The first Jurassic theropod from the Sergi Formation, Jatobá Basin, Brazil.

Abstract Archosaur osteological remains are abundant in Brazil, particularly from the Triassic and Cretaceous strata, but in Jurassic, the record is predominantly represented by ichnofossils. The Upper Jurassic archosaur records comprise the Paralligatoridae Batrachomimus pastosbonensis, from the Pastos Bons Formation (Parnaiba Basin), remains of Mesoeucrocodylia from the Alianca Formation (Jatoba Basin), and fragments of Dinosauria from the Brejo Santo Formation (Araripe Basin) with a dubious assignment. Here, we present the first undoubted Dinosauria record for the Jurassic of Brazil, MCT 2670-LE, a middle to distal caudal vertebra belonging to a theropod. MCT 2670-LE was excavated in the 60s by prof. Ignacio Machado Brito, being primarily attributed to strata of the Alianca Formation but the rock matrix involving the specimen allows us to correlate MCT 2670-LE to Sergi Formation, marking this specimen as the first archosaur record of this unit. The caudal vertebra is assigned to Carcharodontosauria based on the hourglass shaped centrum and the deep and narrow ventral groove. The specimen provides new data to the paleogeographic distribution of carcharodontosaurians before the South America-Africa break-up, as well as understanding the theropod faunal turnover of paleoenvironments during the Jurassic-Cretaceous transition in Brazil.