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Aetosaur

Overview

The aetosaurs (literally "Eagle Lizards") are an extinct clade

Clade

A clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.The term "monophyletic group" is used in this article...

of heavily armoured, medium- to large-sized Late Triassic

Triassic

The Triassic is a geologic period and system that extends from about 251 to 199 Ma . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

herbivorous

Herbivore

A herbivore is an animal that is adapted to eat plants and not meat.Herbivory is a form of predation in which an organism consumes principally autotrophs such as plants, algae and photosynthesizing bacteria....

archosaur

Archosaur

Archosaurs are a group of diapsid amniotes represented by modern birds and crocodilians. This group also includes extinct non-avian dinosaurs, pterosaurs and relatives of crocodiles....

s. Two distinct subdivisions of aeotosaurs are currently recognized, the Desmatosuchinae and the Aetosaurinae, based primarily on differences in the morphology

Morphology (biology)

In biology morphology is the form, structure and configuration of an organism.This includes aspects of the outward appearance as well as the form and structure of the internal parts like bones and organs...

of the bony scutes of the two groups (Parker et al., 2008; p. 692).

The head is small relative to the large body, and quite distinctive in shape, being flat and blunt at the front, like the snout of a pig

Pig

Pigs are a genus of even-toed ungulates within the family Suidae. The name hog most commonly refers to the domestic pig in everyday parlance, but technically encompasses several distinct species, including the wild boar...

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Encyclopedia

The aetosaurs (literally "Eagle Lizards") are an extinct clade

Clade

of heavily armoured, medium- to large-sized Late Triassic

Triassic

herbivorous

Herbivore

archosaur

Archosaur

Archosaurs are a group of diapsid amniotes represented by modern birds and crocodilians. This group also includes extinct non-avian dinosaurs, pterosaurs and relatives of crocodiles....

s. Two distinct subdivisions of aeotosaurs are currently recognized, the Desmatosuchinae and the Aetosaurinae, based primarily on differences in the morphology

Morphology (biology)

Pig

. The chisel-shaped teeth are small and leaf-like, indicating a probable herbivorous diet (Carroll, 1988; p.273), although peg-like teeth and a keratin

Keratin

Keratins are a family of fibrous structural proteins; tough and insoluble, they form the hard but un-mineralized structures found in reptiles, birds, amphibians, and mammals...

ous snout have been described in at least one species as possible adaptations for feeding on colonial insects (Small, 2002). Study of the braincase indicates that aetosaurs are actually closely related to crocodylomorphs

Crocodylomorpha

The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.During Mesozoic and early Tertiary times the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were...

(Gower & Walker, 2002).

As with the Rauisuchia

Rauisuchia

Rauisuchia are a poorly known assemblage of predatory and mostly large Triassic archosaurs. Originally it was believed that they were related to erythrosuchids, but it is now known that they are crurotarsans. Three families are generally recognised: Prestosuchidae, Rauisuchidae, and...

, they had a "pillar-erect" erect limb posture (Heckert & Lucas, 2002). The feet, however, resemble those of the phytosaur

Phytosaur

Phytosaurs - family Phytosauridae or Parasuchidae - were a group of large semi-aquatic predatory archosaurs that flourished during the Late Triassic period...

s in the retention of primitive characteristics (Carroll 1988 p.273). In other respects, they have a typically crurotarsan

Crurotarsi

The Crurotarsi are a group of archosaurs, whose name was erected as a node-based clade by Paul Sereno in 1991 to supplant the old term Pseudosuchia. Crurotarsi are by definition the sister group of the Avemetatarsalia .- Description :Crurotarsi is one of the two primary daughter clades of the...

(rauisuchia

Rauisuchia

n or crocodylian) body and large powerful tail. Although the fore-limbs are much smaller than the hind limbs, all aetosaurs were quadrupeds.

These animals were very heavily armored (most certainly as a defense against predators), with large quadrangular, interlocking bony plates, or osteoderms, protecting the back and sides, belly, and tail (Carroll, 1988 p.273). In life, these plates were probably covered in horn (Colbert, 1969 p.159).

Primitive genera, like the widespread 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...

genus Aetosaurus
Aetosaurus
Aetosaurus is an extinct genus of archosaur reptile belonging to the aetosaur order. Remains of Aetosaurus were found in South Africa....

and the Carnian

Carnian

The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228,7 till 216,5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...

Coahomasuchus
Coahomasuchus
Coahomasuchus is an extinct genus of aetosaurine stagonolepidid. Fossils have been found from the Dockum Group in western Texas and date back to the Otischalkian faunachron of the Late Triassic. It was small for an aetosaur, being less than 1 meter long...

(Heckert & Lucas, 1999), tended to be small, about a meter in length. However more advanced forms were larger - about 3 meters in length - with taxa some, such as Typothorax
Typothorax
Typothorax is a genus of aetosaur that lived in the Late Triassic. Its remains have been found in North America.Even though Typothorax was one of the first vertebrate fossils named from the Chinle Formation, most of the skull has not yet been described.-Sources:* King of the Crocodylians: The...

and Paratypothorax, possessing broad turtle-like bodies, and others, like 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....

