| Rastodon Temporal range: Mid-Late Permian ~ | |
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Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Suborder: | † Anomodontia |
| Clade: | † Dicynodontia |
| Clade: | † Bidentalia |
| Genus: | † Rastodon Boos et al. 2016 |
| Species | |
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Rastodon is an extinct genus of dicynodont. Uniquely among dicynodonts, its tusks curve forward. The type and only species is R. procurvidens. [1]
Rastodon is derived from the Rio do Rasto Formation, where its remains were found, and the Greek word for "tooth". The species name, R. procurvidens, means "curved forward tooth" and describes its uniquely shaped teeth. [1]
Only a single specimen of Rastodon has been discovered so far. It comes from Guadalupian deposits found at an outcrop of the Rio do Rasto Formation at the Boqueirão Farm, in the municipality of São Gabriel, Rio Grande do Sul, Brazil. .
Rastodon is a fairly typical dicynodont. It bore a beaked head with a single pair of tusks and a keratin-covered nasal boss. However, it does possess several distinctive traits, of which its anteriorly-curved tusks are the most distinctive. Furthermore, its skull is relatively long and shallow compared to its close relatives. Its tusks contacted the lower jaw during propalinal mastication.
Rastodon has been recovered as the basalmost bidentalian dicynodont. [1] However, the phylogenetic position of Rastodon is contentious, [2] for it has also been recovered as the basalmost emydopoid dicynodont. [3]
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.
Stahleckeria is an extinct genus of Middle Triassic (Ladinian) dicynodonts. It lived about 240 million years ago in what is now Brazil and Namibia. As a member of the group Kannemeyeriiformes, it was similar to the genus Kannemeyeria. The genus is known from the type species Stahleckeria potens, which was first collected from the Ladinian-age Santa Maria Formation in the Paleorrota fossil site of Brazil. Stahleckeria was named in honor of Rudolf Stahlecker, who discovered the first specimens during a 1935 expedition led by paleontologist Friedrich von Huene to the Chiniquá fossil site.
Stahleckeriidae is a family of dicynodont therapsids whose fossils are known from the Triassic of North America, South America, Asia and Africa.
Dinodontosaurus is a genus of dicynodont therapsid. It was medium to large dicynodont of the Triassic and had a beak corneum. It lived in the Middle Triassic but disappeared in the Upper Triassic.
Eosimops is an extinct genus of pylaecephalid dicynodonts. They were small synapsids superficially resembling modern mammals. Eosimops is known from several skull specimens, as well as one complete skeleton. Eosimops lived during the Middle Permian of South Africa.
Rechnisaurus is an extinct genus of dicynodont from the Middle Triassic (Anisian) Yerrapalli Formation of India. It contains a single species, Rechnisaurus cristarhynchus.
Vinceria is an extinct genus of kannemeyeriiform dicynodont in the family Shansiodontidae. Fossils of the genus have been found in the Anisian Cerro de las Cabras Formation and Carnian Río Seco de la Quebrada Formation of Argentina. One species, V. argentinensis, named in 1966, was moved to its own genus, Acratophorus, in 2021. Another species, V. vieja, was merged with Acratophorus argentinensis in 2021, leaving V. andina as the only species in the genus.
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.
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.
Pylaecephalidae is a family of dicynodont therapsids that includes Diictodon, Robertia, and Prosictodon from the Permian of South Africa. Pylaecephalids were small burrowing dicynodonts with long tusks. The family was first named in 1934 and was redefined in 2009. Diictodontidae and Robertiidae are considered junior synonyms of Pylaecephalidae; although Pylaecephalus itself is considered a junior synonym of Diictodon, the name Pylaecephalidae predates these names and therefore takes priority.
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.
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.
Pampaphoneus is an extinct genus of carnivorous dinocephalian therapsid belonging to the family Anteosauridae. It lived 268 to 265 million years ago during the Wordian age of the Guadalupian period in what is now Brazil. Pampaphoneus is known by an almost complete skull with the lower jaw still articulated, discovered on the lands of the Boqueirão Farm, near the city of São Gabriel, in the state of Rio Grande do Sul. A second specimen from the same locality was reported in 2019 and 2020 but has not yet been described. It is composed of a skull associated with postcranial remains. It is the first South American species of dinocephalian to have been described. The group was previously known in South America only by a few isolated teeth and a jaw fragment reported in 2000 in the same region of Brazil. Phylogenetic analysis conducted by Cisneros and colleagues reveals that Pampaphoneus is closely related to anteosaurs from European Russia, indicating a closer faunal relationship between South America and Eastern Europe than previously thought, thus promoting a Pangea B continental reconstruction.
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.
The Rio do Rasto Formation is a Late Permian sedimentary geological formation in the South Region of Brazil. The official name is Rio do Rasto, although in some publications it appears as Rio do Rastro.
Anomocephaloidea is a clade of basal anomodont therapsids related to the dicynodonts known from what is now South Africa and Brazil during the Middle Permian. It includes only two species, Anomocephalus africanus from the Karoo Basin of South Africa and Tiarajudens eccentricus from the Paraná Basin of Brazil. Anomocephaloidea was named in 2011 with the discovery of Tiarajudens, although Anomocephalus itself has been known since 1999.
Bulbasaurus is an extinct genus of dicynodont that is known from the Lopingian epoch of the Late Permian period of what is now South Africa, containing the type and only species B. phylloxyron. It was formerly considered as belonging to Tropidostoma; however, due to numerous differences from Tropidostoma in terms of skull morphology and size, it has been reclassified the earliest known member of the family Geikiidae, and the only member of the group known from the Tropidostoma Assemblage Zone. Within the Geikiidae, it has been placed close to Aulacocephalodon, although a more basal position is not implausible.
Taoheodon is an extinct genus of dicynodont therapsid from the Sunjiagou Formation in the Shanxi province of China, dated to the Wuchiapingian age of the Late Permian. Its type and only known species is T. baizhijuni. Taoheodon was a close relative of the well known Dicynodon, and may represent a biogeographical link between the South African Dicynodon and similar dicynodonts found in Laos.
Acratophorus is an extinct genus of dicynodont that lived during the Anisian age of the Middle Triassic-aged Río Seco de la Quebrada Formation in what is now Argentina. The type species, A. argentinensis, was originally placed in the genus Kannemeyeria by Jose Bonaparte in 1966, and later sometimes referred to Vinceria, before being transferred to a new, distinct genus, Acratophorus, in 2021 by Christian Kammerer and Angi Ordoñez. The species Vinceria vieja was also made a synonym of A. argentinensis in 2021. The holotype is PVL 3645, a partial skeleton discovered near a farm house in Puesto Viejo.
Elphidae is a clade of bidentalian dicynodonts containing Elph, Katumbia, and Interpresosaurus. It is exclusively known from the Late Permian of Russia and Tanzania. Elphidae is variously recovered as either at the base of a paraphyletic Cryptodontia, or as basal dicynodontoids.
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