Recumbirostran ‘microsaurs’ are a clade of Palaeozoic tetrapods that possess numerous morphological adaptations for fossorial ecologies. Re‐study of many ‘microsaurs’ using tomographic methods has provided substantial new data on poorly known anatomy that informs their debated phylogenetic position. Recent studies have identified suites of features among recumbirostrans that place the group within crown Amniota, contrary to hypothesized positions on the amniote stem or the lissamphibian stem. Herein we describe the cranial anatomy of the early Permian gymnarthrid Euryodus dalyae through tomographic analysis of the holotype from South Grandfield, Oklahoma and new specimens from karst deposits near Richards Spur. The braincase of E. dalyae is composed of well‐ossified pleurosphenoids, orbitosphenoids that brace against the skull roof, and unpaired median ossifications. The otic capsules are well‐ossified, and the occiput is unconsolidated. Analysis of the mandibles, typically obscured in articulated specimens, reveals a second tooth row on the dentary, a feature previously unknown in ‘microsaurs’ that is reminiscent of the condition of the co‐occurring captorhinid Captorhinus aguti. The Richards Spur specimens share many of these features, including the second tooth row, but the neurocranium of the scanned specimen (OMNH 53519) differs from that of the holotype of E. dalyae (e.g. absence of unpaired median ossifications), and these specimens are referred to Euryodus sp. These data add to the growing neurocranial dataset of ‘microsaurs’, which is essential for iterative reevaluation of early tetrapod phylogeny. This discovery of multiple tooth rows in ‘microsaurs’ provides further support for the hypothesized close relationships between ‘microsaurs’ and reptiles.

中文翻译：

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对二叠纪recumbirostran'microsaur'Euryodus dalyae的颅骨进行的计算机断层扫描分析揭示了脑壳和下颌骨的新细节

Recumbirostran'microsaurs'是古生代四足动物的进化枝，具有多种形态上的适应生态特征。使用层析成像方法对许多“微型蜥蜴”进行的重新研究提供了关于鲜为人知的解剖学的大量新数据，这些数据为他们所争论的系统发生位置提供了信息。最近的研究已经确定了recumbirostrans中的一系列特征，这些特征将其放置在羊膜冠中，这与在羊膜茎或两栖两栖动物茎上的假定位置相反。在这里，我们通过对俄克拉荷马州南格兰德菲尔德的整体型和理查兹·斯普尔附近岩溶沉积的新标本进行断层成像分析，描述了二叠纪裸露夜蛾Euryodus dalyae的颅骨解剖。大肠埃希氏菌的脑箱由骨化丰富的胸膜蝶窦，支撑在颅骨顶上的眶蝶骨和不成对的中位骨化组成。耳囊骨化良好，枕骨未合并。对下颌骨（通常在关节标本中模糊不清）的分析显示了在牙齿上的第二排牙齿，这是以前在“微蜥蜴”中未知的特征，让人联想到同时发生的鹦鹉螺衣原体Captorhinus aguti的状况。理查兹马刺（Richards Spur）标本具有许多这样的特征，包括第二排牙齿，但是扫描标本的神经颅骨（OMNH 53519）与大肠埃希菌的整型标本不同（例如，不存在成对的中位骨化），这些标本是简称为Euryodussp。这些数据增加了不断增长的'microsaurs'的神经颅数据集，这对于早期四足动物系统发育的迭代重新评估至关重要。在“微刃龙”中发现了多排牙齿，这一发现为“微刃龙”和爬行动物之间的假设紧密关系提供了进一步的支持。