, a narrow-bodied genus up to 5 meters long, equipped with large spines over the shoulders, which added to the animal's defensive armament.

At least some aetosaurs built nests and protected their eggs. In 1996, geologist Stephen Hasiotis discovered 220 million-year-old, fossilized, bowl-like nests in Arizona's Petrified Forest, in part of the Chinle Formation

Chinle Formation

The Chinle is a geologic formation that is spread across the U.S. states of northern Arizona, Nevada, Utah, western New Mexico, and western Colorado. The Chinle is controversially considered to be synonymous to the Dockum Group in eastern Colorado, eastern New Mexico, southwestern Kansas, the...

. The oldest such nests that have been found belonged to phytosaur

Phytosaur

Phytosaurs - family Phytosauridae or Parasuchidae - were a group of large semi-aquatic predatory archosaurs that flourished during the Late Triassic period...

s and aetosaurs. The nests are compacted and appear very similar to the nests of the modern day crocodile

Crocodile

A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all members of the order Crocodilia: i.e...

s who guard their nests. The nests were holes dug in the sand in the bank of an ancient river.

Aetosaur fossil remains are known from Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

, Germany

Germany

Germany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium,...

, Greenland

Greenland

Greenland is an autonomous constituent country within the Kingdom of Denmark located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago...

, the southwest and the eastern United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, Argentina

Argentina

Argentina, officially the Argentine Republic , is the second largest country in South America, constituted as a federation of 23 provinces and an autonomous city, Buenos Aires. It is the eighth largest country in the world by land area and the largest among Spanish-speaking nations, though Mexico,...

, and Madagascar

Madagascar

Madagascar, or Republic of Madagascar , is an island nation in the Indian Ocean off the southeastern coast of Africa. The main island, also called Madagascar, is the fourth-largest island in the world, and is home to 5% of the world's plant and animal species, of which more than 80% are endemic to...

. Since their armoured plates are often preserved, and as they often have a wide geographic distribution, but a relatively short stratigraphic range, aetosaurs can serve, like phytosaurs, as important Late Triassic

Late Triassic

The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...

tetrapod index fossil

Index fossil

Index fossils are fossils used to define and identify geologic periods . They work on the premise that, although different sediments may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil...

s (Heckert & Lucas, 2002; Lucas, 1998).

