Aetosauria

Aetosaurs () are heavily armored reptiles belonging to the extinct order Aetosauria (; from Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs more closely related to crocodilians than to birds and non-avian dinosaurs. All known aetosaurs are restricted to the Late Triassic, and in some strata from this time they are among the most abundant fossil vertebrates. They have small heads, upturned snouts, erect limbs, and a body ornamented with four rows of plate-like osteoderms (bony scutes). Aetosaur fossil remains are known from Europe, North and South America, parts of Africa, and India. Since their armoured plates are often preserved and are abundant in certain localities, aetosaurs serve as important Late Triassic tetrapod index fossils. Many aetosaurs had wide geographic ranges, but their stratigraphic ranges were relatively short. Therefore, the presence of particular aetosaurs can accurately date a site in which they are found.

Nearly all aetosaurs (except for the genus Aetosauroides) belong to the family Stagonolepididae. Over 20 genera of aetosaurs have been described, and recently there has been controversy regarding the description of some of these genera. Two distinct subdivisions of aetosaurs are currently recognized, Desmatosuchia and Aetosaurinae, based primarily on broad differences in skull morphology. Osteoderms structure is generally one of the most useful traits for inferring aetosaur relations more precisely. Among other archosaurs, aetosaurs are most closely related to Revueltosaurus, a small reptile originally known from teeth mistakenly referred to herbivorous dinosaurs.