Cynognathus Assemblage Zone

The Cynognathus Assemblage Zone is a tetrapod assemblage zone or biozone which correlates to the Burgersdorp Formation of the Beaufort Group, a fossiliferous and geologically important geological Group of the Karoo Supergroup in the Karoo Basin of South Africa. The thickest outcrops of this biozone, 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.[1][2][3] The Cynognathus Assemblage Zone is the eighth and youngest of the eight biozones found in the Beaufort Group, and is considered to be early Middle Triassic (around 247 Ma).

Cynognathus Assemblage Zone
Stratigraphic range: Early-Mid Triassic
~249–244 Ma
↓
Cynognathus crateronotus
TypeBiozone
Unit ofBurgersdorp Formation (Beaufort Group)
UnderliesMolteno Formation (Stormberg Group)
OverliesLystrosaurus Assemblage Zone
Thicknessup to 1,968.5 feet (600 m)
Location
RegionEastern Cape, Free State
Country South Africa
ExtentKaroo Basin
Type section
Named forCynognathus
Named byHarry Govier Seeley (1892)
Robert Broom (1906, 1909)

The name of the biozone refers to Cynognathus crateronotus, a large and carnivorous cynodont therapsid. The biozone is characterized by the first appearance of Cynognathus, Diademondon tetragonus, and Trirachodon.[4]

History

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.[5] 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,[6] which he named (from oldest to youngest):

These proposed biozones Seeley named were subdivided further by Robert Broom between 1906 and 1909.[7] 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.[8] The Cynognathus Assemblage Zone was first named by Harry Govier Seeley in 1892 when he made the first attempt to organise the geological sequences of the Karoo Basin[9]. In 1906, Robert Broom reorganised the Karoo geological sequences into six biozones.[10] James Kitching kept the name of the Cynognathus zone in his revision of the biozones in the 1970s and 1980s.[11][12][13]

From the late 1970s onwards, arguments were made to change the name of the biozone either to the Kannemeyeria Assemblage Zone or Kannemeyeria-Diademodon Assemblage Zone.[14][15]

However, more recent analyses 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.[16][17][18] This meant that these species were not good 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.[19] In 2013, it was subdivided into three separate Subzones - Subzones A, B, and C - with Subzone B being the largest of the three. The biozone encompasses the boundary between the late Early Triassic from the bottom of Subzone A and early Middle Triassic through to the uppermost Subzone C.The Cynognathus Assemblage Zone contains argillaceous mudstone successions varying from maroon to reddish, blueish-green, and greyish-green in colour.[20] The mudstones are interbedded with lenticular and feldspathic sandstones which appear greenish-grey when fresh and brownish-yellow when eroded out.[21][22]

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.[23]

Paleontology

The Cynognathus Assemblage Zone holds a rich diversity of fossil species, of which it is most renowned for its cynodont fossils.[24][25] Cynognathids, diademodontids, and trirachodontids are found throughout. In Subzone B the diademodontid Diademodon dominated over trirachodontids, however, by the Subzone C contact trirachodontids had become the dominant taxa. Cynognathus is the common denominator with its fossils being found throughout Subzones A – C, confirming its place as the index taxon of the biozone.

The biozone is likewise rich in other fossil fauna which include procolophonid parareptiles, the crocopod archosauromorph Rhynchosaur Howesia browni,[26] and archosauriformes Erythrosuchus africanus[27] and Euparkeria capensis..[28] In addition, the dicynodont species Kannemeyeria[29] is found from Subzones B – C, anomodonts, and several theracephalian species are found throughout. Plant fossils such as Dicroidium, Dadoxylon, and Schizoneura are likewise found. Finally, numerous temnospondyl amphibian species, fishes, rare occurrences of molluscs, and ichnofossils of arthropod trackways and vertebrate burrows have been discovered.[30]

Many of the cynodont species that are found in the Cynognathus Assemblage Zone have been found in formations in different countries which correlate in age.[31] Most notably Diademodon fossils have been found in the Middle Triassic-aged Río Seco de la Quebrada Formation in Mendoza Province, Argentina.[32] Likewise kannemeyerid and trirachodontid species found in the Cynognathus Assemblage Zone have also been found in Triassic-aged Omingonde Formation of Namibia and in the Manda Formation of Tanzania.[33][34][35] It is currently accepted that Subzone C of the Cynognathus Assemblage Zone correlates in age to the Manda Formation as well as to the upper Denwa Formation in India.[36]

