''Kombuisia'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
dicynodont
Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typic ...
from
Early to
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 ...
(
Induan
The Induan is the first age of the Early Triassic epoch in the geologic timescale, or the lowest stage of the Lower Triassic series in chronostratigraphy. It spans the time between 251.902 Ma and Ma (million years ago). The Induan is sometime ...
to
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 ...
) of
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
and
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
. Two species were described for the genus: ''Kombuisia frerensis'' (
type)
and ''Kombuisia antarctica''.
Dicynodonts were a diverse
clade that inhabited the earth from the
Middle Permian
The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± ...
to the Late Triassic. ''Kombuisia'' is one of few species to survive the
mass extinction event in the
late Permian
Late may refer to:
* LATE, an acronym which could stand for:
** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia
** Local-authority trading enterprise, a New Zealand business law
** Local average treatment effect, ...
.
''Kombuisia'' are non-mammalian synapsid herbivores.
Specimens of this genus were discovered in the 1960s and 1970s and years later were determined to be two different species of the genus.
The two species were found in diverse areas, ''K. frerensis'' in
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
and ''K. antarctica'' in
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
. This indicated that this genus existed in a wider biographical region in the southern hemisphere of
Pangaea
Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
and believed by some to indicate the migration to Antarctica to avoid the rise in global temperatures that lead to the mass extinction.
Migration to avoid global warming has been highly controversial because many of the fossils that are found in this region are juvenile and of small body size. But so far no Permian vertebrate fossils are known from Antarctica, making it less likely that they were already living there prior to the event.
Originally the specimens that were collected in Antarctica were considered to be part of the ''Kingoria'' (now known as ''Dicynodontoides'')
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
. The specimens were originally catalogued in the
American Museum of Natural History as ''Kingoria'', however, with no formal reasoning for this categorization, this has since been revised with more up-to-date knowledge of features and speciation.
''Kingoria'' was defined early on as a close relative to ''Kombuisia'' and Hotton describes the two groups as
sister taxa
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and ...
. ''Kingoria'' and ''K. frerensis'' were relatively close geographically during their time of existence.
''Kingoria'' fossils are found in the mid to southern region of Africa. In a re-evaluation of the cranial anatomy of ''K. frerensis'' using the rule of parsimony the most recent conclusion is that ''Kingoria'' and ''Kombuisia'' are sister taxa of the ''Kingoriidae'' clade.
Discovery and geographic range
''Kombuisia frerensis'' was found in the ''Cynognathus'' Assemblage Zone in South Africa.
The zone is subdivided into 3 layers and encompasses the boundary of Late Early Triassic and Early Middle Triassic period. The specimen was collected from the middle zone, B, and considered to of the early
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 ...
age.
There is no evidence of the exact stratigraphic location of ''K. antarctica''. The specimens are from the central Transantarctic Mountains and were found at
Shenk Peak (AMNH 9562) and
Graphite Peak Graphite Peak () is a peak, high, standing at the northeast end of a ridge running northeast from Mount Clarke, just south of the head of Falkenhof Glacier in Antarctica. It was so named by the New Zealand Geological Survey Antarctic Expedition ...
(AMNH 9545). The fossils were found in the lower member of the 3 members of the
Fremouw Formation
The Fremouw Formation is a Triassic-age rock formation in the Transantarctic Mountains of Antarctica. It contains the oldest known fossils of tetrapods from Antarctica, including synapsids, reptiles and amphibians. Fossilized trees have also been ...
.
The lower member refers to the Early Triassic and Late Permian in some areas.
Classification of species
Early controversial specification
Defining the species and lineages of these fossils was difficult due to the lack of preservation and minimal cranial fossils that had been collected and catalogued.
There are two types of ''Kombuisia'' species. One of these, ''K. frerensis'', was collected in 1961 by J. W. Kitching and Nicholas Hotton in South Africa,
and the other was collected in the early 1970s from the Fremouw Formation of the Transantarctic Mountains. The specimens from South Africa were catalogued in the National Museum of Natural History and were later moved to the Bernard Price Institute for Paleontological Research in Johannesburg. The specimens from the Transantarctic Mountains are catalogued in the American Museum of Natural History (AMNH) and until 2009 had not been correctly identified. Christian Sidor, Kenneth Angielcyzk, and Jorg Frobisch worked to define this specimen as a new species of ''Kombuisia''. Prior to 2009, the species was considered to be part of the genus ''Kingoria'', but there was no written description and evaluation of the specification.
The similarities in the skull features between ''Kingoria'' and ''Kombuisia'' made classification of the species very difficult. The two both share common traits such as a lack of premaxillary ridges and the midline ridge of the vomerine is depressed. Unlike any other dicynodont the two genera share a similar feature of a longitudinal ridge at the edge of the
premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
.
