The ''Daptocephalus'' Assemblage Zone is a

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

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 taxon, taxa, as opposed to a Lithostratigraphy, lithostratigraphic unit which is defined by the ...

found in the Adelaide Subgroup of the Beaufort Group, a majorly

fossiliferous 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 i ...

and geologically important Group of the Karoo Supergroup in

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

.Rubidge, B. S. (1995). Biostratigraphy of the Beaufort Group (Karoo Supergroup). ''Biostratigraphic series''. This biozone has outcrops located in the upper Teekloof Formation west of 24°E, the majority of the Balfour Formation east of 24°E, and the Normandien Formation in the north. It has numerous localities which are spread out from Colesberg in the

Northern Cape The Northern Cape ( ; ; ) is the largest and most sparsely populated Provinces of South Africa, province of South Africa. It was created in 1994 when the Cape Province was split up. Its capital is Kimberley, South Africa, Kimberley. It includes ...

, Graaff-Reniet to Mthatha in 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 from

Bloemfontein Bloemfontein ( ; ), also known as Bloem, is the capital and the largest city of the Free State (province), Free State province in South Africa. It is often, and has been traditionally, referred to as the country's "judicial capital", alongsi ...

to Harrismith in the Free State. The ''Daptocephalus'' Assemblage Zone is one of eight biozones found in the Beaufort Group and is considered Late

Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...

(

Lopingian The Lopingian is the uppermost series/last epoch of the Permian. It is the last epoch of the Paleozoic. The Lopingian was preceded by the Guadalupian and followed by the Early Triassic. The Lopingian is often synonymous with the informal te ...

) in age. Its contact with the overlying ''Lystrosaurus'' Assemblage Zone marks the Permian-Triassic boundary. Previously known as the ''Dicynodon'' Assemblage Zone, the name of the biozone refers to '' Daptocephalus'', a medium-sized

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

therapsid. It is characterized by the presence of this species in co-occurrence with '' Theriognathus microps'', and '' Dicynodon lacerticeps.''

History

The first

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 preserve ...

s to be found in the Beaufort Group 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 Beaufort Group could be differentiated based on their

taxa In biology, a taxon (back-formation from ''taxonomy''; : 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 name and ...

. The initial undertaking was done by Harry Govier Seeley who subdivided the Beaufort Group 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 osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Per ...

ians" * Zone of "

Dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

s" * Zone of "highly specialized group of

theriodont The theriodonts (clade Theriodontia) are a major group of therapsids which appeared during the Middle Permian and which includes the gorgonopsians and the eutheriodonts, itself including the therocephalians and the cynodonts. Naming In 1876, ...

s" These proposed biozones Seeley named were subdivided further by

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

between 1906 and 1909.

Broom A broom (also known 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. It is thus a ...

proposed the following

s (from oldest to youngest): * ''

Pareiasaurus ''Pareiasaurus'' (from , "cheek" and , "lizard") is an extinct genus of Pareiasauromorpha, pareiasauromorph reptile from the Permian period. It was a typical member of its family (biology), family, the pareiasaurids, which take their name from th ...

'' beds * '' Endothiodon'' beds * '' Kistecephalus'' beds * '' Lystrosaurus'' beds * '' Procolophon'' beds * '' Cynognathus'' beds These

divisions were approved by paleontologists of the time and were left largely unchanged for several decades. The ''Daptocephalus'' Assemblage Zone was first named after the

'' Daptocephlaus leoniceps'' by James Kitching due to the high prevalence, and localized appearance, of this species. However, the name of the biozone was changed to the ''Dicynodon'' Assemblage Zone as it was argued that '' Daptocephalus'' was in fact a juvenile of '' Dicynodon''. In addition it was thought that '' Dicynodon'' was a more suitable taxon for global biostratigraphic correlation of other Karoo-aged basins, namely to those in

Zambia Zambia, officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa. It is typically referred to being in South-Central Africa or Southern Africa. It is bor ...

Tanzania Tanzania, officially the United Republic of Tanzania, is a country in East Africa within the African Great Lakes region. It is bordered by Uganda to the northwest; Kenya to the northeast; the Indian Ocean to the east; Mozambique and Malawi to t ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

, and

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

. In recent years, with new paleontological finds and updated logging of geological formations and biostratigraphy of the Karoo Basin, it was found that there has been some taxonomic confusion with '' Dicynodon'' fossils. In addition, recent taxonomic studies have shown that '' Daptocephalus'' is indeed its own species, and is only found within the confines of the biozone. Subsequently it was renamed the ''Daptocephalus'' Assemblage Zone.

