First leptosuchomorph phytosaur (Diapsida, Archosauria) from the Upper Triassic of India reveals new insights on biostratigraphy and palaeobiogeography

The Upper Triassic of India preserves a rich record of phytosaurs, encompassing both early- and later-diverging parasuchids. We report here a new leptosuchomorph phytosaur from the Maleri Formation of Pranhita-Godavari basin. The new taxon, represented by an incomplete cranium, is characterised by a tripartite upper jaw dentition, narial crest, naris-antorbital fenestra overlap, partially depressed parietal–squamosal bar, dorsoventrally high posterior process of squamosal, posteroventrally directed opisthotic process, subsidiary opisthotic process of the squamosal, a pair of fossae on the parietal that meet along a raised median wall, and a deep pit on the parietal–supraoccipital shelf. Phylogenetic analysis places the new taxon, Primisuchus gen. et sp. nov., among the later-diverging leptosuchomorphs, as sister taxon to Mystriosuchini. This discovery represents the first definitive record of a non-Mystriosuchini leptosuchomorph from Gondwana, defining the lower boundary of the Upper Maleri–Lower Dharmaram Assemblage Eubiozone at the base of the Adamanian holochron. Biogeographic considerations suggest a Middle Triassic origin of Phytosauria with early parasuchids becoming cosmopolitan during the late Carnian, coincident with the terminal phase of the Carnian Pluvial Event. A climate-induced faunal turnover straddling the Carnian–Norian boundary led to the disappearance of non-leptosuchomorphs. The early Norian saw endemic radiations followed by renewed intercontinental dispersal of leptosuchomorphs during the middle–late Norian.