''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. L., Vega C. S., Aumond J. J. "On the presence of the Late Permian dicynodont ''Endothiodon'' in Brazil" Palaeontology 56:4, 837-848 (2013)) is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of large

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typic ...

from the Late

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 ...

. Like other dicynodonts, ''Endothiodon'' was an herbivore, but it lacked the two tusks that characterized most other dicynodonts. The anterior portion of the upper and lower jaw are curved upward, creating a distinct beak that is thought to have allowed them to be specialized grazers.Latimer E. M., Gow C. E., Rubidge B. S. "Dentition and feeding niche of ''Endothiodon'' (Synapsida;Anomodontia)" Palaeontologia Africana 32, 75-82 (1995) ''Endothiodon'' was widespread and is found across the southern region of what was then a single large continent known as

Pangea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...

. It was originally only found in southern

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

but has now also been found in

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

and

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, which were both close to Africa at the time. The finding in Brazil marks the first dicynodont to be reported for the Permian of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

. This finding also shows that part of the

Rio do Rasto Formation 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''. Geography It is found mainly in the B ...

in Brazil can now be correlated with deposits in India,

Malawi Malawi (; or aláwi Tumbuka: ''Malaŵi''), officially the Republic of Malawi, is a landlocked country in Southeastern Africa that was formerly known as Nyasaland. It is bordered by Zambia to the west, Tanzania to the north and northeas ...

Mozambique Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...

Zambia Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central, Southern and East Africa, although it is typically referred to as being in Southern Africa at its most central point. Its neighbours are t ...

, and

Zimbabwe Zimbabwe (), officially the Republic of Zimbabwe, is a landlocked country located in Southeast Africa, between the Zambezi and Limpopo Rivers, bordered by South Africa to the south, Botswana to the south-west, Zambia to the north, and ...

. Originally there were thought to be nine

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

, but this was reduced down to just 3 species.Cox Barry C. "On the palate, dentition, and classification of the fossil reptile ''Endothiodon'' and related genera" American Museum of Natural History 2171 (1964) A fourth species was later discovered. The four currently known species of ''Endothiodon'' are ''E. bathystoma'', ''E. uniseries'', ''E. whaitsi'', and ''E. mahalanobsi''. However, the basic distinction among the four species is size, which leads some to believe that ''E. uniseries'', ''E. bathystoma'', and ''E. whaitsi'' may actually represent an

ontogenetic Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the st ...

series rather than three distinct taxa. ''E. mahalanobsi'', on the other hand, is most likely a separate, truly smaller species based on the size of both juvenile and adult forms that have been found. Apart from size, ''E. mahalanobsi'' also has a single longitudinal ridge on the snout (compared to three on the other species), a lower position of the pineal boss, and a swollen prefrontal bone.

Description

Skull

The skull of ''Endothiodon'' is most quickly recognized by the prominent upturned beak. The premaxilla and palate of the upper jaw are vaulted and allows for the upturned and pointed lower jaw to fit into this region. On the lower jaw, lateral to the teeth, is a broad groove. ''Endothiodon'' lacks a lateral dentary shelf but has a bulbous swelling of the

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

. The function of this swelling is not yet known. The

pineal foramen A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhyth ...

is situated on a boss, which is high in three of the species and low in one of them (''E. mahalanobsi''). There is also a boss situated on the ventral margin of the

jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...

. The anteroventral process is an anteroposteriorly short triangular bone, while in most other dicynodonts it is long and pointed.Modesto Sean P., Rubidge B. S., Welman J. "A new dicynodont therapsid from the lowermost Beaufort Group, Upper Permian of South Africa" Canadian Journal of earth Sciences 30: 1755-1765 (2002)

Teeth

The teeth in the upper and lower jaw differ both in

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

as well as in tooth replacement. The teeth of the upper jaw tend to be larger (5-9mm) than those of the lower jaw (<5mm) and are

serrated Serration is a saw-like appearance or a row of sharp or tooth-like projections. A serrated cutting edge has many small points of contact with the material being cut. By having less contact area than a smooth blade or other edge, the applied p ...

