Archosaurs are a group of reptiles that include dinosaurs, birds, and crocodilians. Some synonyms for archosaurs are diapsids, thecodonts, and saurischians. Diapsids are a group of reptiles that have two openings in their skulls behind their eyes, while thecodonts are a group of extinct reptiles that had teeth set in sockets. Saurischians are a group of dinosaurs that include the long-necked sauropods and carnivorous theropods. Other synonyms for archosaurs include avemetatarsalians, which are a group of dinosaurs and their bird descendants, and pseudosuchians, which are a group of reptiles that include crocodiles and their extinct relatives.