Age and correlations

The Cynognathus Assemblage Zone dates to approximately 249 to 244 Ma, and correlates with the Petropavlovskaya, Gostevskaya and Kzylsaiakaya Formations of Russia,[37] and with the Ermaying and Heshanggou Formations of China, the Knocklofty Formation of Australia (lower Cynognathus Assemblage Zone), and the Yerrapalli Formation (upper Cynognathus Assemblage Zone) of India.[38]

See also

References
  1. Rubidge, B. S. (ed.) 1995b. Biostratigraphy of the Beaufort Group (Karoo Supergroup). South African Committee of Stratigraphy. Biostratigraphic Series 1. Pretoria, Council for Geoscience.
  2. Merrill, van der Walt; Michael, Day; Bruce, Rubidge; K., Cooper, Antony; Inge, Netterberg (December 2010). "A new GIS-based biozone map of the Beaufort Group (Karoo Supergroup), South Africa". Palaeontologia Africana : Annals of the Bernard Price Institute for Palaeontological Research. ISSN 0078-8554.
  3. Kitching, J.W.; Welman, J.; Groenewald, G.H. (1991-01-01). "Confirmation of the occurrence of Cynognathus Zone (Kannemeyeria-Diademodon Assemblage-zone) deposits (uppermost Beaufort Group) in the northeastern Orange Free State, South Africa". South African Journal of Geology. 94 (2–3). ISSN 1012-0750.
  4. Abdala, Fernando; Hancox, P. John; Neveling, Johann (2005-03-11). "Cynodonts from the Uppermost Burgersdorp Formation, South Africa, and their bearing on the biostratigraphy and correlation of the TriassicCynognathusAssemblage Zone". Journal of Vertebrate Paleontology. 25 (1): 192–199. doi:10.1671/0272-4634(2005)025[0192:cftubf]2.0.co;2. ISSN 0272-4634.
  5. Bain, Andrew Geddes (1845-02-01). "On the Discovery of the Fossil Remains of Bidental and other Reptiles in South Africa". Quarterly Journal of the Geological Society. 1 (1): 317–318. doi:10.1144/GSL.JGS.1845.001.01.72. hdl:2027/uc1.c034667778. ISSN 0370-291X. S2CID 128602890.
  6. Seeley, H. G. (1895). "Researches on the Structure, Organization, and Classification of the Fossil Reptilia. Part IX., Section 4. On the Gomphodontia". Philosophical Transactions of the Royal Society of London B. 186: 1–57. Bibcode:1895RSPTB.186....1S. doi:10.1098/rstb.1895.0001. JSTOR 91793.
  7. Broom, R. (January 1906). "V.—On the Permian and Triassic Faunas of South Africa". Geological Magazine. 3 (1): 29–30. Bibcode:1906GeoM....3...29B. doi:10.1017/S001675680012271X. ISSN 1469-5081.
  8. Watson, D. M. S. (May 1914). "II.—The Zones of the Beaufort Beds of the Karroo System in South Africa". Geological Magazine. 1 (5): 203–208. Bibcode:1914GeoM....1..203W. doi:10.1017/S001675680019675X. ISSN 1469-5081.
  9. Seeley, H. G. (1894). "Researches on the Structure, Organisation, and Classification of the Fossil Reptilia. Part IX., Section 1. On the Therosuchia". Philosophical Transactions of the Royal Society of London, Series B. 185: 987–1018. doi:10.1098/rstb.1894.0021. JSTOR 91788.
  10. Broom, R. (January 1906). "V.—On the Permian and Triassic Faunas of South Africa". Geological Magazine. 3 (1): 29–30. Bibcode:1906GeoM....3...29B. doi:10.1017/S001675680012271X. ISSN 1469-5081.
  11. Kitching, J. W. (1970). A short review of the Beaufort zoning in South Africa. In Second Gondwana Symposium Proceedings and Papers (Vol. 1, pp. 309-312).
  12. "Inside front cover". South African Journal of Science. 75 (2). 1979-02-01. ISSN 0038-2353.
  13. Kitching, J. W. (1984). A reassessment of the biozonation of the Beaufort Group. Paleo News, 4(1), 12-13.
