The ''Cynognathus'' 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 ...
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 ...
utilized in 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 ...
of
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 ...
. It is equivalent to the Burgersdorp Formation, the youngest
lithostratigraphic
Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology.
In general, strata are primarily igneou ...
formation
Formation may refer to:
Linguistics
* Back-formation, the process of creating a new lexeme by removing or affixes
* Word formation, the creation of a new word by adding affixes
Mathematics and science
* Cave formation or speleothem, a secondar ...
in 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 ...
, which is part of the fossiliferous and geologically important
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 ...
. The ''
Cynognathus'' Assemblage Zone is the youngest of the eight biozones found in the Beaufort Group, and is considered to be late
Early Triassic
The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is ...
(
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 i ...
) to early
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 an ...
(
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 ...
) in age (around 247 Ma). The name of the biozone refers to ''
Cynognathus crateronotus'', a large and carnivorous
cynodont
The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide varie ...
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 ...
which occurs throughout the entire biozone.
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 preserved ...
s to be found in 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 ...
rocks that encompass the current eight
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 ...
s were discovered by
Andrew Geddes Bain
Andrew Geddes Bain (baptised 11 June 1797 – 20 October 1864), was a South African geologist, road engineer, palaeontologist and explorer.
Life history
The only child of Alexander Bain and Jean Geddes, both of whom died when Bain was still a ...
in 1856. However, it was not until 1892 that it was observed that the geological strata 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 ...
could be differentiated based on their
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 ...
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
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 ...
into three
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 ...
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"
Under Seeley's system, the "highly specialized theriodonts" zone corresponds to the modern ''Cynognathus'' Assemblage Zone. Seeley's proposed biozones 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
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 ...
s (from oldest to youngest):
* ''
Pareiasaurus
''Pareiasaurus'' is an extinct genus of pareiasauromorph reptile from the Permian period. It was a typical member of its family, the pareiasaurids, which take their name from this genus.
Fossils have been found in the Beaufort Group.
Descript ...
'' 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
These
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 ...
divisions were approved by paleontologists of the time and were left largely unchanged for several decades.
James Kitching
James William Kitching (6 February 1922 – 24 December 2003) was a South African vertebrate palaeontologist and regarded as one of the world’s greatest fossil finders.
Career
His work in the southern hemisphere, including Antarctica, led ...
retained the name of the ''
Cynognathus z''one in his revision of the biozones in the 1970s and 1980s. In 1995, he formalized the biozone under the name "''Cynognathus'' Assemblage Zone".
In the mid-1990s, new discoveries of additional outcrops presented the possibility that the Cynognathus Assemblage Zone could be subdivided further. A 1995 paper split it into three subzones: a lower subzone characterized by ''
Kestrosaurus'', a middle subzone characterized by the "classic" zone fauna which was already well-established, and an upper zone with reduced diversity. This informal three-part subdivision scheme was later labelled with letters (as subzones A, B, and C from oldest to youngest) until it was formalized with robust
index taxa and
type section A stratotype or type section in geology is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the stan ...
s in 2020. Subzone A was formalized as the ''
Langbergia
''Langbergia'' is an extinct genus of trirachodontid cynodont from the Early Triassic of South Africa. The type and only species ''L. modisei'' was named in 2006. ''Langbergia'' was found in the Burgersdorp Formation in the Beaufort Group, a pa ...
''-''
Garjainia
''Garjainia'' is an extinct genus of erythrosuchid archosauriform reptile from the Olenekian of Russia and South Africa. It was approximately 1.50–2 m (5–6 ft 8 in) long. It contained two species, ''Garjainia prima'' from the Yarengian/ ...
'' Subzone, subzone B as the ''
Trirachodon
''Trirachodon'' (Greek: "three ridge tooth") is an extinct genus of cynodonts. Fossils have been found in the ''Cynognathus'' Assemblage Zone of the Beaufort Group in South Africa and the Omingonde Formation of Namibia, dating back to the Early ...
''-''
Kannemeyeria
''Kannemeyeria'' is a genus of dicynodont that lived during the Anisian age of Middle Triassic period in what is now Africa and South America. The generic name is given in honor of Dr. Daniel Rossouw Kannemeyer, the South African fossil collect ...
