First definitive record of a silesaurid (Avemetatarsalia: Dinosauriformes) from the Upper Triassic of India with new insights on its origin and dispersal

We report the first record of a silesaurid based on an incomplete skull and articulated mandible recovered from the Upper Triassic Tiki Formation of India. The new taxon, Rewasaurus minori gen et sp. nov., is distinguished from other silesaurids by a unique combination of craniodental features, including five premaxillary teeth, of which three anterior teeth are procumbent and cylindrical, upper dentition proportionally shorter than the lower dentition, and an anterior dentary tip positioned nearly in the same plane with the remainder alveolar margin. Additionally, two isolated partial femora were recovered from the same stratigraphic horizon though from a different fossil locality. Our comprehensive phylogenetic analyses based on two different data matrices recovered Rewasaurus as either having a polytomous relationship within the monophyletic clade Silesauridae or as an early-diverging sulcimentisaurian ornithischian having a sister-taxon relationship with Diodorus scytobrachion. Although the isolated femora are recovered as a silesaurid, the absence of overlapping skeletal elements precludes a confident assignment to Rewasaurus. A grasping feeding apparatus adapted for exploiting easily processed soft-bodied preys and plant material available in the Tiki floodplains is suggested for Rewasaurus. A time-calibrated phylogenetic tree suggests that the silesaurids underwent two major diversification phases and dispersed eastward and northward, with the former commencing considerably later. The notable scarcity of silesaurids and/or unambiguous ornithischians during the Rhaetian may be associated with global environmental perturbation across the Norian-Rhaetian Boundary.