The ''Pristerognathus'' Assemblage Zone is 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 ...

assemblage zone or

biozone In biostratigraphy, biostratigraphic units or biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxa, as opposed to a lithostratigraphic unit which is defined by the lithological properties ...

which correlates to the upper

Abrahamskraal Formation The Abrahamskraal Formation is a geological formation and is found in numerous localities in the Northern Cape, Western Cape, and the Eastern Cape of South Africa. It is the lowermost formation of the Adelaide Subgroup of the Beaufort Group, a ma ...

and lowermost Teekloof Formation, Adelaide Subgroup of the

Beaufort Group The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup in South Africa. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and unconformably underli ...

, a fossiliferous and geologically important geological

Group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...

of the

Karoo Supergroup 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 peri ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...

. The thickest

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...

s, reaching not more than , occur just east of

Sutherland Sutherland ( gd, Cataibh) is a historic county, registration county and lieutenancy area in the Highlands of Scotland. Its county town is Dornoch. Sutherland borders Caithness and Moray Firth to the east, Ross-shire and Cromartyshire (later c ...

through to

Beaufort West Beaufort West (Afrikaans: ''Beaufort-Wes''; Xhosa: ''eBhofolo'') is a town in the Western Cape province in South Africa. It is the largest town in the arid Great Karoo region, and is known as the "Capital of the Karoo". It forms part of the Beau ...

in the south and

Victoria West Victoria West is a town in the central Karoo region of South Africa's Northern Cape province. It is situated on the main N12 route, at an elevation of . It is the seat of the Ubuntu Local Municipality within the Pixley ka Seme District Municipa ...

in the north. Exposures are also found west of

Colesberg Colesberg is a town with 17,354 inhabitants in the Northern Cape province of South Africa, located on the main N1 road from Cape Town to Johannesburg. In a sheep-farming area spread over half-a-million hectares, greater Colesberg breeds many ...

and south of

Graaff-Reinet Graaff-Reinet is a town in the Eastern Cape Province of South Africa. It is the oldest town in the province. It is also the sixth-oldest town in South Africa, after Cape Town, Stellenbosch, Simon's Town, Paarl and Swellendam. The town was the ...

. The '' Pristerognathus'' Assemblage Zone is the third biozone of the

. The name of the

refers to ''

Pristerognathus polyodon ''Pristerognathus'' is an extinct genus of therocephalian, known from the late Middle Permian (Capitanian) of South Africa.F. Abdala, B. Rubidge, and J. van der Heever, "The oldest therocephalians (Therapsida, Eutheriodonta) and the early diversi ...

'', a medium-sized

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

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 thei ...

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 ...

. It is characterized by the presence of this

n species in association with '' Diictodon feliceps'', a small,

fossorial A fossorial () animal is one adapted to digging which lives primarily, but not solely, underground. Some examples are badgers, naked mole-rats, clams, meerkats, and mole salamanders, as well as many beetles, wasps, and bees. Prehistoric evid ...

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 ...

whose

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s are especially common in this biozone.

History

The first

s to be found in the

rocks that encompass the current eight

s were discovered by Andrew Geddes Bain in 1856. However, it was not until 1892 that it was observed that the geological strata of the

could be differentiated based on their

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

. The initial undertaking was done by

Harry Govier Seeley Harry Govier Seeley (18 February 1839 – 8 January 1909) was a British paleontologist. Early life Seeley was born in London on 18 February 1839, the second son of Richard Hovill Seeley, a goldsmith, and his second wife Mary Govier. When his fat ...

who subdivided the

into three

s, which he named (from oldest to youngest): * Zone of "

Pareiasaur Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with scutes which covered large areas of the body. They first appeared in southern Pangea during the Middle Permi ...

ians" * Zone 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 ...

s" * Zone of "highly specialized group of theriodonts" These proposed biozones Seeley named were subdivided further by

Robert Broom Robert Broom FRS FRSE (30 November 1866 6 April 1951) was a British- South African doctor and palaeontologist. He qualified as a medical practitioner in 1895 and received his DSc in 1905 from the University of Glasgow. From 1903 to 1910, he ...

between 1906 and 1909.

