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 medium to large dicynodont from the Late Permian. Like other dicynodonts, Endothiodon was an herbivore, but it typically lacked the two tusks that characterized most other dicynodonts and instead had long rows of teeth inset in the jaws that replaced in waves. 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 eastern Africa, 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.

Historically, nine named species in total from South Africa have been attributed to Endothiodon during the late 19th and early 20th centuries (sometimes variably split into distinct genera), but these were reduced down to just three accepted species of Endothiodon in 1964. In the 21st century, these three were further thought to likely represent only a single species, the original type species E. bathystoma, a conclusion upheld by a thorough revision of their taxonomy in 2024. A second valid species, E. mahalanobisi, was discovered in India and named in 2000. Although smaller than E. bathystoma, E. mahalanobisi is recognised as a distinct species rather than simply juveniles of E. bathystoma. Apart from size, E. mahalanobisi also has a pointed snout with only a single, low longitudinal ridge (compared to three raised crests on E. bathystoma), a narrow pineal foramen lacking a bony boss or collar, and a flat prefrontal bone. A third species was discovered in Tanzania and named E. tolani in 2015. Unlike the other species, E. tolani has a pair of small tusks. Although initially discovered in and thought to characterise separate regions, their ranges have since been found to overlap in eastern Africa, with potentially all three present in Mozambique. E. bathystoma appears to be particularly widespread, with a range from Brazil, through southern and eastern Africa and into India.