The Pirabas Formation (Oligo-Miocene) is a geological unit that Á stands out for its great diversity and richness of fossiliferous content, located mainly in northwestern Pará. This formation is recognized both for the diversity of the paleoflora and the paleofauna, which consists of both invertebrates and vertebrates. The latter constitute a diverse group, represented by sharks, rays, bony fish, sirenians, birds, crocodilians and chelonians. Due to the great faunistic diversity of the Pirabas Formation, the detailed knowledge of the fossil groups, as well as of their environmental context, is essential to help the studies of paleoenvironmental reconstitution, biostratigraphy and to elucidate paleobiogeographic problems, mainly because the flora and fauna recorded in the formation contain taxonomic groups whose representatives/descendants are still present in modern ecosystems. In order to contribute to the knowledge of the vertebrate fauna of the Pirabas Formation, a detailed study of the chelonian material from the formation was carried out, aiming to refine the taxonomic status of the group and to provide paleoecological and paleobiogeographic data on the fossil chelonians of this formation. The material studied is deposited in the paleontology collection of the Museu Paraense Emílio Goeldi (MPEG), and is represented by 90 complete and incomplete carapace and plastron plates from 52 specimens. The plates were analyzed for general morphology and their length, width and thickness measurements. Preliminary results reveal that the specimens differ greatly in the characteristics analyzed, indicating the presence of at least two distinct taxa in the formation
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