''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 Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus of large dicynodont from the Late Permian. Like other dicynodonts, ''Endothiodon'' was an

herbivore 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 mouthpart ...

, 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. It was originally only found in southern Africa but has now also been found in India and Brazil, 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. 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, Mozambique, South Africa, Tanzania, Zambia, and Zimbabwe. Originally there were thought to be nine species, 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 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

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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. The function of this swelling is not yet known. The pineal foramen 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 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 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 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. 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 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 underlie ...

, South Africa based on a skull and mandible. The genus 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, 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 than an herbivore. It is possible that the different tooth morphology might be due to a change in diet from insectivorous or omnivorous 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 The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe !Orakobab or Khoemana word ''ǃ’Aukarob'' "Hardveld") is a semi-desert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its ext ...

region of Beaufort West, 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 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 Formation The Usili Formation is a Late Permian geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Permian, including temnospondyls, pareiasaurs, therapsids and the archosauromorph ''Aenigmastropheus''. History ...

s of Tanzania, the basal beds of Madumabisa Mudstone of Zambia, and

Chiweta Beds Chiweta is an area in Rumphi District, Malawi. It is located north of Rumphi. Politically, it falls within the north constituency. It has a number of villages and each village is managed by a village headman. It is undeveloped area with a high prop ...

, 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 Assemblage Zones and dates back to a Late Permian (

Tatarian The Tatars ()Tatar
in the Collins English Dictionary is an umbrella term for different

) 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, Andhra Pradesh, India. The Kundaram Formation is characterized by

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

, sandstone, and ferruginous

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

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

in the Paraná Basin, 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 A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

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 with its beak before processing it with its specialized and extensive oral cavity.

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