''Microgomphodon'' 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 ...

therocephalia 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 te ...

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 ...

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 ...

of South Africa and Namibia. Currently only one species of ''Microgomphodon'', ''M. oligocynus'', is recognized. With fossils present in the ''Cynognathus'' Assemblage Zone (CAZ) of the

Burgersdorp Formation The ''Cynognathus'' Assemblage Zone is a tetrapod biozone utilized in the Karoo Basin of South Africa. It is equivalent to the Burgersdorp Formation, the youngest lithostratigraphic formation in the Beaufort Group, which is part of the fossil ...

in South Africa and

Omingonde Formation The Omingonde Formation is an Early Triassic, Early to Middle Triassic (Anisian to Ladinian) geologic Formation (geology), formation, part of the Karoo Supergroup, in the western Otjozondjupa Region and northeastern Erongo Region of north-central N ...

of Namibia and ranging in age from late

Olenekian In the geologic timescale, the Olenekian is an age in the Early Triassic epoch; in chronostratigraphy, it is a stage in the Lower Triassic series. It spans the time between Ma and Ma (million years ago). The Olenekian is sometimes divided into ...

Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from million years ago until million years ago. The Anisian Age succeeds the Olenekian Age (part of the Lower Triassic Ep ...

, it is one of the most geographically and temporally widespread therocephalian species. Moreover, its occurrence in the upper Omigonde Formation of Namibia makes ''Microgomphodon'' the latest-surviving therocephalian. ''Microgomphodon'' is a member of the family

Bauriidae Bauriidae is an extinct family of therocephalian therapsids. Bauriids were the latest-surviving group of therocephalians after the Permian–Triassic extinction event, going extinct in the Middle Triassic. They are among the most advanced euther ...

and a close relative of ''

Bauria ''Bauria'' is an extinct genus of the suborder Therocephalia that existed during the Early and MiddleTriassic period, around 246-251 million years ago. It belonged to the family Bauriidae. ''Bauria'' was probably a carnivore or insectivore ...

'', another South African bauriid from the CAZ. Like other bauriids, it possesses several mammal-like features such as a

secondary palate The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates. In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medi ...

and broad, molar-like postcanine teeth, all of which evolved independently from mammals.

Description

''Microgomphodon'' has a short snout and large eye sockets that are roughly equal in size to the temporal openings behind them (these openings are typically much larger in therocephalians). Its

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whe ...

s are large and pointed, with the lower set splaying forward from the lower jaw. A pair of enlarged canines in the upper jaw separates the incisors in the front from the postcanines in the back. The postcanine teeth are widened and bear cusps that interlock with the postcanines of the lower jaw. They are positioned closer to the midlines of the upper and lower jaws than are the incisors due to an inward expansion of the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

and

dentary bone In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

s. ''Microgomphodon'' is very similar in appearance to ''Bauria'', but differs in having a small hole called a

pineal foramen A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhyth ...

at the top of the skull behind the eye sockets, a complete

postorbital bar The postorbital bar (or postorbital bone) is a bony arched structure that connects the frontal bone of the skull to the zygomatic arch, which runs laterally around the eye socket. It is a trait that only occurs in mammalian taxa, such as most strep ...

enclosing the eye sockets from behind, fewer postcanine teeth, and canines located farther back along the upper jaw. Additionally, the two taxa can be distinguished by many subtle differences relating to the shape of the skull. For example, ''Microgomphodon'' has a deeper snout, slightly larger eyes, and a sharper angle to the

zygomatic arch In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygomati ...

es than does ''Bauria''. Specimens of ''Microgomphodon'' are generally smaller than those of ''Bauria''; the largest skull of ''Microgomphodon'' is long whereas the largest of ''Bauria'' is .

Geographic and temporal distribution

Most fossils of ''Microgomphodon'' come from the

Karoo Basin The Karoo Supergroup is the most widespread stratigraphy, stratigraphic unit in Africa south of the Kalahari Desert. The group (stratigraphy), supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Pennsylvan ...

of South Africa. Skulls of ''Microgomphodon'' have been found in two regions within the country: one southwest of

Lesotho Lesotho ( ), officially the Kingdom of Lesotho, is a country landlocked country, landlocked as an Enclave and exclave, enclave in South Africa. It is situated in the Maloti Mountains and contains the Thabana Ntlenyana, highest mountains in Sou ...

spanning the border between the Free State and the

Eastern Cape The Eastern Cape is one of the provinces of South Africa. Its capital is Bhisho, but its two largest cities are East London and Gqeberha. The second largest province in the country (at 168,966 km2) after Northern Cape, it was formed in ...

and another northeast of Lesotho within the Free State near its border with

KwaZulu-Natal KwaZulu-Natal (, also referred to as KZN and known as "the garden province") is a province of South Africa that was created in 1994 when the Zulu bantustan of KwaZulu ("Place of the Zulu" in Zulu) and Natal Province were merged. It is locate ...

. Fossil localities in the first region contain both ''Microgomphodon'' and ''Bauria'' remains, while localities in the second contain only ''Microgomphodon''. A skull of ''Microgomphodon'' has also been found in the upper Omingonde Formation in Namibia. The oldest occurrence of ''Microgomphodon'' is in Subzone A of the ''Cynognathus'' Assemblage Zone, which dates to the Late

. ''Microgomphodon'' continues into Subzone B of the CAZ, which dates to the

. The youngest known specimen of ''Microgomphodon'' is the skull from Namibia, found in the upper part of the Omingonde Formation near its contact with the overlying Etjo Formation. The specimen is not only the youngest of ''Microgomphodon'' but the youngest of any therocephalian, making ''Microgomphodon'' the latest-surviving member of the group.

References

{{Taxonbar, from=Q6839565 Bauriids Middle Triassic synapsids of Africa Anisian life Triassic South Africa Fossils of South Africa Fossils of Namibia Omingonde Formation Fossil taxa described in 1895 Taxa named by Harry Seeley