| Euscolosuchus Temporal range: Late Triassic | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | † Aetosauriformes |
| Genus: | † Euscolosuchus Sues, 1992 |
| Type species | |
| †Euscolosuchus olseni Sues, 1992 | |
Euscolosuchus is an extinct genus of suchian archosaurs from the Late Triassic of Virginia. It is probably an aetosauriform, as the sister taxon to Acaenasuchus and a relative of aetosaurs. [1]
Fossils have been found from the Tomahawk Creek Member of the Turkey Branch Formation (part of the Newark Supergroup), outcropping in the Richmond Basin of east-central Virginia. The locality from which the material was found dates back to the early Carnian stage of the Late Triassic, based on palynological studies. These strata are known for the abundance of fossil material belonging to tetrapod vertebrates in relation to other sites of the Newark Supergroup in the Richmond Basin that generally lack such material. The site is unique among others in the supergroup and closely resembles localities in the southern hemisphere, as is suggested by the presence of numerous fossils of traversodont cynodonts found from the area. Other tetrapods present include procolophonians, [2] chiniquodontids, and sphenodonts. [3]
The name Euscolosuchus, meaning "well pointed crocodile" in Greek, refers to the prominent lateral spikes projecting from the posterior cervical and dorsal osteoderms that are characteristic of the genus. These osteoderms imbricate (overlap) paramedially down the back and form a narrow dorsal carapace similar to the desmatosuchine stagonolepidids. A spinal table formed by broadened neural arches help support these osteoderms on the back. The scutes interlock with one another through a series of grooves and projections, with each plate overlapping the one posterior to it and having an anterolateral articulatory process project anteriorly from it and lie over the plate in front of it. These osteoderms, as well as the fragmentary vertebrae, are all that are known from the genus and thus the only material from which the genus can be classified. [4]
Euscolosuchus is widely considered to be a pseudosuchian, the side of archosaur reptiles which are more closely related to crocodiles than to birds and other dinosaurs. It was originally described as a close relative of crocodylomorphs, a long-lasting pseudosuchian clade that includes living crocodilians. Other pseudosuchians initially thought to be closely related to crocodylomorphs include the lightly-built Gracilisuchus and possibly Erpetosuchus . [5] [6] More recently, the large carnivorous rauisuchids such as Postosuchus have been singled out as the closest relatives of crocodylomorphs, and some early crocodylomorphs (such as Carnufex and Redondavenator ) were similarly large carnivores. [7]
In the midst of these interpretations of archosaur evolution, Euscolosuchus was left without clear affinities. Some compared it with Acaenasuchus , an equally ambiguous armored archosaur from the Chinle Formation. Acaenasuchus was generally considered a valid small aetosaur or juvenile fossils from an already established aetosaur genus. A 2020 redescription recovered Acaenasuchus and Euscolosuchus as sister taxa (each other's closest relative), and as members of the Aetosauriformes. This means that they were not true aetosaurs, but were still related to them. The herbivorous archosaur Revueltosaurus was also placed as an aetosauriform, a result recovered by many previous analyses. [1]
"Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilians than to birds and other dinosaurs. First named in the 1940s, Rauisuchia was a name exclusive to Triassic archosaurs which were generally large, carnivorous, and quadrupedal with a pillar-erect hip posture, though exceptions exist for all of these traits. Rauisuchians, as a traditional taxonomic group, were considered distinct from other Triassic archosaur groups such as early dinosaurs, phytosaurs, aetosaurs, and crocodylomorphs.
Aetosaurs are 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 and other dinosaurs. 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 in which they are found.
Gracilisuchus is an extinct genus of tiny pseudosuchian from the Late Triassic of Argentina. It contains a single species, G. stipanicicorum, which is placed in the clade Suchia, close to the ancestry of crocodylomorphs. Both the genus and the species were first described by Alfred Romer in 1972.
Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs". Despite Pseudosuchia meaning "false crocodiles", the name is a misnomer as true crocodilians are now defined as a subset of the group.
Prestosuchidae is a polyphyletic grouping of carnivorous archosaurs that lived during the Triassic. They were large active terrestrial apex predators, ranging from around 2.5 to 7 metres in length. They succeeded the Erythrosuchidae as the largest archosaurs of their time. While resembling erythrosuchids in size and some features of the skull and skeleton, they were more advanced in their erect posture and crocodile-like ankle, indicating more efficient gait. "Prestosuchids" flourished throughout the whole of the middle, and the early part of the late Triassic, and fossils are so far known from Europe, India, Africa (Tanzania), Argentina, and Paleorrota in Brazil. However, for a long time experts disagree regarding the phylogenetic relationships of the group, what genera should be included, and whether indeed the "Prestosuchidae" constitute a distinct family.
