Impidens
Impidens is an extinct genus of large omnivorous cynodont from the Triassic of South Africa and Antarctica. Its type and only species is Impidens hancoxi. "Impidens" inhabited high-latitude environments of southern Gondwana during the Middle Triassic, where it was probably the apex predator. History. A specimen of "Impidens" was collected from Antarctica in 1986. In 1995, it was described as an indeterminate diademodontid possibly belonging to "Titanogomphodon". The holotype of "Impidens hancoxi" was found in South Africa in 2014. It was described as a new species in 2021, with the Antarctic specimen and a less complete specimen from  South Africa being referred to the species. Description. "Impidens" was one of the largest non-mammalian cynodonts, with a skull well over long, though the herbivorous "Scalenodontoides" from the Late Triassic was even larger. Classification. "Impidens" is a member of Trirachodontidae, a family of gomphodont cynodonts. It is closely related to its smaller contemporary "Cricodon" as well as the earlier "Langbergia" and "Trirachodon". However, the phylogeny of Trirachodontidae is not well-understood, and the family may be paraphyletic, with some species more closely related to traversodontids than others. Paleoecology. "Impidens" fossils are known from the "Cricodon"-"Ufudocyclops" subzone of the "Cynognathus  Assemblage Zone of the Beaufort Group in South Africa and the upper Fremouw Formation in Antarctica. The dating of these strata is controversial; they are conventionally regarded as Middle Triassic in age, probably late Anisian or early Ladinian, but a biostratigraphically correlated fauna in South America has been dated to the beginning of the Late Triassic, in the early Carnian. However, another biostratigraphically correlated fauna in China has been dated to the Anisian, suggesting the traditional dating may be correct. Impidens" was probably the apex predator of its environment, as the only other large predator known to have coexisted with  it was the somewhat smaller cynodont "Cynognathus". The known large herbivores of the fauna are the cynodont "Diademodon" and the dicynodont "Ufudocyclops". A smaller trirachodontid, "Cricodon", was also present in the environment. The "Cricodon"-"Ufudocyclops" subzone was deposited in a meandering river environment, with a deep channel and high banks. Both it and the Fremouw Formation were high-paleolatitude environments, which may explain some of the faunal differences between them and lower-paleolatitude fauna.