The defining feature of the aven group is feathers, not flight. This definition excludes anyother flying animal, such as the Pterosaurs a second archosaurs flying type.
Left: Pterosaurs .
.Bats are another species that is not apart of the this group. Both the Bats and the Pterosaurs have no feathers, for flight they both have membranous wings. Their are also other structural and evolutionary reason why these two groups are not apart of the aven group.