Scalenodon
Encyclopedia
Scalenodon is a genus
of traversodontid cynodont
from the Middle Triassic
of Africa
and possibly Russia
. The type species
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.
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
of Orenburg Oblast
.
A 2003 analysis of traversodontid relationships did not find the species of Scalenodon from the Manda Formation to form a single clade
, 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. 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of traversodontid cynodont
Cynodont
Cynodontia or cynodonts are a taxon of therapsids which first appeared in the Late Permian and were eventually distributed throughout all seven continents by the Early Triassic . This clade includes modern mammals and their extinct close relatives. They were one of the most diverse groups of...
from the Middle Triassic
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. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
and possibly Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
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 ZambiaZambia
Zambia , officially the Republic of Zambia, is a landlocked country in Southern Africa. The neighbouring countries are the Democratic Republic of the Congo to the north, Tanzania to the north-east, Malawi to the east, Mozambique, Zimbabwe, Botswana and Namibia to the south, and Angola to the west....
and assigned to Trirachodon
Trirachodon
Trirachodon is an extinct genus of tritylodontoid cynodont. Fossils have been found from the Cynognathus Assemblage Zone of the Beaufort Group in South Africa, dating back to the Early and Middle Triassic.-Description:...
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
Luangwa (cynodont)
Luangwa is a genus of traversodontid cynodonts. The species Luangwa drysdalli was discovered 1963 in the valley of the Luangwa river in Zambia, Africa. Luangwa lived in the Triassic period 240 Million years ago....
. 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
Ural Mountains
The Ural Mountains , or simply the Urals, are a mountain range that runs approximately from north to south through western Russia, from the coast of the Arctic Ocean to the Ural River and northwestern Kazakhstan. Their eastern side is usually considered the natural boundary between Europe and Asia...
of Orenburg Oblast
Orenburg Oblast
Orenburg Oblast is a federal subject of Russia . Its administrative center is the city of Orenburg. From 1938 to 1957, it bore the name Chkalov Oblast in honor of Valery Chkalov...
.
A 2003 analysis of traversodontid relationships did not find the species of Scalenodon from the Manda Formation to form a single clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, meaning that many were not referable to the genus. The study suggested that S. hirschoni had more in common with other traversodontids like Luangwa
Luangwa
Luangwa may refer to:*Luangwa River, the major river of eastern Zambia;*the Luangwa Bridge, which crosses the Luangwa River*the Luangwa Valley, a rift valley branch of the Great Rift Valley, named after the Luangwa River flowing in it;...
. S. attridgei was viewed as a possible synonym of S. charigi, which was also found to be only distantly related to S. angustifrons.
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.