Avemetatarsalia

Avemetatarsalia, meaning "bird-line archosaurs," is a clade within Archosauria defined as all archosaurs more closely related to birds than to crocodilians. In cladistic terms, it comprises the last common ancestor of birds and all of its descendants, and it contrasts with Pseudosuchia, the crocodile line.

Within Avemetatarsalia are several major lineages. Basal avemetatarsalians such as lagerpetids are among the earliest known members. The crown group Ornithodira includes Pterosauria (pterosaurs) and Dinosauria (dinosaurs), the latter including birds. In this framework, birds are the living dinosaurs and represent the only surviving members of Avemetatarsalia.

The fossil record places the origin of Avemetatarsalia in the Middle Triassic. Pterosaurs appear by the Late Triassic, and dinosaurs diversify through the Jurassic and Cretaceous. Birds arise from theropod dinosaurs in the Mesozoic and survive to the present as the only living dinosaurs. The precise content of Avemetatarsalia can vary with ongoing phylogenetic analyses, but the core concept remains that it is the bird-related, rather than crocodile-related, branch of archosaurs.