Young Jesse W
Department of Anthropology, University of Texas at Austin, Austin, TX 78712, USA.
Am J Phys Anthropol. 2009 Apr;138(4):403-20. doi: 10.1002/ajpa.20953.
Studies of skeletal pathology indicate that injury from falling accounts for most long bone trauma in free-ranging primates, suggesting that primates should be under strong selection to manifest morphological and behavioral mechanisms that increase stability on arboreal substrates. Although previous studies have identified several kinematic and kinetic features of primate symmetrical gaits that serve to increase arboreal stability, very little work has focused on the dynamics of primate asymmetrical gaits. Nevertheless, asymmetrical gaits typify the rapid locomotion of most primates, particularly in smaller bodied taxa. This study investigated asymmetrical gait dynamics in growing marmosets and squirrel monkeys moving on terrestrial and simulated arboreal supports (i.e., an elevated pole). Results showed that monkeys used several kinematic and kinetic adjustments to increase stability on the pole, including reducing peak vertical forces, limiting center of mass movements, increasing substrate contact durations, and using shorter and more frequent strides (thus limiting disruptive whole-body aerial phases). Marmosets generally showed greater adjustment to pole locomotion than did squirrel monkeys, perhaps as a result of their reduced grasping abilities and retreat from the fine-branch niche. Ontogenetic increases in body size had relatively little independent influence on asymmetrical gait dynamics during pole locomotion, despite biomechanical theory suggesting that arboreal instability is exacerbated as body size increases relative to substrate diameter. Overall, this study shows that 1) symmetrical gaits are not the only stable way to travel arboreally and 2) small-bodied primates utilize specific kinematic and kinetic adjustments to increase stability when using asymmetrical gaits on arbo real substrates.
骨骼病理学研究表明，在自由放养的灵长类动物中，跌倒造成的损伤是大多数长骨创伤的原因，这表明灵长类动物应该受到强烈的选择，以表现出能够增加在树栖基质上稳定性的形态和行为机制。尽管先前的研究已经确定了灵长类动物对称步态的几个运动学和动力学特征，这些特征有助于提高树栖稳定性，但很少有研究关注灵长类动物不对称步态的动力学。然而，不对称步态是大多数灵长类动物快速移动的典型特征，尤其是在体型较小的类群中。本研究调查了生长中的狨猴和松鼠猴在陆地和模拟树栖支撑物（即高架杆）上移动时的不对称步态动力学。结果表明，猴子使用了几种运动学和动力学调整来增加在杆上的稳定性，包括降低垂直力峰值、限制质心运动、增加与基质的接触持续时间，以及使用更短、更频繁的步幅（从而限制破坏性的全身空中阶段）。狨猴通常比松鼠猴对杆上运动表现出更大的适应性调整，这可能是由于它们抓握能力的下降以及从细树枝生态位的退缩。尽管生物力学理论表明，随着身体大小相对于基质直径的增加，树栖不稳定性会加剧，但在杆上运动期间，个体发育过程中身体大小的增加对不对称步态动力学的独立影响相对较小。总体而言，本研究表明：1）对称步态不是在树上移动的唯一稳定方式；2）体型较小的灵长类动物在树栖基质上使用不对称步态时，会利用特定的运动学和动力学调整来增加稳定性。
