''Scalenodon'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

traversodontid 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. Tra ...

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 ...

s from the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

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

and possibly

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

. The

type species In 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 species that contains the biological type specimen ...

''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 The Manda Formation (also known as the Manda Beds) is a Middle Triassic (Anisian?) or possibly Late Triassic (Carnian?) geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Triassic, including some of the e ...

Zambia Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa, although it is typically referred to as being in Southern Africa at its most cent ...

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 The Ntawere Formation is a Middle Triassic (Anisian) geological formation in Zambia, preserving fossils of synapsids, archosaurs, and temnospondyls. Geology Several different facies are present in the Ntawere Formation, reconstructing a floodpla ...

in the

Luangwa Valley The Luangwa River is one of the major tributaries of the Zambezi River, and one of the four biggest rivers of Zambia. The river generally floods in the rainy season (December to March) and then falls considerably in the dry season. It is one of ...

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 ( ; rus, Ура́льские го́ры, r=Uralskiye gory, p=ʊˈralʲskʲɪjə ˈɡorɨ; ba, Урал тауҙары) or simply the Urals, are a mountain range that runs approximately from north to south through western ...

Orenburg Oblast Orenburg Oblast (russian: Оренбургская область, ''Orenburgskaya oblast'') is a federal subject of Russia (an oblast). Its administrative center is the city of Orenburg. From 1938 to 1957, it bore the name ''Chkalov Oblast'' () ...

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

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

, 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 ''Mandagomphodon'' is an extinct genus of traversodontid cynodonts from the Middle Triassic Lifua Member of the Manda Beds of Ruhuhu Valley, Tanzania. The type species ''Mandagomphodon hirschsoni'' was named by Crompton in 1972 as a species refe ...

'', 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 Traversodontids Prehistoric cynodont genera Middle Triassic synapsids of Africa Triassic synapsids of Europe Fossil taxa described in 1955