The oldest abelisaurid record from Brazil and the palaeobiogeographic significance of mid-Cretaceous dinosaur assemblages from northern South America

Knowledge on the faunal record from the mid-Cretaceous of northern South America has come mainly from the Araripe Basin, northeastern Brazil. However, the Cenomanian Alcântara Formation of the São Luís-Grajaú Basin has recently increased in paleontological importance. Regarding their non-avian dinosaur diversity, the formation has yielded body and trace fossils of spinosaurid, carcharodontosaurid, noasaurid, and maniraptoran theropods, rebbachisaurid and titanosaur sauropods, and possible ornithopods. Here, we report the first unequivocal record of an abelisaurid theropod from the Alcântara Formation, consisting of two shed tooth crowns from the Baronesa Beach locality. They are the oldest occurrence of Abelisauridae from Brazil. With this new record, the non-avian dinosaur assemblage from the Alcântara Formation is most similar to that of the Kem Kem Beds, as suggested by previous works and supported here by similarity analyses of mid-Cretaceous dinosaur-bearing units. Our results also indicate a faunal heterogeneity within northern South America, previously overlooked by studies of this whole landmass as a single sampling unit. We also suggest future approaches treat the dinosaur assemblage from each fossil site or formation as a particular sample unit instead of combining geographically and temporally distinct records.