''Scalenodon'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of traversodontid

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

s from the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

and possibly

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. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

''S. angustifrons'' was named in 1946 and several other species were named in the following years. Most of the species from Africa are now thought to belong to different genera than ''Scalenodon''.

History and species

The first fossils belonging to ''Scalenodon'' were found in the Manda Formation of

Zambia Zambia, officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa. It is typically referred to being in South-Central Africa or Southern Africa. It is bor ...

and assigned to '' Trirachodon angustifrons'' in 1946. In 1955, the species was given its own genus, ''Scalenodon''. In 1963, a second species called ''S. drysdalli'' was named from the Ntawere Formation in the Luangwa Valley of Zambia. Later that year ''S. drysdalli'' was placed in its own genus, '' Luangwa''. Three additional species, ''S. attridgei'', ''S. charigi'', and ''S. hirschoni'', were named from the Manda Formation in 1972. In 1973, a Russian species of ''Scalenodon'' was named ''S. boreus''. ''S. boreus'' is known from the southern

Ural Mountains The Ural Mountains ( ),; , ; , or simply the Urals, are a mountain range in Eurasia that runs north–south mostly through Russia, from the coast of the Arctic Ocean to the river Ural (river), Ural and northwestern Kazakhstan.

Orenburg Oblast Orenburg Oblast (also Orenburzhye) is a federal subject of Russia (an oblast), mainly located in Eastern Europe. Its administrative center is the city of Orenburg. From 1938 to 1957, it bore the name Chkalov Oblast in honor of Valery Chkal ...

. A 2003 analysis of traversodontid relationships did not find the species of ''Scalenodon'' from the Manda Formation to form a single

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

, meaning that many were not referable to the genus. The study suggested that ''S. hirschoni'' had more in common with other traversodontids like '' Luangwa''. ''S. attridgei'' was viewed as a possible synonym of ''S. charigi'', which was also found to be only distantly related to ''S. angustifrons''. ''S. hirschsoni'' was placed in its own genus, '' Mandagomphodon'', in 2013. ''S. angustifrons'' and ''S. boreus'' remain valid species of ''Scalenodon''. While ''S. angustifrons'' is known from partial skulls, teeth, and a lower jaw, ''S. boreus'' is known only from two upper postcanine teeth.

References

{{Taxonbar, from=Q7429753 Traversodontidae Middle Triassic synapsids of Africa Middle Triassic synapsids of Europe Fossil taxa described in 1955