A new alligatoroid from the Eocene of Vietnam highlights an extinct Asian clade independent from extant Alligator sinensis

During systematic paleontological surveys in the Na Duong Basin in North Vietnam between 2009 and 2012, well-preserved fossilized cranial and postcranial remains belonging to at least 29 individuals of a middle to late Eocene (late Bartonian to Priabonian age (39–35 Ma)) alligatoroid were collected. Comparative anatomical study of the material warrants the diagnosis of a new taxon, Orientalosuchus naduongensis gen. et sp. nov. The combined presence of an enlarged fifth maxillary tooth, prominent preorbital ridges, a large supraoccipital exposure on the skull table, a palatine-pterygoid suture anterior to the posterior end of the suborbital fenestra, and a pterygoid forming a neck surrounding the choana is unique to this species. Unlike previous phylogenies, our parsimony analysis recovers a monophyletic Late Cretaceous to Paleogene East to Southeastern Asian alligatoroid group, here named Orientalosuchina. The group includes Orientalosuchus naduongensis, Krabisuchus siamogallicus, Eoalligator chunyii, Jiangxisuchus nankangensis and Protoalligator huiningensis, all of them sharing a medial shifted quadrate foramen aerum. The recognition of this clade indicates at least two separate dispersal events from North America to Asia: one during the Late Cretaceous by Orientalosuchina and one by the ancestor of Alligator sinensis during the Paleogene or Neogene, the timing of which is poorly constrained.