Early diversification of avian limb morphology and the role of modularity in the locomotor evolution of crown birds

High disparity among avian forelimb and hind limb segments in crown birds relative to non-avialan theropod dinosaurs, potentially driven by the origin of separate forelimb and hind limb locomotor modules, has been linked to the evolution of diverse avian locomotor behaviors. However, this hypothesized relationship has not been quantitatively investigated in a phylogenetic framework. We assessed the relationship between the evolution of limb morphology and locomotor behavior by comparing a numerical proxy for locomotor diversity to morphospace sizes derived from a dataset of 1241 extant species. We then estimated how limb disparity accumulated during the crown avian radiation. Lastly, we tested whether limb segments evolved independently between each limb module using phylogenetically informed regressions. Disparity increased significantly with behavioral diversity after accounting for clade age and species richness. We found that forelimb disparity accumulated rapidly early in avian evo...

相较于非鸟类兽脚类恐龙（non-avialan theropod），现生鸟类冠群（crown birds）的前肢与后肢节段间存在显著差异，这一差异可能源于独立前肢与后肢运动模块（locomotor modules）的演化起源，且已被证实与鸟类多样化运动行为的演化存在关联。然而，这一假说关联尚未在系统发育框架（phylogenetic framework）下开展定量研究。本研究通过将运动多样性的数值代理指标（numerical proxy）与基于1241种现生物种数据集构建的形态空间（morphospace）规模进行对比，评估了肢体形态演化与运动行为之间的关联。随后，我们估算了鸟类冠群辐射演化过程中肢体差异的积累模式。最后，我们借助系统发育校正回归（phylogenetically informed regressions），检验了不同肢体模块间的肢节是否独立演化。在校正支系年龄（clade age）与物种丰富度（species richness）的影响后，肢体差异随行为多样性显著升高。研究发现，前肢差异在鸟类演化早期迅速积累...