Embryonic muscle splitting patterns reveal homologies of amniote forelimb muscles

Limb muscles are remarkably complex and evolutionarily labile; although their anatomy is of great interest for studies of the evolution of form and function, their homologies among major amniote clades have remained obscure. Studies of adult musculature are inconclusive owing to the highly derived morphology of modern amniote limbs, but correspondences become increasingly evident earlier in ontogeny. Amniote forelimb muscles derive from early embryonic muscle masses of somitic origin, which grow and cleave into recognizable divisions that split into the individualized muscles. We followed the embryonic development of forelimb musculature in representatives of six major amniote clades and found, contrary to current consensus, that these early splitting patterns are highly conserved across Amniota. Muscle mass cleavage patterns and topology are highly conserved in reptiles including birds, irrespective of their skeletal modifications: the avian flight apparatus results from slight early t...

肢体肌肉（limb muscles）的结构极为复杂且进化可塑性极强；尽管其解剖学特征对于形态与功能演化研究具有重要价值，但主要羊膜类（amniote）支系间的肌肉同源关系（homologies）始终模糊不清。由于现代羊膜类肢体的形态高度特化，针对成体肌肉组织的研究往往难以得出确定性结论，而在个体发育（ontogeny）早期阶段，肌肉对应关系的辨识则愈发清晰。羊膜类的前肢肌肉起源于体节来源（somitic origin）的早期胚胎肌团（embryonic muscle masses），这些肌团会生长并分裂为可识别的亚单元，最终进一步分化为独立的肌肉。我们对六大主要羊膜类支系代表物种的前肢肌肉胚胎发育过程进行了追踪，结果与当前学界共识相悖：整个羊膜总纲（Amniota）的早期肌肉分裂模式高度保守。肌团分裂模式与肌肉拓扑结构（topology）在包括鸟类（birds）在内的爬行动物（reptiles）中均高度保守，且不受骨骼修饰的影响：鸟类的飞行器官（flight apparatus）仅由早期轻微的……