  14. Keyser, A. W., & Smith, R. M. H. (1978). Vertebrate biozonation of the Beaufort Group with special reference to the western Karoo Basin. Geological Survey, Department of Mineral And Energy Affairs, Republic of South Africa.
  15. Keyser, A. W. (1979). A review of the biostratigraphy of the Beaufort Group in the Karoo Basin of South Africa. Geocongress, Geological Society of South Africa, 2, 13-31.
  16. Abdala, Fernando; Hancox, P. John; Neveling, Johann (2005-03-11). "Cynodonts from the Uppermost Burgersdorp Formation, South Africa, and their bearing on the biostratigraphy and correlation of the TriassicCynognathusAssemblage Zone". Journal of Vertebrate Paleontology. 25 (1): 192–199. doi:10.1671/0272-4634(2005)025[0192:cftubf]2.0.co;2. ISSN 0272-4634.
  17. Merrill, van der Walt; Michael, Day; Bruce, Rubidge; K., Cooper, Antony; Inge, Netterberg (December 2010). "A new GIS-based biozone map of the Beaufort Group (Karoo Supergroup), South Africa". Palaeontologia Africana : Annals of the Bernard Price Institute for Palaeontological Research. ISSN 0078-8554.
  18. Rubidge, Bruce S.; Day, Michael O.; Barbolini, Natasha; Hancox, P. John; Choiniere, Jonah N.; Bamford, Marion K.; Viglietti, Pia A.; McPhee, Blair W.; Jirah, Sifelani (2016), "Advances in Nonmarine Karoo Biostratigraphy: Significance for Understanding Basin Development", Origin and Evolution of the Cape Mountains and Karoo Basin, Springer International Publishing, pp. 141–149, doi:10.1007/978-3-319-40859-0_14, ISBN 9783319408583
  19. Abdala, Fernando; Hancox, P. John; Neveling, Johann (2005-03-11). "Cynodonts from the Uppermost Burgersdorp Formation, South Africa, and their bearing on the biostratigraphy and correlation of the TriassicCynognathusAssemblage Zone". Journal of Vertebrate Paleontology. 25 (1): 192–199. doi:10.1671/0272-4634(2005)025[0192:cftubf]2.0.co;2. ISSN 0272-4634.
  20. Hancox, P. John; Angielczyk, Kenneth D.; Rubidge, Bruce S. (May 2013). "AngonisaurusandShansiodon, dicynodonts (Therapsida, Anomodontia) from subzone C of theCynognathusAssemblage Zone (Middle Triassic) of South Africa". Journal of Vertebrate Paleontology. 33 (3): 655–676. doi:10.1080/02724634.2013.723551. ISSN 0272-4634. S2CID 128538910.
  21. Rubidge, B. S. (ed.) 1995b. Biostratigraphy of the Beaufort Group (Karoo Supergroup). South African Committee of Stratigraphy. Biostratigraphic Series 1. Pretoria, Council for Geoscience.
  22. J, Neveling (2016-09-22). "Biostratigraphic and sedimentological investigation of the contact between the Lystrosaurus and Cynognathus assemblage zones (Beaufort group : Karoo supergroup)". Cite journal requires |journal= (help)
  23. Rubidge, Bruce S.; Day, Michael O.; Barbolini, Natasha; Hancox, P. John; Choiniere, Jonah N.; Bamford, Marion K.; Viglietti, Pia A.; McPhee, Blair W.; Jirah, Sifelani (2016), "Advances in Nonmarine Karoo Biostratigraphy: Significance for Understanding Basin Development", Origin and Evolution of the Cape Mountains and Karoo Basin, Springer International Publishing, pp. 141–149, doi:10.1007/978-3-319-40859-0_14, ISBN 9783319408583
  24. Botha, Jennifer; Chinsamy, Anusuya (2001-01-19). "Growth patterns deduced from the bone histology of the cynodonts Diademodon and Cynognathus". Journal of Vertebrate Paleontology. 20 (4): 705–711. doi:10.1671/0272-4634(2000)020[0705:gpdftb]2.0.co;2. ISSN 0272-4634.
  25. Abdala, Fernando; Hancox, P. John; Neveling, Johann (2005-03-11). "Cynodonts from the Uppermost Burgersdorp Formation, South Africa, and their bearing on the biostratigraphy and correlation of the Triassic Cynognathus Assemblage Zone". Journal of Vertebrate Paleontology. 25 (1): 192–199. doi:10.1671/0272-4634(2005)025[0192:cftubf]2.0.co;2. ISSN 0272-4634.
