Aetosaurus

''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. Additional specimens referred to ''Aetosaurus'' have been found in the Chinle Group of the southwestern United States, and the Fleming Fjord Formation of Greenland. Specimens of ''Aetosaurus'' occur in Norian-age strata.

Description

''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.

Behaviour

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.

Species

''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. Thirty years later, Fraas' son Eberhard described a second species, ''A. crassicauda'', also from Germany. ''A. crassicauda'' can be distinguished from ''A. ferratus'' by its larger size; ''A. crassicauda'' reached a maximum length of while ''A. ferratus'' reached a length of up to .

In addition to the Stubensandtein in Germany, ''A. ferratus'' is also known from the Calcare di Zorzino Formation in Cene, Italy. Specimens of ''Aetosaurus'' that have been recovered from the Fleming Fjord Formation in Greenland likely represent ''A. ferratus''. Some material from the Chinle Group in the southwestern United States probably represent ''A. ferratus'', as well.

In 1998, the genus ''Stegomus'' was synonymized with ''Aetosaurus''. In 1896, paleontologist Othniel Charles Marsh named ''Stegomus arcuatus'' from a cast of an aetosaur known as YPM 1647 from the New Haven Formation in the Fair Haven Heights neighborhood of New Haven. 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.


''A. arcuatus'' has paramedian scutes that are much wider than they are long, even in comparison to other species of ''Aetosaurus''. There is very little pitting on the surface of the scutes, although the porosity of the sandstone that makes up the casts has been mistaken for pitting. The tail narrows significantly past the base. The carapace is "waisted", meaning that it narrows in front of the pelvis.

The following cladogram is simplified after an analysis presented by Julia B. Desojo, Martin D. Ezcurra and Edio E. Kischlat (2012).

References

External links

''Aetosaurus''
in the Paleobiology Database

{{Taxonbar, from=Q3496825

Late Triassic reptiles of Europe
Aetosauria
Late Triassic reptiles of Africa
Aetosaurs of North America
Late Triassic pseudosuchians
Prehistoric pseudosuchian genera
Fossil taxa described in 1877
Fossil taxa described in 1887