Hotton analyzed the small skull that was found just south of Lady Frere, Cape Province, north of the Cacadu River in South Africa. The specimen had a complete lower jaw and stapes that proved pivotal in the description and definition of the species. ''K. frerensis'' has many similar features as ''Kingoria'' which made it difficult to diagnose as a new species. The two share features such as no post-canine teeth, a wider inter orbital bar than inter temporal bar, and the length of the post orbital region equals the distance from the post orbital bar to the snout.
Current specification
The differences that make the two genera distinguishable and the species distinguishable from other dicynodonts are seen in the
dentary
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 ...
. The ventral profile slopes upward and forward from the
splenial
The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side (closest to the tongue) between the angular and surangular
The suprangular or surangular is a jaw bone found in most land ver ...
to the tip of the beak, the front and side margins of the beak are sharp, and the symphysis tapers to a squared-off anterior margin as opposed to being parallel sided. The most distinctive feature that defined the new genus at the time was the lack of a pineal opening.
This led Hotton to the determination that the fossils belonged to a new Dicynodont species, ''Kombuisia frerensis''. Until 2009 this was the only species of the genus that was thought to have existed.
In 2009 Christian Sidor, Jorg Frobisch, and Kenneth Angielczyk identified the new species as ''K. antarctica''. The two species had been catalogued in the American Museum of Natural History as specimens AMNH 9562 and 9545. One of the most definitive differences between the two species is the slit-like pineal opening in ''K. antarctica''. There is also no contact between the post orbitals in ''K. antartica'', which is a feature seen in the ''K. frerensis'' specimens.
Cranial description
''K. frerensis''
*Fused premaxilla
*Absence of 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 ...
*Inverted triangular shape of the interparietal bone
*Lack of fusion of articular and prearticular bones
*Presence of an elongate, slender parietal posterolateral process that extends onto the occipital edge of the skull roof.
*Skull length approximately 76.8 mm
''K. antarctica''
*Skull length of approximately 73 mm (AMNH 9562)
*Skull length of approximately 69 mm (AMNH 9545)
*Lacking tusks
*Lack of premaxillary or postcanine teeth
*Antorbital region is greatly abbreviated
*Slit-like pineal foramen
*Anterior tip of the snout is rounded
*Narrow intertemporal region
*Parietals exposed as a narrow ridge between the ventrolaterally sloping postorbitals.
*No clarity whether ''K. antarctica'' possesses the elongate posterolateral process of the parietal found in ''K. frerensis'' due to lack of preservation of both existing specimens.
Paleobiology
The lack of a complete skeleton makes it difficult to re-create what the species may have looked like; however, analysis of the skull allows for an estimate of the animal's body size. The skull length of ''K. frerensis'' and ''K. antarctica'' differs by only 4–8 mm, ''K. frerensis'' being the larger of the two. While the exact body size cannot be determined, the skull size indicates that the genus was relatively small in body size.
Since Fröbisch reviewed the cranial anatomy of ''K. frerensis'' and was able to closely relate the genus to ''Kingoria'', subsequent attempts to re-create the species represent similar body plans. However, ''Kingoria'' are typically just over 50% larger than that of ''Kombuisia''.
It has often been proposed that Antarctica was a destination of migration to avoid the global warming in the Middle to Late Permian. However, further analysis of the body size of many of the specimens found in the lower member of the Fremouw Formation indicated that these species already existed in Antartica. ''Kombuisia'' provides knowledge of specimens in both
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
and Antarctica; in addition, examination of the cranial length and features indicates a small body size for ''Kombuisia''—too small to migrate seasonally from the
''Cynognathus'' Assemblage Zone in South Africa to the central
Transantarctic Mountains
The Transantarctic Mountains (abbreviated TAM) comprise a mountain range of uplifted (primarily sedimentary) rock in Antarctica which extend, with some interruptions, across the continent from Cape Adare in northern Victoria Land to Coats Land. ...
, which provides further argument against the proposed hypothesis. Evidence of tetrapod burrows is also found in the lower member of the Fremouw Formation. These burrows indicate that the environment may have been too harsh for a
tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
to live above ground and suggest a permanent subterranean residence of many of the species in Antarctica.
This may also suggest that ''K. antarctica'' was fossorial, like many of the other tetrapods that existed in this environment around the same time. According to Dr. Angielczyk, "''K. antarctica'' was about the size of a small house cat, considerably different from today’s mammals – it likely laid eggs, didn't nurse its young, and didn't have fur, and it is uncertain whether it was warm blooded."
References
{{Taxonbar, from=Q6428275
Dicynodonts
Triassic synapsids
Triassic synapsids of Africa
Extinct animals of Antarctica
Triassic Antarctica
Anisian life
Anomodont genera