Community hub
Recent from talks
Knowledge base stats:
Talk channels stats:
Members stats:
Cynognathus Assemblage Zone
The Cynognathus Assemblage Zone is a tetrapod biozone utilized in the Karoo Basin of South Africa. It is equivalent to the Burgersdorp Formation, the youngest lithostratigraphic formation in the Beaufort Group, which is part of the fossiliferous and geologically important Karoo Supergroup. The Cynognathus Assemblage Zone is the youngest of the eight biozones found in the Beaufort Group, and is considered to be late Early Triassic (Olenekian) to early Middle Triassic (Anisian) in age (around 247 Ma). The name of the biozone refers to Cynognathus crateronotus, a large and carnivorous cynodont therapsid which occurs throughout the entire biozone.
The first fossils to be found in the Beaufort Group rocks that encompass the current eight biozones 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 fossil taxa. The initial undertaking was done by Harry Govier Seeley who subdivided the Beaufort Group into three biozones, which he named (from oldest to youngest):
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 between 1906 and 1909. Broom proposed the following biozones (from oldest to youngest):
These biozone divisions were approved by paleontologists of the time and were left largely unchanged for several decades. James Kitching retained the name of the Cynognathus zone 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 sections in 2020. Subzone A was formalized as the Langbergia-Garjainia Subzone, subzone B as the Trirachodon-Kannemeyeria Subzone, and subzone C as the Cricodon-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 trirachodontids 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.
The Cynognathus Assemblage Zone correlates with the Burgersdorp Formation in the upper Tarkastad Subgroup of the Beaufort Group. The Cynognathus Assemblage Zone contains argillaceous mudstone successions varying from maroon to reddish, blueish-green, and greyish-green in colour. The mudstones are interbedded with lenticular and feldspathic sandstones which appear greenish-grey when fresh and brownish-yellow when eroded out. Clay-rich pebble conglomerates are also observed in some areas. Complete, articulated fossils are frequently found encased in calcareous nodules within the mudstone layers while complete skulls are mainly found in the sandstone. The mudstones were likely deposited in low-energy, meandering fluvial environments alongside sand-rich river channels. The environment during time of deposition was semi-arid, but with seasonal rain and flooding due to the presence of crevasse splays in the mudstone layers. A lack of well developed channel sandstones provides evidence for more lacustrine areas in the more northerly occurring outcrops of the biozone.
The thickest outcrops of the Cynognathus Assemblage Zone, reaching approximately 600 metres (2,000 ft), occur between Queenstown and Lady Frere in the Eastern Cape. Outcrops then thin out to between 200 and 100 metres (660 and 330 ft) around Aliwal North, Burgersdorp, Steynsburg, and Rouxville. Thin outcrops are also found in areas in the Free State that border Lesotho.
Hub AI
Cynognathus Assemblage Zone AI simulator
(@Cynognathus Assemblage Zone_simulator)
Cynognathus Assemblage Zone
The Cynognathus Assemblage Zone is a tetrapod biozone utilized in the Karoo Basin of South Africa. It is equivalent to the Burgersdorp Formation, the youngest lithostratigraphic formation in the Beaufort Group, which is part of the fossiliferous and geologically important Karoo Supergroup. The Cynognathus Assemblage Zone is the youngest of the eight biozones found in the Beaufort Group, and is considered to be late Early Triassic (Olenekian) to early Middle Triassic (Anisian) in age (around 247 Ma). The name of the biozone refers to Cynognathus crateronotus, a large and carnivorous cynodont therapsid which occurs throughout the entire biozone.
The first fossils to be found in the Beaufort Group rocks that encompass the current eight biozones 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 fossil taxa. The initial undertaking was done by Harry Govier Seeley who subdivided the Beaufort Group into three biozones, which he named (from oldest to youngest):
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 between 1906 and 1909. Broom proposed the following biozones (from oldest to youngest):
These biozone divisions were approved by paleontologists of the time and were left largely unchanged for several decades. James Kitching retained the name of the Cynognathus zone 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 sections in 2020. Subzone A was formalized as the Langbergia-Garjainia Subzone, subzone B as the Trirachodon-Kannemeyeria Subzone, and subzone C as the Cricodon-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 trirachodontids 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.
The Cynognathus Assemblage Zone correlates with the Burgersdorp Formation in the upper Tarkastad Subgroup of the Beaufort Group. The Cynognathus Assemblage Zone contains argillaceous mudstone successions varying from maroon to reddish, blueish-green, and greyish-green in colour. The mudstones are interbedded with lenticular and feldspathic sandstones which appear greenish-grey when fresh and brownish-yellow when eroded out. Clay-rich pebble conglomerates are also observed in some areas. Complete, articulated fossils are frequently found encased in calcareous nodules within the mudstone layers while complete skulls are mainly found in the sandstone. The mudstones were likely deposited in low-energy, meandering fluvial environments alongside sand-rich river channels. The environment during time of deposition was semi-arid, but with seasonal rain and flooding due to the presence of crevasse splays in the mudstone layers. A lack of well developed channel sandstones provides evidence for more lacustrine areas in the more northerly occurring outcrops of the biozone.
The thickest outcrops of the Cynognathus Assemblage Zone, reaching approximately 600 metres (2,000 ft), occur between Queenstown and Lady Frere in the Eastern Cape. Outcrops then thin out to between 200 and 100 metres (660 and 330 ft) around Aliwal North, Burgersdorp, Steynsburg, and Rouxville. Thin outcrops are also found in areas in the Free State that border Lesotho.