Aetosaur
Encyclopedia
Aetosaurs are an extinct order
of heavily armoured, medium- to large-sized Late Triassic
herbivorous
archosaur
s. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scute
s. All aetosaurs belong to the family
Stagonolepididae. Two distinct subdivisions of aeotosaurs are currently recognized, Desmatosuchinae
and Aetosaurinae
, based primarily on differences in the morphology
of the bony scutes of the two groups. Over 20 genera
of aetosaurs have been described, and recently there has been controversy regarding the description of some of these genera.
Aetosaur fossil remains are known from Europe
, North
and South America
, parts of Africa
and India
. Since their armoured plates are often preserved and are abundant in certain localities, aetosaurs serve as important Late Triassic
tetrapod
index fossil
s. Many aetosaurs had wide geographic ranges, but their stratigraphic ranges were relatively short. Therefore, the presence of particular aetosaurs can accurately date a site that they are found in.
Aetosaur remains have been found since the early 19th century, although the very first remains that were described were mistaken for fish scales. Aetosaurs were later recognized as crocodile relatives, with early paleontologists considering them to be semiaquatic scavengers. They are now considered to have been entirely terrestrial animals. Some forms have characteristics that may have been adaptations to digging for food. There is also evidence that some if not all aetosaurs made nests.
. Some teeth are chisel-shaped, small and leaf-like, indicating a probable herbivorous diet, although peg-like teeth and a keratin
ous snout have been considered possible adaptations in some species for feeding on colonial insects. A study of the braincase of Stagonolepis robertsoni has shown that there are similarities between it and those of crocodylomorphs
, which may indicate a close relationship.
Aetosaurs had a "pillar-erect" erect limb posture similar to that seen in Rauisuchia
, a related group of Triassic archosaurs. A pillar-erect limb posture is one where the femur
articulates
vertically with the acetabulum
of the hip, which is angled downward, so that the leg is positioned beneath the body and acts as a pillar bearing weight. While the limb posture is similar to rauisuchians, the feet resemble those of phytosaur
s (crocodile-like semiaquatic crurotarsans) in the retention of primitive characteristics. Although the forelimbs are much smaller than the hind limbs, all aetosaurs were quadrupeds.
Aetosaurs 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. In life, these plates were probably covered in horn. Dorsal osteoderms, which are found on the backs of aetosaurs, are often ornamented with radial grooves. Dorsal paramedians, those found along the midline of the animal, are often wide and quadrangular with a small boss called a dorsal eminence on the dorsal surface of each plate. In aetosaurs, paramedian plates often have raised or depressed anterior edges where the plates articulate with the ones in front of them. If the anterior edge is raised, the area is called an anterior bar, while if it is depressed, the area is called an anterior lamina. In lateral plates, which are positioned on either side of the paramedian plates, the dorsal eminence is often enlarged into a prominent spike. This spike is especially noticeable in desmatosuchines such as Longosuchus
and Desmatosuchus
. Osteoderms are useful in diagnosing aetosaur taxa, and aetosaur species can often be identified from individual scutes based on their ornamentation pattern.
Primitive genera, like the widespread Norian
genus Aetosaurus
and the Carnian
Coahomasuchus
, tended to be small, about a metre (3.2 ft) in length. However, more advanced forms were larger - about 3 metres (9.8 ft) in length - with some taxa, such as Typothorax
and Paratypothorax
, possessing broad turtle-like bodies, and others, like Desmatosuchus, a narrow-bodied genus at least 4 metres (13.1 ft) long, equipped with large spines over the shoulders, which added to the animal's defensive armament.
in 1844. He named the genus Stagonolepis from the Lossiemouth Sandstone
in Elgin
, Scotland
, but considered it to be a Devonian
fish rather than a Triassic reptile. This may be because he considered the strata to be part of the Old Red Sandstone
, and thus Paleozoic
in age. Agassiz mistook the osteoderms for large rhomboidal scales, which he thought were arranged in a similar pattern to those of gar
s. He also thought that these supposed scales were very similar to those of the lobe-finned fish Megalichthys
due to their large size.
English
biologist Thomas Henry Huxley reconsidered the fish scales described by Agassiz and considered them to belong to a crocodilian. He first proposed this to the Geological Society of London
in 1858, and went into more detail in an 1875 paper in the society's quarterly journal. By this time, new material had been uncovered from Elgin that indicated that Stagonolepis was not a fish, but a reptile. However, Stagonolepis was still known primarily by scutes and imprints of scutes, many of which were not well preserved.
More complete aetosaur remains were found from the Lower Stubensandtein of Germany
in the 1870s. Among them were complete articulated skeletons of 22 aetosaurs. These specimens were found in a large sandstone outcrop
near Stuttgart
and were preserved together in an area less than 2 square metres in size. The animals were probably buried under lake sediment soon after they died, with the flow of water repositioning their bodies on the lake bed and putting them in close proximity to one another. In 1877, German paleontologist Oskar Fraas assigned these specimens to the newly erected genus Aetosaurus. Fraas named the genus after the skull's resemblance to the head of an eagle, with a narrow, elongate skull and a pointed snout.
The first aetosaurs from North America were also being described at this time. American paleontologist Edward Drinker Cope
named Typothorax in 1875 and Episcoposaurus in 1877, both of which were from New Mexico
. However, Cope considered these genera to be phytosaurs, crocodile-like aquatic archosaurs that were also common in the Late Triassic. While new material referable to Typothorax has been found in recent years throughout the American southwest, Episcoposaurus is no longer considered valid. Cope, along with later paleontologists such as Friedrich von Huene
, recognized that remains of the type species
E. horridus actually belonged to Typothorax. Another species, E. haplocerus, was reassigned to Desmatosuchus in 1953.
A third North American genus called Stegomus was named by Othniel Charles Marsh
in 1896. Marsh had a long-time rivalry with Cope that was made famous in the Bone Wars
of the late 19th century, in which the two tried to out-compete one another in the field and in scientific literature. Unlike Cope's aetosaurs, Stegomus was found from the eastern United States in Connecticut
. Marsh also recognized Stegomus as an aetosaur rather than a phytosaur in his initial description of the genus. Like Cope, many paleontologists tended to consider aetosaur scutes to belong to phytosaurs during this time period.
Aetosauria was first named in 1889 by English naturalist
Richard Lydekker
and zoologist Henry Alleyne Nicholson
. They considered Aetosauria to be one of three suborders of the order Crocodilia, the other two being Parasuchia (a Triassic group) and Eusuchia
(a group including all post-Triassic crocodiles). At the time, Cope considered Aetosauria to belong to Rhynchocephalia, an order of reptiles that includes the living tuatara
. He also thought that the tightly fitting osteoderms, which were thought to be fused to the ribs, indicated that aetosaurs were transitional between rhynchocephalians and turtle
s. Nicholson and Lydekker placed a single family within the suborder, Aëtosauridæ. They considered aetosaurs to be similar to living crocodilians apart from their elongated metatarsals, which were compared to those of dinosaurs. In fact, Marsh considered aetosaurs to be closely related to dinosaurs because both had similar metatarsals.
Aetosaur material continued to be described into the early 20th century, with notable paleontologists such as Barnum Brown
and Charles Camp collecting specimens. However, aetosaur remains were still being confused with those of phytosaurs. During this time, aetosaurs were usually considered to be members of Pseudosuchia
, a now obsolete group consisting of various Triassic archosaurs including phytosaurs. However, similarities were often observed between aetosaurs and Crocodilia, the group to which aetosaurs were initially referred in the 19th century. While the skull had many features in common with pseudosuchians, parts of the postcranial skeleton, in particular the scutes, seemed to be similar to those of crocodilians.
and Antarctica, giving them a nearly worldwide distribution during the Late Triassic. Many aetosaur remains have been found from the Chinle Group in the southwestern United States. Most fossils have been found from Arizona
, New Mexico
, and Texas
. Some remains have also been found from Utah
, particularly in Canyonlands National Park
and Zion National Park
. Aetosaurs are also known from the Newark Supergroup along the East Coast of the United States in states such as Connecticut
and North Carolina
. Two genera are known from Greenland: Aetosaurus and Paratypothorax. They have been found from the Fleming Fjord Formation
in Jameson Land
. Longosuchus is the only aetosaur known from Africa, with scutes having been found from the late Carnian Timesgadiouine Formation in Morocco. During the Late Triassic, Morocco would have been in close proximity with the Newark Supergroup of North America in the supercontinent
of Pangaea
. It is also possible that Desmatosuchus was present in Africa, as fossils have been found from the Zarzaitine Series in Algeria
that were referred to the genus.
