Extending the Geographic Range of Pterosaurs in the Araripe Basin: First Record from the Romualdo Formation (Araripe Basin) in Piauí, Brazil

The Araripe Basin in northeastern Brazil is a key site for Cretaceous pterosaur fossils from Gondwanan deposits. Most discoveries are concentrated in its northern portion, particularly in Ceará state, within the Crato and Romualdo formations. In contrast, records from the southern part of the basin, especially in Piauí and Pernambuco, remain scarce. This study reports the first pterosaur fossils from the Romualdo Formation in Piauí, represented by two three-dimensionally preserved, incomplete wing phalanges: LPP Pt-002 and LPP Pt-005. Osteohistological analysis of LPP Pt-002 reveals a cortex composed of parallel-fibered bone, with endosteal lamellae and an external fundamental system (EFS), indicating skeletal maturity. In contrast, LPP Pt-005 displays a cortex of woven bone and circumferential lamellae, with a highly vascularized matrix and no evidence of EFS or endosteal lamellae, suggesting a post-juvenile stage. These differences indicate that the specimens represent distinct individuals. Although the reasons for the lower abundance of pterosaur remains in the southern Araripe Basin are unclear, these findings expand the known geographic range of Pterosauria within the basin and underscore the importance of further paleontological exploration in underrepresented regions to better understand pterosaur diversity and distribution during the Cretaceous.

Key words
Araripe Basin; Cretaceous; Piauí; Pterosauria; Romualdo Formation; Osteohistology