Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typically toothless beak, unique amongst all synapsids. Dicynodonts first appeared in Southern Pangaea during the mid-Permian, ca. 270–260 million years ago, and became globally distributed and the dominant herbivorous animals in the Late Permian, ca. 260–252 Mya. They were devastated by the end-Permian Extinction that wiped out most other therapsids ca. 252 Mya. They rebounded during the Triassic but died out towards the end of that period. They were the most successful and diverse of the non-mammalian therapsids, with over 70 genera known, varying from rat-sized burrowers to elephant-sized browsers.
Robertia is an extinct genus of small herbivorous dicynodonts from the Middle to Late Permian of South Africa, between 260 and 265 million years ago. It is a monospecific genus, consisting of the type-species R. broomiana, which was classified by Lieuwe Dirk Boonstra in 1948 and named in honor of Robert Broom for his study of South African mammal-like reptiles.
Cistecephalus is an extinct genus of dicynodont therapsid from the Late Permian of southern Africa. It was a small, specialised, burrowing dicynodont, possibly with habits similar to a modern mole. The head was flattened and wedge-shaped, the body long, and the forelimbs very strong, with similarities in structure to the forelimb of modern burrowing mammals.
"Dromasaurs" are an artificial grouping of small anomodont therapsids from the Middle and Late Permian of South Africa. They represent either a paraphyletic grade or a polyphyletic grouping of small non-dicynodont basal anomodonts rather than a clade, and as such are considered an invalid group today. "Dromasaurs" were historically united by their superficially similar appearances that were unlike other known anomodonts. They are all small in size with slender limbs and long tails, and have short skulls with very large eye sockets. "Dromasauria" traditionally includes three genera, all from the Karoo Supergroup of South Africa: Galepus, Galechirus, and Galeops. These genera have sometimes been divided into two subgroups, the monotypic family Galeopidae and the Galechiridae for Galechiris and Galepus.
Dicynodon is a genus of dicynodont therapsid that flourished during the Upper Permian period. Like all dicynodonts, it was an herbivorous animal. This synapsid was toothless, except for prominent tusks, hence the name. It probably cropped vegetation with a horny beak, much like a tortoise, while the tusks may have been used for digging up roots and tubers.
Emydops is an extinct genus of dicynodont therapsids from the Middle Permian to Late Permian of what is now South Africa. The genus is generally small and herbivorous, sharing the dicynodont synapomorphy of bearing two tusks. In the following years, the genus grew to include fourteen species. Many of these species were erected on the basis of differences in the teeth and the positioning of the frontal and parietal bones. A 2008 study narrowed Emydops down to two species, E. arctatus and the newly described E. oweni.
Aelurognathus is an extinct genus of gorgonopsian therapsids from the Permian of South Africa and Zambia.
Dicynodontoides is a genus of small to medium-bodied, herbivorous, emydopoid dicynodonts from the Late Permian. The name Dicynodontoides references its “dicynodont-like” appearance due to the caniniform tusks featured by most members of this infraorder. Kingoria, a junior synonym, has been used more widely in the literature than the more obscure Dicynodontoides, which is similar-sounding to another distantly related genus of dicynodont, Dicynodon. Two species are recognized: D. recurvidens from South Africa, and D. nowacki from Tanzania.
Pelanomodon is an extinct genus of dicynodont therapsids that lived in the Late Permian period. Fossil evidence of this genus is principally found in the Karoo Basin of South Africa, in the Dicynodon Assemblage Zone. Lack of fossil record after the Late Permian epoch suggests that Pelanomodon fell victim to the Permian-Triassic extinction event.
Lystrosauridae is a family of dicynodont therapsids from the Permian and Triassic time periods. It includes two genera, Lystrosaurus and Kwazulusaurus. Kwazulusaurus includes a single species, K. shakai, from the Late Permian of South Africa and Lystrosaurus includes many species from the Late Permian and Early Triassic of South Africa, India, and Antarctica.
Venyukovioidea is an infraorder of anomodont therapsids related to dicynodonts from the Permian of Russia. They have also been known as 'Venjukovioidea', as well as by the similar names 'Venyukoviamorpha' or 'Venjukoviamorpha' in literature. This in part owes to a misspelling by Russian palaeontologist Ivan Efremov in 1940 when he mistakenly spelt Venyukovia, the namesake of the group, with a 'j' instead of a 'y', which permeated through subsequent therapsid literature before the mistake was caught and corrected. The order Ulemicia has also been coined for a similar taxonomic concept in Russian scientific literature, which notably excludes Suminia and Parasuminia.