List

Genus	Status	Age	Location	Description
†Acaenasuchus Acaenasuchus Acaenasuchus is an extinct, actively mobile herbivorous member of the genus aetosaur, endemic to what would be North America during the Triassic living from 228—216.5 mya, existing for approximately ....	Valid.	Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age... .	North America North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific...	An herbivore that was protected by spikes and armor plating, Acaenasuchus Acaenasuchus Acaenasuchus is an extinct, actively mobile herbivorous member of the genus aetosaur, endemic to what would be North America during the Triassic living from 228—216.5 mya, existing for approximately .... was a stagonolepid aetosaur Aetosaur The aetosaurs are an extinct clade of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. Two distinct subdivisions of aeotosaurs are currently recognized, the Desmatosuchinae and the Aetosaurinae, based primarily on differences in the morphology of the bony scutes of... .
†Acompsosaurus Acompsosaurus An aetosaur whose name means "sturdy lizard." It may be a junior synonym of Stagonolepis....	Nomen dubium Nomen dubium In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application. Note that in the ICBN and ICNB the phrase "nomen dubium" has no status In zoological nomenclature, a nomen dubium (Latin for "doubtful name", plural nomina dubia) is a scientific name that... .	Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age... .	North America North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific... .	An aetosaur whose name means "sturdy lizard." It may be a junior synonym of Stagonolepis Stagonolepis Stagonolepis is an extinct genus of archosaur reptile belonging to the aetosaur order. It was about long.An aetosaur, Stagonolepis was a quadrupedal animal covered in thick armoured scales that ran down the length of the its body. A slow-moving browser, it would have used this heavy body armour to... .
† Aetosauroides Aetosauroides Aetosauroides is an extinct genus of reptile of the Late Triassic of South America. It was an aetosaur....	Junior synonym.	N/A.	N/A.	Junior synonym of Stagonolepis Stagonolepis Stagonolepis is an extinct genus of archosaur reptile belonging to the aetosaur order. It was about long.An aetosaur, Stagonolepis was a quadrupedal animal covered in thick armoured scales that ran down the length of the its body. A slow-moving browser, it would have used this heavy body armour to... .
†Aetosaurus Aetosaurus Aetosaurus is an extinct genus of archosaur reptile belonging to the aetosaur order. Remains of Aetosaurus were found in South Africa....	Valid.	Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age... .	Africa Africa Africa is the world's second-largest and second most-populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area. With a billion people in 61 territories, it accounts for about 14.8% of the... . Europe Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains , and the Black Sea to the southeast... . North America North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific... .	A small (1.5 m, 5 ft long) but robustly armored herbivore with an upturned snout. Several species have been described. It had a wide range, skeletal remains have been discovered in both Europe and North America. Fossiliized scutes have been discovered in Madagascar as well.
†Argentinosuchus	Junior synonym.	N/A.	N/A.	Junior synonym of Stagonolepis Stagonolepis Stagonolepis is an extinct genus of archosaur reptile belonging to the aetosaur order. It was about long.An aetosaur, Stagonolepis was a quadrupedal animal covered in thick armoured scales that ran down the length of the its body. A slow-moving browser, it would have used this heavy body armour to...
†Calyptosuchus Calyptosuchus Calyptosuchus is an extinct genus of crurotarsan from the Late Triassic of North America. As an aetosaur, it was heavily armored and had a pig-like snout used to uproot plants. The genus might be a junior synonym of Stagonolepis....	Junior synonym.	N/A	N/A	Junior synonym of Stagonolepis Stagonolepis Stagonolepis is an extinct genus of archosaur reptile belonging to the aetosaur order. It was about long.An aetosaur, Stagonolepis was a quadrupedal animal covered in thick armoured scales that ran down the length of the its body. A slow-moving browser, it would have used this heavy body armour to... .
†Chilenosuchus Chilenosuchus Chilenosuchus is an extinct genus of aetosaur. Fossils have been found from the Antofagasta Region in northern Chile. The presence of Chilenoasaurus in the beds that it was found in conflicts with the inferred age of the strata...	Valid.
†Coahomasuchus Coahomasuchus Coahomasuchus is an extinct genus of aetosaurine stagonolepidid. Fossils have been found from the Dockum Group in western Texas and date back to the Otischalkian faunachron of the Late Triassic. It was small for an aetosaur, being less than 1 meter long...	Valid.
†Desamatosuchus	Lapsus calami.			— lapsus calami of 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....
†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....	Valid.	Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age... .	North America North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific... .
†Heliocanthus Heliocanthus Heliocanthus is the name of a problematic genus of aetosaur that has underwent many taxonomic revisions in recent years, and may prove to be synonymous with Rioarribasuchus...	Junior synonym.			Possible junior synonym of Rioarribasuchus
†Longosuchus Longosuchus Longosuchus is an extinct genus of aetosaur from the Late Triassic of North America....	Valid.	Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age... .	North America North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific... .
†Lucasuchus Lucasuchus Lucasuchus is an extinct genus of aetosaur. Fossils have been found from the Bull Canyon Formation of the Dockum Group outcropping in the Revuelto Creek locality in Quay County, New Mexico. All specimens date back to the Norian stage of the Late Triassic. The genus was named in 1995 after the...	Valid.
†Neoaetosauroides Neoaetosauroides Neoaetosauroides is an extinct genus of primitive aetosaur. Its type and only species is N. engaeus. Fossils have been found from the Los Colorados Formation outcropping along the Sierra Morada River in La Rioja, Argentina, and date back to the Norian age of the Late Triassic. It was the first...	Valid.
†Paratypothorax	Valid.
†Redondasuchus	Valid.			Might not be an aetosaur.
†Rioarribasuchus	Valid.			— possible junior synonym of Heliocanthus Heliocanthus Heliocanthus is the name of a problematic genus of aetosaur that has underwent many taxonomic revisions in recent years, and may prove to be synonymous with Rioarribasuchus...
†Sierritasuchus	Valid.	Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age... .	North America North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific... .
†Stagonolepis Stagonolepis Stagonolepis is an extinct genus of archosaur reptile belonging to the aetosaur order. It was about long.An aetosaur, Stagonolepis was a quadrupedal animal covered in thick armoured scales that ran down the length of the its body. A slow-moving browser, it would have used this heavy body armour to...	Valid.	Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age... .	Europe Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains , and the Black Sea to the southeast... , Geopark Geopark A Geopark is defined by the United Nations Educational, Scientific and Cultural Organization in its UNESCO Geoparks International Network of Geoparks programme as follows:... of Paleorrota Paleorrota Paleorrota , is a geopark located in the center of the Brazilian state of Rio Grande do Sul. The rocks and fossils found along the route date back to the times when there was only one supercontinent Pangaea.... Brazil Brazil Brazil , officially the Federative Republic of Brazil , is a country in South America. It is the fifth largest country by geographical area, occupying nearly half of South America, the fifth most populous country, and the fourth most populous democracy in the world. Bounded by the Atlantic Ocean... .
†Stegomus Stegomus Stegomus is a genus of aetosaur that lived in the Late Triassic. Its remains have been found in North America.-Sources:* A Pictorial Guide to Fossils by Gerard Ramon Case* When Dinosaurs Roamed New Jersey by William B. Gallagher...	Valid.	Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age... .	North America North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific... .
†Tecovasuchus	Valid.
†Typothorax Typothorax Typothorax is a genus of aetosaur that lived in the Late Triassic. Its remains have been found in North America.Even though Typothorax was one of the first vertebrate fossils named from the Chinle Formation, most of the skull has not yet been described.-Sources:* King of the Crocodylians: The...	Valid.	Late Triassic Late Triassic The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age... .	North America North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific... .

External links

Archosauromorpha: Suchia (Aetosauridae) - Palaeos
Aetosauria Translation and Pronunciation Guide - Ben Creisler
Introduction to the Aetosauria - UCMP