South American aetosaurs have been found from Argentina, Brazil, and Chile. In Argentina, they are known from the Carnian Ischigualasto Formation. Common genera from Ischigualasto include Aetosauroides and Stagonolepis. In Brazil, fossils have been found in the Santa Maria
and Caturrita Formation
s in Rio Grande do Sul
(Paleorrota
). Chilean aetosaurs are represented by one genus, Chilenosuchus, from the Antofagasta Region
. Aetosaurs have also been found from India, which, along with South America, was part of Gondwana
during the Late Triassic. Early descriptions of aetosaurs included material from the Maleri Formation in south-central India, although it was too inadequate to assign specimens to any particular genus. Based on such descriptions, the Indian aetosaurs most closely resemble Longosuchus and Paratypothorax. Reports of aetosaurs from Madagascar are based on probable crocodylomorph
scutes.
Footprints
belonging to the ichnogenus Brachychirotherium are often associated with aetosaurs. Brachychirotherium has been found from Rio Grande do Sul
(Paleorrota
) as well as Italy
, Germany
, and the eastern United States. They are also common in the southwestern United States, having been found from Canyonlands National Park and Dinosaur National Monument
.
, a clade of archosaurs that includes living crocodilians and is characterized by the distinctive structure of the ankle bones
. Aetosaurs were traditionally referred to a (now obsolete) group called the thecodont
s, which included all "primitive
" crocodilian relatives that lived in the Triassic. With the rise of phylogenetics
, aetosaurs were later placed in a group called Suchia
, which included many Triassic crurotarsans as well as later crurotarsans, including crocodilians.
All aetosaurs are members of the family Stagonolepidae. Stagonolepidae is split into two subfamilies, Aetosaurinae and Desmatosuchinae. Aetosaurinae is characterized by projections called eminences on the dorsal paramedian osteoderms that are close to the midline of the back. Desmatosuchinae has a few more distinguishing characteristics, including grooves on the dorsal paramedians that help them lock to the lateral plates in a tight articulation. Many desmatosuchines have long spikes projecting from the lateral plates. These spikes are especially prominent in Desmatosuchus. Aetosaurines, on the other hand, tend to have less spikes. Many aetosaurines, such as Aetosaurus and Neoaetosauroides, have smooth carapaces and lack spikes altogether.
Aetosaur phylogeny was first investigated in 1994 by paleontologist J. Michael Parrish. Aetosauroides, Aetosaurus, Desmatosuchus, Longosuchus, Neoaetosauroides, Stagonolepis, and Typothorax were included in the phylogenetic analysis. Aetosaurs were found to form a clade
with rauisuchians, which Parrish termed Rauisuchiformes. Rauisuchiformes also included the superorder Crocodylomorpha
, to which living crocodilia
ns belong. Parrish found Aetosauria to be a monophyletic group and thus a true clade consisting of a common aetosaur ancestor and all of its descendants. To phylogenetically define Aetosauria, Parrish identified five synapomorphies, or shared characteristics. The first synapomorphy concerned the jaw, with the premaxilla
at its tip being edentulous, upturned, and wide to form a "shovel". Moreover, the dentary bone in the lower jaw is also toothless, upturned, and broad. The reduced size and simple conical shape of the teeth was considered another synapomorphy. Two more synapomorphies of aetosaurs are shared with crocodylomorphs, but were not considered to be an indication of a close phylogenetic relationship; the body is covered in dorsal and ventral armor to form a complete carapace, and the paramedian osteoderms are much wider than they are long, with distinctive pitting. A final synapomorphy was found in the structure of the limb bones. In all aetosaurs, the limbs are very robust, with large muscle attachments such as the deltopectoral crest of the humerus
, the fourth trochanter
of the femur
, the intracondylar ridge of the tibia
, and the iliofibularis trochanter of the fibula.
In Parrish's phylogenetic analysis, Aetosaurus was found to be the most basal
member of the clade, the earliest to diverge after the most recent common ancestor
. After Aetosaurus, there is a polytomy
of three smaller clades in which it is unknown which clade diverged first from the group. Within this polytomy there was Neoaetosauroides, a clade containing Aetosauroides and Stagonolepis, and another polytomy that included Longosuchus, Desmatosuchus, and a clade containing Paratypothorax and Typothorax.
A later study by paleontologists Andrew B. Heckert and Spencer G. Lucas
in 1999 expanded the number of synapomorphies that diagnose Aetosauria to 18. New synapomorphies included temporal fenestrae, or holes, that opened on the side of the skull rather than the top, lateral osteoderms articulating with the paramedians, and osteoderms covering the limbs. Aetosaurus was still found to be the most basal member, but the phylogeny of more derived
aetosaurs differed in that Typothorax and Paratypothorax were split into two different clades with their sister taxa being Desmatosuchus and Longosuchus, respectively. More importantly, a new aetosaur called Coahomasuchus was included in the analysis. Coahomasuchus was found to be a basal aetosaur closely related to Stagonolepis, and also appeared early in the fossil record of aetosaurs. Previously, basal members were only known from later times, occurring after more advanced aetosaurs.
In 2003, paleontologists Simon R. Harris, David J. Gower
, and Mark Wilkinson examined previous phylogenetic studies of aetosaurs and criticized the way in which they used certain characters to produce cladograms. They concluded that only three hypotheses of aetosaur relationships from previous studies were still true: that Aetosaurus is the most basal aetosaur, that Aetosauroides is the sister taxon of Stagonolepis robertsoni, and that Longosuchus and Desmatosuchus are more closely related to each other than either is to Neoaetosauroides. They also went on to correct the trees from all previous analyses.
More recently, a 2007 analysis by paleontologist William G. Parker resulted in a larger tree of aetosaur phylogenetics with the inclusion of Heliocanthus. Based on the tree, Parker defined the clades Typothoracisinae
and Paratypothoracisini
, both within Aetosaurinae. Parker also gave a revised phylogenetic definition of Aetosauria, mentioning that the previous definition, made by Heckert and Lucas in 2000, was somewhat ambiguous. Heckert & Lucas (2000) defined Aetosauria as a stem-based taxon, claiming that Aetosauria included all crurotarsans that were more closely related to Desmatosuchus than to the immediate sister group of Aetosauria. Because the immediate sister group of Aetosauria was uncertain, Parker offered a new definition with several non-aetosaur crurotarsan genera rather than one sister group. According to Parker, Aetosauria included all taxa more closely related to Aetosaurus and Desmatosuchus than to Leptosuchus
, Postosuchus
, Prestosuchus
, Poposaurus
, Sphenosuchus
, Alligator
, Gracilisuchus
, and Revueltosaurus
.
In 2008, Parker, along with Michelle R. Stocker and Randall B. Irmis, conducted a new phylogenetic analysis which included the newly described Sierritasuchus. Below is the cladogram from Parker et al. (2008):
described aetosaurs as carnivorous aquatic animals of the order Parasuchia, mentioning that "[Parasuchia] constitutes an independent order, probably freshwater, littoral, carnivorous, short snouted (Aëtosaurus) or long snouted (Phytosaurus, Mystriosuchus) forms, analogous in their habits to the modern Crocodilia". Early aetosaur remains were often found in clays beside skeletons of aquatic animals such as phytosaurs and terrestrial animals such as dinosaur
s and trilophosaur
s. This may have led some paleontologists to believe that the animals had died in swampy environments. Because there were a large number of skeletons of animals that would not normally have inhabited swamps in these clays, some paleontologists even suggested that aetosaurs scavenged off the carcasses of animals that became trapped in the swamps and died. Doubts were later raised over this lifestyle, since aetosaur teeth show little indication of carnivory and the weight of the armor suggests that aetosaurs had "a passive mode of life." However, aetosaurs were still regarded as partly aquatic into the mid-20th century.
s and seed ferns that were common in the Triassic. The upturned shape of their snout suggests that aetosaurs may have dug up roots and tubers. Aetosaurs have several anatomical features that may have been adaptations to digging, including a short radius relative to the humerus (seen in many other digging tetrapods) and a large deltopectoral crest on the humerus that served as an attachment for muscles. Aetosaurs also have large hind feet, or pes
, with large claws that were likely used for skratch-digging. One aetosaur, Typothorax, has an entepicondyle on the humerus, which is the origin of forearm pronator
and manual flexor muscles often used in digging. Moreover, it has a large olecranon process on the ulna which projects backward past the elbow, giving a large area for the insertion of the triceps muscle. While many studies have suggested that aetosaurs had a fossorial
or burrowing lifestyle, aetosaurs have few of the characteristics that fossorial animals have as adaptations to digging. Therefore, it is likely that aetosaurs were able to dig to some extent, possibly rooting for food, but were unable to burrow.
