Akidnognathidae is an extinct family of

therocephalian Therocephalia is an extinct suborder of eutheriodont therapsids (mammals and their close relatives) from the Permian and Triassic. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of their t ...

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...

s from the

Late Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

and

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...

and China. The family includes many large-bodied therocephalians that were probably carnivorous, including '' Moschorhinus'' and ''

Olivierosuchus ''Olivierosuchus'' is an extinct genus of therocephalian therapsids. It is a member of the family Akidnognathidae. Fossils of ''Olivierosuchus'' have been found from the Early Triassic ''Lystrosaurus'' Assemblage Zone in South Africa. Unlike ot ...

''. One akidnognathid, ''

Euchambersia ''Euchambersia'' is an extinct genus of therocephalian therapsids that lived during the Late Permian in what is now South Africa and China. The genus contains two species. The type species ''E. mirabilis'' was named by paleontologist Robert Broo ...

'', may even have been venomous. Akidnognathids have robust skulls with a pair of large caniniform teeth in their upper jaws. The family is morphologically intermediate between the more basal therocephalian group

Scylacosauridae Scylacosauridae is an extinct family of therocephalian therapsids. Scylacosaurids lived during the Permian period and were among the most basal therocephalians. The family was named by South African paleontologist Robert Broom in 1903. Scylacos ...

and the more derived group Baurioidea.

Classification

History

The first family-level name used to classify an akidnognathid was Euchambersidae, erected by South African paleontologist Lieuwe Dirk Boonstra in 1934,Boonstra L.D. 1934. "A contribution to the morphology of the mammal-like reptiles of the suborder Therocephalia". ''Annals of the South African Museum'', 31: 215–267 in reference for the genus ''

'', which is possibly one of the oldest known

venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a st ...

ous

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s. In 1940, German paleontologist Friedrich von Huene changed the spelling of the name to Euchambersiidae, the correct form of Latin. Akidnognathidae was first named in 1954 by South African paleontologists

Sidney H. Haughton Sidney Henry Haughton FRS (7 May 1888 – 24 May 1982) was an English-born South African paleontologist and geologist best known for his description of the sauropodomorph dinosaur '' Melanorosaurus'' in 1924, and his work on the geology of ...

and A. S. Brink. It included several therocephalians still recognized as akidnognathids as well as several now classified as scylacosaurids. English and American paleontologists

D. M. S. Watson Prof David Meredith Seares Watson FRS FGS HFRSE LLD (18 June 1886 – 23 July 1973) was the Jodrell Professor of Zoology and Comparative Anatomy at University College, London from 1921 to 1951. Biography Early life Watson was born in the Highe ...

and

Alfred Romer Alfred Sherwood Romer (December 28, 1894 – November 5, 1973) was an American paleontologist and biologist and a specialist in vertebrate evolution. Biography Alfred Romer was born in White Plains, New York, the son of Harry Houston Romer an ...

moved many of these therocephalians into the family Whaitsiidae in 1956, although many were moved back to Akidnognathidae in later years. Whaitsiids and akidnognathids are similar in appearance, leading some paleontologists to propose placing them in a superfamily called Whaitsioidea. Moschorhinidae was erected as another name for the family in 1974, and Annatherapsididae was proposed in 1975. Three subfamilies were also proposed in 1975: Annatherapsidinae, Moschorhininae and Euchambersiinae. While the name Euchambersiidae may have priority over Akidnognathidae because it was named first, Akidnognathidae is currently considered the valid name because it is based on the first named genus of the group, '' Akidnognathus'' (''Akidnognathus'' was named in 1918 while ''Euchambersia'' was named in 1931).

Phylogeny

Topology recovered by the 2016 analysis of Huttenlocker ''et al.'' is showed below.

References

Permian synapsids Lopingian first appearances Early Triassic extinctions Prehistoric therapsid families {{paleo-therapsid-stub