Archosauria is a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term, which includes birds. Extinct archosaurs include non-avian dinosaurs, pterosaurs and extinct relatives of crocodilians. Modern paleontologists define Archosauria as a crown group that includes the most recent common ancestor of living birds and crocodilians, and all of its descendants. The base of Archosauria splits into two clades: Pseudosuchia, which includes crocodilians and their extinct relatives; and Avemetatarsalia, which includes birds and their extinct relatives.
Archosauriformes is a clade of diapsid reptiles encompassing archosaurs and some of their close relatives. It was defined by Jacques Gauthier (1994) as the clade stemming from the last common ancestor of Proterosuchidae and Archosauria. Phil Senter (2005) defined it as the most exclusive clade containing Proterosuchus and Archosauria. Archosauriforms are a branch of archosauromorphs which originated in the Late Permian and persist to the present day as the two surviving archosaur groups: crocodilians and birds.
Phytosaurs are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. and are sometimes referred to as parasuchians. Phytosauria, Parasuchia, Parasuchidae, and Phytosauridae have often been considered equivalent groupings containing the same species. Some recent studies have offered a more nuanced approach, defining Parasuchidae and Phytosauridae as nested clades within Phytosauria as a whole. Phytosaurs were long-snouted and heavily armoured, bearing a remarkable resemblance to modern crocodilians in size, appearance, and lifestyle, as an example of convergence or parallel evolution
Euparkeria is an extinct genus of archosauriform reptile from the Triassic of South Africa. Euparkeria is close to the ancestry of Archosauria, the reptile group that includes crocodilians, pterosaurs, and dinosaurs.
Erythrosuchidae are a family of large basal archosauriform carnivores that lived from the later Early Triassic (Olenekian) to the early Middle Triassic (Anisian).
Proterosuchus is an extinct genus of archosauriform reptiles that lived during the Early Triassic. It contains three valid species: the type species P. fergusi and the referred species P. alexanderi and P. goweri. All three species lived in what is now South Africa. The genus was named in 1903 by the South African paleontologist Robert Broom. The genus Chasmatosaurus is a junior synonym of Proterosuchus.
Ornithosuchidae is an extinct family of pseudosuchian archosaurs from the Triassic period. Ornithosuchids were quadrupedal and facultatively bipedal, meaning that they had the ability to walk on two legs for short periods of time. They had distinctive, downturned snouts, unique, "crocodile-reversed" ankle bones, and several other features that distinguish them from other archosaurs. Ornithosuchids were geographically widespread during the Carnian and Norian stages of the Late Triassic with members known from Argentina, Brazil, and the United Kingdom. Four genera, comprising Ornithosuchus, Venaticosuchus, Dynamosuchus, and Riojasuchus are presently known. The family was first erected by German paleontologist Friedrich von Huene in 1908.
Tasmaniosaurus is an extinct genus of archosauromorph reptile known from the Knocklofty Formation of West Hobart, Tasmania, Australia. The type species is T. triassicus. This genus is notable not only due to being one of the most complete Australian Triassic reptiles known, but also due to being a very close relative of Archosauriformes. Once believed to be a proterosuchid, this taxon is now believed to have been intermediate between advanced non-archosauriform archosauromorphs such as Prolacerta, and basal archosauriforms such as Proterosuchus. Features traditionally used to define Archosauria and later Archosauriformes, such as the presence of an antorbital fenestra and serrated teeth, are now known to have evolved prior to those groups due to their presence in Tasmaniosaurus.
Mesosuchus is an extinct genus of basal Rhynchosaur from early Middle Triassic deposits of Eastern Cape, South Africa. It is known from the holotype SAM 5882, a partial skeleton, and from the paratypes SAM 6046, SAM 6536, SAM 7416 and SAM 7701 from the Aliwal North Euparkeria site. Mesosuchus is quite small, spanning around 30 cm in length. Mesosuchus was discovered and named by David Meredith Seares Watson in 1912.
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.
Euparkeriidae is an extinct family of small carnivorous archosauriforms which lived from the Early Triassic to the Middle Triassic (Anisian). While most other early archosauriforms walked on four limbs, euparkeriids were probably facultative bipeds that had the ability to walk on their hind limbs at times. The most well known member of Euparkeriidae is the species Euparkeria capensis, which was named by paleontologist Robert Broom from the Karoo Basin of South Africa in 1913 and is known from several nearly complete skeletons. The family name was first proposed by German paleontologist Friedrich von Huene in 1920; Huene classified euparkeriids as members of Pseudosuchia, a traditional name for crocodilian-line archosaurs from the Triassic. However, phylogenetic analyses performed in the 21st century place Euparkeriidae as a group of Archosauriformes, a position outside Pseudosuchia and close to the ancestry of both crocodile-line archosaurs and bird-line archosaurs. However, they are probably not direct ancestors of archosaurs.
