What are Archosaurs?
A great radiation of diapsid animals derived from small, lizard-like ancestors. In the past they were loosely termed thecodonts to distinguish them from acrodont lizards – they crudely resembled crocodilians in size and shape, and evidently appear in the record near the end of early Triassic time (Parrish). Many papers were published during the late 1980s and 1990s on the phylogeny of archosaurs of dinosaurian ancestry. The literature is summarized and/or cited in Sereno 1991 JVP Mem. 2), 1997, 1999; Benton 1999 (Phil. Trans. Roy. Soc. London B 354: 1423-1446), and Arcucci, Padian and Parrish in the “Encyclopedia of Dinosaurs,” (1997, Academic Press). These papers are not easy to read, because of the multiplication of similar-sounding clade names resulting from the rigorous application of cladistic methodology on diverse and poorly sampled organisms, and (for me) heavy emphasis on ankle bones that are geometrically difficult to visualize. Archosaurs were “defined” by Parrish as the las
Archosaurs, or “ruling lizards,” are an infraclass of reptile, one of three infraclasses of diapsid, or “two-arched,” reptiles. Diapsids are one of two classes of reptile, the other being anapsids, meaning “without arches.” The difference between diapsids and anapsids is that the latter have two holes on each side of their skulls, near the temples — made to decrease the weight of the skull — while anapsids only have holes for the eyes, like primates. Anapsids are represented today by turtles, tortoises, and terrapins, while diapsids make up all other reptiles, as well as birds. It is unknown whether living anapsids descended from anapsid or diapsid ancestors. Archosaurs, one type of diapsid, are the group most famously known for having dinosaurs as its members. Every dinosaur was an archosaur, from the leaf-eating Stegosaurus to the titanic Brachiosaurus and the deadly Tyrannosaurus rex. Pterosaurs, a type of flying reptile that ruled the skies before birds, were also archosaurs, as ar
