Osteology of the small archosaur Aetosaurus from the upper triassic of Germany

Aetosaurus ferratus is the classic aetosaur, both because of its early discovery and the relatively vast original material. A detailed revision of all available material revealed various unknown features. In the Stubensandstein (Norian) of Germany, only the type species is present, with A. crassicauda being a junior synonym of the latter. Autapomorphies of Aetosaurus are the broad and short jugal, the anterior extension of the maxilla, the tiny size of the supratemporal fenestra, a series of three supraorbitals. Other unique features are the posteriorly constricted infratemporal fenestra, a short suture between postorbital and quadratojugal, dorsal paramedian plates that are transversely curved rather than flat or arched, and a total of 12 ventral plates per segment. The dentition of Aetosaurus is more similar to that of other aetosaurs than previously reported. A. ferratus differs further clearly from all other aetosaurs in the following potentially plesiomorphic features: the snout is shorter and lacks an edentulous anterior portion, the premaxilla does not expand to give a shovel, the paramedian plates are poorly differentiated, the limbs are gracile and the pubis has an abbreviated symphysis.