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Ornithodira is a clade within the larger group Archosauria. Members of this clade are characterized by an upright gait and an S-curved neck, hence the name "Ornithodira" ("bird neck"). It contains two sub-clades, Dinosauromorpha and Pterosauromorpha.

Dinosauromorpha contains the lagosuchians, and their famous descendants, the dinosaurs, some of which (specifically theropods) are considered by most modern scientists to be ancestors of modern birds.

Pterosauromorpha contains Pterosauria, which are the famous flying reptiles, and perhaps the first vertebrates capable of true flight. 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.

Phylogeny

   ORNITHODIRA
        |--Pterosauromorpha
        |       |--Scleromochlus
        |       |--Sharovipteryx
        |       `Pterosauria
        `--Dinosauromorpha
               |--Lagerpeton
               `--Dinosauriformes
                     |-?Saltopus
                     |--Lagosuchus
                     |--Marasuchus
                     |--Pseudolagosuchus
                     |--Marasuchus
                     |--Lewisuchus
                     |--Eucoelophysis
                     |--Silesaurus
                     `--Dinosauria
                           |--Ornithischia
                           `--Saurischia
                                 `--Aves

• Archosaurs