High Quality Content by WIKIPEDIA articles! Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most recent common ancestor of living birds and crocodilians. It includes two main clades: Crurotarsi, which includes crocodilians and their extinct relatives, and Avemetatarsalia, which includes pterosaurs and dinosaurs (of which birds are the only living clade).