on the anterior edge while the lower jaw has serrations on the posterior edge. Although it was originally thought that E. bathystoma had several rows of teeth on the upper jaw, it was later discovered that the tips of the teeth from the lower jaw had been left behind in the upper jaw. Now it is known that the upper teeth are roughly positioned into a single row. The entire row is moved posteriorly so that the anterior portion of the premaxilla contains no teeth but the most posterior portion still holds two teeth. The teeth are also situated internally to the edge of the maxilla. It was first thought that the dentary contained three parallel rows of teeth. Instead of arranging the teeth in longitudinal rows, they are now known to fall into obliquely arranged Zahnreihen. In each Zahnreihe, the anteriormost tooth is the oldest and the posterior most tooth is the youngest. There is active ongoing replacement of these tooth rows. The distal portion of each tooth is compressed from side to side and is somewhat pear shaped in cross section. Endothiodon12DB

The palate shows two distinct regions that are covered in minute

foramina In anatomy and osteology, a foramen (;Entry "foramen"
in

. These areas probably had a horny covering in life. The broad groove running along the tooth row on the dentary was probably also covered by a horny layer. It is possible that these regions allowed for

occlusion Occlusion may refer to: Health and fitness * Occlusion (dentistry), the manner in which the upper and lower teeth come together when the mouth is closed * Occlusion miliaria, a skin condition * Occlusive dressing, an air- and water-tight trauma ...

where the upper teeth met the groove lateral to the lower teeth and the lower teeth met one of the regions of the palatine. This is still under scrutiny as the palatine region is short in comparison to the lower tooth row and the second horn covered area on the palatine does not oppose any structure in the lower jaw. Because the palatine region is shortened, effective occlusion for shearing would only be possible when the lower jaw was in a retracted position.Ray Sanghamitra "Endothiodont dicynodont from the Late Permian Kundaram formation, India" Paleontology 42:2, 375-404 (2000)

History of discovery

''Endothiodon'' was first discovered by Richard Owen in 1876 in the Karoo region of

Beaufort Group The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup in South Africa. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and unconformably underli ...

, South Africa based on a skull and mandible. The

was described based on the anterior portion of a snout and the corresponding part of the dentary, creating an upturned beak. Several more specimens have since been collected, many of them in the Beaufort Group in South Africa, it is here that the first partial skeleton was discovered by Broom in 1915. In the 1970s a skull and lower jaw was discovered in Brazil. The specimen was originally assigned to the genus ''Endothiodon''. Boos later reexamined the specimen and confirmed this assignment which marked ''Endothiodon'' as the first Permian dicynodont to be found in South America. Four main endothiodont genera, ''Endothiodon'', ''Esoterodon'', ''Endogomphodon'', and ''Emydochampsa'', were originally separated under the subfamily Endothiodontinae. When ''E. uniseries'' was first discovered it was thought to be the type species of the genus ''Esoterodon''.Seeley H. G. "Researches on the structure, organisation, and classification of the fossil reptilia. Part IX. Section 1. On the therosuchia. (Abstract)" The Royal Society 55, 224-226 (1894) In 1964 Cox sorted out all of the taxa of endothiodonts and found that the characters originally separating the four genera were not valid. The four genera were grouped into the one genus ''Endothiodon''. With originally nine species of ''Endothiodon'', Cox was able to narrow it down to just three species based on skull size and robustness of the lower jaw. A fourth species of ''Endothiodon'' was found in India that was unique compared to the other three species. It had a small size, a single longitudinal ridge on the snout, an elongated pineal foramen situated on a low boss located midway on the intertemporal bar, and a slender dentary symphysis. Some of these characteristics such as the shape of the pineal foramen and the presence of three longitudinal ridges were thought to be distinguishing characteristics of the genera as a whole, but are now only valid at specific level. Another new species was collected in Tanzania in 1963 and is under description. It is distinguished from all other specimens based on the lack of a pineal boss and the presence of a pair of tusks lateral to the tooth row.

Palaeobiology

Diet

In adult ''Endothiodons'' the lower jaw teeth are pear shaped in

cross section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **Abs ...

, compressed distolaterally, and has posterior serrated edges while the upper jaw teeth have anterior serrated edges. In the juveniles, the lower jaw is a lot smaller and more slender. The lower jaw contains one functional tooth row with 5-6 teeth. The teeth are small, conical, and pointed. The distal edge contains serrations that are just starting to appear. The juvenile teeth are much simpler and are more similar to that of a

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...

than an herbivore. It is possible that the different tooth morphology might be due to a change in diet from insectivorous or

omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...

as a juvenile to herbivorous as an adult. This would be achieved as size increases and it is more able to adapt to being herbivorous.

