''Aetosaurus'' is an extinct genus of pseudosuchian

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...

belonging to the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

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 North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. Additional specimens referred to ''Aetosaurus'' have been found in the

Chinle Group The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In Ne ...

of the southwestern United States, and the

Fleming Fjord Formation The Fleming Fjord Formation, alternatively called the Fleming Fjord Group is an Upper Triassic geological formation in the northeastern coast of Jameson Land, Greenland. It consists of terrestrial sediments and is known for its fossil content. De ...

of Greenland. Specimens of ''Aetosaurus'' occur in

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

-age strata.

Description

''Aetosaurus'' was a small, primitive aetosaur. Unlike more

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

aetosaurs such as '' Desmatosuchus'' or ''

Typothorax ''Typothorax'' is an extinct genus of typothoracine aetosaur that lived in the Late Triassic. Its remains have been found in North America. Two species are known: ''T. coccinarum'', the type species, and ''T. antiquum''. Description ''Typothor ...

'', the

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

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 Oscar Friedrich von Fraas (17 January 1824, in Lorch (Württemberg) – 22 November 1897, in Stuttgart) was a German clergyman, paleontologist and geologist. He was the father of geologist Eberhard Fraas (1862–1915). Biography He studied theol ...

. At the time, ''Aetosaurus'' was known from 22 articulated skeletons that had been found in the

Lower Stubensandtein Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Gloucestershire, England See also *Nizhny Nizhny (russian: Ни́жний; masculine), Nizhnyaya (; feminine), or Nizhneye (russian: Ни́� ...

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 The Calcare di Zorzino, Italian for Zorzino Limestone is a Late Triassic (Norian) geological formation in Italy (Cene and ).Cene Cene may refer to: People * Cene Marković, Serbian commander * Cene Prevc (born 1996), Slovenian ski jumper * Charles Le Cène (1647?–1703), French controversialist * Ilhami Çene (born 1909), Turkish fencer * Michel-Charles Le Cène (1684–17 ...

, 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 The New Haven Formation is a geologic formation in Connecticut. It preserves fossils dating back to the Triassic period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entert ...

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. Stegomus arcuatus Marsh

''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 pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

. 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 Aetosaurs Late Triassic reptiles of Africa Aetosaurs of North America Late Triassic pseudosuchians Prehistoric pseudosuchian genera