Department of Earth and Planetary Sciences, Yale University, New Haven, CT, USA.
Yale Peabody Museum of Natural History, New Haven, CT, USA.
Nat Ecol Evol. 2022 May;6(5):604-613. doi: 10.1038/s41559-022-01699-x. Epub 2022 Mar 21.
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. 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 topological modifications that are exaggerated during ontogeny. Therian mammals, while conservative in their cleavage patterns, depart drastically from the ancestral amniote musculoskeletal organization in terms of topology. These topological changes occur through extension, translocation and displacement of muscle groups later in development. Overall, the simplicity underlying the apparent complexity of forelimb muscle development allows us to resolve conflicting hypotheses about homology and to trace the history of each individual forelimb muscle throughout the amniote radiations.
肢体肌肉非常复杂，在进化上也很不稳定。尽管它们的解剖结构对于研究形态和功能的进化具有重要意义，但它们在主要羊膜动物类群中的同源性仍然不清楚。由于现代羊膜动物四肢的高度衍生形态，对成年肌肉的研究尚无定论，但在胚胎发生早期，对应关系变得越来越明显。我们研究了六个主要羊膜动物类群代表的前肢肌肉的胚胎发育，结果与当前的共识相反，这些早期的分裂模式在羊膜动物中高度保守。包括鸟类在内的爬行动物的肌肉质量分裂模式和拓扑结构高度保守，无论其骨骼如何变化：鸟类的飞行器官是由早期的轻微拓扑变化引起的，这些变化在胚胎发生过程中被夸大了。合弓类哺乳动物在分裂模式上虽然保守，但在拓扑结构上与祖先羊膜动物的骨骼肌肉组织有很大的不同。这些拓扑变化是通过在发育后期的肌肉群的延伸、移位和位移产生的。总的来说，前肢肌肉发育的明显复杂性背后的简单性使我们能够解决关于同源性的相互矛盾的假设，并追踪每个前肢肌肉在羊膜动物辐射过程中的历史。