Palaeoecology

''Endothiodon'' was first discovered in the Karoo region of

Beaufort West Beaufort West (Afrikaans: ''Beaufort-Wes''; Xhosa: ''eBhofolo'') is a town in the Western Cape province in South Africa. It is the largest town in the arid Great Karoo region, and is known as the "Capital of the Karoo". It forms part of the Beau ...

, South Africa.Owen R. "Descriptive and illustrated catalogue of the fossil reptilia of South Africa in the collections of the British Museum" Taylor and Francis (1876) The Karoo region is characteristic of

siltstones Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

that are fine-to medium- or coarse-grained, dark or greenish grey, and very finely crossbedded.Verniers J., Jourdan P. P., Paulis R. V., Frasca-Spada L., De Bock F. R. "The Karroo Graben of Metangula Northern Mozambique" Journal of African Earth Sciences 9:1, 137-158 (1989) Since then several more specimens have been found in African countries including the Usili, Ruhuhu and lower part of the Kawinga Formations of Tanzania, the basal beds of Madumabisa Mudstone of Zambia, and Chiweta Beds, Malawi.Ray Sanghamitra "Permian reptilian fauna from the Kundaram Formation, Pranhita-Godavari Valley, India" Journal of African earth Sciences 29:1, 211-218 (1999) ''Endothiodon'' has been placed in the

Tropidostoma ''Tropidostoma'' is a medium-sized herbivorous oudenodontid dicynodont therapsid that lived during the Late Permian (Lopingian) period in South Africa. The first ''Tropidostoma'' fossil was described by Harry Govier Seeley in 1889. Later two sub ...

and/or

Cistecephalus ''Cistecephalus'' is an extinct genus of dicynodont therapsid from the Late Permian of southern Africa (South Africa and Zambia). It was a small, specialised, burrowing dicynodont, possibly with habits similar to a modern mole. The head was flat ...

Assemblage Zones and dates back to a Late Permian ( Tatarian) age. In 1997 the first specimen of ''E. mahalanobsi'' was found in the

Kundaram Formation The Kundaram Formation is a geological formation in India, located within the Pranhita–Godavari Basin. The unit is between 250–400 metres thick and at its base consists of sandstone-mudstone alterations, followed by a sequence dominated by re ...

in the north-western part of Pranhita-Godavari valley near Golet in

Adilabad district Adilabad district is a district located in the northern region of Telangana, India. It is known as the gateway district to South and Central India. The town of Adilabad is its headquarters. The district shares boundaries with Asifabad, Nirma ...

Andhra Pradesh Andhra Pradesh (, abbr. AP) is a state in the south-eastern coastal region of India. It is the seventh-largest state by area covering an area of and tenth-most populous state with 49,386,799 inhabitants. It is bordered by Telangana to the ...

, India. The Kundaram Formation is characterized by mudstone,

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

, and ferruginous shale. In addition to Africa and India, ''Endothiodon'' is also known from the Morro Pelado Member of

in the

Paraná Basin The Paraná Basin ( pt, Bacia do Paraná, es, Cuenca del Paraná) is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande d ...

, Brazil. A

taphonomic Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov t ...

reconstruction of the Late Permian showed that there were well established, dense, riverine vegetation.Smith Roger M. H. "Vertebrate taphonomy of Later Permian floodplain deposits in the southwestern Karoo basin of South Africa" South African Museum 8, 45-67 (1993) It was originally thought that ''Endothiodon'' would grub matter out of the ground using its beak. This is now seen as implausible because of the position of the external nares on the snout being placed so far anteriorly. Instead, it is now thought that ''Endothiodon'' inhabited the dense riverine vegetation and would crop

foliage A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, s ...

with its beak before processing it with its specialized and extensive

oral cavity In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on t ...

References

{{Taxonbar, from=Q1027697 Dicynodonts Permian synapsids of Asia Fossils of India Lopingian synapsids of Africa Fossils of Malawi Fossils of South Africa Fossils of Tanzania Fossils of Zambia Karoo Permian animals of South America Permian Brazil Fossils of Brazil Paraná Basin Wuchiapingian genus first appearances Wuchiapingian genus extinctions Fossil taxa described in 1876 Taxa named by Richard Owen Anomodont genera