Ornithodira is a division of the Archosauromorpha (and perhaps Archosauria) clade. Members of this clade were characterized by an upright gait and an S-curved neck, hence the name "Ornithodira" ("bird neck"). It contains two superorders, Dinosauromorpha and Pterosauromorpha.

Dinosauromorpha contains the lagosuchians, and their famous descendants, the dinosaurs, which are believed to be the ancestors of modern birds.

Pterosauromorpha contains Pterosauria, which are the famous flying reptiles, and perhaps the first vertebrates capable of true flight. It should be noted that most researchers think pterosaurians had neither an S-curved neck, nor an upright gait. However, the Ornithodira clade is still valid because it is defined as the last common ancestor of the dinosaurs and the pterosaurs, and all its descendants. Exactly which species are included in this definition is still not very clear.