''Impidens'' 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 omnivorous

cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...

from the Triassic of South Africa and Antarctica. Its type and only species is ''Impidens hancoxi''. ''Impidens'' inhabited high-latitude environments of southern

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

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 Diademodontidae is an extinct family of Triassic gomphodonts. The best-known genus is ''Diademodon'' from South Africa. '' Titanogomphodon'' from Namibia may also be a member of Diademodontidae. The Chinese genera ''Hazhenia'' and ''Ordosiodon'' ...

possibly belonging to ''

Titanogomphodon ''Titanogomphodon'' is an extinct genus of diademodontid cynodonts from the Middle Triassic Omingonde Formation of Namibia. It is known from a single partial skull that was described in 1973 from the Omingonde Formation. The type and only species ...

''. The holotype of ''Impidens hancoxi'' was found in South Africa in 2014. It was described as a new species in

2021 File:2021 collage V2.png, From top left, clockwise: the James Webb Space Telescope was launched in 2021; Protesters in Yangon, Myanmar following the 2021 Myanmar coup d'état, coup d'état; A civil demonstration against the October–November 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 ''Scalenodontoides'' is an extinct genus of traversodontidae, a family of herbivorous cynodonts. It lived during the Late Triassic in what is now South Africa. Its type species is ''Scalenodontoides macrodontes''. It was named in 1957 by A. W. Cr ...

'' 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 ''Trirachodon'' (Greek: "three ridge tooth") is an extinct genus of cynodonts. Fossils have been found in the ''Cynognathus'' Assemblage Zone of the Beaufort Group in South Africa and the Omingonde Formation of Namibia, dating back to the Early ...

''. However, the phylogeny of Trirachodontidae is not well-understood, and the family may be paraphyletic, with some species more closely related to

traversodontids Traversodontidae is an extinct family of herbivorous cynodonts. Traversodonts were primarily Gondwanan, with many species known from Africa and South America. Recently, traversodonts have also been found from Europe and eastern North America. ...

than others.

Paleoecology

''Impidens'' fossils are known from the ''Cricodon''-''Ufudocyclops'' subzone of the ''Cynognathus'' Assemblage Zone of the

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 ...

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 China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

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.

Footnotes

References

Bibliography

* * * {{Taxonbar, from=Q108084621 Cynognathians Prehistoric cynodont genera Fossil taxa described in 2021 Middle Triassic synapsids of Africa Triassic Antarctica Fossils of Antarctica Extinct animals of Antarctica Fossils of South Africa