Mechanics of limb bone loading during terrestrial locomotion in river cooter turtles (Pseudemys concinna)
Mechanics of limb bone loading during terrestrial locomotion in river cooter turtles (Pseudemys concinna)
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DOI：
10.1242/jeb.012989
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发表时间：
2008-04-15
影响因子：
2.8
通讯作者：
Blob, Richard W.
中科院分区：
文献类型：
--
作者：
Butcher, Michael T.;Blob, Richard W.
在陆地运动过程中的肢体骨负荷的研究主要集中在鸟类和哺乳动物。然而，来自更广泛的物种功能和系统发育范围的数据对于理解肢体骨功能和设计的进化至关重要。在这种背景下，海龟是一个有趣的谱系。尽管它们缓慢的行走速度和坚固的四肢骨骼可能会导致与其他非鸟类爬行动物类似的低运动力和四肢骨骼应力，但它们高度摊开的姿势可能会产生高弯曲载荷，导致与鸟类和哺乳动物类似的高四肢骨骼应力物种，以及高扭转。为了测试这些可能性之间，我们评估了在陆地行走过程中所经历的压力由股骨的河cooter龟（Pseudemys concinna）的三维关节运动学和地面反作用力（GRF）的同步测量孤立的后肢脚步。此外，我们通过比较我们的运动应力计算与力学性能测试的结果，评估了该物种的股骨安全系数。峰值拉伸骨应力时的净GRF幅度平均为0.35 BW（体重），并且在中间40 - 65%的接触间隔内几乎垂直，基本上垂直于股骨。股骨承受的峰值弯曲应力较低（拉伸：24.9 +/- 9.0 MPa;压缩：- 31.1 +/- 9.1 MPa），与其他爬行动物相当，但峰值剪切应力高于其他爬行动物，平均为13.7 +/- 4.2 MPa。这种高扭转是存在的，尽管没有一个大的尾巴，一个功能，已被假设有助于扭转在其他爬行动物的尾巴是沿着地面拖动。股骨应力的测量肢骨的力学性能的比较表明，在弯曲和扭转的安全系数，产量为13.9，大大高于鸟类和哺乳动物的典型值，更接近其他爬行动物物种计算的升高值。因此，不仅龟肢骨似乎相当。但是四足动物谱系之间的骨负荷比较与以下假设一致：低肢体骨负荷、高扭转和高安全系数可能是肢体骨设计的原始特征。
Studies of limb bone loading during terrestrial locomotion have focused primarily on birds and mammals. However, data from a broader functional and phylogenetic range of species are critical for understanding the evolution of limb bone function and design. Turtles are an interesting lineage in this context. Although their slow walking speeds and robust limb bones might lead to low locomotor forces and limb bone stresses similar to other non-avian reptiles, their highly sprawled posture could produce high bending loads, leading to high limb bone stresses similar to those of avian and mammalian species, as well as high torsion. To test between these possibilities, we evaluated stresses experienced by the femur of river cooter turtles (Pseudemys concinna) during terrestrial walking by synchronizing measurements of three-dimensional joint kinematics and ground reaction forces (GRFs) during isolated hindlimb footfalls. Further, we evaluated femoral safety factors for this species by comparing our locomotor stress calculations with the results of mechanical property tests. The net GRF magnitude at peak tensile bone stress averaged 0.35 BW ( body weight) and was directed nearly vertically for the middle 40 - 65% of the contact interval, essentially orthogonal to the femur. Peak bending stresses experienced by the femur were low ( tensile: 24.9 +/- 9.0 MPa; compressive: - 31.1 +/- 9.1 MPa) and comparable to those in other reptiles, yet peak shear stresses were higher than those in other reptiles, averaging 13.7 +/- 4.2 MPa. Such high torsion is present despite cooters lacking a large tail, a feature that has been hypothesized to contribute to torsion in other reptiles in which the tail is dragged along the ground. Comparison of femoral stresses to measurements of limb bone mechanical properties in cooters indicates safety factors to yield of 13.9 in bending and 6.3 in torsion, considerably higher than values typical for birds and mammals, and closer to the elevated values calculated for other reptile species. Thus, not only do turtle limb bones seem considerably. over-designed' for resisting the loads that they encounter, but comparisons of bone loading across tetrapod lineages are consistent with the hypothesis that low limb bone loads, elevated torsion and high safety factors may be primitive features of limb bone design.