Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...

. Dicynodonts were

herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

animals Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

with 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 Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...

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 Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

, 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 ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

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 Browse, browser or browsing may refer to: Programs * Web browser, a program used to access the World Wide Web *Code browser, a program for navigating source code * File browser or file manager, a program used to manage files and related objects * ...

Characteristics

The dicynodont

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

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 an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked t ...

s and ceratopsian

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

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. Many genera also have a pair of tusks, which it is thought may have been an example of

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

. Several genera, such as

Stahleckeria ''Stahleckeria'' is an extinct genus of Middle Triassic (Ladinian) dicynodonts.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 ''Dinodontosaurus'' (meaning "terrible-toothed lizard") is a genus of dicynodont therapsid. It was medium to large dicynodont of the Triassic (with skull up to long) and had a beak corneum. It lived in the Middle Triassic but disappeared in the ...

'') the hindlimbs were held erect, but the forelimbs bent at the elbow. Both the

pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of ...

and the ilium are large and strong. The tail is short.

Endothermy and hair

Dicynodonts have long been suspected of being

warm-blooded Warm-blooded is an informal term referring to animal species which can maintain a body temperature higher than their environment. In particular, homeothermic species maintain a stable body temperature by regulating metabolic processes. The onl ...

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 of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

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 is de ...

s paradoxically showcase digestive patterns more typical of animals with slow metabolisms. More recently, the discovery of hair 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 251.9 Mya. It is the last ...

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.

Feet

'' Pentasauropus'' dicynodont tracks suggest that dicynodonts had fleshy pads on their feet.

Tusks

Dicynodonts are the only vertebrates beside mammals to have true tusks. Their development prior to the evolution of the mammalian tooth replacement offers an insight into the acquisition of tusks.

History

Dicynodonts have been known since the mid-1800s. The South African geologist

Andrew Geddes Bain Andrew Geddes Bain (baptised 11 June 1797 – 20 October 1864), was a South African geologist, road engineer, palaeontologist and explorer. Life history The only child of Alexander Bain and Jean Geddes, both of whom died when Bain was still a ...

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 The Corps of Royal Engineers, usually called the Royal Engineers (RE), and commonly known as the ''Sappers'', is a corps of the British Army. It provides military engineering and other technical support to the British Armed Forces and is heade ...

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 The Geological Society of London, known commonly as the Geological Society, is a learned society based in the United Kingdom. It is the oldest national geological society in the world and the largest in Europe with more than 12,000 Fellows. Fe ...

'', 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 ''Dicynodon'' ("two dog-teeth") is a genus of dicynodont therapsid that flourished during the Permian, Upper Permian Period (geology), period. Like all dicynodonts, it was herbivore, herbivorous animal. This reptile was toothless, except for prom ...

'' 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 The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± ...

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. Radiations may affect one clade or many, and be rapid ...

, becoming globally distributed and amongst the most successful and abundant land vertebrates during the

. 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 Great may refer to: Descriptions or measurements * Great, a relative measurement in physical space, see Size * Greatness, being divine, majestic, superior, majestic, or transcendent People * List of people known as "the Great" *Artel Great (born ...

; the first three represented with a single genus each: ''

Myosaurus ''Myosaurus'' is an extinct genus of dicynodont found primarily in Antarctica and South Africa. History The family Myosauridae is known only from fossilized skull specimens. The family is distinguished from other families in the infraorder Dic ...

'', '' Kombuisia'', and ''

Lystrosaurus ''Lystrosaurus'' (; 'shovel lizard'; proper Greek is λίστρον ''lístron'' ‘tool for leveling or smoothing, shovel, spade, hoe’) is an extinct genus of herbivorous dicynodont therapsids from the late Permian and Early Triassic epochs ( ...

'', 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 251.902 Ma and Ma (million years ago). The Induan is sometime ...

(earliest

). None of these survived long into the Triassic. The fourth group was the

Kannemeyeriiformes Kannemeyeriiformes is a group of large-bodied Triassic dicynodonts. As a clade, Kannemeyeriiformes has been defined to include the species '' Kannemeyeria simocephalus'' and all dicynodonts more closely related to it than to the species ''Lystros ...

, 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 in the Early Triassic epoch; in chronostratigraphy, it is a stage in the Lower Triassic series. It spans the time between Ma and Ma (million years ago). The Olenekian is sometimes divided i ...

to the

Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic ...

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 m ...

they had been supplanted by traversodont cynodonts and

rhynchosaur Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...

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 Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...

dinosaurs. Fossils of an

Asian elephant The Asian elephant (''Elephas maximus''), also known as the Asiatic elephant, is the only living species of the genus ''Elephas'' and is distributed throughout the Indian subcontinent and Southeast Asia, from India in the west, Nepal in the no ...