  26. Dilkes, D. W. (1995). The rhynchosaur Howesia browni from the Lower Triassic of South Africa. Palaeontology, 38(3), 665-686.
  27. Botha-Brink, Jennifer; Smith, Roger M. H. (November 2011). "Osteohistology of the Triassic archosauromorphs such as Prolacerta, Proterosuchus, Euparkeria, and Erythrosuchus from the Karoo Basin of South Africa". Journal of Vertebrate Paleontology. 31 (6): 1238–1254. doi:10.1080/02724634.2011.621797. ISSN 0272-4634. S2CID 130744235.
  28. Sobral, Gabriela; Sookias, Roland B.; Bhullar, Bhart-Anjan S.; Smith, Roger; Butler, Richard J.; Müller, Johannes (2016-07-01). "New information on the braincase and inner ear of Euparkeria capensis Broom: implications for diapsid and archosaur evolution". Royal Society Open Science. 3 (7): 160072. Bibcode:2016RSOS....360072S. doi:10.1098/rsos.160072. ISSN 2054-5703. PMC 4968458. PMID 27493766.
  29. Romala, Govender; John, Hancox, Phillip; M., Yates, Adam (April 2008). "Re-evaluation of the postcranial skeleton of the Triassic dicynodont Kannemeyria simocephalus from the Cynognathus Assemblage Zone (Subzone B) of South Africa". Palaeontologia Africana : Annals of the Bernard Price Institute for Palaeontological Research. ISSN 0078-8554.
  30. RUBIDGE, B. S. (1995). "Biostratigraphy of the Beaufort Group. South African Commission for Stratigaphy". Biostratigraphic Series. 1: 1–45.
  31. Hancox, P.J; Rubidge, B.S (2001-01-01). "Breakthroughs in the biodiversity, biogeography, biostratigraphy, and basin analysis of the Beaufort group". Journal of African Earth Sciences. 33 (3–4): 563–577. Bibcode:2001JAfES..33..563H. doi:10.1016/S0899-5362(01)00081-1. ISSN 1464-343X.
  32. Martinelli, Agustín G.; Fuente, Marcelo De La; Abdala, Fernando (2009-09-12). "Diademodon tetragonusSeeley, 1894 (Therapsida: Cynodontia) in the Triassic of South America and its biostratigraphic implications". Journal of Vertebrate Paleontology. 29 (3): 852–862. doi:10.1671/039.029.0315. ISSN 0272-4634. S2CID 83776819.
  33. Abdala, Fernando; Marsicano, Claudia A.; Smith, Roger M.H.; Swart, Roger (2013-04-01). "Strengthening Western Gondwanan correlations: A Brazilian Dicynodont (Synapsida, Anomodontia) in the Middle Triassic of Namibia". Gondwana Research. 23 (3): 1151–1162. Bibcode:2013GondR..23.1151A. doi:10.1016/j.gr.2012.07.011. ISSN 1342-937X.
  34. CRUICKSHANK, A. R. I. (June 1965). "On a specimen of the Anomodont reptile Kannemeyeria latifrons (Broom) from the Manda Formation of Tanganyika, Tanzania". Proceedings of the Linnean Society of London. 176 (2): 149–157. doi:10.1111/j.1095-8312.1965.tb00941.x. ISSN 0370-0461.
  35. Abdala, Fernando; Smith, Roger M. H. (2009-09-12). "A Middle Triassic cynodont fauna from Namibia and its implications for the biogeography of Gondwana". Journal of Vertebrate Paleontology. 29 (3): 837–851. doi:10.1671/039.029.0303. ISSN 0272-4634. S2CID 129096876.
  36. Sengupta, Saradee; Ezcurra, Martín D.; Bandyopadhyay, Saswati (2017-08-21). "A new horned and long-necked herbivorous stem-archosaur from the Middle Triassic of India". Scientific Reports. 7 (1): 8366. Bibcode:2017NatSR...7.8366S. doi:10.1038/s41598-017-08658-8. ISSN 2045-2322. PMC 5567049. PMID 28827583.
  37. "Magnetostratigraphy - Background to stratigraphy across the PTB in Russia". Archived from the original on 2019-02-16. Retrieved 2019-03-15.
  38. Ezcurra, 2016, p.8

Bibliography
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.