Aetosaurs were heavily armored reptiles belonging to the extinct order Aetosauria. They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs more closely related to crocodilians than to birds. All known aetosaurs are restricted to the Late Triassic, and in some strata from this time they are among the most abundant fossil vertebrates. They have small heads, upturned snouts, erect limbs, and a body ornamented with four rows of plate-like osteoderms. 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 fossils. 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.
Revueltosaurus is an extinct genus of suchian pseudosuchian from Late Triassic deposits of New Mexico, Arizona and North Carolina, United States. Many specimens, mostly teeth, have been assigned to Revueltosaurus over the years. Currently, three species are included in this genus, all of which were originally thought to represent monospecific genera of basal ornithischian dinosaurs. It was 1 meter long.
Aetosaurus is an extinct genus of pseudosuchian reptile belonging to the order Aetosauria. It is generally considered to be the most primitive aetosaur. Three species are currently recognized: A. ferratus, the type species from Germany and Italy; A. crassicauda from Germany; and A. arcuatus from eastern North America. Additional specimens referred to Aetosaurus have been found in the Chinle Group of the southwestern United States, and the Fleming Fjord Formation of Greenland. Specimens of Aetosaurus occur in Norian-age strata.
Calyptosuchus is an extinct genus of aetosaur from the Late Triassic of North America. Like other aetosaurs, it was heavily armored and had a pig-like snout used to uproot plants.
Nicrosaurus (/nɛkroʊˈsɔrəs/) is an extinct genus of phytosaur reptile existing during the Late Triassic period. Although it looked like a crocodile, it was not closely related to these creatures, instead being an example of parallel evolution. The main difference between Nicrosaurus and modern crocodiles is the position of the nostrils – Nicrosaurus's nostrils, or external nares, were placed directly in front of the forehead, whereas in crocodiles, the nostrils are positioned on the end of the snout. A 2013 study has also found that illium of Nicrosaurus is quite distinctive from all other phytosaurs.
Aetosauroides is an extinct genus of aetosaur from the Late Triassic of South America. It is one of four aetosaurs known from South America, the others being Neoaetosauroides, Chilenosuchus and Aetobarbakinoides. Three species have been named: the type species A. scagliai, A. subsulcatus and A. inhamandensis. Fossils have been found in the Cancha de Bochas Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern Argentina and the Santa Maria Formation in the Paraná Basin in southeastern Brazil. The strata date to the late Carnian and early Norian stages, making Aetosauroides one of the oldest aetosaurs.
Redondasaurus is an extinct genus of phytosaur from the Late Triassic of the southwestern United States. It was named by Hunt & Lucas in 1993, and contains two species, R. gregorii and R. bermani. It is the youngest and most evolutionarily-advanced of the phytosaurs.
Typothorax is an extinct genus of typothoracisine 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.
Coahomasuchus is an extinct genus of aetosaurine aetosaur. Remains of the genus have been found from deposits in Texas and North Carolina that date to the Otischalkian faunachron of the Late Triassic. It was small for an aetosaur, being less than 1.5 metres long. The dorsal plates are distinctively flat and unflexed, and have a faint sub-parallel to radial ornamentation. The genus lacked spines or keels on these plates, features seen in many other aetosaurs. Coahomasuchus was very similar in appearance to the closely related Aetosaurus.
Neoaetosauroides is an extinct genus of primitive aetosaur. Its type and only species is N. engaeus. Fossils have been found in Los Colorados Formation outcropping along the Sierra Morada River in the Ischigualasto-Villa Unión Basin in La Rioja, Argentina, and date back to the Norian age of the Late Triassic. It was the first aetosaur known from the formation, with remains being discovered in the 1960s.
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 American paleontologist Spencer G. Lucas.
Paratypothorax is an extinct genus of aetosaur, known by one species, Paratypothorax andressi. 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 Rhaetian in age, respectively. The genus was described from osteoderms that were initially referred to the phytosaur Belodon kappfi. Material from Paratypothorax has also been reported from the Norian-age Fleming Fjord Formation in Greenland.
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 lower Norian. Material is also known from several other localities of the Chinle Group in New Mexico and Arizona, such as older Carnian outcrops and younger Rhaetian outcrops. Specimens of Tecovasuchus have been collected from the Tecovas Formation, the Bluewater Creek Formation, and the Los Esteros Member of the Santa Rosa Formation.
