Tainrakuasuchus is an extinct genus of poposauroid pseudosuchians known from the Middle Triassic Dinodontosaurus Assemblage Zone, part of the Santa Maria Supersequence of Brazil. The genus contains a single species, Tainrakuasuchus bellator, known from part of the lower jaw, five vertebrae, and a partial pelvic girdle.
Discovery and naming
In May 2025, Rodrigo T. Müller and a group of paleontologists from the Federal University of Santa Maria (UFSM) visited fossiliferous outcrops of the Pinheiros-Chiniquá Sequence of the Santa Maria Supersequence in Dona Francisca, Rio Grande do Sul, Brazil. These layers are referable to the Dinodontosaurus Assemblage Zone. At 'sector c' of the 'Posto site' (separated from sectors 'a' and 'b' by vegetation), the team discovered and collected a partial pseudosuchian skeleton. It was subsequently prepared and accessioned in the collections of the Centro de Apoio à Pesquisa Paleontológica da Quarta Colônia at the UFSM as specimen CAPPA/UFSM 0506. The specimen comprises the disarticulated remains of a single individual, including part of the left lower jaw (dentary, splenial, and four partial teeth), two cervical (neck) vertebrae, three dorsal (back) vertebrae, and the right ilium. In 2025, Müller and colleagues described Tainrakuasuchus bellator as a new genus and species of poposauroid pseudosuchian based on these fossil remains, establishing CAPPA/UFSM 0506 as the holotype (name-bearing) specimen. The generic name, Tainrakuasuchus, combines the Guarani words tain, meaning 'tooth', rakua, meaning 'pointed', with the Greek word soûkhos (suchus), derived from the Greek name of Sobek, the crocodile-headed deity of Ancient Egyptian myth. This is intended to morphology of the teeth of the lower jaw. The specific name, bellator, is a Latin word meaning 'warrior' or 'fighter', honoring the people of Rio Grande do Sul near the type locality and their endurance and resilience during severe flooding in the region happening near the time of the discovery of the holotype.
Description As a poposauroid, Tainrakuasuchus was likely a quadrupedal active predator with a long neck, slender jaws, and recurved, sharp teeth. The holotype has been estimated to belong to an animal around 2.4 metres (7.9 ft) long and 60 kilograms (130 lb) in weight.
Lower jaw The dentary bone of Tainrakuasuchus is described as slender, with a height to length ratio of 0.1, which resembles the closely related Mandasuchus from Africa while setting it apart from the tall dentaries seen in the ornithosuchid Dynamosuchus. The lateral face of the dentary prominently features a groove that begins about two-thirds down the bone's length and runs just below the toothrow until the elevated posterodorsal process. Similar structures have been identified in other early poposauroids, namely Mambawakale, while a series of foramina occupies the same position in Mandasuchus. Towards the back of the element, the dentary forms a posterodorsal process that rises above the toothrow and is split into a distinct upper and lower surface by a notch. The dentary is the only bone to participate in forming the mandibular symphysis, the part of the mandible where the two halves are sutured to each other, excluding the splenial as in most other poposauroids. The symphysis itself is short and only occupies the front-most part of the dentary, which contrasts with Mambawakale and ornithosuchids, which have a more substantially elongated symphysis. In contrast to the lateral surface of the dentary, the medial face of the splenial is generally described as plain, lacking foramina or grooves. The splenial begins anteriorly as a slender bone, but grows taller further back in the lower jaw. Like the dentary, the splenial forms a posterodorsal and ventrolateral process, the latter of which extends further back than the former. Here, the splenial does bear a ridge and accompanying groove. While only four actual teeth are preserved in the holotype specimen of Tainrakuasuchus, the dentary bone bears 17 dental alveoli, a count that is comparable to Mambawakale. Some more derived poposauroids bear fewer teeth or lost them altogether in the case of shuvosaurids. The preserved teeth show a blade-like morphology, being lateromedially compressed and recurved. While the teeth bear some features indicative of ziphodonty, the actual presence of serrations that define this tooth morphology cannot be determined due to the holotype's poor preservation.
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