Stowers Amanda K, Matloff Laura Y, Lentink David
Department of Mechanical Engineering, Stanford University, 416 Escondido Mall, Stanford, CA 94305, USA
Department of Mechanical Engineering, Stanford University, 416 Escondido Mall, Stanford, CA 94305, USA.
J R Soc Interface. 2017 Aug;14(133). doi: 10.1098/rsif.2017.0224.
Birds change the shape and area of their wings to an exceptional degree, surpassing insects, bats and aircraft in their ability to morph their wings for a variety of tasks. This morphing is governed by a musculoskeletal system, which couples elbow and wrist motion. Since the discovery of this effect in 1839, the planar 'drawing parallels' mechanism has been used to explain the coupling. Remarkably, this mechanism has never been corroborated from quantitative motion data. Therefore, we measured how the wing skeleton of a pigeon () moves during morphing. Despite earlier planar assumptions, we found that the skeletal motion paths are highly three-dimensional and do not lie in the anatomical plane, ruling out the 'drawing parallels' mechanism. Furthermore, micro-computed tomography scans in seven consecutive poses show how the two wrist bones contribute to morphing, particularly the sliding ulnare. From these data, we infer the joint types for all six bones that form the wing morphing mechanism and corroborate the most parsimonious mechanism based on least-squares error minimization. Remarkably, the algorithm shows that all optimal four-bar mechanisms either lock, are unable to track the highly three-dimensional bone motion paths, or require the radius and ulna to cross for accuracy, which is anatomically unrealistic. In contrast, the algorithm finds that a six-bar mechanism recreates the measured motion accurately with a parallel radius and ulna and a sliding ulnare. This revises our mechanistic understanding of how birds morph their wings, and offers quantitative inspiration for engineering morphing wings.
鸟类能够在很大程度上改变翅膀的形状和面积，在为各种任务改变翅膀形态的能力方面超过了昆虫、蝙蝠和飞机。这种形态变化由一个肌肉骨骼系统控制，该系统将肘部和腕部的运动联系起来。自1839年发现这种效应以来，平面“画平行线”机制一直被用来解释这种联系。值得注意的是，这一机制从未从定量运动数据中得到证实。因此，我们测量了鸽子翅膀骨骼在形态变化过程中的运动方式。尽管早期有平面假设，但我们发现骨骼运动路径是高度三维的，并不位于解剖平面内，这排除了“画平行线”机制。此外，对七个连续姿势的微型计算机断层扫描显示了两块腕骨在形态变化中的作用，特别是尺腕骨的滑动。根据这些数据，我们推断出构成翅膀形态变化机制的所有六块骨头的关节类型，并基于最小二乘误差最小化证实了最简洁的机制。值得注意的是，该算法表明，所有最优的四杆机制要么锁定，无法跟踪高度三维的骨骼运动路径，要么为了精确性需要桡骨和尺骨交叉，这在解剖学上是不现实的。相比之下，该算法发现一个六杆机制能够通过平行的桡骨和尺骨以及滑动的尺腕骨准确地再现测量到的运动。这修正了我们对鸟类如何改变翅膀形态的机械理解，并为工程上的变形翅膀提供了定量灵感。
