Granatosky Michael C, Tripp Cameron H, Schmitt Daniel
Department of Evolutionary Anthropology, Duke University, Durham, NC 27708, USA
Department of Evolutionary Anthropology, Duke University, Durham, NC 27708, USA.
J Exp Biol. 2016 Jan;219(Pt 1):53-63. doi: 10.1242/jeb.120840.
For primates and other mammals moving on relatively thin branches, the ability to effectively adopt both above- and below-branch locomotion is seen as critical for successful arboreal locomotion, and has been considered an important step prior to the evolution of specialized suspensory locomotion within our Order. Yet, little information exists on the ways in which limb mechanics change when animals shift from above- to below-branch quadrupedal locomotion. This study tested the hypothesis that vertical force magnitude and distribution do not vary between locomotor modes, but that the propulsive and braking roles of the forelimb change when animals shift from above- to below-branch quadrupedal locomotion. We collected kinetic data on two lemur species (Varecia variegata and Lemur catta) walking above and below an instrumented arboreal runway. Values for peak vertical, braking and propulsive forces as well as horizontal impulses were collected for each limb. When walking below branch, both species demonstrated a significant shift in limb kinetics compared with above-branch movement. The forelimb became both the primary weight-bearing limb and propulsive organ, while the hindlimb reduced its weight-bearing role and became the primary braking limb. This shift in force distribution represents a shift toward mechanics associated with bimanual suspensory locomotion, a locomotor mode unusual to primates and central to human evolution. The ability to make this change is not accompanied by significant anatomical changes, and thus likely represents an underlying mechanical flexibility present in most primates.
对于在相对细的树枝上移动的灵长类动物和其他哺乳动物来说，有效采用树枝上方和下方移动的能力被视为成功进行树栖移动的关键，并且被认为是我们这个目内专门的悬垂移动进化之前的重要一步。然而，关于动物从树枝上方四足移动转变为树枝下方四足移动时肢体力学如何变化的信息却很少。本研究检验了这样一个假设，即垂直力的大小和分布在不同移动模式之间没有变化，但当动物从树枝上方四足移动转变为树枝下方四足移动时，前肢的推进和制动作用会发生变化。我们收集了两种狐猴（黑白领狐猴和环尾狐猴）在有仪器的树栖跑道上方和下方行走时的动力学数据。收集了每个肢体的垂直、制动和推进力峰值以及水平冲量的值。当在树枝下方行走时，与在树枝上方移动相比，这两个物种的肢体动力学都表现出显著变化。前肢既成为主要的承重肢体，又成为推进器官，而后肢减轻了其承重作用，成为主要的制动肢体。这种力分布的变化代表了向与双手悬垂移动相关的力学的转变，双手悬垂移动是一种灵长类动物不常见但对人类进化至关重要的移动模式。做出这种变化的能力并不伴随着显著的解剖学变化，因此可能代表了大多数灵长类动物潜在的机械灵活性。
