Evolutionary history of quadrupedal walking gaits shows mammalian release from locomotor constraint

Vertebrates employ an impressive range of strategies for coordinating their limb movements while walking. Although this gait variation has been quantified and hypotheses for its origins tested in select tetrapod lineages, a comprehensive understanding of gait evolution in a macroevolutionary context is currently lacking. We used freely-available internet videos to nearly double the number of species with quantitative gait data and used phylogenetic comparative methods to test key hypotheses about gait origin and evolution. We find strong support for an ancestral Lateral-Sequence Diagonal-Couplet gait in gnathostomes, and this mode is remarkably conserved throughout tetrapod phylogeny. Evolutionary rate analyses show that mammals overcame this ancestral constraint, resulting in a greater range of gait values than any other tetrapod lineage. Diagonal-Sequence Diagonal-Couplet gaits are significantly associated with arboreality in mammals, though this relationship is not recovered for othe...脊椎动物在行走时演化出了极为多样的肢体运动协调策略。尽管学界已对这类步态多样性完成量化分析，并在部分选定的四足动物类群中验证了其起源相关假说，但目前学界仍缺乏宏观演化框架下对步态演化的全面认知。本研究借助公开可获取的网络视频，将带有定量步态数据的物种数量提升近一倍，并通过系统发育比较方法检验了关于步态起源与演化的核心假说。研究结果显示，有颌脊椎动物（gnathostomes）的祖先步态为侧序对角耦合步态（Lateral-Sequence Diagonal-Couplet gait），且该步态模式在整个四足动物系统发育历程中保持了高度保守性。演化速率分析表明，哺乳动物突破了这一祖先演化约束，其步态参数的变化范围远超其他所有四足动物类群。在哺乳动物中，对角序对角耦合步态与树栖性（arboreality）存在显著关联，但这一关联在其他类群中尚未得到验证……