Dracohors is a clade of dinosauriform archosaurs that includes dinosaurs and silesaurids. The oldest known dracohorsian is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period. According to Andrea Cau (2018), the synapomorphies of dracohorsians are:
The anterior tympanic recess, the axial epipophyses, the centrodiapophyseal laminae in the presacral vertebrae, the relative size enlargement of the postacetabular process of ilium, the elongation of the pubis, the proximal sulcus and the reduction of the ligament tuber in the femoral head, and the further reduction in length of the fourth metatarsal and toe compared to the third.
Cau defined the group as the "most inclusive clade containing Megalosaurus bucklandii Mantell, 1827, but excluding Marasuchus lilloensis (Romer, 1971)." A good consensus of phylogenetic work supports the sister grouping of silesaurids and dinosaurs, but the interrelationships within Dinosauria have been debated. Of particular debate are the positions of various basal Triassic dinosaurs such as Eodromaeus, Daemonosaurus, Pisanosaurus, and herrerasaurids; and the interrelationships of the major dinosaur groups Sauropodomorpha, Theropoda, and Ornithischia. The reason for this uncertainty is the taxon sampling size and the implications of how they affect the coding for the phylogenetic tree. In his paper about the stepwise evolution of the avian bauplan, Cau (2018) found in the parsimony analysis polytomy between herrerasaur-grade taxa, Sauropodomorpha and the controversial Ornithoscelida. The Bayesian analysis, however, found a weak support for the sister grouping of a Dinosauria and Herrerasauria, but showed strong support for the dichotomy between Sauropodomorpha and Ornithoscelida as shown below:
|Mounted skeleton of Asilisaurus, the oldest known dracohorsian.|
Agnosphitys (; "unknown begetter"; sometimes mistakenly called Agnostiphys or Agnosphytis is a genus of silesaurid dinosauriform that lived during the Late Triassic. It contains only one species, the type species A. cromhallensis. Its remains include an ilium, maxilla, astragalus and humerus, which date variously from the Norian and Rhaetian stages of the Late Triassic.
The type species, Agnosphitys cromhallensis, was described by Nicholas Fraser, Kevin Padian, Gordon Walkden and A. L. M Davis in early 2002. The fossils, consisting of a partial skeleton including referred material, were found in Avon, England.Avemetatarsalia
Avemetatarsalia (meaning "bird metatarsals") is a clade name established by British palaeontologist Michael Benton in 1999 for all crown group archosaurs that are closer to birds than to crocodilians. An alternate name is Pan-Aves, or "all birds", in reference to its definition containing all animals, living or extinct, which are more closely related to birds than to crocodilians. Almost all avemetatarsalians are members of a similarly defined subgroup, Ornithodira. Ornithodira is defined as the last common ancestor of dinosaurs and pterosaurs, and all of its descendants.Members of this group include the Dinosauromorpha, Pterosauromorpha, the genus Scleromochlus, and Aphanosauria. Dinosauromorpha contains more basal forms, including Lagerpeton and Marasuchus, as well as more derived forms, including dinosaurs. Birds belong to the dinosaurs as members of the theropods. Pterosauromorpha contains Pterosauria, which were the first vertebrates capable of true flight. Aphanosauria is a Triassic group of gracile carnivorous quadrupeds which was recognized in 2017.Averostra
Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.Avetheropoda
Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.Cerapoda
Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.Dinosauriformes
Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.Diodorus scytobrachion
Diodorus is a genus of silesaurid dinosauriforms (relatives of basal dinosaurs) from the Late Triassic (Carnian - Norian) Timezgadiouine Formation of the Argana Basin of Morocco. It is named after Diodorus, a legendary king of the Berber people and son of Sufax, the founder of Tangier and also in honour of Diodorus Siculus, a 1st-century Greek historian who wrote about North Africa. The specific epithet, scytobrachion, is ancient Greek for "leather armed", but also honors Dionysius Scytobrachion, a mythographer who chronicled the mythical history of North Africa. The holotype and all referred remains were found in a single quarry at the base of the Irohalene Mudstone Member of the Timezgadiouine Formation in the northeastern Argana Basin, 2.9 kilometres (1.8 mi) east of Imziln, Morocco.
