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 maxilla) is an extinct genus of large dicynodont from the Late Permian. 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.

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 in Brazil can now be correlated with deposits in India, Malawi, Mozambique, South Africa, Tanzania, Zambia, and Zimbabwe.

Originally, nine species of Endothiodon in total were named in the late 19th and early 20th centuries, all from South Africa, but these were reduced down to just three accepted species in 1964 and today they are thought to likely represent only a single species, the type species E. bathystoma. The basic distinction among the three species is size and robustness of the jaw, which has led some researchers to conclude they represent an ontogenetic series instead. A second species, E. mahalanobsi, was discovered in India and named in 2000. Although smaller than E. bathystoma, E. mahalanobsi is likely a separate 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 E. bathystoma), a lower position of the pineal boss, and a swollen prefrontal bone. A third species was discovered in Tanzania and named E. tolani in 2015. Unlike the other species, E. tolani still has a pair of small tusks and lacks a pineal boss.