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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.
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.
Stagonolepis is an extinct genus of stagonolepidid aetosaur known from the Late Triassic Hassberge Formation of Germany, the Drawno Beds of Poland, the Lossiemouth Sandstone of Scotland, the Chinle Formation of Arizona and Utah and the Bluewater Creek Formation of New Mexico.
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.
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.
Rioarribasuchus is a genus of aetosaur. Fossils have been found from the Chinle Formation in Arizona and New Mexico that date back to the upper Late Carnian stage of the Late Triassic.
Hoplitosuchus is an extinct genus of aetosaur. Fossils have been found from the Santa Maria Formation in Rio Grande do Sul, Brazil that date back to the Late Triassic. At first the genus was named Hoplitosaurus, but this name had previously been assigned to a polacanthine ankylosaurian dinosaur in 1902, thirty-six years before it had been referred to the aetosaur. Thus Hoplitosuchus was constructed as a replacement name for Hoplitosaurus. Because the holotype specimen consists of unidentifiable osteoderms and any other material attributed to the genus may actually be considered a composite of rauisuchian and dinosaurian remains, Hoplitosuchus is now considered to be a nomen dubium. The saurischian dinosaur Teyuwasu was named in 1999 on the basis of material originally attributed to Hoplitosuchus.
Leptosuchus is an extinct genus of leptosuchomorph phytosaurid with a complex taxonomical history. Fossils have been found from the Dockum Group and lower Chinle Formation outcropping in Texas, New Mexico, and Arizona, USA, and date back to the Carnian stage of the Late Triassic.
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.
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 in the osteoderms. These include tongue-and-groove articulations for lateral plates present in dorsal presacral paramedian plates and large spikes on the lateral cervical, dorsal, and caudal plates.
Kayentavenator is a genus of small carnivorous tetanuran dinosaur that lived during the Early Jurassic Period; fossils were recovered from the Kayenta Formation of northeastern Arizona and were described in 2010.
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 genus has been found from the Redonda Formation in east-central New Mexico. The type species, R. reseri, was named in 1991 after having been referred to as a species of Typothorax since 1985. A second species, R. rineharti, was described in 2006.
Francosuchus is a dubious genus of probably basal phytosaur known from the Late Triassic of Bavaria, southern Germany. It was named by Oskar Kuhn in 1933 and the type species is Francosuchus broilii. In the same article Kuhn also named a second species Francosuchus latus. Both species were known solely from their holotypes, two partial skulls that were housed at the Bavarian State Collection for Palaeontogy and Geology. Both specimens were collected at Ebrach Quarry, bed number 13 from the late Carnian-aged Blasensandstein Member of the Hassberge Formation. As the holotypes were destroyed during World War II and poorly documented, Francosuchus and its species are usually considered to be nomina dubia.
Apachesuchus is an extinct genus of aetosaur from the Late Triassic of Quay County, eastern New Mexico.
References
- ↑ Carroll, R.L. (1988). Vertebrate Paleontology and Evolution . WH Freeman and Company, New York ISBN 0-7167-1822-7
- ↑ Kuhn, O. (1936). "Weitere Parasuchier und Labyrinthodonten aus dem Blasensandstein des mittleren Keuper von Ebrach". Palaeontographica. 83: 61–98.
- ↑ Langer, M. C. (2005). "Studies on continental Late Triassic tetrapod biochronology. II. The Ischigualastian and a Carnian global correlation" (PDF). Journal of South American Earth Sciences. 19 (2): 219–239. Bibcode:2005JSAES..19..219L. doi:10.1016/j.jsames.2005.04.002.
- ↑ Benton, M.J.; Walker, A.D. (1985). "Palaeoecology, taphonomy, and dating of Permo-Triassic reptiles from Elgin, north-east Scotland". Palaeontology . 28: 207–234.
- ↑ Heckert, A. B.; Lucas, S. G. (1999). "A new aetosaur (Reptilia: Archosauria) from the Upper Triassic of Texas and the phylogeny of aetosaurs". Journal of Vertebrate Paleontology . 19 (1): 50–68. CiteSeerX 10.1.1.563.9516 . doi:10.1080/02724634.1999.10011122.
- ↑ Heckert, A. B., and Lucas, S. G. (2000). Taxonomy, phylogeny, biostratigraphy, biochronology, paleobiogeography, and evolution of the Late Triassic Aetosauria (Archosauria:Crurotarsi). Zentralblatt für Geologie und Paläontologie Teil I 1998 Heft 11-12, p. 1539-1587.
- ↑ Lucas, S. G. (2007). "Global Triassic tetrapod biostratigraphy and biochronology: 2007 status". New Mexico Museum of Natural History and Science Bulletin. 41: 229–240.
- ↑ Parker, W. G. (2003). Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of Northern Arizona. Unpublished MS thesis. Northern Arizona University, Flagstaff. 315 pp.
