Ornithodira is 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 year he defined a stem clade Avemetatarsalia for all Archosauria sensu Gauthier (Benton's own Avesuchia) that were closer to dinosaurs than to Crocodylia. In 2004 Benton gave a formal definition of Ornithodira sensu Gauthier. In 2005 Sereno stated the opinion that Ornithodira was not a useful con