archosaursare

The term archosaursare appears to be a concatenation rather than a distinct term. The intended topic is archosaurs, also known as Archosauria, a major clade of diapsid reptiles that first appeared in the late Permian period, about 250 million years ago. Archosaurs form the crown group that includes the living birds and crocodilians, as well as numerous extinct lineages such as non-avian dinosaurs and pterosaurs.

The two principal lineages within Archosauria are the avemetatarsalians (bird-line archosaurs) and the pseudosuchians (crocodile-line archosaurs). Avemetatarsalians gave rise to dinosaurs and pterosaurs; birds are the living descendants of theropod dinosaurs. Pseudosuchians include the ancestors of modern crocodilians and many extinct crocodile-like forms. This split reflects deep differences in anatomy, locomotion, and ecology that persisted for hundreds of millions of years.

A characteristic feature of many archosaurs is an open skull with an antorbital fenestra—a hollow opening in the skull in front of the eye socket. Many archosaurs also show differences in jaw and postcranial anatomy that supported their diverse lifestyles, from fast-running predators to aquatic or semi-aquatic forms. Over time, Archosauria underwent several major radiations, especially after the Permian–Triassic extinction, leading to a wide range of sizes and ecologies.

Today, archosaurs are represented by two living lineages: birds and crocodilians, which together harbor considerable ecological diversity. The fossil record of archosaurs documents a long and influential chapter in vertebrate evolution, illustrating the rise and fall of many lineages and the ultimate survival of the bird–crocodile axis.