The stem lineage of Archosauria is populated by a diverse fossil record that remains notably understudied relative to the crown clade. Prominent among these specimens is a beautifully preserved skull of the early mid-Triassic rhynchosaur Mesosuchus browni [Iziko South African Museum (SAM) 6536], whose phylogenetic position has considerable influence on patterns of pan-archosaurian cranial evolution. We used high-resolution, micro-computed tomography to re-examine the anatomy of this specimen, building on previous studies that were either limited to external observations or restricted to the braincase. A digital segmentation of the cranial elements and primary neurovascular canals of SAM-PK-6536 allows for expanded character scoring and constitutes a foundation for future comparative insights. Our data support the phylogenetically oldest instance of a pneumatized maxilla in a pan-archosaur, bringing the record of antorbital pneumatization into closer alignment with that of the neurocranium. The nasal cavity and primary palate of Mesosuchus includes a complex septomaxilla, a novel element anterior to the vomer, and is likely to have supported a well-developed vomeronasal system. The evolution of this system is discussed in terms of both phylogenetic pattern and how the skeletal architecture of Mesosuchus and other fossils could inform the signalling dynamics that pattern the vomeronasal system during development.

中文翻译：

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基于计算机断层扫描的三叠纪中型鳄龙的颅骨解剖，并讨论爬行动物中的犁鼻系统及其深层历史


主龙类的茎谱系由多种化石记录组成，相对于冠类进化枝，这些化石记录的研究仍然明显不足。这些标本中最引人注目的是保存完好的三叠纪中期早期喙龙中鳄科布朗尼头骨[Iziko 南非博物馆 (SAM) 6536]，其系统发育位置对泛祖龙类颅骨进化模式具有相当大的影响。我们在之前仅限于外部观察或仅限于脑壳的研究的基础上，使用高分辨率微型计算机断层扫描重新检查了该标本的解剖结构。 SAM-PK-6536 的颅骨元件和主要神经血管管的数字分割可以扩大字符评分，并为未来的比较见解奠定基础。我们的数据支持系统发育上最古老的泛祖龙上颌骨气化的实例，使眶前气化的记录与神经颅骨的记录更加一致。中鳄的鼻腔和初级腭包括复杂的中隔上颌骨，这是犁骨前面的一个新元素，并且可能支持发育良好的犁鼻系统。该系统的进化从系统发育模式以及中鳄类和其他化石的骨骼结构如何影响发育过程中犁鼻系统模式的信号动力学方面进行了讨论。