While features of the limbs indicate that aetosaurs probably dug for food, features of the skull and teeth can indicate what kind of food they were eating. Aetosaurs have many derived features not seen in other crurotarsans which indicate that they are adapted to a different diet. Unlike the sharp, recurved teeth of other triassic archosaurs, aetosaurs had simple, conical teeth. The tips of the jaws were edentulous
, or toothless, and probably supported a beak.
The teeth have very little wear, suggesting that aetosaurs did not consume stiff and tough plant material. It is more likely that they consumed non-abrasive vegetation such as soft leaves.
Alternative theories have been proposed for the diet of aetosaurs. In 1947, H J Sawin proposed that the aetosaur Longosuchus was a scavenger based on the close proximity of some specimens to a large number of skeletons that were likely carcasses. A 2009 study of the jaw biomechanics of the South American genus Neoaetosauroides suggested that the animal may have fed on larvae and insects without hard exoskeletons. This is because Neoaetosauroides lacks serrations or wear facets on the teeth and has a jaw leverage that is not designed for strong forces such as crushing and chopping. The study recognized that northern aetosaurs such as Desmatosuchus and Stagonolepis did have jaws that would have supported a strong musculature, and were likely better suited to eating plant material.
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
. The oldest such nests that have been found belonged to phytosaur
s and aetosaurs. The nests are compacted and appear very similar to the nests of the modern day crocodile
s who guard their nests. The nests were holes dug in the sand in the bank of an ancient river.
A second possible aetosaur nest site is known from northeastern Italy. The nests are preserved as depressions in carbonate
rock that are circular or horseshoe-shaped, with high ridges around the sides. They appear to be unusually complex for nests created by Triassic reptiles. Archosaur footprints were found nearby that resembled aetosaurs, although they were not present in the same layer. Because the tracks were found so close to the nests, it is likely that aetosaurs built them.
. Osteoderms are the most common remains associated with aetosaurs, so a single identifiable scute can accurately date the layer it is found in.
One aetosaur, Typothorax coccinarum, has been used to define the Revueltian land vertebrate faunachron. A land vertebrate faunachron (LVF) is a time interval that is defined by the first appearance datum (FAD), or first occurrence, of a tetrapod
index fossil and is commonly used to date Late Triassic and Early Jurassic
terrestrial strata. Since the FAD of T. coccinarum is at the beginning of the Norian
stage, the Revueltian LVF starts at the beginning of the Norian around 216 million years ago. The Revueltian ends with the next FAD, which happens to be that of the phytosaur Redondasaurus
and the start of the Apachean LVF.
Biochrons for aetosaur genera have been developed for dating strata in the Chinle Group of the southwestern United States. Up to 13 genera of aetosaurs are known from the Chinle Group, with most occurring in multiple localities and over short time spans. In 1996, paleontologists Spencer G. Lucas
and Andrew B. Heckert recognized five biochrons based on the presence of aetosaurs throughout the Chinle Group. The number of biochrons grew to 11 in a 2007 study by Heckert and Lucas along with Adrian P. Hunt and Justin A. Spielmann. These biochrons occurred from the Otischalkian LVF to the Apachean LVF and included genera such as Longosuchus, Tecovasuchus, and Typothorax.
in Albuquerque, New Mexico
were accused of plagiarism
in some of their published articles dealing with aetosaurs. In late 2006, the genus Rioarribasuchus was erected as a replacement name for "Desmatosuchus" chamaensis in the museum's bulletin. However, four years earlier paleontologist William Parker reassigned "D." chamaensis to the newly named genus Heliocanthus in an unpublished thesis. Because the name was not published, it was considered a nomen nudum
until 2007 when it was described in the Journal of Systematic Palaeontology
. The authors of the 2006 paper, Spencer G. Lucas, Adrian P. Hunt, and Justin A. Spielmann, were accused of "intellectual theft" by paleontologists Jeff Martz, Mike Taylor
, Matt Wedel, and Darren Naish
, who claimed that they knew that Parker was eventually going to redescribe the species and formally erect a new genus. According to Martz, Taylor, Wedel, and Naish, the authors rushed to publish their own name before Parker could publish his.
Another controversy occurred after Spielmann, Hunt, and Lucas published a 2006 paper mentioning that the holotype
of Redondasuchus was not a left paramedian but a right one. In 2002, Martz came to the same conclusion in an unpublished thesis. He, along with Taylor, Wedel, and Naish, claimed that this was another form of plagiarism.
These allegations were brought to the attention of the Ethics Education Committee of the Society of Vertebrate Paleontology
(SVP) in 2007, and a response was given in 2008. In regard to Redondasuchus, the SVP found no plagiarism involved, while in the case of Heliocanthus and Rioarribasuchus, the SVP did not try to resolve the issue.
The entire controversy came to be known as "Aetogate", in reference to the famous Watergate scandal
of the 1970s. It received wide attention from local Albuquerque newspapers and science blogs. It was also the focus of a news article in a 2008 issue of the journal Nature
.
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...
of heavily armoured, medium- to large-sized 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...
herbivorous
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
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...
s. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like 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. All aetosaurs belong to the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Stagonolepididae. Two distinct subdivisions of aeotosaurs are currently recognized, Desmatosuchinae
Desmatosuchinae
Desmatosuchinae is one of the two subfamilies of aetosaurs, the other being Aetosaurinae. It is a stem-based taxon defined as all aetosaurs more closely related to Desmatosuchus than the last common ancestor of Desmatosuchus and Stagonolepis. All synapomorphies that diagnose the clade can be found...
and Aetosaurinae
Aetosaurinae
Aetosaurinae is one of the two subfamilies of aetosaurs, the other being Desmatosuchinae. It is a stem-based taxon defined as all aetosaurs more closely related to Aetosaurus than to the last common ancestor of Aetosaurus and Desmatosuchus. The only synapomorphy that diagnoses the clade...
, based primarily on differences in the morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
of the bony scutes of the two groups. Over 20 genera
Genera
Genera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...
of aetosaurs have been described, and recently there has been controversy regarding the description of some of these genera.
Aetosaur fossil remains are known from 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 watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, North
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...
and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, parts of 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...
and India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
. Since their armoured plates are often preserved and are abundant in certain localities, aetosaurs serve 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
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
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. Many aetosaurs had wide geographic ranges, but their stratigraphic ranges were relatively short. Therefore, the presence of particular aetosaurs can accurately date a site that they are found in.
Aetosaur remains have been found since the early 19th century, although the very first remains that were described were mistaken for fish scales. Aetosaurs were later recognized as crocodile relatives, with early paleontologists considering them to be semiaquatic scavengers. They are now considered to have been entirely terrestrial animals. Some forms have characteristics that may have been adaptations to digging for food. There is also evidence that some if not all aetosaurs made nests.
Description
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 pigPig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
. Some teeth are chisel-shaped, small and leaf-like, indicating a probable herbivorous diet, although peg-like teeth and a keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
ous snout have been considered possible adaptations in some species for feeding on colonial insects. A study of the braincase of Stagonolepis robertsoni has shown that there are similarities between it and those of 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...
, which may indicate a close relationship.
Aetosaurs had a "pillar-erect" erect limb posture similar to that seen in Rauisuchia
Rauisuchia
Rauisuchia is a group of predatory and mostly large Triassic archosaurs. As a clade, Rauisuchia includes these Triassic forms and all crocodylomorphs, which are descendants of Triassic rauisuchians. The group in its traditional sense is paraphyletic, because it does not include crocodylomorph...
, a related group of Triassic archosaurs. A pillar-erect limb posture is one where the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
articulates
Joint
A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.-Classification:...
vertically with the acetabulum
Acetabulum
The acetabulum is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.-Structure:...
of the hip, which is angled downward, so that the leg is positioned beneath the body and acts as a pillar bearing weight. While the limb posture is similar to rauisuchians, the feet resemble those of phytosaur
Phytosaur
Phytosaurs are an extinct group of large semi-aquatic Late Triassic archosaurs. Phytosaurs belong to the family Phytosauridae and the order Phytosauria. They were long-snouted and heavily armoured, bearing a remarkable resemblance to modern crocodiles in size, appearance, and lifestyle, an example...
s (crocodile-like semiaquatic crurotarsans) in the retention of primitive characteristics. Although the forelimbs are much smaller than the hind limbs, all aetosaurs were quadrupeds.
Aetosaurs 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. In life, these plates were probably covered in horn. Dorsal osteoderms, which are found on the backs of aetosaurs, are often ornamented with radial grooves. Dorsal paramedians, those found along the midline of the animal, are often wide and quadrangular with a small boss called a dorsal eminence on the dorsal surface of each plate. In aetosaurs, paramedian plates often have raised or depressed anterior edges where the plates articulate with the ones in front of them. If the anterior edge is raised, the area is called an anterior bar, while if it is depressed, the area is called an anterior lamina. In lateral plates, which are positioned on either side of the paramedian plates, the dorsal eminence is often enlarged into a prominent spike. This spike is especially noticeable in desmatosuchines such as Longosuchus
Longosuchus
Longosuchus is an extinct genus of aetosaur from the Late Triassic of North America. It measured about 3 metre in length....
and 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....