'' Subzone, and subzone C as the ''
Cricodon
''Cricodon'' is an extinct genus of trirachodontid cynodonts that lived during the Early Triassic and Middle Triassic periods of Africa.Abdala, F., J. Neveling, and J. Welman. 2006. A new trirachodontid cynodont from the lower levels of the Burg ...
''-''
Ufudocyclops'' Subzone.
From the late 1970s onwards, some authors argued that ''Cynognathus'' was less common than previously considered, so they instead renamed the biozone to the ''Kannemeyeria'' Assemblage Zone or ''Kannemeyeria-
Diademodon'' Assemblage Zone. However, later work found that ''Kannemeyeria'' fossils were absent from Subzone A, and while ''Diademodon'' was found throughout the biozone it had been usurped as a dominant taxon by larger triracodontids by Subzone C.
This meant that these species were not ideal index taxa for the biozone. As ''Cynognathus'' fossils are found consistently throughout, the current name for the biozone was retained.
Lithology
The ''Cynognathus'' Assemblage Zone correlates with the Burgersdorp Formation in the upper Tarkastad 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 ...
.
The ''Cynognathus'' Assemblage Zone contains
argillaceous
Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces.
Clay minerals ...
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.' ...
successions varying from maroon to reddish, blueish-green, and greyish-green in colour. The
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 are
interbedded
In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology. For example, sedimentary rocks may be interbedded if there were sea level variations in their sedi ...
with
lenticular
Lenticular is an adjective often relating to lenses. It may refer to:
* A term used with two meanings in botany: see
* Lenticular cloud, a lens-shaped cloud
* Lenticular galaxy, a lens-shaped galaxy
* Lenticular (geology), adjective describing a ...
and
feldspathic 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 ...
s which appear greenish-grey when fresh and brownish-yellow when eroded out.
Clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...
-rich
pebble
A pebble is a clast of rock with a particle size of based on the Udden-Wentworth scale of sedimentology. Pebbles are generally considered larger than granules ( in diameter) and smaller than cobbles ( in diameter). A rock made predomina ...
conglomerates are also observed in some areas. Complete, articulated
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 frequently found encased in
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 within the
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.' ...
layers while complete skulls are mainly found in the
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 ...
. The
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 were likely deposited in low-energy,
meandering
A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank (cut bank) and deposits sediments on an inner, convex bank ...
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 ...
environments alongside sand-rich
river channels
In physical geography, a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of water or of other fluids (e.g., lava), most commonly the confine of a river, river delta or strait. The word is c ...
. The environment during time of deposition was
semi-arid
A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi- ...
, but with seasonal rain and flooding due to the presence of
crevasse splay
A crevasse splay is a sedimentary fluvial deposit which forms when a stream breaks its natural or artificial levees and deposits sediment on a floodplain. A breach that forms a crevasse splay deposits sediments in similar pattern to an alluvial f ...
s in the
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.' ...
layers. A lack of well developed channel
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 ...
s provides evidence for more
lacustrine
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
areas in the more northerly occurring outcrops of the biozone.
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 of the ''Cynognathus'' Assemblage Zone, reaching approximately , occur between
Queenstown and
Lady Frere
Lady Frere (officially Cacadu) is a small town in Chris Hani District Municipality in the Eastern Cape province of South Africa. The town was renamed to Cacadu in 2017 after changes to the country's colonial names. Cacadu, meaning “bulrush wat ...
in 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 ...
. Outcrops then thin out to between around
Aliwal North
Aliwal North (officially Maletswai) is a town in central South Africa on the banks of the Orange River, Eastern Cape Province. It is a medium-sized commercial centre in the northernmost part of the Eastern Cape.
History
Sir Harry Smith, then ...
,
Burgersdorp
Burgersdorp is a medium-sized town in Walter Sisulu in the Joe Gqabi District Municipality of the Eastern Cape province of South Africa.
In 1869 a Theological Seminary was established here by the ''Gereformeerde Kerk'', but in 1905 it was move ...
,
Steynsburg
Steynsburg is a small town in the Walter Sisulu Local Municipality of the Joe Gqabi District Municipality, Eastern Cape province of South Africa. Steynsburg is located on the intersection of the R56 and R390.
The town lies south-west of Bu ...
