Divergence in forelimb morphology is often associated with functional habits exhibited within the Xenarthra, ranging from terrestrial-digging in armadillos to arboreal-suspension in sloths. We hypothesized that quantitative differences in hind limb form also will be predictive of the diverse lifestyles observed in this small clade. A total of 26 morphofunctional indices were calculated from 42 raw measurements of bone length/width/depth in a sample of N = 76 skeletal specimens (18 species). Index data for each species were categorized by substrate preference and use and then evaluated using a combination of stepwise Discriminant Function Analysis (DFA) and Principal Component Analysis (PCA) to determine significant osteological correlates (traits) among extant taxa. Additionally, character states of the morphometric data were inferred using a recent hypothesis of xenarthran phylogeny. DFA determined 14 distinct morphofunctional indices relating to femur robustness, hip/ankle/limb mechanical advantage, and foot and claw length as the most discriminating features. PCA clearly separated armadillos from sloths in morphospace based on overall robustness versus gracility, as well as proximal versus distal lengths of skeletal elements (including the claws), whereas these characteristics were intermediate in the hind limbs of anteaters and selected armadillos having either a larger greater trochanter or modified foot/claw proportions. Two-toed and three-toed sloths showed further separation from each other in morphospace primarily driven by proportions of their tibia and hind feet despite evidence of convergence for numerous functional traits. Moreover, the majority of the traits measured had significant phylogenetic signal and several of these indicated clear patterns of convergent and divergent evolution in xenarthrans by evaluation of their tip states. Our assessments expand functional interpretations of xenarthran limb form and identify potentially conserved and secondarily modified traits related to fossoriality across taxa, including in three-toed sloths, demonstrate possible morphological trade-offs between digging and climbing habits, and suggest derived traits adapted for arboreal lifestyle and suspensory function.

前肢形态的差异通常与Xenarthra中表现出的功能习惯有关，从犰狳的陆地挖掘到树懒的树栖悬浮。我们假设后肢形态的数量差异也可以预测在这个小进化枝中观察到的多种生活方式。在42个N = 76骨骼样本（18种）的样本中，通过对42个骨骼长度/宽度/深度的原始测量值，总共计算出26个形态功能指数。根据底物偏好和用途对每种物种的索引数据进行分类，然后结合逐步判别功能分析（DFA）和主成分分析（PCA）进行评估，以确定现存生物分类之间的重要骨学相关性（特征）。此外，使用xenarthran系统发育的最新假说来推断形态计量学数据的特征状态。DFA确定了14个不同的形态功能指标，这些指标与股骨的健壮性，髋部/踝部/肢体的机械优势以及脚和爪的长度有关是最明显的特征。基于总体健壮性和可塑性以及骨骼元素（包括爪）的近端长度与远端长度，PCA在形态空间中从树懒中清楚地分离了犰狳，而这些特征在食蚁兽的后肢和选定的犰狳中居中，或者更大。转子或调整的脚/爪比例。尽管有许多功能性特征的证据表明，但两趾树懒和三趾树懒在形态空间上显示出进一步的分离，这主要是由它们的胫骨和后脚的比例驱动的。此外，所测量的大多数性状具有显着的系统发生信号，其中一些通过评价其尖端状态指示出了雪草炭疽的趋同和趋异演化的清晰模式。我们的评估扩展了对Xenarthran肢体形态的功能性解释，并确定了与三类树懒相关的，与整个分类群相关的潜在保守和继发性状特征，证明了挖掘和攀爬习惯之间可能存在的形态上的取舍，并提出了适合于树栖生活方式的衍生特征和悬架功能。所测量的大多数特征具有显着的系统发生信号，其中一些通过评估其尖端状态显示出明显的收敛和发散进化模式。我们的评估扩展了对Xenarthran肢体形态的功能性解释，并确定了与三类树懒相关的，与整个分类群相关的潜在保守和继发性状特征，证明了挖掘和攀爬习惯之间可能存在的形态上的取舍，并提出了适合于树栖生活方式的衍生特征和悬架功能。所测量的大多数特征具有显着的系统发生信号，其中一些通过评估其尖端状态显示出明显的收敛和发散进化模式。我们的评估扩展了对Xenarthran肢体形态的功能性解释，并确定了与三类树懒（包括三趾树懒）中的类群相关的潜在保守的和第二次修饰的特征，展示了挖掘和攀爬习惯之间可能的形态取舍，并提出了适合于树栖生活的衍生特征和悬架功能。