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.
Terrestrisuchus is an extinct genus of very small early crocodylomorph that was about 76 centimetres (30 in) long. Fossils have been found in Wales and Southern England and date from near the very end of the Late Triassic during the Rhaetian, and it is known by type and only known species T. gracilis. Terrestrisuchus was a long-legged, active predator that lived entirely on land, unlike modern crocodilians. It inhabited a chain of tropical, low-lying islands that made up southern Britain, along with similarly small-sized dinosaurs and abundant rhynchocephalians. Numerous fossils of Terrestrisuchus are known from fissures in limestone karst which made up the islands it lived on, which formed caverns and sinkholes that preserved the remains of Terrestrisuchus and other island-living reptiles.
Longosuchus is an extinct genus of desmatosuchin aetosaur from the Late Triassic of North America. Reported fossils from Morocco are likely misidentified scutes of a paratypothoracin aetosaur. Longosuchus measured about 3 metres in length.
Dromicosuchus is an extinct genus of sphenosuchian, a type of basal crocodylomorph, the clade that comprises the crocodilians and their closest kin. It was found in Upper Triassic rocks of North Carolina, United States, and is known from a nearly complete skull and partial skeleton. This specimen is unusual in that it was found beneath the skeleton of a larger rauisuchian and has apparent bite damage, suggesting that it was attacked by the larger carnivore before both died and were buried together.
Typothorax is an extinct genus of typothoracine 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.
Turfanosuchus is a genus of archosauriform reptile, likely a gracilisuchid archosaur, which lived during the Middle Triassic (Anisian) of northwestern China. The type species, T. dabanensis, was described by C.C. Young in 1973, based on a partially complete but disarticulated fossil skeleton found in the Kelamayi Formation of the Turfan Basin.
Dyoplax is an extinct genus of pseudosuchian archosaur, possibly an erpetosuchid. Fossils have been found from the type locality within the upper Schilfsandstein Formation in Stuttgart, Germany. The holotype specimen was a natural cast of a nearly complete skeleton that lacked only parts of the tail and limb bones.
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.
Platyognathus is an extinct genus of protosuchian crocodyliform. Fossils are known from the Early Jurassic Lower Lufeng Formation in Yunnan, China and belong to the type and only species, P. hsui.
Suchia is a clade of archosaurs containing the majority of pseudosuchians. It was defined as the least inclusive clade containing Aetosaurus ferratus, Rauisuchus tiradentes, Prestosuchus chiniquensis, and Crocodylus niloticus by Nesbitt (2011). Generally the only pseudosuchian group which is omitted from Suchia is the family Ornithosuchidae, although at least one analysis classifies ornithosuchids as close relatives of erpetosuchids and aetosaurs. Phytosaurs are also excluded from Suchia, although it is not certain whether they qualify as pseudosuchians in the first place.
Paracrocodylomorpha is a clade of pseudosuchian archosaurs. The clade includes the diverse and unusual group Poposauroidea as well as the generally carnivorous and quadrupedal members of Loricata, including modern crocodylians. Paracrocodylomorpha was named by paleontologist J. Michael Parrish in 1993, although the group is now considered to encompass more reptiles than his original definition intended. The most recent definition of Paracrocodylomorpha, as defined by Sterling Nesbitt in 2011, is "the least inclusive clade containing Poposaurus and Crocodylus niloticus. Most groups of paracrocodylomorphs became extinct at the end of the Triassic period, with the exception of the crocodylomorphs, from which crocodylians such as crocodiles and alligators evolved in the latter part of the Mesozoic.
Erpetosuchidae is an extinct family of pseudosuchian archosaurs. Erpetosuchidae was named by D. M. S. Watson in 1917 to include Erpetosuchus. It includes the type species Erpetosuchus granti from the Late Triassic of Scotland, Erpetosuchus sp. from the Late Triassic of eastern United States and Parringtonia gracilis from the middle Middle Triassic of Tanzania; the group might also include Dyoplax arenaceus from the Late Triassic of Germany, Archeopelta arborensis and Pagosvenator candelariensis from Brazil and Tarjadia ruthae from Argentina.
The Manda Formation is a Middle Triassic (Anisian?) or possibly Late Triassic (Carnian?) geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Triassic, including some of the earliest dinosauromorph archosaurs. The formation is often considered to be Anisian in age according to general tetrapod biochronology hypotheses and correlations to the Cynognathus Assemblage Zone of South Africa. However, some recent studies cast doubt to this age, suggesting that parts deposits may actually be younger (Carnian) in age.
The Colorado City Formation is a Late Triassic geologic formation in the Dockum Group of Texas, United States. It has previously been known as the Iatan Member, Colorado City Member or 'Pre-Tecovas Horizon'.
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