The manus of <i>mylodon darwinii</i> Owen (Tardigrada, Mylodontidae) and its phylogenetic implications

The first nearly complete and articulated manus of the ground sloth <i>Mylodon darwinii</i>, from the upper Pleistocene of Argentina, is described. It shares similarities with <i>Mylodonopsis ibseni</i> from Brazil, including a cuneiform with a distinct pisiform facet, an obliquely concave ulnar facet, and a prominent distolateral process, as well as a gracile metacarpal III. It shares a flattened pisiform with <i>Glossotherium robustum</i>. The trapezoid is unique in the obliquely elongate proportions of its dorsal surface. Shapes of the articular facets indicate different functions in digits II and III, with the former having a greater range of motion and the latter greater stability at the joints. Clear arboreal or fossorial adaptations are absent. A phylogenetic analysis recovered <i>M. darwinii</i> as closely related to <i>M. ibseni</i> and agrees with larger phylogenetic analyses of sloths based on craniomandibular evidence. Our data support more than two mylodontine dispersal events to North America. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Haro, J. A., A. A. Tauber, and J. M. Krapovickas. 2016. The manus of <i>Mylodon darwinii</i> Owen (Tardigrada, Mylodontidae) and its phylogenetic implications. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1188824.本文记述了一件产自阿根廷更新统上部的近乎完整且关节原位关联的达尔文磨齿地懒（*Mylodon darwinii*）前肢掌部标本。该标本与巴西的伊布森磨齿地懒（*Mylodonopsis ibseni*）具有诸多形态共性：二者均拥有带有独立豌豆骨关节面的楔骨、斜凹型尺骨关节面及显著的远侧外侧突，且第三掌骨纤细；此外，该标本的豌豆骨与粗壮舌面地懒（*Glossotherium robustum*）一样呈扁平形态。其小多角骨（trapezoid）的背侧表面呈独特的斜长形比例。关节面形态显示第二指与第三指具备不同的功能：前者运动幅度更广，后者关节稳定性更强。该标本未表现出明确的树栖或穴居适应性特征。系统发育分析结果表明，达尔文磨齿地懒与伊布森磨齿地懒亲缘关系紧密，这一结论与基于颅下颌证据开展的更大范围树懒系统发育分析结果相符。本研究数据支持磨齿地懒类至少存在两次以上的北美扩散事件。补充数据——本文的补充材料可于www.tandfonline.com/UJVP免费获取。本文引用格式：Haro, J. A., A. A. Tauber, 及 J. M. Krapovickas. 2016. 《达尔文磨齿地懒（*Mylodon darwinii* Owen, Tardigrada, 磨齿地懒科（Mylodontidae））的前肢及其系统发育意义》. 《脊椎动物古生物学杂志》. DOI: 10.1080/02724634.2016.1188824.