Archosaurs (Archosauria) (meaning "leading reptiles" or "ruling reptiles") are a group of diapsid sauropsids/"reptiles" that includes modern birds and crocodilians and their common ancestor plus other grops that descend from that ancestor but are now extinct, like the pterosaurs.
Archosaur ancestors and reign
The Archosauromorpha is the group that includes archosaurs and their early relatives and ancestors. First archosauromorphs like Archosaurus appeared during Late Permian period when therapsids still ruled the Earth. After the Great Dying, the Permian extinction that made most therapsids to go extinct the archosauromorps were able to take new niches and they became more diverse and widespread during the Triassic. The archosaurs were even more successful than their ancestors and they soon ruled the Triassic world. The archosaur group Dinosauria, the dinosaurs became the rulers of the Earth for the next more than 100 million years.
Archosaur groups and characteristics
There is two main groups of archosaurs: Pseudosuchia (crocodiles and their relatives like rauisuchians and aetosaurs) and Avemetatarsalia (birds and their relatives like non-bird dinosaurs, pterosaurs and silesaurids)
Archosaur characteristics include:
- Teeth set in sockets
- Antorbital and mandibular fenestrae (openings in front of the eyes and in the jaw)
- A prominent ridge on the femur (femur = a bone closest to the center of the body)