CR2P, Centre de Recherche en Paléontologie-Paris, Muséum national d'Histoire naturelle, Sorbonne Université, Centre National de la Recherche Scientifique, Paris cedex 05, France.
UMR 7179 (MNHN-CNRS) MECADEV, Département Adaptations du Vivant, Muséum National d'Histoire Naturelle, Paris, France.
J Anat. 2021 May;238(5):1082-1105. doi: 10.1111/joa.13362. Epub 2021 Jan 7.
The anatomy of sharks, rays, and chimaeras (chondrichthyans) is crucial to understanding the evolution of the cranial system in vertebrates due to their position as the sister group to bony fishes (osteichthyans). Strikingly different arrangements of the head in the two constituent chondrichthyan groups-holocephalans and elasmobranchs-have played a pivotal role in the formation of evolutionary hypotheses targeting major cranial structures such as the jaws and pharynx. However, despite the advent of digital dissections as a means of easily visualizing and sharing the results of anatomical studies in three dimensions, information on the musculoskeletal systems of the chondrichthyan head remains largely limited to traditional accounts, many of which are at least a century old. Here, we use synchrotron tomographic data to carry out a digital dissection of a holocephalan and an elasmobranch widely used as model species: the elephantfish, Callorhinchus milii, and the small-spotted catshark, Scyliorhinus canicula. We describe and figure the skeletal anatomy of the head, labial, mandibular, hyoid, and branchial cartilages in both taxa as well as the muscles of the head and pharynx. In Callorhinchus, we make several new observations regarding the branchial musculature, revealing several previously unreported or ambiguously characterized muscles, likely homologous to their counterparts in the elasmobranch pharynx. We also identify a previously unreported structure linking the pharyngohyal of Callorhinchus to the neurocranium. Finally, we review what is known about the evolution of chondrichthyan cranial muscles from their fossil record and discuss the implications for muscle homology and evolution, broadly concluding that the holocephalan pharynx is likely derived from a more elasmobranch-like form which is plesiomorphic for the chondrichthyan crown group. This dataset has great potential as a resource, particularly for researchers using these model species for zoological research, functional morphologists requiring models of musculature and skeletons, as well as for palaeontologists seeking comparative models for extinct taxa.
鲨鱼、鳐鱼和锯鳐（软骨鱼纲）的解剖结构对于理解脊椎动物颅系统的进化至关重要，因为它们是硬骨鱼（硬骨鱼纲）的姊妹群。这两个软骨鱼纲群体——全头鱼和软骨鱼——的头部结构截然不同，在形成针对主要颅结构（如颌骨和咽腔）的进化假说方面发挥了关键作用。然而，尽管数字解剖已成为一种易于可视化和共享三维解剖学研究结果的手段，但有关软骨鱼头部肌肉骨骼系统的信息在很大程度上仍然局限于传统描述，其中许多描述至少有一个世纪的历史。在这里，我们使用同步加速器断层扫描数据对广泛用作模式物种的全头鱼和软骨鱼进行数字解剖：象鼻鱼 Callorhinchus milii 和小斑点猫鲨 Scyliorhinus canicula。我们描述并描绘了这两个分类群的头部、唇、下颌、舌骨和鳃弓软骨的骨骼解剖结构，以及头部和咽腔的肌肉。在 Callorhinchus 中，我们对鳃肌进行了一些新的观察，揭示了几个以前未报道或描述不明确的肌肉，可能与软骨鱼咽腔的对应肌肉同源。我们还发现了一个以前未报道的结构，将 Callorhinchus 的咽舌骨与脑颅连接起来。最后，我们回顾了从化石记录中了解到的软骨鱼颅肌肉的进化，并讨论了肌肉同源性和进化的意义，总的来说，我们得出结论，全头鱼的咽腔可能来自于一种更类似于软骨鱼的形式，这种形式是软骨鱼冠群的原始形式。这个数据集具有很大的潜力，可以作为资源，特别是对于使用这些模式物种进行动物学研究、需要肌肉和骨骼模型的功能形态学家以及寻求灭绝分类群比较模型的古生物学家。