-sized dicynodont ''

Lisowicia ''Lisowicia'' is an extinct genus of giant dicynodont synapsid that lived in what is now Poland during the late Norian or earliest Rhaetian age of the Late Triassic Period, about 210–205 million years ago. ''Lisowicia'' is the largest known d ...

bojani'' discovered in

Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populou ...

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 discovered in

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , establishe ...

, 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 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

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 considered this fossil to be of Plio-

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

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 that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

epoch (60 Ma) when mammals, distant descendants of cynodonts, began to diversify after the extinction of the non-avian dinosaurs.

Systematics

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 ''Dicynodon'' ("two dog-teeth") is a genus of dicynodont therapsid that flourished during the Upper Permian period. Like all dicynodonts, it was herbivorous animal. This reptile was toothless, except for prominent tusks, hence the name. It proba ...

'' and '' Ptychognathus''. Other groups of Anomodontia included Gnathodontia, which included ''

Rhynchosaurus ''Rhynchosaurus'' (''beaked lizard'') is a genus of rhynchosaur that lived during the Middle Triassic period. It lived in Europe. It was related to the archosaurs, but not within that group. The type species of ''Rhynchosaurus'' is ''R. articep ...

'' (now known to be an

archosauromorph Archosauromorpha ( Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, l ...

) and

Cryptodontia Cryptodontia is a group of dicynodont therapsids that includes the families Geikiidae, Oudenodontidae, and Rhachiocephalidae. It was first named in 1860 by English paleontologist Richard Owen. Owen intended Cryptodontia to be a family, and the n ...

, 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 Thomas Henry Huxley (4 May 1825 – 29 June 1895) was an English biologist and anthropologist specialising in comparative anatomy. He has become known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution. The stori ...

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,

tae, Emydopidae, Endothiodontidae, Kannemeyeriidae, Kingoriidae,

Lystrosauridae 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 ...

, Myosauridae, Oudenodontidae, Pristerodontidae, and

Robertiidae 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 ...

. However, with the rise of

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

s, 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.

Current classification

*Dicynodontia **'' Colobodectes'' **''

Eodicynodon ''Eodicynodon'' (''eo-,'' early or primitive, dicynodont) is an extinct genus of dicynodont therapsids, a highly diverse group of herbivorous synapsids that were widespread during the middle-late Permian and early Triassic. As its name suggests, ...

'' **

Endothiodontia Endothiodontia is a clade of dicynodont therapsids that includes the family Endothiodontidae and possibly the family Eumantellidae Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were he ...

***'' Abajudon'' ***''

Endothiodon ''Endothiodon'' (/ɛndoʊθiːoʊdɔːn/ "inner tooth" from Greek endothi (ἔνδοθῐ), "within", and odon (ὀδών), "tooth", most likely named for the characteristic of the teeth being placed internally to the maxillaBoos A. S., Schultz C ...

'' ***'' Lanthanostegus'' ***'' Niassodon'' ** Eumantellidae ***'' Emyduranus''? ***'' Eurychororhinus''? ***'' Pristerodon'' ***'' Synostocephalus''? **

Therochelonia 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 ...

Phylogeny

Below is a

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

modified from Angielczyk and Rubidge (2010) showing the

relationships of Dicynodontia: Below is a cladogram from Kammerer et al. (2013). The data matrix of Kammerer et al. (2013), a list of characteristics that was used in the analysis, was based on that of Kammerer et al. (2011), which followed a comprehensive taxonomic revision of ''

''. Because of this, many of the relationships found by Kammerer et al. (2013) are the same as those found by Kammerer et al. (2011). However, several taxa were added to the analysis, including ''

Tiarajudens ''Tiarajudens'' (" Tiaraju tooth") is an extinct genus of saber-toothed herbivorous anomodonts which lived during the Middle Permian period ( Capitanian stage) in what is now Rio Grande do Sul, Brazil. It is known from the holotype UFRGS P ...

'' '' Eubrachiosaurus'', '' Shaanbeikannemeyeria'', ''

Zambiasaurus ''Zambiasaurus'' is an extinct genus of dicynodonts that was discovered in the Middle Triassic (Anisian) Ntawere Formation of Zambia, southern Africa. It was a large dicynodont, reconstructed using several fossil fragments, in majority belonging ...

'' and many "outgroup" taxa (positioned outside Anomodontia), while other taxa were re-coded. As in Kammerer et al. (2011), the interrelationships of non- kannemeyeriiform

dicynodontoid Dicynodontoidea is an infraorder of dicynodont therapsids that includes the famous dicynodont ''Dicynodon'', ''Lystrosaurus'' and the Triassic Kannemeyeriiformes, as well as numerous other closely related species. The name was coined by American ...

s are weakly supported and thus vary between the analyses.

References

External links

Therapsida : Neotherapsida : Dicynodontia
- Palaeos {{Taxonbar, from=Q131682 Guadalupian first appearances Late Triassic extinctions Taxa named by Richard Owen Fossil taxa described in 1859