Dunbar Donald C
Department of Anatomy and Caribbean Primate Research Center, School of Medicine, University of Puerto Rico, San Juan, Puerto Rico.
Am J Primatol. 1988;16(4):291-303. doi: 10.1002/ajp.1350160402.
Several prosimian species begin a leap from a vertical support with their back toward the landing target. To reorient themselves from this dorsally facing, head-first lift-off to a ventrally facing, feet-first landing, the animals combine an initial twist with a partial backward somersault. Cinefilms of a captive colony of ringtailed lemurs (Lemur catta) revealed that during leaps from vertical poles to horizontal supports, the backward somersaulting rotations were often initiated while the animals were airborne. How could these prosimians initiate rotations in the absence of externally applied forces without violating angular momentum conservation? The problem was approached through vector analysis to demonstrate angular momentum (H) changes about the three principal (symmetrical) axes of rotation for a series of critical body positions that were extracted from the filmed sequences. One L. catta specimen was segmented to provide the dimensions and weights necessary for modeling the various body positions. These data were also used to calculate moments of inertia about the three principal axes in order to predict if rotations about these axes were stable or metastable. Lemurs, like any projectile, must conserve the total angular momentum (H ) established at lift-off. H , however, is a vector quantity that is the resultant of component vectors about the three principal axes. Thus, H about the individual axes may change as long as H remains constant. Strategically timed tail movements tilted the body, thereby changing the H value about the head-to-toe (twisting) axis. To conserve H , also aligned along the twisting axis, angular momentum transferred to the somersaulting axis. Owing to the direction of tail-throw, the initiated rotations were partial backward somersaults that brought the hindlimbs forward for landing. This strategy for initiating specific rotations parallels that practiced by human springboard divers.
几种原猴类物种从垂直支撑物起跳时，背部朝向着陆目标。为了从这种背部朝前、头先离地的姿势重新调整为腹部朝前、脚先着地的姿势，这些动物会先进行一次扭转，再做一个部分向后的翻滚动作。对圈养的环尾狐猴（Lemur catta）群体拍摄的电影胶片显示，在从垂直杆跳到水平支撑物的过程中，向后翻滚的动作常常在动物在空中时就开始了。在没有外力作用的情况下，这些原猴类是如何启动旋转而不违反角动量守恒定律的呢？通过矢量分析来解决这个问题，以证明在从拍摄序列中提取的一系列关键身体姿势下，角动量（H）围绕三个主要（对称）旋转轴的变化。对一只环尾狐猴标本进行了分段处理，以提供对各种身体姿势进行建模所需的尺寸和重量数据。这些数据还用于计算围绕三个主轴的转动惯量，以预测围绕这些轴的旋转是稳定的还是亚稳定的。狐猴和任何抛射体一样，必须保持起跳时建立的总角动量（H）。然而，H是一个矢量，是围绕三个主轴的分量矢量的合成。因此，只要H保持不变，围绕各个轴的H可能会发生变化。经过策略性定时的尾巴动作使身体倾斜，从而改变了围绕从头到脚（扭转）轴的H值。为了保持同样沿扭转轴排列的H，角动量转移到了翻滚轴上。由于尾巴摆动的方向，启动的旋转是部分向后的翻滚动作，使后肢向前以便着陆。这种启动特定旋转的策略与人类跳板跳水运动员所采用的策略相似。