. Osteoderms are useful in diagnosing aetosaur taxa, and aetosaur species can often be identified from individual scutes based on their ornamentation pattern.
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 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...
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. The dorsal plates are distinctively flat...
, tended to be small, about a metre (3.2 ft) in length. However, more advanced forms were larger - about 3 metres (9.8 ft) in length - with some taxa, such as 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:...
and Paratypothorax
Paratypothorax
Paratypothorax is an extinct genus of aetosaur. It was first named in 1985 from specimens collected from the Lower Stubensandstein in Germany and was also noted to be present in the Chinle Group of the southwestern United States in both the Dockum and Chinle Formations, which are latest Carnian and...
, possessing broad turtle-like bodies, and others, like Desmatosuchus, a narrow-bodied genus at least 4 metres (13.1 ft) long, equipped with large spines over the shoulders, which added to the animal's defensive armament.
History
Aetosaur material was first described by Swiss paleontologist Louis AgassizLouis Agassiz
Jean Louis Rodolphe Agassiz was a Swiss paleontologist, glaciologist, geologist and a prominent innovator in the study of the Earth's natural history. He grew up in Switzerland and became a professor of natural history at University of Neuchâtel...
in 1844. He named the genus Stagonolepis from the Lossiemouth Sandstone
Lossiemouth Sandstone
The Lossiemouth Sandstone is a Late Triassic geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation.-Paleofauna:-See also:* List of dinosaur-bearing rock formations...
in Elgin
Elgin, Moray
Elgin is a former cathedral city and Royal Burgh in Moray, Scotland. It is the administrative and commercial centre for Moray. The town originated to the south of the River Lossie on the higher ground above the flood plain. Elgin is first documented in the Cartulary of Moray in 1190...
, 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...
, but considered it to be a Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
fish rather than a Triassic reptile. This may be because he considered the strata to be part of the Old Red Sandstone
Old Red Sandstone
The Old Red Sandstone is a British rock formation of considerable importance to early paleontology. For convenience the short version of the term, 'ORS' is often used in literature on the subject.-Sedimentology:...
, and thus Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
in age. Agassiz mistook the osteoderms for large rhomboidal scales, which he thought were arranged in a similar pattern to those of gar
Gar
In American English the name gar is strictly applied to members of the Lepisosteidae, a family including seven living species of fish in two genera that inhabit fresh, brackish, and occasionally marine, waters of eastern North America, Central America, and the Caribbean islands.-Etymology:In...
s. He also thought that these supposed scales were very similar to those of the lobe-finned fish Megalichthys
Megalichthys
Megalichthys is a genus of prehistoric lobe-finned fish which lived during the Carboniferous period. It is the type genus of the family Megalichthyidae....
due to their large size.
English
English people
The English are a nation and ethnic group native to England, who speak English. The English identity is of early mediaeval origin, when they were known in Old English as the Anglecynn. England is now a country of the United Kingdom, and the majority of English people in England are British Citizens...
biologist Thomas Henry Huxley reconsidered the fish scales described by Agassiz and considered them to belong to a crocodilian. He first proposed this to the Geological Society of London
Geological Society of London
The Geological Society of London is a learned society based in the United Kingdom with the aim of "investigating the mineral structure of the Earth"...
in 1858, and went into more detail in an 1875 paper in the society's quarterly journal. By this time, new material had been uncovered from Elgin that indicated that Stagonolepis was not a fish, but a reptile. However, Stagonolepis was still known primarily by scutes and imprints of scutes, many of which were not well preserved.
More complete aetosaur remains were found from the Lower Stubensandtein of 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...
in the 1870s. Among them were complete articulated skeletons of 22 aetosaurs. These specimens were found in a large sandstone outcrop
Outcrop
An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...
near Stuttgart
Stuttgart
Stuttgart is the capital of the state of Baden-Württemberg in southern Germany. The sixth-largest city in Germany, Stuttgart has a population of 600,038 while the metropolitan area has a population of 5.3 million ....
and were preserved together in an area less than 2 square metres in size. The animals were probably buried under lake sediment soon after they died, with the flow of water repositioning their bodies on the lake bed and putting them in close proximity to one another. In 1877, German paleontologist Oskar Fraas assigned these specimens to the newly erected genus Aetosaurus. Fraas named the genus after the skull's resemblance to the head of an eagle, with a narrow, elongate skull and a pointed snout.
The first aetosaurs from North America were also being described at this time. American paleontologist Edward Drinker Cope
Edward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...
named Typothorax in 1875 and Episcoposaurus in 1877, both of which were from New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
. However, Cope considered these genera to be phytosaurs, crocodile-like aquatic archosaurs that were also common in the Late Triassic. While new material referable to Typothorax has been found in recent years throughout the American southwest, Episcoposaurus is no longer considered valid. Cope, along with later paleontologists such as Friedrich von Huene
Friedrich von Huene
Friedrich von Huene was a German paleontologist who named more dinosaurs in the early 20th century than anyone else in Europe.-Biography:...
, recognized that remains of 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...
E. horridus actually belonged to Typothorax. Another species, E. haplocerus, was reassigned to Desmatosuchus in 1953.
A third North American genus called Stegomus was named by 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...
in 1896. Marsh had a long-time rivalry with Cope that was made famous in the Bone Wars
Bone Wars
The Bone Wars, also known as the "Great Dinosaur Rush", refers to a period of intense fossil speculation and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope and Othniel Charles Marsh...
of the late 19th century, in which the two tried to out-compete one another in the field and in scientific literature. Unlike Cope's aetosaurs, Stegomus was found from the eastern United States in Connecticut
Connecticut
Connecticut is a state in the New England region of the northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, and the state of New York to the west and the south .Connecticut is named for the Connecticut River, the major U.S. river that approximately...
. Marsh also recognized Stegomus as an aetosaur rather than a phytosaur in his initial description of the genus. Like Cope, many paleontologists tended to consider aetosaur scutes to belong to phytosaurs during this time period.
Aetosauria was first named in 1889 by English naturalist
Naturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Richard Lydekker
Richard Lydekker
Richard Lydekker was an English naturalist, geologist and writer of numerous books on natural history.-Biography:...
and zoologist Henry Alleyne Nicholson
Henry Alleyne Nicholson
Henry Alleyne Nicholson was a British palaeontologist and zoologist.The son of Dr. John Nicholson, a biblical scholar, was born at Penrith, Cumbria on 11 September 1844. He was educated at Appleby Grammar School and at the universities of Göttingen and Edinburgh...
. They considered Aetosauria to be one of three suborders of the order Crocodilia, the other two being Parasuchia (a Triassic group) and Eusuchia
Eusuchia
Eusuchia is a clade of crocodylomorphs that first appears in the Early Cretaceous with Hylaeochampsa. All living crocodilian species are eusuchians, as are many extinct forms.-Description:...
(a group including all post-Triassic crocodiles). At the time, Cope considered Aetosauria to belong to Rhynchocephalia, an order of reptiles that includes the living tuatara
Tuatara
The tuatara is a reptile endemic to New Zealand which, though it resembles most lizards, is actually part of a distinct lineage, order Sphenodontia. The two species of tuatara are the only surviving members of its order, which flourished around 200 million years ago. Their most recent common...
. He also thought that the tightly fitting osteoderms, which were thought to be fused to the ribs, indicated that aetosaurs were transitional between rhynchocephalians and turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s. Nicholson and Lydekker placed a single family within the suborder, Aëtosauridæ. They considered aetosaurs to be similar to living crocodilians apart from their elongated metatarsals, which were compared to those of dinosaurs. In fact, Marsh considered aetosaurs to be closely related to dinosaurs because both had similar metatarsals.
Aetosaur material continued to be described into the early 20th century, with notable paleontologists such as Barnum Brown
Barnum Brown
Barnum Brown , a paleontologist born in Carbondale, Kansas, and named after the circus showman P.T. Barnum, discovered the second fossil of Tyrannosaurus rex during a career that made him one of the most famous fossil hunters working from the late Victorian era into the early 20th century.Sponsored...
and Charles Camp collecting specimens. However, aetosaur remains were still being confused with those of phytosaurs. During this time, aetosaurs were usually considered to be members of Pseudosuchia
Pseudosuchia
Pseudosuchia is the name originally given to a group of prehistoric reptiles from the Triassic period. The name has been variously interpreted, and it is still sometimes, if infrequently, used in scientific literature today. A more commonly used name, Crurotarsi, is often substituted for...
