Aetosaurus

***Aetosaurus*** is an extinct genus of archosaur reptile belonging to the aetosaur order. It is generally considered to be the most primitive aetosaur. Three species are currently recognized: *A. ferratus*, the type species from Germany and Italy;[2] *A. crassicauda* from Germany; and *A. arcuatus* from eastern North America. Additional specimens referred to *Aetosaurus* have been found from South Africa, 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 paramedians and formed a row on either side of the animal, do not bear any spikes or other projections.

## 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 Template:Convert while *A. ferratus* reached a length of up to Template:Convert.

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).

## Dinosaur Field Guide Description

Aetosaurus (eagle lizard") was a plant-eater built low to the ground. It had legs that sprawled out to the side and heavy armor protecting its back. Aetosaurus had a pig-like snout, which it might have used to sniff out tasty plants. Its hands, however, do not seem to have been specialized for digging. The armor on its back was jointed so that it could roll itself up to protect it’s belly, like a modern armadillo, During the Late Triassic, the armored dinosaurs had not yet evolved. Perhaps this was because the aetosaurs were already present and there wasn't a place in the environment for a new group of armored plant-eating reptiles. At the end of the Late Triassic, there was a series of extinctions among the animals and plants on land and in the sea. These extinctions may have been caused by volcanic eruptions, though other factors may have helped. Whatever the cause, aetosaurs (and many other groups) died out at the end of the Late Triassic.

## Fun Facts

Aetosaurs were found in North America, South America, and Europe.

## Trivia

The first aetosaur fossils discovered were of their armor. Because these plates resembled the armor of extinct fish that were found in similar rocks, paleontologist thought they had found a new kind of extinct fish. It wasn't until an setosaur's bones were discovered that they realused they had found a new kind of reptile,

## References

1. ↑ http://www.wordinfo.info/words/index/info/view\_unit/2727/
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