Chainosauria is a large and speciose clade of anomodont therapsid that includes the highly diverse dicynodonts and a small number of closely related basal genera —although the total composition and taxonomic scope of Chainosauria is in flux. Chainosauria was named in 1923 to group together the dicynodonts and their close relatives, namely three small anomodont genera from South Africa that made up the now defunct group 'Dromasauria'. The name soon fell into disuse, however, as it was functionally replaced by Anomodontia. Chainosauria was later revived cladistically in 2009, preserving the association of dicynodonts and the 'dromasaurs' and has since served in effect as both a cladistic and a biogeographic counterpart to the Laurasian venyukovioids, with early chainosaurs appearing to have been a Gondwanan radiation.
Syops is an extinct genus of dicynodont therapsid. The type species S. vanhoepeni was first named in 1938 as Dicynodon vanhoepeni. Fossils of the genus have been found in the Cistecephalus Assemblage Zone in the Usili Formation of the Ruhuhu Basin, Tanzania and the Upper Madumabisa Mudstone Formation of the Luangwa Basin, Zambia. Its phylogenetic placement is somewhat uncertain, with multiple different studies finding it as either a basal geikiid, rhachiocephalid a dicynodontoid more derived than the most basal genera but less derived than Lystrosauridae, or a lystrosaurid.
Basilodon is an extinct genus of dicynodont therapsid. The type species, Basilodon woodwardi was originally named in 1921 as Dicynodon woodwardi. Fossils have been found in the Cistecephalus Assemblage Zone and Dicynodon Assemblage Zone of the Balfour Formation of the Beaufort Group in South Africa.
Therochelonia is a group of dicynodont therapsids. The group was named by British paleontologist Harry Seeley in 1894 and fell into disuse in the following century. Therochelonia was redefined as a node-based clade in 2009. It is defined as the last common ancestor of Cistecephalus microrhinus and Dicynodon lacerticeps, and all of its descendants. Below is a simplified cladogram from Kammerer et al. (2011) showing the phylogenetic placement of Therochelonia:
Gordonia is an extinct genus of dicynodont therapsid from the Late Permian of Scotland. Fossils have been found from the Elgin sandstone of Cutties Hillock Sandstone in Elgin, Moray. These are among the many amniote fossils referred to as the Elgin Reptiles. Gordonia was named in 1893 with four species: G. traquairi, G. duffiana, G. huxleyana, and G. juddiana. Currently, the only recognized species is the type G. traquairi. All other species are considered synonyms of the type.
Bidentalia is a group of dicynodont therapsids. Bidentalia was one of the first names used to describe dicynodonts; the group was established in 1876, while the name "bidentals" dates back as far as 1845. With the increasing prominence of phylogenetics, the group was redefined as a clade in 2009. Bidentalia is now considered a stem-based taxon that includes all taxa more closely related to Aulacephalodon bainii and Dicynodon lacerticeps than Emydops arctatus.
Daqingshanodon is an extinct genus of dicynodont therapsid from the Late Permian of Inner Mongolia, China. The type species D. limbus was described in 1989 from a single skull found in the Naobaogou Formation. Daqingshanodon belongs to a group of dicynodonts called cryptodonts. It is the smallest known cryptodont, and the only one known from China. Like other cryptodonts, it has a pair of rounded nasal bosses above its nostrils and a ridge of bone on the upper jaw called the postcaniniform process. Daqingshanodon has a pair of elongated, recurved tusks extending from its beak-like snout. It is distinguished from other dicynodonts by the presence of a distinct ridge running along the side of the skull from below the eye socket to the area around the tusks. The skull of Daqingshanodon is less than 10 centimetres (3.9 in) long, yet this specimen is thought to have been an adult on the basis of its well-developed nasal bosses.
Kunpania is an extinct genus of dicynodont therapsid from the Quanzijie Formation of Xinjiang, China. The type and only species is K. scopulusa, and it is known only by a single incomplete specimen including parts of the skull and forelimb. Since its initial description in 1978 by palaeontologist Ailing Sun, it has sometimes been considered to be another species of Dicynodon by other researchers, or potentially undiagnostic. However, a redescription in 2021 reaffirmed its distinctiveness, including a uniquely well developed muscle attachment on the humerus. Kunpania is perhaps the oldest known member of the derived dicynodont group Dicynodontoidea, potentially dating to the Middle Permian period during the Capitanian, and so may fill a knowledge gap in the history of dicynodont evolution.
Counillonia is an extinct genus of dicynodont therapsid from the area of Luang Prabang in Laos, Southeast Asia that lived at around the time of the Permian-Triassic boundary and possibly dates to the earliest Early Triassic. Its type and only known species is C. superoculis. Counillonia was related to the Triassic dicynodonts such as Lystrosaurus and the Kannemeyeriiformes that survived the Permian mass extinction, but it was more closely related to the Permian genus Dicynodon than to either of these lineages. Counillonia may then possibly represent another line of dicynodonts that survived the Permian mass extinction into the Triassic period, depending on its age. The discovery of Counillonia in Laos and its unexpected evolutionary relationships hint at the less well understood geographies of dicynodont diversity across the Permo-Triassic boundary outside of well explored regions like the Karoo Basin in South Africa.
