Were pterosaurs mammals?

No, they were orninthodiran archosaurs (or to put it simply, very closely related to dinosaurs) . They did have hairlike structures covering on their bodies, but this wasn't related to mammalian fur. read more

Small azhdarchoid pterosaurs were also present in the Campanian. This suggests that late Cretaceous pterosaur faunas were far more diverse than previously thought, possibly not even having declined significantly from the early Cretaceous. However, Piksi is no longer considered to be a pterosaur. read more

Despite having fur like a mammal, pterosaurs were definitely not mammals. Exactly what they were is up in the air--no one knows what they evolved from, but they seem to fit into the same group of reptiles as the dinosaurs. read more