Broom A broom (also known in some forms as a broomstick) is a cleaning tool consisting of usually stiff fibers (often made of materials such as plastic, hair, or corn husks) attached to, and roughly parallel to, a cylindrical handle, the broomstick. I ...

proposed the following

s (from oldest to youngest): * '' Pareiasaurus'' beds * ''

Endothiodon ''Endothiodon'' (/ɛndoʊθiːoʊdɔːn/ "inner tooth" from Greek endothi (ἔνδοθῐ), "within", and odon (ὀδών), "tooth", most likely named for the characteristic of the teeth being placed internally to the maxillaBoos A. S., Schultz C ...

'' beds * '' Kistecephalus'' beds * '' Lystrosaurus'' beds * ''

Procolophon ''Procolophon'' is a genus of lizard-like procolophonid parareptiles that first appeared in the Early Triassic (Induan) of South Africa, Brazil, and Antarctica. It persisted through the Permian–Triassic extinction event, but went extinct in ...

'' beds * '' Cynognathus'' beds The '' Pristerognathus'' Assemblage Zone as it currently stands was defined by Keyser and Smith in the late 1970s. Initially the

included the upper 300m of the underlying ''Tapinocephalus'' Assemblage Zone due to the disappearance of

Dinocephalia Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. Dinocephal ...

n fossils in those rock deposits and had been named the '' Pristerognathus-

Diictodon ''Diictodon'' is an extinct genus of pylaecephalid dicynodont. These mammal-like synapsids lived during the Late Permian period, approximately 255 million years ago. Fossils have been found in the ''Cistecephalus'' Assemblage Zone of the Mad ...

'' Assemblage Zone. After further research on the rocks of the middle Permian, it was understood that the disappearance of the

dinocephalia Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. Dinocephal ...

ns was not an indication of the boundary of the ''Tapinocephalus'' Assemblage Zone, and the extra 300m of rock was subsequently restored to the underlying

Tapinocephalus Assemblage Zone The ''Tapinocephalus'' Assemblage Zone is a tetrapod assemblage zone or biozone which correlates to the middle Abrahamskraal Formation, Adelaide Subgroup of the Beaufort Group, a fossiliferous and geologically important geological Group of the ...

Lithology

The ''Pristerognathus'' Assemblage Zone correlates with the upper

, the lowermost Teekloof Formation west of 24°E and to the Middleton Formation east of 24°E, Adelaide Subgroup of the

. This

is considered to be Middle

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...

(

Guadalupian 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 � ...

) in age. The rocks of the ''Pristerognathus'' Assemblage Zone are similar to the underlying ''Tapinocephalus'' Assemblage Zone although is dominated by multistory

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...

deposits. The

s are interspaced with

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...

-rich greenish-grey

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.' ...

s and subordinate reddish-brown

layers.

Calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an ad ...

nodules, which weather out brown, are often found in the

layers. Pinkish

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...

bands are found in the lowermost

deposits of this biozone. The ''Pristerognathus'' Assemblage Zone is also known for containing

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

deposits. The presence of the

band confirms that there was

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plat ...

activity taking place during the time the rock sediments were deposited. The rocks of the lower ''Pristerognathus'' Assemblage Zone were deposited at the end of the middle

(end-Guadalupian) extinction event, which is currently thought to have been caused by the eruption of the Emeishan Large Igneous Province. The depositional environment of the ''Pristerognathus'' Assemblage Zone was likewise similar to the ''Tapinocephalus'' Assemblage Zone, having been formed by sedimentary material being deposited by vast,

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

plains. These fluvial plains flowed northwards from a

foreland basin A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithosphere ...

that was being formed from the rising of the Gondwanide mountains in the south. The Gondwanides were the result of crustal uplift that had previously begun to take course due to tectonic activity. The pressure of the growing Gondwanides mountain chain caused the formation of 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 perio ...

where the deposits of the ''Pristerognathus'' Assemblage zone, and all other succeeding assemblage zone deposits, were deposited over tens of millions of years.

