Abstract：
Investigating the evolutionary trajectory of synapsid sensory and cephalic systems is pivotal for understanding the emergence and diversification of mammals. Recent studies using CT-scanning to analyze the rostral foramina and maxillary canals morphology in fossilized specimens of probainognathian cynodonts have contributed to clarifying the homology and paleobiological interpretations of these structures. In the present work, μCT-scannings of three specimens of Riograndia guaibensis, an early Norian cynodont from southern Brazil, were analyzed and revealed an incomplete separation between the lacrimal and maxillary canals, with points of contact via non-ossified areas. While the maxillary canal exhibits a consistent morphological pattern with other Prozostrodontia, featuring three main branches along the lateral region of the snout, the rostral alveolar canal in Riograndia displays variability in the number of extra branches terminating in foramina on the lateral surface of the maxilla, showing differences among individuals and within the same skull. Additionally, pneumatization is observed in the anterior region of the skull, resembling similar structures found in reptiles and mammals. Through this pneumatization, certain branches originating from the maxillary canal extend to the canine alveolus. Further investigation is warranted to elucidate the functionality of this structure and its occurrence in other cynodont groups.
摘要：
研究突触感觉和头部系统的进化轨迹对于理解哺乳动物的出现和多样化至关重要。最近的研究使用CT扫描分析了profainognathiancynodonts化石标本中的头孔和上颌管形态，这有助于阐明这些结构的同源性和古生物学解释。在目前的工作中,Guaibensis的三个标本的μCT扫描，来自巴西南部的早期诺里安犬齿，分析并揭示了泪管和上颌管之间的不完全分离，通过非骨化区域的接触点。虽然上颌管表现出与其他Prozostrodontia一致的形态模式，沿着鼻子的横向区域有三个主要分支，Riograndia的头端牙槽管显示出上颌骨外表面孔处终止的额外分支数量的变异性，显示个体之间和同一头骨内的差异。此外,在颅骨前部观察到气化，类似于爬行动物和哺乳动物中发现的类似结构。通过这种气动，某些源自上颌管的分支延伸到犬牙槽。需要进一步研究以阐明该结构的功能及其在其他犬齿组中的出现。