Diodorus can be distinguished from other silesaurids by the presence of forward-slanted teeth that decrease in size towards the front end of the dentary (lower jaw) and a distinct side ridge running parallel to the dentary tooth socket margin. In a phylogenetic analysis, Diodorus was found to be the sister taxon to the Brazilian silesaurid Sacisaurus.Eucoelophysis
Eucoelophysis (meaning "true hollow form") is a genus of dinosauriform from the Late Triassic (Norian) period Chinle Formation of New Mexico. It was assumed to be a coelophysid upon description, but a study by Nesbitt et al. found that it was actually a close relative of Silesaurus, which was independently supported by Ezcurra (2006), who found it to be the sister group to Dinosauria, and Silesaurus as the next most basal taxon.However, the relationships of Silesaurus are uncertain. Dzik found it to be a dinosauriform (the group of archosaurs from which the dinosaurs evolved), but did not rule out the possibility that it represents a primitive ornithischian.Ignotosaurus
Ignotosaurus is an extinct genus of silesaurid dinosauriform known from the Late Triassic (Carnian) Cancha de Bochas Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern Argentina. It was therefore contemporary with early dinosaurs such as Herrerasaurus, and lived in the same place.Jingshanosaurus
Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.Lewisuchus
Lewisuchus is a genus of archosaur that lived during the Middle Triassic (Ladinian); it was a silesaurid dinosauriform, a member of the group of reptiles which led to the dinosaurs. Lewisuchus was about 1 metre (3.3 ft) long. Fossils have been found in the Chañares Formation of Argentina. It exhibited osteoderms along its back.Lutungutali
Lutungutali (meaning "high hip" in the Bemba language) is an extinct genus of silesaurid dinosauriform from the Middle Triassic of Zambia. The single type species of the genus is Lutungutali sitwensis. Lutungutali was named in 2013 and described from a fossil specimen, holotype NHCC LB32, including hip bones and tail vertebrae. The specimen was collected in 2009 from the upper Ntawere Formation, which dates to the Anisian stage of the Middle Triassic. Lutungutali is the first known silesaurid from Zambia and, along with the Tanzanian silesaurid Asilisaurus and dinosauriform Nyasasaurus, the oldest bird-line archosaur known from body fossils (i.e. parts of the skeleton).Neotheropoda
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Sacisaurus
Sacisaurus is a silesaurid dinosauriform from the Late Triassic (Norian) Caturrita Formation of southern Brazil. The scientific name, Sacisaurus agudoensis, refers to the city where the species was found, Agudo in the Rio Grande do Sul state, whereas Sacisaurus refers to Saci, a famous one-legged creature from Brazilian mythology, because the fossil skeleton was found with a leg missing.Saltopus
Saltopus ("hopping foot") is a genus of very small bipedal dinosauriform containing the single species S. elginensis from the late Triassic period of Scotland. It is one of the most famous Elgin Reptiles.Silesauridae
Silesauridae is an extinct clade of Triassic dinosauriformes consisting of the closest known relatives of dinosaurs. As indicated by coprolite contents, some silesaurids such as Silesaurus may have been insectivorous, feeding selectively on small beetles and other arthropods.Silesaurus
Silesaurus is a genus of silesaurid dinosauriform from the Late Triassic, approximately 230 million years ago in the Carnian faunal stage of what is now Poland.
Fossilized remains of Silesaurus have been found in the Keuper Claystone in Krasiejów near Opole, Silesia, Poland, which is also the origin of its name. The type species, Silesaurus opolensis, was described by Jerzy Dzik in 2003. It is known from some 20 skeletons, making it one of the best-represented of the early dinosauriformes.Soumyasaurus
Soumyasaurus is a small silesaurid dinosauriform from the Late Triassic (Norian) Cooper Canyon Formation of western Texas.