, a now obsolete group consisting of various Triassic archosaurs including phytosaurs. However, similarities were often observed between aetosaurs and Crocodilia, the group to which aetosaurs were initially referred in the 19th century. While the skull had many features in common with pseudosuchians, parts of the postcranial skeleton, in particular the scutes, seemed to be similar to those of crocodilians.
Distribution
Aetosaur fossils have been found on all continents except AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and Antarctica, giving them a nearly worldwide distribution during the Late Triassic. Many aetosaur remains have been found from the Chinle Group in the southwestern United States. Most fossils have been found from Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
, and Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
. Some remains have also been found from Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
, particularly in Canyonlands National Park
Canyonlands National Park
Canyonlands National Park is a U.S. National Park located in southeastern Utah near the town of Moab and preserves a colorful landscape eroded into countless canyons, mesas and buttes by the Colorado River, the Green River, and their respective tributaries. The park is divided into four districts:...
and Zion National Park
Zion National Park
Zion National Park is located in the Southwestern United States, near Springdale, Utah. A prominent feature of the park is Zion Canyon, which is 15 miles long and up to half a mile deep, cut through the reddish and tan-colored Navajo Sandstone by the North Fork of the Virgin River...
. Aetosaurs are also known from the Newark Supergroup along the East Coast of the United States in states such as Connecticut
Connecticut
Connecticut is a state in the New England region of the northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, and the state of New York to the west and the south .Connecticut is named for the Connecticut River, the major U.S. river that approximately...
and North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
. Two genera are known from Greenland: Aetosaurus and Paratypothorax. They have been found from the Fleming Fjord Formation
Fleming Fjord Formation
The Fleming Fjord Formation is a geological formation in eastern Greenland.-Vertebrate fauna:...
in Jameson Land
Jameson Land
Jameson Land is a peninsula in eastern Greenland, bounded to the southwest by Scoresby Sund , to the northwest by the Greenlandic mainland, to the north by Scoresby Land, and to the east by Carlsberg Fjord, Liverpool Land and Hurry Inlet.-Geology:Jameson Land mainly consists of a tilted peneplain...
. Longosuchus is the only aetosaur known from Africa, with scutes having been found from the late Carnian Timesgadiouine Formation in Morocco. During the Late Triassic, Morocco would have been in close proximity with the Newark Supergroup of North America in the supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
of Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
. It is also possible that Desmatosuchus was present in Africa, as fossils have been found from the Zarzaitine Series in Algeria
Algeria
Algeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...
that were referred to the genus.
South American aetosaurs have been found from Argentina, Brazil, and Chile. In Argentina, they are known from the Carnian Ischigualasto Formation. Common genera from Ischigualasto include Aetosauroides and Stagonolepis. In Brazil, fossils have been found in the Santa Maria
Santa Maria Formation
The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It has a late Ladinian – early Carnian age , and is notable for its fossils of early dinosaurs, including the herrerasaur Staurikosaurus, the basal saurischian Teyuwasu, and the basal sauropodomorph...
and Caturrita Formation
Caturrita Formation
The Caturrita Formation is a rock formation found in Rio Grande do Sul, Brazil. Its sediments were deposited in the Paraná Basin. The formation has a late Carnian to early Norian age and forms part of the Santa Maria Supersequence in the upper section of the Rosário do Sul Group.-Etymology:The...
s in Rio Grande do Sul
Rio Grande do Sul
Rio Grande do Sul is the southernmost state in Brazil, and the state with the fifth highest Human Development Index in the country. In this state is located the southernmost city in the country, Chuí, on the border with Uruguay. In the region of Bento Gonçalves and Caxias do Sul, the largest wine...
(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....
). Chilean aetosaurs are represented by one genus, Chilenosuchus, from the Antofagasta Region
Antofagasta Region
The II Antofagasta Region is one of Chile's fifteen first-order administrative divisions. It comprises three provinces, Antofagasta, El Loa and Tocopilla...
. Aetosaurs have also been found from India, which, along with South America, was part of Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
during the Late Triassic. Early descriptions of aetosaurs included material from the Maleri Formation in south-central India, although it was too inadequate to assign specimens to any particular genus. Based on such descriptions, the Indian aetosaurs most closely resemble Longosuchus and Paratypothorax. Reports of aetosaurs from Madagascar are based on probable crocodylomorph
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...
scutes.
Footprints
Ichnite
An ichnite is a fossilised footprint. This is a type of trace fossil. Over the years, many ichnites have been found, around the world, giving important clues about the behaviour of the animals that made them...
belonging to the ichnogenus Brachychirotherium are often associated with aetosaurs. Brachychirotherium has been found from Rio Grande do Sul
Rio Grande do Sul
Rio Grande do Sul is the southernmost state in Brazil, and the state with the fifth highest Human Development Index in the country. In this state is located the southernmost city in the country, Chuí, on the border with Uruguay. In the region of Bento Gonçalves and Caxias do Sul, the largest wine...
(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....
) as well as 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...
, 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 the eastern United States. They are also common in the southwestern United States, having been found from Canyonlands National Park and Dinosaur National Monument
Dinosaur National Monument
Dinosaur National Monument is a National Monument located on the southeast flank of the Uinta Mountains on the border between Colorado and Utah at the confluence of the Green and Yampa Rivers. Although most of the monument area is in Moffat County, Colorado, the Dinosaur Quarry is located in Utah...
.
Taxonomy
Aetosaurs belong to CrurotarsiCrurotarsi
The Crurotarsi are a group of archosauriformes, represented today by the crocodiles,...
, a clade of archosaurs that includes living crocodilians and is characterized by the distinctive structure of the ankle bones
Tarsus (skeleton)
In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...
. Aetosaurs were traditionally referred to a (now obsolete) group called the thecodont
Thecodont
Thecodont , now considered an obsolete term, was formerly used to describe a diverse range of early archosaurs that first appeared in the Latest Permian and flourished until the end of the Triassic period...
s, which included all "primitive
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
" crocodilian relatives that lived in the Triassic. With the rise of phylogenetics
Phylogenetics
In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices...
, aetosaurs were later placed in a group called Suchia
Suchia
Suchia is a clade of archosaurs that includes all pseudosuchians except ornithosuchids. It includes crocodilians and their extinct relatives. Paul Sereno defined Suchia as the least inclusive clade containing Aetosaurus ferratus, Rauisuchus tiradentes, Prestosuchus chiniquensis, Gracilisuchus...
, which included many Triassic crurotarsans as well as later crurotarsans, including crocodilians.
All aetosaurs are members of the family Stagonolepidae. Stagonolepidae is split into two subfamilies, Aetosaurinae and Desmatosuchinae. Aetosaurinae is characterized by projections called eminences on the dorsal paramedian osteoderms that are close to the midline of the back. Desmatosuchinae has a few more distinguishing characteristics, including grooves on the dorsal paramedians that help them lock to the lateral plates in a tight articulation. Many desmatosuchines have long spikes projecting from the lateral plates. These spikes are especially prominent in Desmatosuchus. Aetosaurines, on the other hand, tend to have less spikes. Many aetosaurines, such as Aetosaurus and Neoaetosauroides, have smooth carapaces and lack spikes altogether.
