''Aetosaurus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

pseudosuchian Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Prior to ...

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 Aetosaurs () are heavily armored reptiles belonging to the extinct order Aetosauria (; from Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs m ...

. It is generally considered to be the most primitive aetosaur. Three species are currently recognized: ''A. ferratus'', the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

from

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

and

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...

; ''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 of the southwestern

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

, 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 ...

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...

. 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 ''Desmatosuchus'' (, from Greek δεσμός ''desmos'' 'link' + σοῦχος ''soûkhos'' 'crocodile') is an extinct genus of archosaur belonging to the Order Aetosauria. It lived during the Late Triassic. Description ''Desmatosuchus'' was a ...

'' or '' Typothorax'', 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

scute A scute or scutum (Latin: ''scutum''; plural: ''scuta'' "shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterior po ...

s 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 Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

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 Eberhard is an old Germanic name meaning the strength or courage of a wild boar. People First name *Eberhard of Friuli (815–866), Duke and key figure in the Carolingian Empire *Eberhard of Béthune (died 1212), Flemish grammarian *Eberhard I, Du ...

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 Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among h ...

named ''Stegomus arcuatus'' from a

cast Cast may refer to: Music * Cast (band), an English alternative rock band * Cast (Mexican band), a progressive Mexican rock band * The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis * ''Cast'', a 2012 album by Trespassers William * ...

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 The Passaic Formation is a mapped bedrock unit in Pennsylvania, New Jersey, and New York. It was previously known as the Brunswick Formation since it was first described in the vicinity of New Brunswick, New Jersey. It is now named for the city of ...

of Hunterdon and Somerset counties,

New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...

and an outcrop of the Lower Sanford Formation at the Triangle Brick Co. Quarry in

Durham County, North Carolina Durham County is a county located in the U.S. state of North Carolina. As of the 2020 census, the population was 324,833, making it the sixth-most populous county in North Carolina. Its county seat is Durham, which is the only incorporated mu ...

. ''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 A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

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 The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database (PBDB) originated in the NCEAS-funded Phanerozoic Marine Pale ...

{{Taxonbar, from=Q3496825 Late Triassic reptiles of Europe Aetosaurs Late Triassic reptiles of Africa Aetosaurs of North America Late Triassic pseudosuchians Prehistoric pseudosuchian genera