Clemente Christofer J
School of Biological Sciences, University of Queensland, Queensland, Australia.
Evolution. 2014 Aug;68(8):2171-83. doi: 10.1111/evo.12447. Epub 2014 Jun 3.
The origin of bipedal locomotion in lizards is unclear. Modeling studies have suggested that bipedalism may be an exaptation, a byproduct of features originally designed to increase maneuverability, which were only later exploited. Measurement of the body center of mass (BCOM) in 124 species of lizards confirms a significant rearward shift among bipedal lineages. Further racetrack trials showed a significant acceleration threshold between bipedal and quadrupedal runs. These suggest good general support for a passive bipedal model, in which the combination of these features lead to passive lifting of the front of the body. However, variation in morphology could only account for 56% of the variation in acceleration thresholds, suggesting that dynamics have a significant influence on bipedalism. Deviation from the passive bipedal model was compared with node age, supporting an increase in the influence of dynamics over time. Together, these results show that bipedalism may have first arisen as a consequence of acceleration and a rearward shift in the BCOM, but subsequent linages have exploited this consequence to become bipedal more often, suggesting that bipedalism in lizards may convey some advantage. Exploitation of bipedalism was also associated with increased rates of phenotypic diversity, suggesting exploiting bipedalism may promote adaptive radiation.
蜥蜴双足运动的起源尚不清楚。建模研究表明，双足运动可能是一种适应性变异，是最初为提高机动性而设计的特征的副产品，只是后来才被利用。对124种蜥蜴的身体重心（BCOM）测量证实，双足类谱系之间存在显著的向后移动。进一步的赛道试验表明，双足和四足奔跑之间存在显著的加速阈值。这些结果为被动双足模型提供了有力的总体支持，在该模型中，这些特征的组合导致身体前部的被动抬起。然而，形态学上的差异只能解释加速阈值差异的56%，这表明动力学对双足运动有重大影响。将与被动双足模型的偏差与节点年龄进行比较，支持了动力学影响随时间增加的观点。这些结果共同表明，双足运动可能最初是由于加速和BCOM向后移动而产生的，但随后的谱系更多地利用了这一结果而变成双足动物，这表明蜥蜴的双足运动可能具有某种优势。对双足运动的利用也与表型多样性的增加率相关，这表明利用双足运动可能促进适应性辐射。