Genera
| Genus | Status | Age | Location | Unit | Notes | Images |
|---|---|---|---|---|---|---|
Acaenasuchus Acaenasuchus Acaenasuchus is an extinct member of the order Aetosauria, endemic to what would be North America during the Triassic, existing for approximately .It was a heavily armored aetosaur with thorn-like spikes on its back.... |
Possible junior synonym | 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... |
 United States |
Chinle Group |
Possibly a juvenile Desmatosuchus haplocerus | |
Acompsosaurus Acompsosaurus Acompsosaurus is an extinct genus of aetosaur. It is known from a partial skeleton found from the Petrified Forest Member of the Chinle Formation near Fort Wingate, New Mexico, which is now lost. The generic name means "sturdy lizard." It may be a junior synonym of Stagonolepis as its pelvis... |
Nomen dubium Nomen dubium In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application... |
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... |
United States |
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... |
An aetosaur whose name means "sturdy lizard" and may be a junior synonym of Stagonolepis Stagonolepis Stagonolepis is an extinct genus of aetosaur. 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 repel attacks from contemporary... |
|
Adamanasuchus Adamanasuchus Adamanasuchus is an extinct genus of aetosaur. Fossils have been found from several localities from the Chinle Group in Arizona and date back to the Carnian stage of the Late Triassic. The locality from which it was named after also lends its name to the Adamanian land vertebrate faunachron.... |
Valid | 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... |
United States |
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... |
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Aetosauroides Aetosauroides Aetosauroides is an extinct genus of aetosaur from the Late Triassic of South America. It is one of three aetosaurs known from South America, the others being Neoaetosauroides and Chilenosuchus. Two species have been named: the type species A. scaglia and a second called A... |
Possible junior synonym | 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... |
 Argentina Brazil |
Possible junior synonym of Stagonolepis Stagonolepis Stagonolepis is an extinct genus of aetosaur. 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 repel attacks from contemporary... |
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Aetosaurus Aetosaurus 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... |
Valid | 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... |
 Germany Italy United States Greenland |
Lower Stubensandtein Stubensandtein The Stubensandstein is a geological formation in Germany. It dates back to the middle Norian.-Dinosaurs:Theropod tracks and an unnamed herrersaur genus are known from the Lower Stubensandstein.-See also:* List of dinosaur-bearing rock formations... Calcare di Zorzino Formation Newark Supergroup Fleming Fjord Formation Fleming Fjord Formation The Fleming Fjord Formation is a geological formation in eastern Greenland.-Vertebrate fauna:... |
A small (1.5 m, 5 ft long) aetosaur with a wide geographic distribution |  |
Argentinosuchus |
Junior synonym | Junior synonym of Stagonolepis Stagonolepis Stagonolepis is an extinct genus of aetosaur. 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 repel attacks from contemporary... |
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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 | Junior synonym of Stagonolepis Stagonolepis Stagonolepis is an extinct genus of aetosaur. 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 repel attacks from contemporary... |
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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 | 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... |
 Chile |
Was found in beds that were thought to be Carboniferous Carboniferous The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"... or Permian Permian The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian... in age rather than Triassic |
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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. The dorsal plates are distinctively flat... |
Valid | 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... |
United States |
Dockum Group Dockum Group The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much... |
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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.... |
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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 | 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... - 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... |
United States |
Dockum Group Dockum Group The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much... |
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Heliocanthus Heliocanthus Heliocanthus is the name of a problematic genus of aetosaur that has undergone many taxonomic revisions in recent years, and may prove to be synonymous with Rioarribasuchus... |
Possible junior synonym | 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... |
United States |
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... |
Possible junior synonym of Rioarribasuchus | |
Longosuchus Longosuchus Longosuchus is an extinct genus of aetosaur from the Late Triassic of North America. It measured about 3 metre in length.... |
Valid | 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... |
United States Morocco |
Dockum Group Dockum Group The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much... Timesgadiouine Formation |
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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 | 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... |
United States |
Bull Canyon Formation |
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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... |
Valid | 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... |
Argentina |
Los Colorados Formation Los Colorados Formation The Los Colorados Formation is a sedimentary rock formation found in La Rioja, Argentina. It has a Norian age , and is notable for its fossils of early dinosaurs, including the coelophysoid Zupaysaurus and the "prosauropods" Coloradisaurus, Lessemsaurus, and Riojasaurus.-Dinosaurs:Indeterminate... |
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Paratypothorax Paratypothorax Paratypothorax is an extinct genus of aetosaur. It was first named in 1985 from specimens collected from the Lower Stubensandstein in Germany and was also noted to be present in the Chinle Group of the southwestern United States in both the Dockum and Chinle Formations, which are latest Carnian and... |
Valid | 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... - Rhaetian Rhaetian The Rhaetian is in geochronology the latest age of the Triassic period or in chronostratigraphy the uppermost stage of the Triassic system. It lasted from 203.6 ± 1.5 to 199.6 ± 0.6 million years ago... |
Germany United States Greenland |
Lower Stubensandstein Chinle Group Fleming Fjord Formation Fleming Fjord Formation The Fleming Fjord Formation is a geological formation in eastern Greenland.-Vertebrate fauna:... |
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Redondasuchus Redondasuchus Redondasuchus is an extinct genus of aetosaur. It may a junior synonym of Typothorax coccinarum, another aetosaur. Redondasuchus is a member of the clade Typothoracisinae within the subfamily Aetosaurinae, and lived during the middle Norian stage of the Late Triassic. Material belonging to the... |
Valid | 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... |
United States |
Redonda Formation |
Might not be an aetosaur |
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Rioarribasuchus |
Possible junior synonym | 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... |
United States |
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... |
Possible junior synonym of Heliocanthus Heliocanthus Heliocanthus is the name of a problematic genus of aetosaur that has undergone many taxonomic revisions in recent years, and may prove to be synonymous with Rioarribasuchus... |
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Sierritasuchus Sierritasuchus Sierritasuchus is an extinct genus of aetosaur in the subfamily Desmatosuchinae. It is known from a small holotype skeleton from the Late Triassic Tecovas Formation of Texas. This skeleton was discovered in 1939 and was originally assigned to the genus Desmatosuchus... |
Valid | 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... |
United States |
Tecovas Formation Tecovas Formation -Vertebrate fauna:... |
Originally assigned to Desmatosuchus |
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Stagonolepis Stagonolepis Stagonolepis is an extinct genus of aetosaur. 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 repel attacks from contemporary... |
Valid | 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... |
 Kingdom of Scotland United States Argentina Brazil Poland |
Lossiemouth Sandstone Lossiemouth Sandstone The Lossiemouth Sandstone is a Late Triassic geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation.-Paleofauna:-See also:* List of dinosaur-bearing rock formations... Dockum Group Dockum Group The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much... Caturrita Formation Caturrita Formation The Caturrita Formation is a rock formation found in Rio Grande do Sul, Brazil. Its sediments were deposited in the Paraná Basin. The formation has a late Carnian to early Norian age and forms part of the Santa Maria Supersequence in the upper section of the Rosário do Sul Group.-Etymology:The... Krasiejów Krasiejów Krasiejów is a village in the administrative district of Gmina Ozimek, within Opole County, Opole Voivodeship, in south-western Poland... deposits |
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Stegomus |
Junior synonym | Junior synonym of Aetosaurus Aetosaurus 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... |
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Tecovasuchus Tecovasuchus Tecovasuchus is an extinct genus of aetosaur. It is known primarily from osteoderms found from the Tecovas Formation in Texas, which is Late Triassic in age, dating back to the upper Carnian. Material is also known from several other localities of the Chinle Group in New Mexico and Arizona... |
Valid | 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... |
United States |
Tecovas Formation Tecovas Formation -Vertebrate fauna:... |
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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:... |
Valid |
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... |
United States |
Dockum Group Dockum Group The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much... |
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Phylogeny
Cladogram A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational... from Parrish (1994) |
Aetosaur phylogeny was first investigated in 1994 by paleontologist J. Michael Parrish. Aetosauroides, Aetosaurus, Desmatosuchus, Longosuchus, Neoaetosauroides, Stagonolepis, and Typothorax were included in the phylogenetic analysis. Aetosaurs were found to form a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
with rauisuchians, which Parrish termed Rauisuchiformes. Rauisuchiformes also included the superorder Crocodylomorpha
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...
, to which living crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns belong. Parrish found Aetosauria to be a monophyletic group and thus a true clade consisting of a common aetosaur ancestor and all of its descendants. To phylogenetically define Aetosauria, Parrish identified five synapomorphies, or shared characteristics. The first synapomorphy concerned the jaw, with the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
at its tip being edentulous, upturned, and wide to form a "shovel". Moreover, the dentary bone in the lower jaw is also toothless, upturned, and broad. The reduced size and simple conical shape of the teeth was considered another synapomorphy. Two more synapomorphies of aetosaurs are shared with crocodylomorphs, but were not considered to be an indication of a close phylogenetic relationship; the body is covered in dorsal and ventral armor to form a complete carapace, and the paramedian osteoderms are much wider than they are long, with distinctive pitting. A final synapomorphy was found in the structure of the limb bones. In all aetosaurs, the limbs are very robust, with large muscle attachments such as the deltopectoral crest of the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
, the fourth trochanter
Fourth trochanter
The fourth trochanter is a shared characteristic common to archosaurs. It is a knob-like feature on the medial side of the femur that serves as a muscle attachment....
of the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
, the intracondylar ridge of the tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
, and the iliofibularis trochanter of the fibula.
In Parrish's phylogenetic analysis, Aetosaurus was found to be the most basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
member of the clade, the earliest to diverge after the most recent common ancestor
Most recent common ancestor
In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly descended...
. After Aetosaurus, there is a polytomy
Polytomy
A polytomy , meaning many temporal based branches, is a section of a phylogeny in which the evolutionary relationships can not be fully resolved to dichotomies. In a phylogenetic tree, a polytomy is represented as a node which has more than two immediate descending branches...
of three smaller clades in which it is unknown which clade diverged first from the group. Within this polytomy there was Neoaetosauroides, a clade containing Aetosauroides and Stagonolepis, and another polytomy that included Longosuchus, Desmatosuchus, and a clade containing Paratypothorax and Typothorax.
