Abelisauroids from equatorial Brazil: New records from the Açu Formation (Cenomanian), Potiguar Basin, Northeast Brazil

Abstract

Despite the growing number of discoveries in South America, the theropod fossil record from equatorial Gondwana remains fragmentary, limiting our understanding of mid-Cretaceous faunal composition and biogeographic patterns. Here, we report a set of isolated theropod teeth from the Açu Formation (Cenomanian), Potiguar Basin, Northeast Brazil, and analyze them using an integrative framework that combines morphometrics and cladistic analysis. Three well-preserved specimens were taxonomically assigned to Abelisauridae and a likely Noasauridae, with the latter representing the first formal record of this group in the Potiguar Basin. While the phylogenetic analysis placed one tooth within Noasauridae and two within Abelisauridae, the morphometric analysis did not recover the noasaurid specimen within the expected morphospace for this clade, suggesting possible convergent dental morphologies or undersampling bias. We further present a reconstructed trophic web for the Açu Formation paleoecosystem, and compare its theropod assemblage to those of coeval mid-Cretaceous formations in Brazil and North Africa. The results reveal faunal affinities at both regional and intercontinental scales with other Cenomanian deposits, reinforcing the Cenomanian age of the Açu Formation. Furthermore, it underscores the role of this formation as a key area for understanding one of the final episodes of biotic interchange prior to the establishment of the South Atlantic as a biogeographic barrier.