Dicynodontia is an extinct

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

anomodont Anomodontia is an extinct group of non-mammalian therapsids from the Permian and Triassic periods. By far the most speciose group are the dicynodonts, a clade of beaked, tusked herbivores. Anomodonts were very diverse during the Middle Pe ...

s, an extinct type of non-mammalian therapsid. Dicynodonts were

herbivore A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

s 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

synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...

s. 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 The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

but died out towards the end of that period. They were the most successful and diverse of the non-mammalian therapsids, with over 80-90

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

known, varying from rat-sized burrowers to elephant-sized browsers.

Characteristics

The dicynodont

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

is highly specialised, light but strong, with the

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

turtle Turtles are reptiles of the order (biology), order Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Crypt ...

s and

ceratopsia Ceratopsia or Ceratopia ( or ; Ancient Greek, Greek: "horned faces") is a group of herbivore, herbivorous, beaked dinosaurs that thrived in what are now North America, Asia and Europe, during the Cretaceous Period (geology), Period, although ance ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s. 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. Dicynodonts typically had a pair of enlarged maxillary caniniform teeth, analogous to the

tusk Tusks are elongated, continuously growing front teeth that protrude well beyond the mouth of certain mammal species. They are most commonly canine tooth, canine teeth, as with Narwhal, narwhals, chevrotains, musk deer, water deer, muntjac, pigs, ...

s present in some living mammals. In the earliest genera, they were merely enlarged teeth, but in later forms they independently evolved into ever-growing teeth like mammal tusks multiple times. In some dicynodonts, the presence of tusks has been suggested to be

sexually dimorphic Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

. Some dicynodonts such as '' Stahleckeria'' lacked true tusks and instead bore tusk-like extensions on the side of the beak. Colbert, E. H., (1969), ''Evolution of the Vertebrates'', John Wiley & Sons Inc (2nd ed.) 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. '' Pentasauropus'' dicynodont tracks suggest that dicynodonts had fleshy pads on their feet. Mummified skin from specimens of '' Lystrosaurus'' in South Africa have numerous raised bumps.

Endothermy and soft tissue anatomy

Dicynodonts have long been suspected of being

warm-blooded Warm-blooded is a term referring to animal species whose bodies maintain a temperature higher than that of their environment. In particular, homeothermic species (including birds and mammals) maintain a stable body temperature by regulating ...

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 The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

dicynodont

coprolite A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name ...

s paradoxically showcase digestive patterns more typical of animals with slow metabolisms. More recently, the discovery of

hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and ...

remnants in

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

s possibly 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. A new study using chemical analysis seemed to suggest that cynodonts and dicynodonts both developed warm blood independently before the Permian extinction.

History

A 2024 paper posited that

rock art In archaeology, rock arts are human-made markings placed on natural surfaces, typically vertical stone surfaces. A high proportion of surviving historic and prehistoric rock art is found in caves or partly enclosed rock shelters; this type al ...

of a superficially walrus-like imaginary creature with downcurved tusks created by the

San people The San peoples (also Saan), or Bushmen, are the members of any of the indigenous hunter-gatherer cultures of southern Africa, and the oldest surviving cultures of the region. They are thought to have diverged from other humans 100,000 to 200 ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

prior to 1835 may have been partly inspired by fossil dicynodont skulls which erode out of rocks in the area. Dicynodonts have been known to science 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 Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomy, comparative anatomist and paleontology, palaeontologist. Owen is generally considered to have been an outstanding naturalist with a remarkabl ...

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. In the same year, 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.

Evolutionary history

Dicynodonts first appeared during the Middle Permian in the Southern Hemisphere, with South Africa being the centre of their known diversity, and underwent a rapid

evolutionary radiation An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. A significantly large and diverse radiation within ...

, becoming globally distributed and amongst the most successful and abundant land vertebrates during 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 Great Dying; 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 The Induan is the first age of the Early Triassic epoch in the geologic timescale, or the lowest stage of the Lower Triassic series in chronostratigraphy. It spans the time between 251.9 Ma and 249.9 Ma (million years ago). The Induan is so ...

(earliest

). 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 In the geologic timescale, the Olenekian is an age (geology), age in the Early Triassic epoch (geology), epoch; in chronostratigraphy, it is a stage (stratigraphy), stage in the Lower Triassic series (stratigraphy), series. It spans the time betw ...

to the Ladinian age. By the

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...

they had been supplanted by traversodont cynodonts and rhynchosaur reptiles. During the

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

(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 The Asian elephant (''Elephas maximus''), also known as the Asiatic elephant, is the only living ''Elephas'' species. It is the largest living land animal in Asia and the second largest living Elephantidae, elephantid in the world. It is char ...

-sized dicynodont '' Lisowicia bojani'' discovered in

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It extends from the Baltic Sea in the north to the Sudetes and Carpathian Mountains in the south, bordered by Lithuania and Russia to the northeast, Belarus and Ukrai ...

indicate that dicynodonts survived at least until the late Norian or earliest

Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...

(latest Triassic); this animal was also the largest known dicynodont species. Six fragments of fossil bone discovered in

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

, Australia, were interpreted as remains of a skull in 2003. This suggested to indicate that dicynodonts survived into the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

in southern

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

. 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 considered this fossil to be of Plio-

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

age, and reinterpreted it as a fossil of a large mammal, probably a diprotodontid. With the decline and extinction of the kannemeyerids, there were to be no more dominant large synapsid herbivores until the middle

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

epoch (60 Ma) when

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s, distant descendants of

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

s, began to diversify after the extinction of the non-avian dinosaurs.

