Zeininger Angel, Shapiro Liza J, Raichlen David A
Department of Evolutionary Anthropology, Duke University, Box 90383, Durham, North Carolina, 27708.
Department of Anthropology, The University of Texas at Austin, 2201 Speedway C3200, Austin, Texas, 78712.
Am J Phys Anthropol. 2017 Jun;163(2):231-241. doi: 10.1002/ajpa.23201. Epub 2017 Mar 16.
Digitigrade hand and foot postures and extended elbows and knees are considered adaptations to running in cursorial mammals because they increase effective limb lengths (ELLs). However, the relationship between digitigrady and ELL in primates is not well understood. We documented the ontogeny of limb postures in baboons to better understand the function of digitigrady during walking. We hypothesized that the hand and foot would become more elevated and the elbow and knee more extended, leading to increased relative ELLs throughout ontogeny.
Longitudinal kinematic data were collected on four infant yellow baboons (Papio cynocephalus) as they aged from two to nine months, and again at two to three years. Hand/foot postures, elbow/knee angles, relative fore/hind limb ELLs, and dimensionless velocity were measured for 404 symmetrical walking strides.
Digitigrade hand and foot postures were preferred at all ages. The elbow extended slightly and the knee flexed slightly with age. Elevated proximal hands, extended elbows, and extended knees were associated with long relative ELLs. For a given age, relative hind limb ELL was longer than relative forelimb ELL.
In the forelimb, digitigrade hand postures and extended elbows function to increase relative ELL at slow walking velocity. Increased forelimb ELL may be an attempt to equalize forelimb and hind limb ELLs in baboons with an absolutely longer hind limb. Pedal digitigrady is not a main contributing factor to hind limb ELL. Results suggest that manual and pedal digitigrady in terrestrial cercopithecoids does not function to increase velocity.
趾行式的手足姿势以及伸直的肘部和膝部被认为是对奔跑的适应，因为它们增加了有效肢体长度（ELL）。然而，灵长类动物中趾行式与ELL之间的关系尚未得到很好的理解。我们记录了狒狒肢体姿势的个体发育情况，以更好地理解行走过程中趾行式的功能。我们假设在个体发育过程中，手和脚会抬得更高，肘部和膝部会更伸直，从而导致相对ELL增加。
收集了4只幼年黄狒狒（豚尾狒狒）从2个月到9个月龄，以及2到3岁时的纵向运动学数据。对404个对称行走步幅测量了手/足姿势、肘/膝角度、相对前/后肢ELL以及无量纲速度。
所有年龄段都更倾向于趾行式的手足姿势。随着年龄增长，肘部略有伸直，膝部略有弯曲。近端手部抬高、肘部伸直和膝部伸直与较长的相对ELL相关。对于给定年龄，相对后肢ELL比相对前肢ELL长。
在前肢中，趾行式的手部姿势和伸直的肘部在慢步行走速度下起到增加相对ELL的作用。增加前肢ELL可能是为了使后肢绝对长度更长的狒狒的前肢和后肢ELL相等。足部趾行式不是后肢ELL的主要促成因素。结果表明，陆生猕猴的手部和足部趾行式并非用于提高速度。