, and
Rouxville. Thin outcrops are also found in areas in the
Free State that border
Lesotho
Lesotho ( ), officially the Kingdom of Lesotho, is a country landlocked as an enclave in South Africa. It is situated in the Maloti Mountains and contains the highest mountains in Southern Africa. It has an area of over and has a population ...
.
The ''Langbergia''-''Garjainia'' Subzone (Subzone A) is most well-exposed and fossiliferous in northeast Free State, between
Senekal
Senekal is a town situated on the banks of the Sand River in the eastern part of the Free State province of South Africa. It was named after Commandant FP Senekal. It is the second largest town in Setsoto Municipality after Ficksburg, the lar ...
and
Bethlehem
Bethlehem (; ar, بيت لحم ; he, בֵּית לֶחֶם '' '') is a city in the central West Bank, Palestine, about south of Jerusalem. Its population is approximately 25,000,Amara, 1999p. 18.Brynen, 2000p. 202. and it is the capital ...
. At the
stratotype A stratotype or type section in geology is the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the stan ...
near Bethlehem, it reaches around 50 m in thickness. Exposures of this subzone rapidly decrease to the east, disappearing around
Bergville
Bergville is a small town situated in the foothills of the Drakensberg mountains, KwaZulu-Natal, South Africa. It was established as Bergville Mountain Village in 1897 and is now the commercial centre for a 2,500 km2 dairy and cattle ranchin ...
. Although the subzone thickens further south (to up to 100 m) towards Aliwal North, fossils diminish in abundance. Sediments of Subzone A are likely present in the Eastern Cape, though a lack of sufficient fossil material prevents it from being distinguished from younger strata.
The ''Trirachodon''-''Kannemeyeria'' Subzone (Subzone B) is the thickest and historically the most well-studied portion of the Assemblage Zone. It is primarily exposed in the Eastern Cape south of Lesotho. Subzone B reaches up to 500 m thick at the stratotype between Queenstown and Lady Frere, thinning northwards until it disappears east of
Thaba 'Nchu
Thaba 'Nchu is a town in Free State, South Africa, 63 km east of Bloemfontein and 17 km east of Botshabelo. The population is largely made up of Tswana and Sotho people. The town was settled in December 1833 and officially established ...
. The ''Cricodon''-''Ufudocyclops'' Subzone (Subzone C) has limited exposures in the vicinity of
Molteno
Molteno (; lmo, label= Brianzöö, Mültée) is a '' comune'' (municipality) and a hill-top town in the Province of Lecco in the Italian region Lombardy, located about northeast of Milan and about southwest of Lecco. As of 31 December 2004, it ...
and
Sterkstroom in the Eastern Cape. It reaches up to 150 m at its stratotype in Sterkstroom.
Biostratigraphy
The ''
Cynognathus'' Assemblage Zone holds a rich diversity of
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 ...
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
, of which it is most renowned for its
cynodont
The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide varie ...
fossils.
Cynognathids,
diademodontids, and
trirachodontids are found throughout the Assemblage Zone. In Subzone B, the diademodontid ''
Diademodon'' is far more common than trirachodontids. However, by the contact with Subzone C, trirachodontids had become the dominant taxa. ''Cynognathus'' is the common denominator, with its fossils found throughout Subzones A – C, confirming its place as the index taxon of the biozone as a whole. The large
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 ...
''
Kannemeyeria simocephalus
''Kannemeyeria'' is a genus of dicynodont that lived during the Anisian age of Middle Triassic period in what is now Africa and South America. The generic name is given in honor of Dr. Daniel Rossouw Kannemeyer, the South African fossil collect ...
'' appears in Subzone B alongside other anomodonts, and
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 ...
n species can be found throughout the biozone. Apart from
synapsid
Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...
s, the biozone is rich in other
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 ...
fauna
Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is '' flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. ...
, including
procolophonid
Procolophonidae is an extinct family of small, lizard-like parareptiles known from the Late Permian to Late Triassic that were distributed across Pangaea, having been reported from Europe, North America, China, South Africa, South America, Antarc ...
parareptiles and archosauromorph reptiles. Plant fossils such as ''
Dicroidium
''Dicroidium'' is an extinct genus of fork-leaved seed ferns that were widely distributed over Gondwana during the Triassic (). Their fossils are known from South Africa, the Arabian Peninsula, Australia, New Zealand, South America, Madagascar, ...
