Dicynodont

Dicynodontia is a taxon of anomodont therapsids with beginnings in the mid-Permian, which were dominant in the Late Permian, survived the Permian Extinction that wiped out most other therapsids and continued on throughout the Triassic before dying out at the end of the period. Dicynodonts were herbivorous
 animals with two tusks, hence their name, which means 'two dog tooth'.
They are also the most successful and diverse of the non-mammalian
therapsids, with over 70 genera known, varying from rat- to elephant-sized.

The dicynodont skull is highly specialised, light but strong, with the synapsid
 temporal openings at the rear of the skull greatly enlarged to
accommodate larger jaw muscles. The front of the skull and the lower jaw
 are generally narrow and, in all but a number of primitive forms,
toothless. Instead, the front of the mouth is equipped with a horny
beak, as in turtles and ceratopsian dinosaurs.
 Food was processed by the retraction of the lower jaw when the mouth
closed, producing a powerful shearing action, which would have enabled
dicynodonts to cope with tough plant material. Many genera also have a
pair of tusks, which it is thought may have been an example of sexual dimorphism.
The body is short, strong and barrel-shaped, with strong limbs. In large genera (such as Dinodontosaurus) the hindlimbs were held erect, but the forelimbs bent at the elbow. Both the pectoral girdle and the ilium are large and strong. The tail is short.
Endothermy and hair
Dicynodonts have long been suspected of being warm-blooded animals. Their bones are highly vascularised and possess Haversian canals,
 and their bodily proportions are conducive to heat preservation. In
young specimens, the bones are so highly vascularised that they exhibit
higher channel densities than most other therapsids. Yet, studies on Late Triassic dicynodont coprolites paradoxically showcase digestive patterns more typical of animals with slow metabolisms.
More recently, the discovery of hair remnants in Permian coprolitespossibly
 vindicates the status of dicynodonts as endothermic animals. As these
coprolites come from carnivorous species and digested dicynodont bones
are abundant, it has been suggested that at least some of these hair
remnants come from dicynodont prey.

Dicynodonts have been known since the mid-1800s. The South African geologist Andrew Geddes Bain
 gave the first description of dicynodonts in 1845. At the time, Bain
was a supervisor for the construction of military roads under the Corps of Royal Engineers
 and had found many reptilian fossils during his surveys of South
Africa. Bain described these fossils in an 1845 letter published in Transactions of the Geological Society of London, calling them "bidentals" for their two prominent tusks. In that same year, the English paleontologist Richard Owen named two species of dicynodonts from South Africa: Dicynodon lacerticeps and Dicynodon bainii.
 Since Bain was preoccupied with the Corps of Royal Engineers, he wanted
 Owen to describe his fossils more extensively. Owen did not publish a
description until 1876 in his Descriptive and Illustrated Catalogue of
the Fossil Reptilia of South Africa in the Collection of the British
Museum. By this time, many more dicynodonts had been described. In
1859, another important species called Ptychognathus declivis was named
from South Africa. A year later, in 1860, Owen named the group
Dicynodontia. In his Descriptive and Illustrated Catalogue, Owen
honored Bain by erecting Bidentalia
 as a replacement name for his Dicynodontia. The name Bidentalia
quickly fell out of use in the following years, replaced by popularity
of Owen's Dicynodontia.

Dicynodonts first appear during Middle Permian, and underwent a rapid evolutionary radiation, becoming the most successful and abundant land vertebrates of the Late Permian.
 During this time, they included a large variety of ecotypes, including
large, medium-sized, and small herbivores and short-limbed mole-like
burrowers.
Only four lineages are known to have survived the end of Permian extinction; the first three represented with a single genus each: Myosaurus, Kombuisia, and Lystrosaurus, the latter being the most common and widespread herbivores of the Induan (earliest Triassic). None of these survived long into the Triassic. The fourth group was the Kannemeyeriiformes,
 the only dicynodonts who diversified during the Triassic. These
stocky, pig- to ox-sized animals were the most abundant herbivores
worldwide from the Olenekian to the Ladinian age. By the Carnian they had been supplanted by traversodont cynodonts and rhynchosaur reptiles. During the Norian
 (middle of the Late Triassic), perhaps due to increasing aridity, they
drastically declined, and the role of large herbivores was taken over by
 sauropodomorph dinosaurs.
Fossils of an Asian elephant-sized dicynodont Lisowicia bojani discovered in Poland indicate that dicynodonts survived at least until the late Norian or earliest Rhaetian
 (latest Triassic); this animal was also the largest known dicynodont
species. Six fragments of fossil bone interpreted as remains of a
skull discovered in Australia (Queensland) were suggested to indicate that dicynodonts survived into the Cretaceous in southern Gondwana. The dicynodont affinity of these specimens was questioned (including a proposal that they belonged to a baurusuchian crocodyliform by Agnolin et al. in 2010), and in 2019 Knutsen and Oerlemans (in press) considered this fossil to be of Pliocene-Pleistocene age, and reinterpreted it as a fossil of a large mammal, probably a diprotodontid.

Taxonomy
Dicynodontia was originally named by the English paleontologist Richard Owen. It was erected as a family of the order Anomodontia and included the genera Dicynodon and Ptychognathus. Other groups of Anomodontia included Gnathodontia, which included Rhynchosaurus (now known to be an archosauromorph) and Cryptodontia, which included Oudenodon.
 Cryptodonts were distinguished from dicynodonts from their absence of
tusks. Although it lacks tusks, Oudenodon is now classified as a
dicynodont, and the name Cryptodontia is no longer used. Thomas Henry Huxley
 revised Owen's Dicynodontia as an order that included Dicynodon and
Oudenodon. Dicynodontia was later ranked as a suborder or infraorder
with the larger group Anomodontia, which is classified as an order. The
ranking of Dicynodontia has varied in recent studies, with Ivakhnenko
(2008) considering it a suborder, Ivanchnenko (2008) considering it an
infraorder, and Kurkin (2010) considering it an order.
Many higher
taxa, including infraorders and families, have been erected as a means
of classifying the large number of dicynodont species. Cluver and King
(1983) recognised several main groups within Dicynodontia, including
Diictodontia, Endothiodontia, Eodicynodontia, Kingoriamorpha,
Pristerodontia, and Venyukoviamorpha. Many families have been proposed, including Cistecephalidae, Diictodontidae, Dicynodontae, Emydopidae, Endothiodontidae, Kannemeyeriidae, Kingoriidae, Lystrosauridae, Myosauridae, Oudenodontidae, Pristerodontidae, and Robertiidae. However, with the rise of phylogenetics,
 most of these taxa are no longer considered valid. Kammerer and
Angielczyk (2009) suggested that the problematic taxonomy and
nomenclature of Dicynodontia and other groups results from the large
number of conflicting studies and the tendency for invalid names to be
mistakenly established.