''Microgomphodon'' 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 ...

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

n therapsid 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 ...

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 fossili ...

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 (geology), age in the Early Triassic epoch (geology), epoch; in chronostratigraphy, it is a stage (stratigraphy), stage in the Lower Triassic series (stratigraphy), series. It spans the time betw ...

Anisian In the geologic timescale, the Anisian is the lower stage (stratigraphy), stage or earliest geologic age, age of the Middle Triassic series (stratigraphy), series or geologic epoch, epoch and lasted from million years ago until million years ag ...

, 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 and a close relative of ''

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

'', 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 med ...

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, wher ...

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 In vertebrates, the maxilla (: maxillae ) 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 two maxil ...

and

dentary bone In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

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

pineal foramen A parietal eye (third eye, pineal eye) is a part of the epithalamus in some vertebrates. The eye is at the top of the head; is photoreceptive; and is associated with the pineal gland, which regulates circadian rhythmicity and hormone production ...

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 (colloquially known as the cheek bone), is a part of the skull formed by the zygomatic process of temporal bone, zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the ...

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 stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a per ...

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

Lesotho Lesotho, formally the Kingdom of Lesotho and formerly known as Basutoland, is a landlocked country in Southern Africa. Entirely surrounded by South Africa, it is the largest of only three sovereign enclave and exclave, enclaves in the world, t ...

spanning the border between the Free State and the

Eastern Cape The Eastern Cape ( ; ) is one of the nine provinces of South Africa. Its capital is Bhisho, and its largest city is Gqeberha (Port Elizabeth). Due to its climate and nineteenth-century towns, it is a common location for tourists. It is also kno ...

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

KwaZulu-Natal KwaZulu-Natal (, also referred to as KZN) is a Provinces of South Africa, province of South Africa that was created in 1994 when the government merged the Zulu people, Zulu bantustan of KwaZulu ("Place of the Zulu" in Zulu language, Zulu) and ...

. 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 Baurioidea 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