'', ''
Dadoxylon'', and ''
Schizoneura'' have been uncovered from limited areas corresponding to Subzones B - C. Aquatic life is well represented: numerous species 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 ...
, fishes, rare occurrences of
molluscs
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estim ...
, and
ichnofossils of
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
trackways and
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 ...
burrow
An Eastern chipmunk at the entrance of its burrow
A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of s ...
s have been discovered.
Subzone A
The ''Langbergia''-''Garjainia'' Subzone (Subzone A) is the oldest subzone in the ''Cynognathus'' Assemblage Zone. Its base is defined by the first appearance of ''Cynognathus crateronotus'', as well as the trirachodontid cynodont ''
Langbergia modisei'' and the
erythrosuchid
Erythrosuchidae (meaning "red crocodiles" in Greek) are a family of large basal archosauriform carnivores that lived from the later Early Triassic (Olenekian) to the early Middle Triassic (Anisian).
Naming
The family Erythrosuchidae was named b ...
archosauriform
Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Latest Permian (roughly 252 million years ago). It was defined by Jacques Gauthier ...
''
Garjainia madiba
''Garjainia'' is an extinct genus of erythrosuchid archosauriform reptile from the Olenekian of Russia and South Africa. It was approximately 1.50–2 m (5–6 ft 8 in) long. It contained two species, ''Garjainia prima'' from the Yarengian/ ...
''. The temnospondyl amphibians ''
Kestrosaurus'' and ''
Parotosuchus haughtoni'' are also common and distinctive fossils of the ''Langbergia-Garjainia'' Subzone. Dicynodonts are absent, unlike every other zone and subzone in the Beaufort Group.
Subzone B
The ''Trirachodon-Kannemeyeria'' Subzone (Subzone B) corresponds to traditional conceptions of the ''Cynognathus'' Assemblage Zone. Alongside abundant fossils of ''Cynognathus crateronotus'', the base of Subzone B sees the first appearance of fellow cynodonts ''Diademodon tetragonus'' and ''
Trirachodon berryi
''Trirachodon'' (Greek: "three ridge tooth") is an extinct genus of cynodonts. Fossils have been found in the ''Cynognathus'' Assemblage Zone of the Beaufort Group in South Africa and the Omingonde Formation of Namibia, dating back to the Ea ...
''. Dicynodonts reappear with ''Kannemeyeria simocephalus'', while ''
Xenotosuchus africanus'' is the most common temnospondyl in this subzone. The ''Trirachodon-Kannemeyeria'' Subzone also has the highest diversity of fish, plants, and
archosauromorph
Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, liza ...
reptiles in the entire Assemblage Zone. The erythrosuchid ''
Erythrosuchus africanus
''Erythrosuchus'' (from el, ἐρυθρός , 'red' and el, σοῦχος , 'crocodile') is an extinct genus of archosauriform reptile from the Triassic of South Africa. Remains have been found from the Cynognathus Assemblage Zone of the Beauf ...
'' is a common component of the fauna, living alongside its smaller relative ''
Euparkeria capensis'' and several species of early
rhynchosaur
Rhynchosaurs are a group of extinct herbivorous Triassic archosauromorph reptiles, belonging to the order Rhynchosauria. Members of the group are distinguished by their triangular skulls and elongated, beak like premaxillary bones. Rhynchosaurs ...
s (''
Howesia browni
''Howesia'' is an extinct genus of basal rhynchosaur from early Middle Triassic (early Anisian stage) deposits of Eastern Cape, South Africa. It is known from the holotype SAM 5884, a partial skeleton with palate and partial lower jaws and from ...
'', ''
Eohyosaurus wolvaardti
''Eohyosaurus'' is an extinct genus of basal rhynchosaur known from the early Middle Triassic (early Anisian stage) Burgersdorp Formation of Free State, South Africa. It contains a single species, ''Eohyosaurus wolvaardti''.
Discovery
''E ...
'', ''
Mesosuchus browni'').