Aetosaurinae is one of the two main clades of aetosaurs, the other being Desmatosuchia. It is a stem-based taxon defined as all aetosaurs more closely related to Aetosaurus than to the last common ancestor of Desmatosuchus. The only synapomorphy that diagnoses the clade Aetosaurinae is the medial offset of the dorsal eminences of the paramedian osteoderms. A phylogenetic study in 2012 found Aetosaurinae to be paraphyletic, with Aetosaurus being the basal-most stagonolepidid and aetosaurines like Calyptosuchus, Neoaetosauroides, and the newly described Aetobarbakinoides being successively more derived taxa leading up to a clade containing Desmatosuchinae and Typothoracisinae. Under this phylogeny, most traditional aetosaurines are more closely related to Desmatosuchus than they are to Aetosaurus, and the clade Aetosaurinae can only include Aetosaurus. However, new phylogenies have recovered Typothoracisinae within Aetosaurinae, making Aetosaurinae a valid clade once more.
Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids comprised an early diverging clade or a paraphyletic grade within ornithischian dinosaurs. Silesaurids have a consistent general body plan, with a fairly long neck and legs and possibly quadrupedal habits, but it is important to note that most sileaurids are heavily fragmentary nonetheless. Furthermore, they occupied a variety of ecological niches, with early silesaurids being carnivorous and later taxa having adaptations for specialized herbivory. As indicated by the contents of referred coprolites, Silesaurus may have been insectivorous, feeding selectively on small beetles and other arthropods.
Doswelliidae is an extinct family of carnivorous archosauriform reptiles that lived in North America and Europe during the Middle to Late Triassic period. Long represented solely by the heavily-armored reptile Doswellia, the family's composition has expanded since 2011, although two supposed South American doswelliids were later redescribed as erpetosuchids. Doswelliids were not true archosaurs, but they were close relatives and some studies have considered them among the most derived non-archosaurian archosauriforms. They may have also been related to the Proterochampsidae, a South American family of crocodile-like archosauriforms.
Aetobarbakinoides is an extinct genus of stagonolepidid aetosaur known from the Late Triassic of Rio Grande do Sul state, southern Brazil. Fossils have been found from the Santa Maria Supersequence of the late Carnian and early Norian stages, making Aetobarbakinoides one of the oldest aetosaurs. The type species, A. brasiliensis, was named in 2012, and is notable for being described primarily by features of the vertebrae; most other aetosaurs are diagnosed by features in bony plates called osteoderms, which are by far the most common material. Although placed in a basal phylogenetic position among aetosaurs, Aetobarbakinoides is closely related to both desmatosuchines and typothoracisines, two derived clades of aetosaurs.
Polesinesuchus is an extinct genus of stagonolepidid aetosaur known from the Late Triassic of southern Brazil. Fossils have been found from the Santa Maria Supersequence of the late Carnian and early Norian stages, making Polesinesuchus one of the oldest aetosaurs. It contains a single species, Polesinesuchus aurelioi, the fifth aetosaur species known from South America to date. Anatomical evidence suggests that Polesinesuchus likely represents a juvenile individual of the contemporary Aetosauroides.
Gorgetosuchus is an extinct genus of aetosaur from the Late Triassic of the eastern United States, represented by the type species Gorgetosuchus pekinensis. G. pekinensis was named and described by Heckert et al. (2015) on the basis of ten rows of bony plates called osteoderms, representing the front part of an armored carapace that would have covered the back of the animal. These plates were found embedded in sandstone and conglomerate boulders near a brick quarry in Chatham County, North Carolina, which likely originated from the Late Triassic Pekin Formation.. Gorgetosuchus was part of a diverse faunal community in a continental rift valley system during the Late Triassic, which also included traversodontids, phytosaurs, dicynodonts, and temnospondyls. Gorgetosuchus coexisted with two other aetosaurs, Lucasuchus and Coahomasuchus.
Kwanasaurus is an extinct genus of silesaurid dinosauromorph reptiles from the Late Triassic of Colorado. It is known from a single species, Kwanasaurus williamparkeri. Kwanasaurus had a deeper, stronger skull and greater specialization for herbivory compared to other silesaurids. It also possessed many unique characteristics of the snout, ilium, and lower part of the femur. It was described along with new specimens of Dromomeron from the Eagle Basin, the northernmost extent of the Chinle Formation.
