Archosauria was one of the great turning points in vertebrate evolution. Emerging in the wake of the Permian-Triassic extinction, this clade gave rise to some of the most successful animals in Earth’s history. The archosaurs eventually split into two major branches: the crocodile line, called Pseudosuchia, and the bird line, called Avemetatarsalia. That bird line later produced pterosaurs, dinosaurs, and ultimately birds, while the crocodile line produced crocodilians and a wide variety of extinct relatives.

In other words, Archosauria sits above the split between the great reptilian dynasties of the Mesozoic. On one side were the crocodile-line archosaurs, many of which were once far more diverse than modern crocodiles suggest. On the other side were the bird-line archosaurs, which led to pterosaurs, dinosaurs, and the only dinosaurs still alive today: birds. So when we speak of Archosauria, we are speaking of the larger family branch that united crocodiles and birds long before their descendants came to dominate land, sea, and sky.