Subzone C
The ''Cricodon''-''Ufudocyclops'' Subzone (Subzone C) is the youngest subzone, and has the most restricted exposures and fossil content. Its base is defined by the first appearance of the trirachodontid ''
Cricodon metabolus'' and the dicynodont ''
Ufudocyclops mukanelai'', the only species which are common in this subzone. ''Cynognathus'' and ''Diademodon'' still persist, though they are far more rare than in the previous subzone. Other species with utility for correlation include the temnospondyl ''
Paracyclotosaurus morganorum'' and the dicynodont ''
Shansiodon
''Shansiodon'' is a genus of dicynodont from Middle Triassic (Anisian and Ladinian) of China and South Africa (sp. indet.).
Dicynodonts
Anisian life
Middle Triassic synapsids of Africa
Triassic South Africa
Fossils of South Africa
Triassic sy ...
'' sp., which co-occur in the lower part of the subzone.
Paleobiota
Temnospondyls
Synapsids
Reptiles
Age and correlations
Based on tentative biostratigraphic correlations, the ''Cynognathus'' Assemblage Zone is considered to have been emplaced from approximately 249 to 244 Ma, in the later part of the Early Triassic and early part of the Middle Triassic. Based on the presence of ''Garjainia'' and ''Parotosuchus'', the ''Langbergia-Garjainia'' Subzone is correlated with the
Yarenskian Gorizont ("''Parotosuchus'' fauna") of
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
. The "''Parotosuchus'' fauna", exemplified by the
Petropavlovskya Svita (a local lithological unit), is assigned to the 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 i ...
Stage (latest Early Triassic, about 249-247 Ma) based on correlation with nearby marine fauna.
The classic faunal assemblage of the ''Trirachodon''-''Kannemeyeria'' Subzone is correlated with a wide variety of geological formations. Similar cynodont and dicynodont species are known from the Lower
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
Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...
, the Lower
Ntawere Formation
The Ntawere Formation is a Middle Triassic (Anisian) geological formation in Zambia, preserving fossils of synapsids, archosaurs, and temnospondyls.
Geology
Several different facies are present in the Ntawere Formation, reconstructing a floodp ...
of
Zambia
Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa, although it is typically referred to as being in Southern Africa at its most cent ...
,
and the lower Lifua Member of the
Tanzania
Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands and ...
n
Manda Beds
The Manda Formation (also known as the Manda Beds) is a Middle Triassic (Anisian?) or possibly Late Triassic (Carnian?) geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Triassic, including some of the e ...
. These correlations can be extended beyond Africa, as far as 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 ...
of
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 contine ...
,
Donguz Formation
The Donguz Formation, Donguz Svita, or Donguz Rocks (russian: Донгузские скалы) is a Middle Triassic geological formation that crops out on the right bank of Donguz River in Orenburg Oblast, Russia, across the settlement of Pervoma ...
("''
Eryosuchus
''Eryosuchus'' is an extinct genus of capitosauroid temnospondyl amphibian from the Middle Triassic of northern Russia. It was a very large predator: the largest specimen known could reach up to 3.5 m (11.5 ft) in length, with a skul ...
'' fauna") of Russia, and Lower
Ermaying Formation
The Ermaying Formation is a sedimentary succession of Anisian (Middle Triassic) age. It is found in the Shaanxi Province of China. It is composed of an up to 600 m thick sequence of mudstone and sandstone. It is famous for its fossils of tetrapods. ...
of China.
''Cynognathus'' and ''Diademodon'' fossils have even been found in the
Río Seco de la Quebrada Formation
The Río Seco de la Quebrada Formation is a Triassic geological formation in Mendoza Province, Argentina. Fossils of cynodonts such as '' Cynognathus, Diademodon,'' and ''Pascualgnathus'' have been found in this formation, along with dicynodonts ...
of
Mendoza Province
Mendoza, officially Province of Mendoza, is a province of Argentina, in the western central part of the country in the Cuyo region. It borders San Juan to the north, La Pampa and Neuquén to the south, San Luis to the east, and the republic o ...
,
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
. These formations are often considered early Anisian in age (earliest Middle Triassic, about 247 Ma).
However, there is some debate over their age; one
ash bed
Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...
below the Rio Seco de la Quebrada Formation was
radiometrically dated
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...
to around 236 Ma (early Carnian), much younger than previously suggested purely based on tetrapod biostratigraphy.
