Germany, Italy, South Africa and North America (map)
Aetosaurus was derived from a sister to Ticinosuchus at the base of a clade that included the other aetosaur, Stagonolepis. Aetosaurs are widely considerd herbivores due to their small, leaf-like teeth.
Distinct from Ticinosuchus, the skull of Aetosaurus had an elongated naris behind an upturned pad of bone at the tip of the premaxilla. The rostrum was shorter. The antorbital fossa was round and the fenestra was half the diameter. The upper portion of the lateral temporal fenestra was closed off by the squamosal broadly contacting the postorbital. The maxilla was toothless anteriorly and it came to a point. The mandible included a very large fenestra.
The scapula was very small. The ilium included an anterior process. The pes was twice the size of the manus. If Brachychirotherium ichnites have been correctly matched to aetosaurs, they were digitigrade.