Ornithurae

Ornithurae (meaning "bird tails") is the group of avialans that includes the common ancestor of ichthyornithines, hesperornithines and neornithines and all of its descendants. Ornithurans are usually seen as different from more primitive avialans, such as enantiornithines, due to having more avian beaks, mostly clawless wings and reduced tails with a defined pygostyle, that often gives them a much more aerodynamic shape.