Systematics

Taxonomy

Dicynodontia was originally named by the English paleontologist

. 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 ''Oudenodon'' is an extinct genus of dicynodont. It was common throughout southern Africa during the Late Permian. Several species of ''Oudenodon'' are known. Both ''O. bainii'', the type species, and ''O. grandis'' are known from South Africa ...

''. 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 Eodicynodontia (containing only Eodicynodon), Endothiodontia (containing only Endothiodontidae), Pristerodontia ( Pristerodontidae, Cryptodontidae, Aulacephalodontidae, Dicynodontidae, Lystrosauridae, and Kannemeyeriidae), Kingoriamorpha (containing only Kingoriidae), Diictodontia ( Diictodontidae, Robertiidae, Cistecephalidae, Emydopidae and Myosauridae), and Venyukoviamorpha. 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. Cistecephalus1DB

Phylogeny

Below is a

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

modified from Angielczyk et al. (2021):

Current classification

*Dicynodontia **'' Brachyprosopus'' **'' Colobodectes'' **'' Eodicynodon'' **'' Lanthanostegus'' **'' Nyaphulia'' ** Endothiodontia ***'' Abajudon'' ***'' Endothiodon'' ***'' Niassodon'' ** Eumantellidae ***'' Pristerodon'' ** Pylaecephalidae ***'' Diictodon'' ***'' Eosimops'' ***'' Prosictodon'' ***'' Robertia'' ** Therochelonia *** Emydopoidea ****'' Digalodon'' ****'' Rastodon'' **** Cistecephalidae *****'' Cistecephalus'' *****'' Cistecephaloides'' *****'' Kawingasaurus'' *****'' Kembawacela'' *****'' Sauroscaptor'' **** Emydopidae *****'' Compsodon'' *****'' Emydops'' **** Kingoriidae *****'' Dicynodontoides'' *****'' Kombuisia'' *****'' Thliptosaurus'' **** Myosauridae *****'' Myosauroides'' *****'' Myosaurus'' *** Bidentalia ****'' Kunpania'' **** Cryptodontia ***** '' Daqingshanodon'' ***** '' Keyseria'' ***** Rhachiocephalidae ****** '' Kitchinganomodon'' ****** '' Rhachiocephalus'' ***** Oudenodontidae ****** '' Australobarbarus'' ****** ''

'' ****** '' Tropidostoma'' ***** Geikiidae ****** '' Bulbasaurus'' ****** ?'' Idelesaurus'' ****** ?'' Odontocyclops'' ****** Geikiinae ******* '' Aulacephalodon'' ******* '' Geikia'' ******* '' Pelanomodon'' **** Dicynodontoidea *****'' Counillonia'' *****'' Daptocephalus'' *****'' Delectosaurus'' *****'' Dicynodon'' *****'' Dinanomodon'' ***** '' Elph'' *****'' Gordonia'' *****'' Interpresosaurus'' *****'' Katumbia'' *****'' Peramodon'' *****'' Taoheodon'' *****'' Turfanodon'' *****'' Vivaxosaurus'' ***** Lystrosauridae ******?'' Basilodon'' ******?'' Jimusaria'' ******?'' Sintocephalus'' ******?'' Syops'' ******'' Euptychognathus'' ******'' Kwazulusaurus'' ******'' Lystrosaurus'' ***** Kannemeyeriiformes ******'' Angonisaurus'' ******Dinodontosauridae *******'' Dinodontosaurus'' ****** Shansiodontidae *******'' Rhinodicynodon'' *******'' Shansiodon'' *******'' Tetragonias'' *******'' Vinceria'' ******Kannemeyeriidae *******'' Acratophorus'' *******'' Dolichuranus'' *******'' Kannemeyeria'' *******'' Parakannemeyeria'' *******'' Rabidosaurus'' *******'' Rechnisaurus'' *******'' Rhadiodromus'' *******'' Shaanbeikannemeyeria'' *******'' Sinokannemeyeria'' *******'' Uralokannemeyeria'' *******'' Wadiasaurus'' *******'' Xiyukannemeyeria'' ****** Stahleckeriidae *******?'' Sungeodon'' *******'' Woznikella'' ******* Placeriinae ******** '' Argodicynodon'' ******** '' Lisowicia'' ******** '' Moghreberia'' ******** '' Placerias'' ******** '' Pentasaurus'' ******** '' Zambiasaurus'' *******Stahleckeriinae ******** '' Eubrachiosaurus'' ******** '' Ischigualastia'' ******** '' Jachaleria'' ******** '' Sangusaurus'' ******** '' Stahleckeria'' ******** '' Ufudocyclops''

South African geomyth

A horned serpent cave art is known from the La Belle France cave in

, often conflated with the Dingonek. It may be based on dicynodont fossils.Benoit J (2024) A possible later stone age painting of a dicynodont (Synapsida) from the South African Karoo. PLoS ONE 19(9): e0309908. https://doi.org/10.1371/journal.pone.0309908

References

External links

Therapsida : Neotherapsida : Dicynodontia
- Palaeos {{Taxonbar, from=Q131682 Guadalupian first appearances Late Triassic extinctions Taxa named by Richard Owen