Paleontology

Vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...

s are most commonly found in the

deposits of the ''Pristerognathus'' Assemblage Zone, especially within the

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an ad ...

nodules. This

is characterized by the presence of ''

'' and its other subspecies ''Pristerognathus baini'' and ''Pristerognathus vanderbyli''. '' Pristerognathus'' fossils are usually found associated with those of ''

''. The fossils of both these

are the most commonly found; other

are markedly more rare.

Species diversity Species diversity is the number of different species that are represented in a given community (a dataset). The effective number of species refers to the number of equally abundant species needed to obtain the same mean proportional species abundan ...

dropped off after the

end-Guadalupian extinction The Capitanian mass extinction event, also known as the end-Guadalupian extinction event or the pre-Lopingian crisis was an extinction event that predated the end-Permian extinction event and occurred around 260 million years ago during a period ...

, which is the reason that this

is lacking in

species richness Species richness is the number of different species represented in an ecological community, landscape or region. Species richness is simply a count of species, and it does not take into account the abundances of the species or their relative ab ...

. Other taxa that have been found in this biozone include a couple

pareiasaur Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with scutes which covered large areas of the body. They first appeared in southern Pangea during the Middle Permi ...

species, namely '' Bradysaurus'', the putative pantestudine '' Eunotosaurus africanus'', and the

varanopid Varanopidae is an extinct family of amniotes that resembled monitor lizards and may have filled a similar niche, hence the name. Typically, they are considered synapsids that evolved from an '' Archaeothyris''-like synapsid in the Late Carbonifer ...

pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an order, but this is ...

'' Heleosaurus scholtzi''. Fossils of the

biarmosuchia Biarmosuchians are an extinct clade of non-mammalian synapsids from the Permian. They are the most basal group of the therapsids. All of them were moderately-sized, lightly-built carnivores, intermediate in form between basal sphenacodont " pelyc ...

n '' Hipposaurus boonstrai'' are likewise found including some

gorgonopsid Gorgonopsia (from the Greek Gorgon, a mythological beast, and 'aspect') is an extinct clade of sabre-toothed therapsids from the Middle to Upper Permian roughly 265 to 252 million years ago. They are characterised by a long and narrow skull, ...

species. Other

species found include '' Endothiodon uniseries'' and '' Pristerodon mackayi''. Finally, fossils of

temnospondyl Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carb ...

amphibian Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...

s such as of '' Rhinesuchus whaitsi'', the fishes ''Namaichthys'' and ''Atherstonia'',

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...

trackways, burrows, and feeding trails such as of Planolites and a variety of plant fossils, namely of ''

Glossopteris ''Glossopteris'' tymology: from Ancient Greek γλῶσσα (glôssa, " tongue ") + πτερίς (pterís, " fern ")is the largest and best-known genus of the extinct Permian order of seed ferns known as Glossopteridales (also known as Arberia ...

'', '' Phyllotheca'', and ''Schizoneura'', have been recovered. Some fossil taxa that have been found from this biozone, namely ''

Hipposaurus ''Hipposaurus'' ('horse lizard') is an extinct genus of basal therapsids known from the ''Tapinocephalus'' Assemblage Zone of the Main Karoo Supergroup, Karoo Basin, South Africa. Chronologically this is within the Capitanian stage of the Guada ...

'', have been recovered from geological formations from different countries which correlate in age. Hipposaurus fossils have been found in the Madumabisa Mudstone Formation in

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

References

{{Reflist South African assemblage zones Permian South Africa Guadalupian

History

Lithology

Paleontology

See also

References