The classic ''Cynognathus'' Assemblage Zone has been equated with the
Nonesian Land Vertebrate Faunachron Land vertebrate faunachrons (LVFs) are biochronological units used to correlate and date terrestrial sediments and fossils based on their tetrapod faunas. First formulated on a global scale by Spencer G. Lucas in 1998, LVFs are primarily used withi ...
, part of a heavily-debated global system of Triassic tetrapod biostratigraphy.
The ''Cricodon-Ufudocyclops'' Subzone may be correlated with the upper parts of the Omingonde, Ntawere, and Manda Formations in Africa.
''Paracyclotosaurus'' is also known from the
Yerrapalli Formation
The Yerrapalli Formation is a Triassic rock formation consisting primarily of mudstones that outcrops in the Pranhita–Godavari Basin in southeastern India. The Yerrapalli Formation preserves fossils of freshwater and terrestrial vertebrates ...
and Upper
Denwa Formation
The Denwa is a river originating around Dhupgarh, in the Indian state of Madhya Pradesh. Denwa is a tributary of the Tawa, which is the largest tributary of Narmada River.
Among the complex of hills around Pachmarhi
Pachmarhi is a hill sta ...
of
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, while ''Shansiodon'' is found in the Upper Ermaying Formation ("''
Sinokannemeyeria
''Sinokannemeyeria'' is a genus of kannemeyeriiform dicynodont that lived during the Anisian age of Middle Triassic period in what is now Shanxi, China.J. Liu. 2015. New discoveries from the Sinokannemeyeria-Shansisuchus Assemblage Zone: 1. Kanne ...
'' fauna") of China.
''Shansiodon'' defines the base of the
Perovkan Land vertebrate faunachrons (LVFs) are Biochronology, biochronological units used to correlate and date terrestrial sediments and fossils based on their tetrapod faunas. First formulated on a global scale by Spencer G. Lucas in 1998, LVFs are primar ...
Land Vertebrate Faunachron Land vertebrate faunachrons (LVFs) are biochronological units used to correlate and date terrestrial sediments and fossils based on their tetrapod faunas. First formulated on a global scale by Spencer G. Lucas in 1998, LVFs are primarily used withi ...
, which has been applied in a global context.
These formations may be late Anisian in age, a suggestion supported by radiometric dating which positions the Upper Ermaying Formation at around 244 Ma.
See also
*
Geology of Lesotho The geology of Lesotho is built on ancient crystalline basement rock up to 3.6 billion years old, belonging to the Kaapvaal Craton, a section of stable primordial crust. Most of the rocks in the country are sedimentary or volcanic units, belonging t ...
*
Geology of Namibia
The geology of Namibia encompasses rocks of Paleoproterozoic, Mesoproterozoic and Neoproterozoic and Paleozoic to Cenozoic age. About 46% of the countryʼs surface are bedrock exposure, while the remainder is covered by the young overburden sedimen ...
*
Geology of South Africa
The geology of South Africa is highly varied including cratons, greenstone belts, large impact craters as well as orogenic belts. The geology of the country is the base for a large mining sector that extracts gold, diamonds, iron and coal from wor ...
*
Santa Maria Formation
The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age (Late Triassic), and is notable for its fossils of cynodonts, "rauisuchian" pseudosuchians, and early dinosaurs and oth ...
*
Triassic land vertebrate faunachrons Land vertebrate faunachrons (LVFs) are biochronological units used to correlate and date terrestrial sediments and fossils based on their tetrapod faunas. First formulated on a global scale by Spencer G. Lucas in 1998, LVFs are primarily used withi ...
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 , url=https://peerj.com/articles/1778.pdf , journal=
PeerJ
''PeerJ'' is an open access peer-reviewed scientific mega journal covering research in the biological and medical sciences. It is published by a company of the same name that was co-founded by CEO Jason Hoyt (formerly at Mendeley) and publisher Pet ...
, volume=4e1778 , pages=e1778 , doi=10.7717/peerj.1778 , pmid=27162705 , pmc=4860341 , doi-access=free , access-date=2019-03-14
South African assemblage zones
Early Triassic Africa
Middle Triassic Africa
Triassic South Africa
Anisian
Olenekian