A later study by paleontologists Andrew B. Heckert and Spencer G. Lucas
Spencer G. Lucas
Spencer George Lucas is an American paleontologist and stratigrapher, and curator of paleontology at the New Mexico Museum of Natural History and Science. His main areas of study are late Paleozoic, Mesozoic and early Cenozoic vertebrate fossils, stratigraphy, and continental deposits,...
in 1999 expanded the number of synapomorphies that diagnose Aetosauria to 18. New synapomorphies included temporal fenestrae, or holes, that opened on the side of the skull rather than the top, lateral osteoderms articulating with the paramedians, and osteoderms covering the limbs. Aetosaurus was still found to be the most basal member, but the phylogeny of more derived
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 differed in that Typothorax and Paratypothorax were split into two different clades with their sister taxa being Desmatosuchus and Longosuchus, respectively. More importantly, a new aetosaur called Coahomasuchus was included in the analysis. Coahomasuchus was found to be a basal aetosaur closely related to Stagonolepis, and also appeared early in the fossil record of aetosaurs. Previously, basal members were only known from later times, occurring after more advanced aetosaurs.
In 2003, paleontologists Simon R. Harris, David J. Gower
David J. Gower
David J. Gower is a palaeontologist.Since 2004 he is a herpetology researcher at the Museum of Natural History in London.-External links:* *...
, and Mark Wilkinson examined previous phylogenetic studies of aetosaurs and criticized the way in which they used certain characters to produce cladograms. They concluded that only three hypotheses of aetosaur relationships from previous studies were still true: that Aetosaurus is the most basal aetosaur, that Aetosauroides is the sister taxon of Stagonolepis robertsoni, and that Longosuchus and Desmatosuchus are more closely related to each other than either is to Neoaetosauroides. They also went on to correct the trees from all previous analyses.
More recently, a 2007 analysis by paleontologist William G. Parker resulted in a larger tree of aetosaur phylogenetics with the inclusion of Heliocanthus. Based on the tree, Parker defined the clades Typothoracisinae
Typothoracisinae
Typothoracisinae is a clade of aetosaurs within the subfamily Aetosaurinae. It is a stem-based taxon defined as all aetosaurs closer to Typothorax than to Stagonolepis or Desmatosuchus. As with many aetosaur taxa, most of the synapomorphies that diagnose the clade are found in the osteoderms...
and Paratypothoracisini
Paratypothoracisini
Paratypothoracisini is a clade of aetosaurs within the subfamily Aetosaurinae. It is a node-based taxon that includes Heliocanthus, Paratypothorax, Tecovasuchus, and all descendants of their most recent common ancestor. All synapomorphies that diagnose the clade can be found in the osteoderms...
, both within Aetosaurinae. Parker also gave a revised phylogenetic definition of Aetosauria, mentioning that the previous definition, made by Heckert and Lucas in 2000, was somewhat ambiguous. Heckert & Lucas (2000) defined Aetosauria as a stem-based taxon, claiming that Aetosauria included all crurotarsans that were more closely related to Desmatosuchus than to the immediate sister group of Aetosauria. Because the immediate sister group of Aetosauria was uncertain, Parker offered a new definition with several non-aetosaur crurotarsan genera rather than one sister group. According to Parker, Aetosauria included all taxa more closely related to Aetosaurus and Desmatosuchus than to Leptosuchus
Leptosuchus
Leptosuchus is an extinct genus of phytosaur with a complex taxonomical history. Fossils have been found from the Dockum Group and lower Chinle Formation outcropping in Texas, New Mexico, and Arizona and date back to the Carnian stage of the Late Triassic.Currently there are believed to be four...
, Postosuchus
Postosuchus
Postosuchus, meaning "crocodile from Post ", was a basal archosaur that lived in what is now North America during the middle through to the late Triassic period...
, Prestosuchus
Prestosuchus
Prestosuchus is an extinct genus of a group of rauisuchians called prestosuchids. Friedrich von Huene named the genus in honor of Vicentino Prestes de Almeida....
, Poposaurus
Poposaurus
Poposaurus is a genus of reptile from the Late Triassic of the southwestern United States. It was a crurotarsan archosaur which lived in what is now Wyoming, Utah, Arizona and Texas. The type species, Poposaurus gracilis, was described by M. G. Mehl in 1915. The second species, P...
, Sphenosuchus
Sphenosuchus
Sphenosuchus is an extinct genus of sphenosuchian from the Elliot Formation of South Africa, discovered and described early in the 20th century. The skull is excellently preserved but other than elements of the forelimb and isolated parts of the hind limb, the Sphenosuchus material is incomplete...
, Alligator
Alligator
An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two extant alligator species: the American alligator and the Chinese alligator ....
, Gracilisuchus
Gracilisuchus
Gracilisuchus is an extinct genus of tiny crurotarsan from the Middle Triassic. It was a suchian close to the ancestry of crocodiles, and was at one time thought to be a dinosaur, but this hypothesis has since been rejected...
, and Revueltosaurus
Revueltosaurus
Revueltosaurus is a genus of prehistoric crurotarsan from Late Triassic New Mexico and Arizona.According to William Parker, who discovered the partial skeleton, "we have pretty much erased the record of Triassic ornithischian dinosaurs from North America, Europe and worldwide, except for South...
.
In 2008, Parker, along with Michelle R. Stocker and Randall B. Irmis, conducted a new phylogenetic analysis which included the newly described Sierritasuchus. Below is the cladogram from Parker et al. (2008):
Early interpretations
In 1904, American paleontologist Henry Fairfield OsbornHenry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...
described aetosaurs as carnivorous aquatic animals of the order Parasuchia, mentioning that "[Parasuchia] constitutes an independent order, probably freshwater, littoral, carnivorous, short snouted (Aëtosaurus) or long snouted (Phytosaurus, Mystriosuchus) forms, analogous in their habits to the modern Crocodilia". Early aetosaur remains were often found in clays beside skeletons of aquatic animals such as phytosaurs and terrestrial animals such as dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s and trilophosaur
Trilophosaur
Trilophosaurs were lizard-like Triassic diapsid reptiles related to the archosaurs. The best known genus is Trilophosaurus, a herbivore up to 2.5 meters long. It had a short, unusually heavily-built skull, equipped with massive, broad flattened cheek teeth with sharp shearing surfaces for cutting...
s. This may have led some paleontologists to believe that the animals had died in swampy environments. Because there were a large number of skeletons of animals that would not normally have inhabited swamps in these clays, some paleontologists even suggested that aetosaurs scavenged off the carcasses of animals that became trapped in the swamps and died. Doubts were later raised over this lifestyle, since aetosaur teeth show little indication of carnivory and the weight of the armor suggests that aetosaurs had "a passive mode of life." However, aetosaurs were still regarded as partly aquatic into the mid-20th century.
Feeding
Aetosaurs were herbivores, likely feeding on fernFern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s and seed ferns that were common in the Triassic. The upturned shape of their snout suggests that aetosaurs may have dug up roots and tubers. Aetosaurs have several anatomical features that may have been adaptations to digging, including a short radius relative to the humerus (seen in many other digging tetrapods) and a large deltopectoral crest on the humerus that served as an attachment for muscles. Aetosaurs also have large hind feet, or pes
Pes (zoology)
The pes is the zoological term for the distal portion of the hind limb of tetrapod animals. It is the part of the pentadactyl limb that includes the metatarsals and digits . During evolution, it has taken many forms and served a variety of functions...
, with large claws that were likely used for skratch-digging. One aetosaur, Typothorax, has an entepicondyle on the humerus, which is the origin of forearm pronator
Pronation
In anatomy, pronation is a rotational movement of the forearm at the radioulnar joint, or of the foot at the subtalar and talocalcaneonavicular joints. For the forearm, when standing in the anatomical position, pronation will move the palm of the hand from an anterior-facing position to a...
and manual flexor muscles often used in digging. Moreover, it has a large olecranon process on the ulna which projects backward past the elbow, giving a large area for the insertion of the triceps muscle. While many studies have suggested that aetosaurs had a fossorial
Fossorial
A fossorial organism is one that is adapted to digging and life underground such as the badger, the naked mole rat, and the mole salamanders Ambystomatidae...
or burrowing lifestyle, aetosaurs have few of the characteristics that fossorial animals have as adaptations to digging. Therefore, it is likely that aetosaurs were able to dig to some extent, possibly rooting for food, but were unable to burrow.
