Data from: The evolution of bipedal running in lizards suggests a consequential origin may be exploited in later lineages.

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.蜥蜴两足行走的起源机制目前仍不明确。建模研究提示，两足行走可能属于一种副适应（exaptation）——即原本为提升运动机动性而演化出的特征的副产物，仅在后续才被开发利用。对124种蜥蜴的身体重心（body center of mass, BCOM）进行测量后发现，两足演化支的重心存在显著后移现象。后续的跑道实验结果显示，两足奔跑与四足奔跑之间存在显著的加速度阈值差异。上述发现为被动两足模型提供了较为充分的一般性支持：该模型认为，相关特征的组合可使躯体前部被动抬起。然而，形态学差异仅能解释56%的加速度阈值变异，这提示运动动力学对两足行走具有显著影响。研究人员将实际观测与被动两足模型的偏差与演化节点年龄进行比对，结果支持运动动力学的影响随演化时间推移逐渐增强这一结论。综合来看，本研究结果表明，蜥蜴的两足行走最初可能源于加速度提升与身体重心后移的共同作用，但后续的演化谱系进一步利用这一特性，更频繁地演化出两足行走方式，提示蜥蜴的两足行走可能具备某种适应性优势。此外，两足行走的开发利用还与表型多样性增速提升存在关联，这表明对两足行走的利用或许可促进适应性辐射。