This split corresponds to the subgroup Ornithodira (Ancient Greek ὄρνις (órnis, “bird”) + δειρή (deirḗ, “throat”), defined as the last common ancestor of dinosaurs and pterosaurs, and all of its descendants.

Probable non-dinosaur dinosauromorphs include the diverse and widespread silesaurids, as well as more controversial and fragmentary taxa such as Marasuchus, Lagosuchus, Nyasasaurus, and Saltopus.

Probably as a result of this change, the common ancestor of the avemetatarsalians had an upright, bipedal posture, with their legs extending vertically, similar to that of mammals.

Their wings are formed by a membrane of skin, muscle, and other tissues stretching from the ankles to a dramatically lengthened fourth finger.

Bird-line archosaurs appear in the fossil record by the Anisian stage of the Middle Triassic about 245 million years ago, represented by the dinosauriform Asilisaurus.

However, Early Triassic fossil footprints reported in 2010 from the Świętokrzyskie (Holy Cross) Mountains of Poland may belong to a more primitive dinosauromorph.

[12] In 1986, Jacques Gauthier defined the name Ornithosuchia (previously coined by Huene) for a branch-based clade including all archosaurs more closely related to birds than to crocodiles.

[6] In the same year, Gauthier also coined and defined a slightly more restrictive node-based clade, Ornithodira, containing the last common ancestor of the dinosaurs and the pterosaurs and all of its descendants.

Gauthier referred Aves, all other Dinosauria, all Pterosauria, and a variety of Triassic archosaurs, including Lagosuchus and Scleromochlus, to this group.

[14] In a 2005 review of archosaur classification, Phil Senter attempted to resolve this conflicting set of terminology by applying strict priority to names based on when and how they were first defined.

[7][4] Bennett (2020) argued that Scleromochlus, a genus historically considered a relative of ornithodirans or even a basal pterosauromorph, was instead a non-archosaur archosauriform (possibly a doswelliid).

The results of the phylogenetic analyses of Nesbit et al. (2023) are shown in the cladogram below:[19] Pseudosuchia Mambachiton Aphanosauria Lagerpetidae Pterosauria Lagosuchus Dinosauria