Aetosaurus

Extinct genus of reptiles

Aetosaurus is an extinct genus of pseudosuchian reptile belonging to the order Aetosauria. It is generally considered to be the most primitive aetosaur. Three species are currently recognized: A. ferratus, the type species from Germany and Italy; A. crassicauda from Germany; and A. arcuatus from eastern North America. and the Fleming Fjord Formation of Greenland. Specimens of Aetosaurus occur in Norian age strata.

Aetosaurus was a small, primitive aetosaur. Unlike more derived aetosaurs such as Desmatosuchus or Typothorax, the carapace was long and narrow and lacked spikes. The paramedian scutes that covered the back (with one row on each side of the vertebrae) are considerably wider than they are long. The lateral scutes, which are beneath the paramedian and formed a row on either side of the animal, do not bear any spikes or other projections.

A 2023 study based on a fossil assemblage found in Kaltental, suggested that juvenile A. ferratus were likely gregarious animals, possibly to increase their chances of survival and to deter predators.

Aetosaurus was first named, with the description of the type species A. ferratus, in 1877 by German paleontologist Oscar Fraas. At the time, Aetosaurus was known from 22 articulated skeletons that had been found in the Lower Stubensandtein of Germany. Specimens of Aetosaurus that have been recovered from the Fleming Fjord Formation in Greenland likely represent A. ferratus. This cast consisted of the dorsal carapace. Several other casts preserving the surface of the skull and tail have been found in the Passaic Formation of Hunterdon and Somerset counties, New Jersey and an outcrop of the Lower Sanford Formation at the Triangle Brick Co. Quarry in Durham County, North Carolina. Stegomus arcuatus was found to be synonymous with Aetosaurus on the basis of several similarities, including a lack of spikes and a distinctive radial pattern of grooves on some of the caudal scutes. The tail narrows significantly past the base. The carapace is "waisted", meaning that it narrows in front of the pelvis.