While features of the limbs indicate that aetosaurs probably dug for food, features of the skull and teeth can indicate what kind of food they were eating. Aetosaurs have many derived features not seen in other crurotarsans which indicate that they are adapted to a different diet. Unlike the sharp, recurved teeth of other triassic archosaurs, aetosaurs had simple, conical teeth. The tips of the jaws were edentulous
Edentulism
Edentulism is the condition of being toothless to at least some degree; it is the result of tooth loss. Loss of some teeth results in partial edentulism, while loss of all teeth results in complete edentulism....
, or toothless, and probably supported a beak.
The teeth have very little wear, suggesting that aetosaurs did not consume stiff and tough plant material. It is more likely that they consumed non-abrasive vegetation such as soft leaves.
Alternative theories have been proposed for the diet of aetosaurs. In 1947, H J Sawin proposed that the aetosaur Longosuchus was a scavenger based on the close proximity of some specimens to a large number of skeletons that were likely carcasses. A 2009 study of the jaw biomechanics of the South American genus Neoaetosauroides suggested that the animal may have fed on larvae and insects without hard exoskeletons. This is because Neoaetosauroides lacks serrations or wear facets on the teeth and has a jaw leverage that is not designed for strong forces such as crushing and chopping. The study recognized that northern aetosaurs such as Desmatosuchus and Stagonolepis did have jaws that would have supported a strong musculature, and were likely better suited to eating plant material.
Nests
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 are an extinct group of large semi-aquatic Late Triassic archosaurs. Phytosaurs belong to the family Phytosauridae and the order Phytosauria. They were long-snouted and heavily armoured, bearing a remarkable resemblance to modern crocodiles in size, appearance, and lifestyle, an example...
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 extant 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.
A second possible aetosaur nest site is known from northeastern Italy. The nests are preserved as depressions in carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
rock that are circular or horseshoe-shaped, with high ridges around the sides. They appear to be unusually complex for nests created by Triassic reptiles. Archosaur footprints were found nearby that resembled aetosaurs, although they were not present in the same layer. Because the tracks were found so close to the nests, it is likely that aetosaurs built them.
Biochronology
Because species of aetosaurs typically have restricted fossil ranges and are abundant in the strata they are found in, they are useful in biochronologyBiochronology
Biochronology is the dating of biological events using biostratigraphic or palaeontological methods.-External links:* * *...
. Osteoderms are the most common remains associated with aetosaurs, so a single identifiable scute can accurately date the layer it is found in.
One aetosaur, Typothorax coccinarum, has been used to define the Revueltian land vertebrate faunachron. A land vertebrate faunachron (LVF) is a time interval that is defined by the first appearance datum (FAD), or first occurrence, of a tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
index fossil and is commonly used to date Late Triassic and Early Jurassic
Early Jurassic
The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...
terrestrial strata. Since the FAD of T. coccinarum is at the beginning of the 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...
stage, the Revueltian LVF starts at the beginning of the Norian around 216 million years ago. The Revueltian ends with the next FAD, which happens to be that of the phytosaur Redondasaurus
Redondasaurus
Redondasaurus is a genus of phytosaur from the Late Triassic of North America. Translated, the name Redondasaurus means "Redonda lizard," referring to the Redonda Formation of east-central New Mexico, USA. It was first named by Hunt & Lucas in 1993, and contains one species, R. gregorii...
and the start of the Apachean LVF.
Biochrons for aetosaur genera have been developed for dating strata in the Chinle Group of the southwestern United States. Up to 13 genera of aetosaurs are known from the Chinle Group, with most occurring in multiple localities and over short time spans. In 1996, paleontologists Spencer G. Lucas
Spencer G. Lucas
Spencer George Lucas is an American paleontologist and stratigrapher, and curator of paleontology at the New Mexico Museum of Natural History and Science. His main areas of study are late Paleozoic, Mesozoic and early Cenozoic vertebrate fossils, stratigraphy, and continental deposits,...
and Andrew B. Heckert recognized five biochrons based on the presence of aetosaurs throughout the Chinle Group. The number of biochrons grew to 11 in a 2007 study by Heckert and Lucas along with Adrian P. Hunt and Justin A. Spielmann. These biochrons occurred from the Otischalkian LVF to the Apachean LVF and included genera such as Longosuchus, Tecovasuchus, and Typothorax.
Naming controversy
In 2007, paleontologists at the New Mexico Museum of Natural History and ScienceNew Mexico Museum of Natural History and Science
The New Mexico Museum of Natural History and Science is a natural history and science museum in Albuquerque, New Mexico near Old Town Albuquerque. The Museum was founded in 1986....
in Albuquerque, New Mexico
Albuquerque, New Mexico
Albuquerque is the largest city in the state of New Mexico, United States. It is the county seat of Bernalillo County and is situated in the central part of the state, straddling the Rio Grande. The city population was 545,852 as of the 2010 Census and ranks as the 32nd-largest city in the U.S. As...
were accused of plagiarism
Plagiarism
Plagiarism is defined in dictionaries as the "wrongful appropriation," "close imitation," or "purloining and publication" of another author's "language, thoughts, ideas, or expressions," and the representation of them as one's own original work, but the notion remains problematic with nebulous...
in some of their published articles dealing with aetosaurs. In late 2006, the genus Rioarribasuchus was erected as a replacement name for "Desmatosuchus" chamaensis in the museum's bulletin. However, four years earlier paleontologist William Parker reassigned "D." chamaensis to the newly named genus Heliocanthus in an unpublished thesis. Because the name was not published, it was considered a nomen nudum
Nomen nudum
The phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...
until 2007 when it was described in the Journal of Systematic Palaeontology
Journal of Systematic Palaeontology
The Journal of Systematic Palaeontology is a peer-reviewed quarterly scientific journal of paleontology published by Taylor & Francis on behalf of the British Natural History Museum. , the editor-in-chief is Paul D. Taylor....
. The authors of the 2006 paper, Spencer G. Lucas, Adrian P. Hunt, and Justin A. Spielmann, were accused of "intellectual theft" by paleontologists Jeff Martz, Mike Taylor
Mike Taylor (paleontologist)
Mike Taylor is a British computer programmer and amateur paleontologist. To date, he has published 13 paleontological papers and is co-credited with naming 2 dinosaur species .Along with paleontologists Darren Naish and Matt Wedel, he founded the paleontology blog .- References :...
, Matt Wedel, and Darren Naish
Darren Naish
Darren Naish is a vertebrate palaeontologist and science writer. He obtained a geology degree at the University of Southampton and later studied vertebrate palaeontology under British palaeontologist David Martill at the University of Portsmouth, where he obtained both an M. Phil...
, who claimed that they knew that Parker was eventually going to redescribe the species and formally erect a new genus. According to Martz, Taylor, Wedel, and Naish, the authors rushed to publish their own name before Parker could publish his.
Another controversy occurred after Spielmann, Hunt, and Lucas published a 2006 paper mentioning that the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of Redondasuchus was not a left paramedian but a right one. In 2002, Martz came to the same conclusion in an unpublished thesis. He, along with Taylor, Wedel, and Naish, claimed that this was another form of plagiarism.
These allegations were brought to the attention of the Ethics Education Committee of the Society of Vertebrate Paleontology
Society of Vertebrate Paleontology
The Society of Vertebrate Paleontology was founded in 1940 for individuals with an interest in vertebrate paleontology. SVP now has almost 2,000 members. The society's website states that SVP "is organized exclusively for educational and scientific purposes...
(SVP) in 2007, and a response was given in 2008. In regard to Redondasuchus, the SVP found no plagiarism involved, while in the case of Heliocanthus and Rioarribasuchus, the SVP did not try to resolve the issue.
The entire controversy came to be known as "Aetogate", in reference to the famous Watergate scandal
Watergate scandal
The Watergate scandal was a political scandal during the 1970s in the United States resulting from the break-in of the Democratic National Committee headquarters at the Watergate office complex in Washington, D.C., and the Nixon administration's attempted cover-up of its involvement...
of the 1970s. It received wide attention from local Albuquerque newspapers and science blogs. It was also the focus of a news article in a 2008 issue of the journal Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
.
External links
- Archosauromorpha: Suchia (Aetosauridae) - PalaeosPalaeosPalaeos.com is a web site on biology, paleontology, cladistics and geology and which covers the history of Earth. The site is well respected and has been used as a reference by professional paleontologists such as Michael J. Benton, the professor of vertebrate palaeontology in the Department of...
.com - Aetosauria Translation and Pronunciation Guide - Ben Creisler
- Introduction to the Aetosauria - University of California Museum of PaleontologyUniversity of California Museum of PaleontologyThe University of California Museum of Paleontology is a paleontology museum located on the campus of the University of California, Berkeley....