Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
Department of Natural History, Royal Ontario Museum, Toronto, Ontario, Canada.
Anat Rec (Hoboken). 2023 Mar;306(3):552-563. doi: 10.1002/ar.25100. Epub 2022 Oct 27.
Captorhinids are a group of Paleozoic amniotes that represents one of the earliest-diverging clades of eureptiles. Although captorhinids are one of the best-known and most well-studied clades of early amniotes, their palaeoneuroanatomy has gone largely unexamined. We utilized neutron computed tomography to study the virtual cranial and otic endocasts of two captorhinid specimens. The neurosensory anatomy of captorhinids shows a mixture of traits considered plesiomorphic for sauropsids (no expansions of the cerebrum or olfactory bulbs, low degree of encephalization, low ossification of the otic capsule) and those considered more derived, including moderate cephalic and pontine flexures and a dorsoventrally tall bony labyrinth. The inner ear clearly preserves the elliptical, sub-orthogonal canals and the short, rounded vestibule, along with an unusually enlarged lateral canal and a unique curvature of the posterior canal. The reconstructed neurosensory anatomy indicates that captorhinids were sensitive to slightly higher frequencies than many of their contemporaries, likely reflecting differences in body size across taxa, while the morphology of the maxillary canal suggests a simple, tubular condition as the plesiomorphic state for Sauropsida and contributes to the ongoing discussions regarding the phylogenetic placement of varanopids. This study represents the first detailed tomographic study of the brain and inner ear of any basal eureptile. The new data described here reveal that the neuroanatomy of early sauropsids is far more complex and diverse than previously anticipated, and provide impetus for further exploration of the palaeoneuroanatomy of early amniotes.
盔头螈类是一类古生代羊膜动物，代表了最早分化的真爬行动物之一。尽管盔头螈类是早期羊膜动物中最著名和研究最充分的类群之一，但它们的古神经解剖学基本上没有被研究过。我们利用中子计算机断层扫描技术研究了两个盔头螈标本的虚拟颅腔和耳腔内膜。盔头螈类的神经感觉解剖结构显示出一些特征的混合，这些特征被认为是主龙形类的原始特征（大脑或嗅球没有扩张，脑化程度低，耳腔壳骨化程度低），也有一些被认为是更衍生的特征，包括中度的颅和桥脑弯曲以及高而垂直的骨迷路。内耳清晰地保留了椭圆形、次正交的管道和短而圆的前庭，以及异常扩大的侧管和独特的后管弯曲。重建的神经感觉解剖结构表明，盔头螈类对稍高的频率比它们的许多同时代的生物更敏感，可能反映了不同的体型大小，而上颌管的形态则表明简单、管状的状态是主龙形类的原始状态，并为关于变蜥形类的系统发育位置的讨论做出了贡献。这项研究代表了对任何基础真爬行动物的大脑和内耳的首次详细的断层扫描研究。这里描述的新数据表明，早期主龙类的神经解剖结构远比以前预期的更加复杂和多样化，并为进一步探索早期羊膜动物的古神经解剖学提供了动力。
