The extremely well-preserved tarsus of the tapejarid Tapejara sp. and the anhanguerid Anhanguera piscator (Pterosauria, Pterodactyloidea) are described and regarded as representative of the ankle structure of Pterosauria. The pterosaur ankle joint (PAJ) shows the following features: astragalus mediolaterally elongated forming a hemicylinder; proximal part of the astragalocalcaneal contact characterized by a ridge bordered on each side by a depression on the astragalus that has a perfect counterpart in the calcaneum, and distal part that is concavo-convex, with the concavity present in the astragalus; calcaneum extremely reduced not reaching the posterior portion of the tarsus; absence of an astragalar posterior groove, perforating foramen, calcaneal tuber, and astragalar ascending process; proximal tarsals fusing very early in ontogeny, forming a tibiotarsus.

The main movement between the crus and foot in the PAJ occurs between the proximal and distal tarsals as in the advanced mesotarsal-reversed joint (AM-R). The main differences from the latter are the lack of an ascending process and the extreme reduction of the calcaneum that make the PAJ unique. The absence of an astragalar groove and the reduction of the calcaneum reinforce the hypothesis that pterosaurs are basal ornithodirans and closely related to the Dinosauromorpha. As has been demonstrated by this and other studies, the ankle structure (a complex of characters) is phylogenetically informative and, in the light of characters from other parts of the animal's body, can contribute to a better understanding of archosaur relationships.