Aetosaurus
Encyclopedia
Aetosaurus is an extinct genus
of archosaur
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 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.
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 scute
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.
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 150 centimetres (59.1 in) while A. ferratus reached a length of up to 90 centimetres (35.4 in).
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 Fairfield, Connecticut
. This cast consisted of the dorsal carapace. Several other casts are known that preserve the surface of the skull and tail, and have been found from the Passaic Formation
in Hunterdon
and Somerset counties
, New Jersey
and the Lower Sanford Formation within 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
.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
belonging to the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Aetosauria. It is generally considered to be the most primitive aetosaur. Three species are currently recognized: A. ferratus, the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
from Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
and Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
; A. crassicauda from Germany; and A. arcuatus from eastern North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Additional specimens referred to Aetosaurus have been found from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, the Chinle Group of the southwestern United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, and the Fleming Fjord Formation
Fleming Fjord Formation
The Fleming Fjord Formation is a geological formation in eastern Greenland.-Vertebrate fauna:...
of Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
. Specimens of Aetosaurus occur in Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...
-age strata.
Description
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
aetosaurs such as Desmatosuchus
Desmatosuchus
Desmatosuchus is an extinct genus of archosaur belonging to the Order Aetosauria. It was one of the largest aetosaurs, being long and about 1.50 m high. It lived during the Late Triassic in Texas....
or Typothorax
Typothorax
Typothorax is an extinct genus of 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:...
, the carapace was long and narrow and lacked spikes. The paramedian scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
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 Oskar Fraas. At the time, Aetosaurus was known from 22 articulated skeletons that were found in the Lower Stubensandtein of Germany. Thirty years later, Fraas' son EberhardEberhard Fraas
Eberhard Fraas was a German geologist and paleontologist. He worked as a curator at the Stuttgarter Naturaliensammlung and discovered the dinosaurs of the Tendaguru formation in then German East Africa ....
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 150 centimetres (59.1 in) while A. ferratus reached a length of up to 90 centimetres (35.4 in).
In addition to the Stubensandtein in Germany, A. ferratus is also known from the Calcare di Zorzino Formation in Cene
Cene
Cene is a comune in the Province of Bergamo in the Italian region of Lombardy, located about 60 km northeast of Milan and about 15 km northeast of Bergamo...
, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
. 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
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
named Stegomus arcuatus from a cast of an aetosaur known as YPM 1647 from the New Haven Formation in Fairfield, Connecticut
Fairfield, Connecticut
Fairfield is a town located in Fairfield County, Connecticut, United States. It is bordered by the towns of Bridgeport, Trumbull, Easton, Redding and Westport along the Gold Coast of Connecticut. As of the 2010 census, the town had a population of 59,404...
. This cast consisted of the dorsal carapace. Several other casts are known that preserve the surface of the skull and tail, and have been found from the Passaic Formation
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 Passaic, New Jersey, which is near where its type...
in Hunterdon
Hunterdon County, New Jersey
Hunterdon County is a county located in the western section of the U.S. state of New Jersey. As of the 2010 United States Census, the population was 128,349. It is part of the New York Metropolitan Area. Its county seat is Flemington....
and Somerset counties
Somerset County, New Jersey
Somerset County is a county located in the U.S. state of New Jersey. In 2010, the population was 323,444. It is part of the New York Metropolitan Area. Its county seat is Somerville....
, New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
and the Lower Sanford Formation within the Triangle Brick Co. Quarry in Durham County, North Carolina
Durham County, North Carolina
-Demographics:As of the census of 2000, there were 223,314 people, 89,015 households, and 54,032 families residing in the county. The population density was 769 people per square mile . There were 95,452 housing units at an average density of 329 per square mile...
. 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
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
.
External links
- Aetosaurus in the Paleobiology DatabasePaleobiology Database' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...