Dorosuchus is an extinct genus of archosauriform previously assigned to the family Euparkeriidae. It lived during the Anisian stage of the Middle Triassic. Fossil material is known from Sol-Iletsk in Orenburg Oblast, Russia. The type species is D. neoetus, named in 1989.
Koilamasuchus is an extinct genus of indeterminate archosauriform from the Triassic of Argentina. It is based on an external mold of a partial postcranial skeleton from the Quebrada de los Fósiles Formation. Due to its incomplete nature, the relationships of this reptile are difficult to establish. Originally described as a non-archosaur archosauriform, later studies tentatively considered it a doswelliid or a suchian archosaur.
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.
Xilousuchus is an extinct genus of poposauroid from lower Triassic deposits of Fugu County of northeastern Shanxi Province, China. It is known from the holotype, IVPP V 6026, a single well-preserved partial skeleton including the skull. It was found from the Heshanggou Formation of the Ordos Basin, Hazhen commune. It was first named by Xiao-Chun Wu in 1981 and the type species is Xilousuchus sapingensis. Wu (1981) referred Xilousuchus to the Proterosuchia. Gower and Sennikov (1996) found it to be an erythrosuchian based strictly on the braincase. A more detailed re-description of the genus was provided by Nesbitt et al. (2010) and found poposauroid affinities. In his massive revision of archosaurs which included a large cladistic analysis, Sterling J. Nesbitt (2011) found Xilousuchus to be a poposauroid which is most closely related to Arizonasaurus. Xilousuchus is the oldest archosaur to date, although Ctenosauriscus and Vytshegdosuchus might be even older by less than one million year. Since Xilousuchus is a suchian archosaur, its early age suggests that most of the major groups of archosaurs developed by the Early Triassic, soon after the appearance of the first archosaur.
Proterochampsia is a clade of early archosauriform reptiles from the Triassic period. It includes the Proterochampsidae and probably also the Doswelliidae. Nesbitt (2011) defines Proterochampsia as a stem-based taxon that includes Proterochampsa and all forms more closely related to it than Euparkeria, Erythrosuchus, Passer domesticus, or Crocodylus niloticus. Therefore, the inclusion of Doswelliidae in it is dependent upon whether Doswellia and Proterochampsa form a monophyletic group to the exclusion of Archosauria and other related groups.
Epipophyses are bony projections of the cervical vertebrae found in archosauromorphs, particularly dinosaurs. These paired processes sit above the postzygapophyses on the rear of the vertebral neural arch. Their morphology is variable and ranges from small, simple, hill-like elevations to large, complex, winglike projections. Epipophyses provided large attachment areas for several neck muscles; large epipophyses are therefore indicative of a strong neck musculature.
Asperoris is an extinct genus of archosauriform reptile known from the Middle Triassic Manda Beds of southwestern Tanzania. It is the first archosauriform known from the Manda Beds that is not an archosaur. However, its relationships with other non-archosaurian archosauriforms are uncertain. It was first named by Sterling J. Nesbitt, Richard J. Butler and David J. Gower in 2013 and the type species is Asperoris mnyama. Asperoris means "rough face" in Latin, referring to the distinctive rough texture of its skull bones.
The Ermaying Formation is a geological formation of Anisian age in north-central China. It is found across much of the Ordos Basin, at outcrops within the provinces of Shaanxi, Shanxi, and Inner Mongolia. It is composed of up to 600 m thick sequence of mudstone and sandstone, overlying the Heshanggou Formation and underlying the Tongchuan Formation. In the southern part of the Ordos Basin, the Zhifang Formation is equivalent to the Ermaying Formation.
Polymorphodon is an extinct genus of archosauriform reptile from the Middle Triassic of Germany. The only known species is Polymorphodon adorfi, discovered in Lower Keuper deposits at a quarry in Eschenau, Germany. Polymorphodon is notable for its heterodont dentition, with long and conical premaxillary teeth followed by thin maxillary teeth with large serrations. Maxillary teeth near the back of the mouth are short and leaf-shaped, similar to some living and extinct reptiles with a herbivorous or omnivorous diet. This may suggest that Polymorphodon had some reliance on plants in its diet, a rarity among basal archosauriforms, most of which are carnivores.
