''Variodens'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

trilophosaur Trilophosaurs are lizard-like Triassic allokotosaur reptiles related to the archosaurs. The best known genus is '' Trilophosaurus'', a herbivore up to long. It had a short, unusually heavily built skull, equipped with massive, broad flattened c ...

. Fossils have been found from the

Emborough Quarries Emborough Quarries () is a 1 hectare (2.5 acre) geological Site of Special Scientific Interest at Emborough in the Mendip Hills, Somerset, notified in 1971. The disused quarry has yielded a wide variety of remains of vertebrate fossils, among ...

in the

Mendip Hills The Mendip Hills (commonly called the Mendips) is a range of limestone hills to the south of Bristol and Bath, Somerset, Bath in Somerset, England. Running from Weston-super-Mare and the Bristol Channel in the west to the River Frome, Somerset ...

Somerset Somerset ( , ), Archaism, archaically Somersetshire ( , , ) is a Ceremonial counties of England, ceremonial county in South West England. It is bordered by the Bristol Channel, Gloucestershire, and Bristol to the north, Wiltshire to the east ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

. These fossils have been uncovered from a

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 ...

fissure fill within

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

-age

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

. The

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

and only known

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

is ''V. inopinatus'', named in 1957.

Description

''Variodens'' is unusual among most reptiles in that it has a

heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. Human dentition is heterodont and diphyodont as an example. In vertebrates, heterodont pertains to animals wher ...

dentition consisting of different types of teeth. The five anteriormost teeth at the front of the jaw are simple and conical in shape. The cheek teeth toward the back of the jaw are wide and have several cusps. They are either

tricuspid The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to allow blood to flow from the right atrium to the right vent ...

multicuspid The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone tooth ...

. The anterior tricuspid teeth of ''Variodens'' are narrower medially (toward the inside of the mouth) than they are laterally (toward the outside of the mouth). ''Variodens'' also has distinctive bulbous-shaped penultimate teeth. The teeth of ''Variodens'' are very similar to the

postcanine Cheek teeth or postcanines comprise the molar and premolar teeth in mammals. Cheek teeth are multicuspidate (having many folds or tubercles). Mammals have multicuspidate molars (three in placentals, four in marsupials, in each jaw quadrant) and p ...

teeth of the

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 ...

Cricodon ''Cricodon'' is an extinct genus of trirachodontid cynodonts that lived during the Early Triassic and Middle Triassic periods of Africa.Abdala, F., J. Neveling, and J. Welman. 2006. A new trirachodontid cynodont from the lower levels of the Burge ...

'' from the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...

Manda Formation The Manda Formation (also known as the Manda Beds) is a Middle Triassic (Anisian?) or possibly Late Triassic (Carnian?) Formation (stratigraphy), geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Triassi ...

East Africa East Africa, also known as Eastern Africa or the East of Africa, is a region at the eastern edge of the Africa, African continent, distinguished by its unique geographical, historical, and cultural landscape. Defined in varying scopes, the regi ...

. Unlike other trilophosaurs, ''Variodens'' did not have an

edentulous Toothlessness or edentulism is the condition of having no teeth. In organisms that naturally have teeth, it is the result of tooth loss. Organisms that never possessed teeth can also be described as edentulous. Examples are the members of the fo ...

, or toothless beak. Teeth are present throughout the jaw including its tip. This characteristic is also seen in some trilophosaurs from the

Dockum Group The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Color ...

of the southwestern

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

Classification

''Variodens'' was named in 1957 and was classified as a trilophosaur along with the genus '' Tricuspisaurus'', also newly described. ''Variodens'' is usually considered to be closely related to ''Tricuspisaurus'' as well as ''Trilophosaurus jacobsi'', a possible species of ''Trilophosaurus''. '' Anisodontosaurus'', from the

Moenkopi Formation The Moenkopi Formation is a geological formation that is spread across the U.S. states of New Mexico, northern Arizona, Nevada, southeastern California, eastern Utah and western Colorado. This unit is considered to be a Geological unit, group ...

, may also be related to ''Variodens''. In 1993, paleontologists

Hans-Dieter Sues Hans-Dieter Sues (born 1956) is a German-born American palaeontologist who is a Senior Research Geologist and Curator of Vertebrate Paleontology at the National Museum of Natural History of the Smithsonian Institution in Washington, DC. Career ...

and Paul E. Olsen classified ''Variodens'', along with ''Tricuspisaurus'' and ''Trilophosaurus jacobsi'', as a

procolophonid Procolophonidae is an extinct family of small, lizard-like parareptiles known from the Late Permian to Late Triassic that were distributed across Pangaea, having been reported from Europe, North America, China, South Africa, South America, Antarc ...

. This reassignment was based on the close similarity between the tricuspid teeth of these trilophosaurs and those of the newly named procolophonid '' Xenodiphyodon''. Sues and Olsen also proposed a new generic name for ''T. jacobsi'', '' Chinleogomphius'', given that it was no longer considered to be related to ''Trilophosaurus''. However, because ''Variodens'' and ''Tricuspisaurus'' are known primarily from teeth, it is difficult to determine their classification. The similarities between the teeth of ''Variodens'' and those of procolophonids may be convergent adaptations to a herbivorous diet, and do not necessarily indicate a close relationship. More recently, new material belonging to ''T. jacobsi'' has been found, including a nearly complete left side of the skull that clearly shows that it belongs to the genus ''Trilophosaurus'' and is not a procolophonid. Since ''Variodens'' is thought to be closely related to ''T. jacobsi'', it too is probably a trilophosaur rather than a procolophonid. Whiteside & Duffin (2017) agreed with Robinson's original interpretation of ''V. inopinatus'' as a trilophosaur, noting that tooth implantation of the specimen (fragment of a left

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

) described by the authors is ankylothecodont, as described for ''Trilophosaurus'' by Heckert ''et al.'' (2006).

References

{{Taxonbar, from=Q7915924 Trilophosauridae Prehistoric reptile genera Late Triassic reptiles of Europe Triassic England Fossils of England Fossil taxa described in 1957