AG Vergleichende Zoologie, Institut für Biologie, Humboldt Universität zu Berlin, Philippstraße 13, 10115 Berlin, Germany.
Institute of Veterinary Anatomy, Histology and Embryology, Leipzig University, An den Tierkliniken 43, 04103 Leipzig, Germany.
J Exp Biol. 2022 Jun 15;225(12). doi: 10.1242/jeb.243625. Epub 2022 Jun 14.
Therian mammals are known to move their forelimbs in a parasagittal plane, retracting the mobilised scapula during stance phase. Non-cursorial therian mammals often abduct the elbow out of the shoulder-hip parasagittal plane. This is especially prominent in Tamandua (Xenarthra), which suggests they employ aspects of sprawling (e.g. lizard-like) locomotion. Here, we tested whether tamanduas use sprawling forelimb kinematics, i.e. a largely immobile scapula with pronounced lateral spine bending and long-axis rotation of the humerus. We analysed high-speed videos and used X-ray motion analysis of tamanduas walking and balancing on branches of varying inclinations and provide a quantitative characterization of gaits and forelimb kinematics. Tamanduas displayed lateral sequence/lateral couplets on flat ground and horizontal branches, but increased diagonality on steeper inclines and declines, resulting in lateral sequence/diagonal couplets gaits. This result provides further evidence for high diagonality in arboreal species, probably maximising stability in arboreal environments. Further, the results reveal a mosaic of sprawling and parasagittal kinematic characteristics. The abducted elbow results from a constantly internally rotated scapula about its long axis and a retracted humerus. Scapula retraction contributes considerably to stride length. However, lateral rotation in the pectoral region of the spine (range: 21 deg) is higher than reported for other therian mammals. Instead, it is similar to that of skinks and alligators, indicating an aspect generally associated with sprawling locomotion is characteristic for forelimb kinematics of tamanduas. Our study contributes to a growing body of evidence of highly variable non-cursorial therian mammal locomotor kinematics.
已知真兽类哺乳动物在矢状面内移动前肢，在支撑阶段缩回活动的肩胛骨。非奔跑真兽类哺乳动物的肘部经常离开肩-髋矢状面外展。这在树懒（贫齿目）中尤为明显，这表明它们采用了伸展（例如蜥蜴状）运动的某些方面。在这里，我们测试了树懒是否使用伸展的前肢运动学，即肩胛骨基本不动，脊柱明显侧向弯曲，肱骨长轴旋转。我们分析了高速视频，并使用 X 射线运动分析树懒在不同倾斜度的树枝上行走和平衡，并对步态和前肢运动学进行了定量描述。树懒在平地和水平树枝上显示出侧向序列/侧向偶联，但在更陡峭的倾斜和下降时增加了对角线，导致侧向序列/对角线偶联步态。这一结果进一步证明了树栖物种的高对角线性，可能最大限度地提高了树栖环境的稳定性。此外，结果显示出伸展和矢状面运动学特征的镶嵌。外展的肘部是由于肩胛骨围绕其长轴不断内旋和肱骨缩回造成的。肩胛骨缩回对步幅长度有很大贡献。然而，脊柱胸区的侧向旋转（范围：21°）高于其他真兽类哺乳动物的报道。相反，它与蜥蜴和短吻鳄相似，表明与伸展运动一般相关的方面是树懒前肢运动学的特征。我们的研究为越来越多的非奔跑真兽类哺乳动物运动学的高度可变证据做出了贡献。
