Traversodontidae is a group of Triassic herbivorous/omnivorous cynodonts that represents the most diversified lineage within Cynognathia. In southern Brazil, a rich fossil record of late Middle/mid-Late Triassic cynodonts has been documented, with Exaeretodon riograndensis Abdala, Barberena, and Dornelles, 2002 and Siriusgnathus niemeyerorum Pavanatto et al., 2018 representing two abundant and well-documented traversodontids. The present study provides a comparative analysis of the morphology of the nasal cavity, nasal recesses, nasolacrimal duct, and maxillary canals of both species using computed tomography, highlighting the changes that occurred in parallel to the origin of mammaliaforms. Our results show that there were no ossified turbinals or a cribriform plate delimiting the posterior end of the nasal cavity, suggesting these structures were probably cartilaginous as in nonmammaliaform cynodonts. Both species show lateral ridges on the internal surface of the roof of the nasal cavity, but the median ridge for the attachment of a nasal septum is absent. Exaeretodon riograndensis and S. niemeyerorum show recesses on the dorsal region of the nasal cavity, which increase the volume of the nasal cavity, potentially enhancing the olfactory chamber and contributing to the sense of smell. On the lateral sides of the nasal cavity, the analyzed taxa show a well-developed maxillary recess. Although E. riograndensis and S. niemeyerorum have roughly similar nasal cavities, in the former taxon, the space between the left and right dorsal recesses of the nasal cavity is uniform along its entire extension, whereas this space narrows posteriorly in S. niemeyerorum. Finally, the nasolacrimal duct of S. niemeyerorum is more inclined anteroposteriorly than in E. riograndensis.

中文翻译：

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来自巴西上三叠纪的两种横齿兽类（Eucynodontia、Gomphodontia）的鼻腔

Traversodontidae 是一组三叠纪草食性/杂食性犬齿动物，代表犬齿兽纲中最多样化的谱系。在巴西南部，已经记录了中晚期/中晚期三叠世犬齿兽的丰富化石记录，其中鲇鱼Abdala、Barberena 和 Dornelles，2002 年和天狼星Pavanatto 等人，2018 年代表了两种丰富且有据可查的横齿动物。本研究使用计算机断层扫描对两种物种的鼻腔、鼻腔、鼻泪管和上颌管的形态进行了比较分析，突出了与哺乳动物起源平行的变化。我们的研究结果表明，鼻腔后端没有骨化的鼻甲或筛状板，这表明这些结构可能是软骨，如非哺乳类犬齿动物。两种物种都在鼻腔顶部的内表面显示侧脊，但没有用于连接鼻中隔的中脊。鲇鱼和S. niemeyerorum在鼻腔的背侧区域显示凹槽，这增加了鼻腔的体积，可能会增强嗅觉室并有助于嗅觉。在鼻腔的外侧，分析的分类群显示出发育良好的上颌隐窝。虽然E. riograndensis和S. niemeyerorum具有大致相似的鼻腔，在前分类群中，鼻腔的左右背隐之间的空间沿其整个延伸是均匀的，而该空间在后部变窄。S. niemeyerorum. 最后是鼻泪管S. niemeyerorum比前后更倾斜E. riograndensis.