Page "Cretaceous–Paleogene extinction event" Paragraph 37

Only one family of pterosaurs, Azhdarchidae, was definitely present in the Maastrichtian, and it became extinct at the K – T boundary.

These large pterosaurs were the last representatives of a declining group that contained 10 families during the mid-Cretaceous.

Smaller pterosaurs became extinct prior to the Maastrichtian during a period that saw a decline in smaller animal species while larger species became more prevalent.

While this was occurring, modern birds were undergoing diversification and replacing archaic birds and pterosaur groups, possibly due to direct competition, or they simply filled empty niches.