in the context of posture and locomotion in each substrate.

中文翻译：

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现存 Xenarthrans 的尺骨：形状、大小和功能

Xenarthra 是胎盘的主要分支之一，包括两个不同的谱系（树懒和食蚁兽，以及犰狳），现存的代表表现出截然不同的形态和生活习惯。树懒是树栖食草动物，食蚁兽是具有挖掘/攀爬能力的食虫动物，犰狳是具有不同饮食的陆生挖掘者。尺骨是表现出不同能力（例如，挖掘和攀爬）的不同形态特化的前肢元素之一。在这项工作中，使用 2-D 几何形态测量法从功能和生态的角度分析了一个 xenarthrans 样本。执行的分析是主成分分析 (PCA)、形状对质心大小的回归，以及具有回归残差的 PCA。第一个主成分分析表明，形态空间受到鹰嘴相对于三个进化枝之间轴的长度差异的强烈影响。对整个样品检测异速生长。在残留的 PCA 中，无异速生长的形态空间允许区分底物偏好的生态类别：犰狳和巨型食蚁兽（陆生）位于 PC1 的负侧，而树懒和丝质食蚁兽（树栖）位于正侧附近最后，将领食蚁兽（半树栖）放置在靠近中心的位置。陆生类群具有更坚固的骨干和相对较长的、与骨干对齐的鹰嘴，而树栖类群具有相对较长的尺骨，具有向前弯曲的轴和向前偏转的腕关节面。