Lithology

The ''Daptocephalus'' Assemblage Zone is located only in the upper Balfour formation and lower Normandien formation east of 24°E. These formations all fall within the Adelaide Subgroup of the Beaufort Group, sediments of which were formed in a large retroarc

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 lithospher ...

in south-western

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

. The biozone is subdivided into the lower '' Daptocephalus- Theriognathus'' subzone and the upper '' Lystrosaurus- Moschorhinus'' subzone. This satisfies the appearance of '' Lystrosaurus maccaigi'' below the ''Lystrosaurus'' Assemblage Zone boundary, and the disappearance of the lower subzone taxa '' Theriognathus'', '' Dicynodon'', and '' Procynosuchus delaharpeae''. At the time of sedimentary deposition, the

Karoo The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe Khoemana (also known as !Orakobab or Korana) word is a semidesert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its extent is ...

retroarc foreland system was in an overfilled phase, and purely terrestrial sediments occupied the Karoo Basin at this time. Two fining-upward sequences are observed in the sedimentary

stratigraphy Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

of '' Daptocephalus'' biozone, bounded by a second-order subaerial

unconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

. These

sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

s comprise greenish-grey

mudrock Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone and shale. Most of the particles of which the stone is composed are less than and are too small to ...

with

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

lenses A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

in the lower to middle sections of the

, which are indicative of a low-energy fluvial environments with meandering rivers. It is in these rocks that

s are most commonly found. As the biozone reaches its termination, its contact with the overlying Katberg Formation marks a sharp change in the lithology. The sedimentary rocks change to being sandstone-rich with these sandstone bodies commonly appearing within outcrops of brownish-red

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

and reddish

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.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

. The appearance and proliferation of these sandstone deposits marks the change to braided river systems where sands were only deposited with the finer sediments being washed further downstream. Fossil abundance and preservation quality does not change across the boundary, however,

species abundance In ecology, local abundance is the relative representation of a species in a particular ecosystem. It is usually measured as the number of individuals found per sample. The ratio of abundance of one species to one or multiple other species livin ...

does due to the extinction event, and also the preservational style of the fossils. More isolated skulls are found in the Permian, whereas in the earliest Triassic, curled up complete skeletons are more common as are bonebeds. These lithological and taphonomic changes are used as evidence for the sudden drying of the climate associated with the Permian-Triassic extinction event.

Paleontology

The lower to middle zones of the ''Daptocephlaus'' Assemblage Zone display a great diversity of vertebrate fauna. These include its current type species '' Daptocephalus'' and other

s such as the ubiquitous '' Diictodon'', '' Dinanomodon'', and '' Pristerodon''. Various species of burnetiamorph

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

ns and Rubidgenae

Gorgonopsia Gorgonopsia (from the Greek Gorgon, a mythological beast, and 'aspect') is an extinct clade of Saber-toothed predator, sabre-toothed therapsids from the Middle Permian, Middle to the Upper Permian, roughly between 270 and 252 million years ago. ...

ns are also found.

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 species such as '' Moschorhinus kitchingi'' and the earliest

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

'' Charassognathus gracilis'' also appear.

Parareptile Parareptilia ("near-reptiles") is an extinct group of Basal (phylogenetics), basal Sauropsida, sauropsids ("Reptile, reptiles"), traditionally considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds ...

species, namely

captorhinids Captorhinidae is an extinct family of tetrapods, traditionally considered primitive reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea. Description Captorhinids are a clade of sm ...

, the Younginiforme ''

Youngina ''Youngina'' (named after John Young (1823–1900)) is an extinct genus of diapsid reptile from the Late Permian Beaufort Group ('' Tropidostoma''-'' Dicynodon'' zones) of the Karoo Red Beds of South Africa. This, and a few related forms, mak ...

'', and a variety of

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...

amphibians, fishes, and plant fossils such as '' Glossopteris'' are likewise found. The upper zones as the Permian-Triassic boundary approaches, there is a marked drop in species diversity as the Permian-Triassic extinction event began to take its course.

Age and correlations

The ''Daptocephalus'' Assemblage Zone dates to approximately 254.5 to 251 Ma, and correlates with the Kutuluksaya and Kulchomovskaya Formations of Russia, and with the lower Buena Vista Formation of the

Paraná Basin The Paraná Basin (, ) is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande do Sul states. The remainder area is distribu ...

, South America.Ezcurra, 2016, p.8

References

Bibliography

* {{cite journal , last=Ezcurra , first=Martín D , year=2016 , title=The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms , journal=

PeerJ ''PeerJ'' is an open access peer-reviewed scientific mega journal covering research in the biological and medical sciences. It officially launched in June 2012, started accepting submissions on December 3, 2012, and published its first articles ...