The origin of modern crocodylians is rooted in the Cretaceous, but their evolutionary history is obscure because the relationships of outgroups and transitional forms are poorly resolved. Here, we describe a new form, Varanosuchus sakonnakhonensis gen. nov., sp. nov., from the Early Cretaceous of Thailand that fills an evolutionary gap between Paralligatoridae and Atoposauridae, two derived neosuchian lineages with previously unsettled phylogenetic relationships. Three individuals, including a complete skull and associated postcranial remains, allow for a detailed description and phylogenetic analysis. The new taxon is distinguished from all other crocodylomorphs by an association of features, including a narrow altirostral morphology, a dorsal part of the postorbital with an anterolaterally facing edge, a depression on the posterolateral surface of the maxilla, and fully pterygoid-bound choanae. A phylogenetic analysis confirms the monophyly and taxonomic content of Atoposauridae and Paralligatoridae, and we underline the difficulty in reaching a robust definition of Eusuchia. Furthermore, we put forward further arguments related to the putative terrestrial ecology with semi-aquatic affinities of atoposaurids based on their altirostral snout morphology and osteoderm ornamentation.

中文翻译：

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来自泰国的新白垩纪新鳄亚目（Crocodylomorpha）连接了阿托龙科和拟鳄鱼科的进化史

现代鳄鱼类的起源可以追溯到白垩纪，但由于外群关系和过渡形式的关系尚未得到很好的解决，因此它们的进化历史并不明确。在这里，我们描述了一种新形式，Varanosuchus sakonnakhonensis gen。十一月，SP。11月，来自泰国早白垩世，它填补了Paralligatoridae和Atoposauridae之间的进化空白，这两个衍生的新鳄类谱系之前尚未确定系统发育关系。三个个体，包括完整的头骨和相关的颅后遗骸，可以进行详细的描述和系统发育分析。新分类单元与所有其他鳄鱼形类动物的区别在于其一系列特征的关联，包括狭窄的前吻部形态、具有前外侧边缘的眶后背侧部分、上颌骨后外侧表面上的凹陷以及完全由翼状体束缚的后鼻孔。系统发育分析证实了 Atoposauridae 和 Paralligatoridae 的单系和分类内容，我们强调了对真鳄亚目做出可靠定义的困难。此外，我们根据极托龙科的顶吻部形态和骨皮装饰，提出了与假定的陆地生态学相关的进一步论据，该生态学与极托龙科具有半水生亲缘关系。