Osteology, taxonomy and phylogenetic affinities of a new pseudosuchian archosaur from the Middle Triassic of southern Brazil

Following the end-Permian mass extinction, archosaurs underwent rapid taxonomic and morphological diversification. While the avian lineage expanded into a broader range of ecological niches during the Late Triassic, the crocodilian lineage dominated ecosystems as early as the Middle Triassic, achieving an impressive range of morphological variation. Among the several pseudosuchian radiations that characterized the Middle Triassic, Poposauroidea stands out as one of the most enigmatic groups. From the Early to the Late Triassic, poposauroids evolved diverse body plans: some species developed dorsal ‘sails’, others became entirely edentulous, some adopted bipedal postures, and others occupied apex predator roles. In South America, the fossil record of Poposauroidea during the Middle Triassic is relatively scarce, being limited to Schultzsuchus loricatus, a relatively large-bodied predator known from fragmentary remains collected at a site within the Pinheiros–Chiniquá Sequence. In the present study, we describe Tainrakuasuchus bellator gen. et sp. nov., a new poposauroid from Brazil. The holotype was discovered at a locality known as the Posto Site, in the municipality of Dona Francisca (Pinheiros–Chiniquá Sequence; Middle Triassic). The specimen preserves a partial lower jaw, cervical and dorsal vertebrae, and an ilium. Tainrakuasuchus bellator gen. et sp. nov. is characterized by a slender mandible, ziphodont dentition and relatively elongated cervical vertebrae, representing a new medium-sized predatory archosaur. Phylogenetic analyses suggest affinities with Mandasuchus tanyauchen, a putative poposauroid from the Tanzanian Manda beds. The close relationship between these taxa, along with the strong faunal similarities between the respective geological units, reinforces the correlation between units and supports a Ladinian age. Finally, the discovery of Tainrakuasuchus bellator gen. et sp. nov. expands the known taxonomic diversity of the Dinodontosaurus Assemblage Zone and provides new insights into the key role played by pseudosuchians in the complex ecosystems of the Middle Triassic of south-western Gondwana.https://zoobank.org/urn:lsid:zoobank.org:pub:3E0FA946-F24A-474A-8AD7-D50B1A09116C