Ornithodira's a clade within the larger group Archosauria. In 1986 Jacques Gauthier coined the name for a node clade, containing the last common ancestor of the dinosaurs and the pterosaurs and all of its descendants. In 1991 Paul Sereno was the first to give a formal definition, that explicitly included Scleromochlus and thus potentially was a larger group than Ornithodira sensu Gauthier. In 1999 Michael Benton concluded that Scleromochlus was indeed outside of Ornithodira sensu Gauthier; that… (More on Ornithodira)