Overabundance of abelisaurid teeth in the Açu Formation (Albian-Cenomanian), Potiguar Basin, Northeastern Brazil: morphometric, cladistic and machine learning approaches

The Açu Formation (Albian-Cenomanian), Potiguar Basin, Northeastern Brazil, has yielded a great variety of fossil terrestrial vertebrates, with theropod dinosaurs standing out as one of the most diverse among them, and a large part of this diversity being known only by isolated teeth. In this study we assess 43 new isolated theropod teeth from this unit through phylogenetic, linear discriminant, and machine learning analyses. We developed an app, Dino Toothier, in which those models can be tested solely by uploading tooth measurements in a file, in order to facilitate and democratize the usage of the machine learning models. Our results revealed not only the first noasaurid record for the Açu Formation but also an unexpectedly high occurrence of abelisaurid specimens for a “Mid” Cretaceous unit in Western Gondwana, with four morphotypes related to different positions along the tooth row. We address this overabundance of abelisaurid teeth through different approaches, yet neither the high tooth replacement rates seen in this clade, the paleoenvironment of the Açu Formation, nor taphonomic preservation biases yield a proper explanation for it. We postulate that the lack of large sauropods in this unit might have hindered the presence of large theropods such as Carcharodontosauridae, favoring instead the predominance of the more generalist abelisaurids. Further studies on the taphonomy and paleoecology of the Açu Formation might reveal a more concrete reason for this abundance of abelisaurids.