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Pristerognathus Assemblage Zone

The Pristerognathus Assemblage Zone is a tetrapod assemblage zone or biozone which correlates to the upper Abrahamskraal Formation and lowermost Teekloof Formation, Adelaide Subgroup of the Beaufort Group, a fossiliferous and geologically important geological Group of the Karoo Supergroup in South Africa. The thickest outcrops, reaching not more than 300 metres (980 ft), occur just east of Sutherland through to Beaufort West in the south and Victoria West in the north. Exposures are also found west of Colesberg and south of Graaff-Reinet. The Pristerognathus Assemblage Zone is the third biozone of the Beaufort Group.[1][2][3]

Pristerognathus Assemblage Zone
Stratigraphic range: Middle Permian
Glanosuchus macrops (formerly "Pristerognathus vanderbyli")
TypeBiozone
Unit ofUpper Abrahamskraal Formation and Teekloof Formation of the Beaufort Group
UnderliesTropidostoma Assemblage Zone
OverliesTapinocephalus Assemblage Zone
Thicknessup to 984.252 feet (300 m)
Location
RegionNorthern, Western & Eastern Cape
Country South Africa
ExtentKaroo Basin
Type section
Named forPristerognathus polyodon
Named byKeyser & Smith
Year defined1979

The name of the biozone refers to Pristerognathus polyodon, a medium-sized carnivorous therocephalian therapsid. It is characterized by the presence of this therocephalian species in association with Diictodon feliceps, a small, fossorial dicynodont whose fossils are especially common in this biozone.

History

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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.[4] 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,[5] which he named (from oldest to youngest):

These proposed biozones Seeley named were subdivided further by Robert Broom between 1906 and 1909.[6] Broom proposed the following biozones (from oldest to youngest):

The Pristerognathus Assemblage Zone as it currently stands was defined by Keyser and Smith in the late 1970s. Initially the biozone included the upper 300m of the underlying Tapinocephalus Assemblage Zone due to the disappearance of Dinocephalian fossils in those rock deposits and had been named the Pristerognathus-Diictodon Assemblage Zone. After further research on the rocks of the middle Permian, it was understood that the disappearance of the dinocephalians 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.

Lithology

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The Pristerognathus Assemblage Zone correlates with the upper Abrahamskraal Formation, the lowermost Teekloof Formation west of 24°E and to the Middleton Formation east of 24°E, Adelaide Subgroup of the Beaufort Group. This biozone is considered to be Middle Permian (Guadalupian) in age.[7]

The rocks of the Pristerognathus Assemblage Zone are similar to the underlying Tapinocephalus Assemblage Zone although is dominated by multistory sandstone deposits. The sandstones are interspaced with silt-rich greenish-grey mudstones and subordinate reddish-brown mudstone layers.[8] Calcareous nodules, which weather out brown, are often found in the mudstone layers. Pinkish chert bands are found in the lowermost mudstone deposits of this biozone. The Pristerognathus Assemblage Zone is also known for containing uranium deposits.[1] The presence of the chert band confirms that there was volcanic 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 Permian (end-Guadalupian) extinction event, which is currently thought to have been caused by the eruption of the Emeishan Large Igneous Province.[9][8]

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 plains. These fluvial plains flowed northwards from a foreland basin 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 where the deposits of the Pristerognathus Assemblage zone, and all other succeeding assemblage zone deposits, were deposited over tens of millions of years.[10][2]

Paleontology

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Vertebrate fossils are most commonly found in the mudstone deposits of the Pristerognathus Assemblage Zone, especially within the calcareous nodules.[11] This biozone is characterized by the presence of Pristerognathus polyodon and its other subspecies Pristerognathus baini and Pristerognathus vanderbyli. Pristerognathus fossils are usually found associated with those of Diictodon. The fossils of both these taxa are the most commonly found; other fossil taxa are markedly more rare. Species diversity dropped off after the end-Guadalupian extinction, which is the reason that this biozone is lacking in species richness. Other taxa that have been found in this biozone include a couple pareiasaur species, namely Bradysaurus, the putative pantestudine Eunotosaurus africanus,[12][13] and the varanopid pelycosaur Heleosaurus scholtzi.[14][15][16] Fossils of the biarmosuchian Hipposaurus boonstrai [17] are likewise found including some gorgonopsid species.[18] Other dicynodont species found include Endothiodon uniseries and Pristerodon mackayi. Finally, fossils of temnospondyl amphibians such as of Rhinesuchus whaitsi,[19] the fishes Namaichthys and Atherstonia, invertebrate trackways, burrows, and feeding trails such as of Planolites and a variety of plant fossils, namely of Glossopteris, Phyllotheca, and Schizoneura, have been recovered.[1][20] Some fossil taxa that have been found from this biozone, namely Hipposaurus, 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.[17][21]

See also

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References

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  1. ^ a b c 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. ^ a b 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, Regional Geology Reviews, Springer International Publishing, pp. 141–149, doi:10.1007/978-3-319-40859-0_14, ISBN 9783319408583
  3. ^ van der Walt, Merrill; Day, Michael; Rubidge, Bruce; Cooper, Antony; Netterberg, Inge (2010-12-31). "A new GIS-based biozone map of the Beaufort Group (Karoo Supergroup), South Africa". Palaeontologia Africana. 45: 1–6.
  4. ^ 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.
  5. ^ 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. doi:10.1098/rstb.1895.0001. JSTOR 91793.
  6. ^ Broom, R. (January 1906). "V.—On the Permian and Triassic Faunas of South Africa". Geological Magazine. 3 (1): 29–30. doi:10.1017/S001675680012271X. ISSN 1469-5081. S2CID 129265956.
  7. ^ Day, Michael Oliver; Rubidge, Bruce Sidney (2014-12-01). "A brief lithostratigraphic review of the Abrahamskraal and Koonap formations of the Beaufort Group, South Africa: Towards a basin-wide stratigraphic scheme for the Middle Permian Karoo". Journal of African Earth Sciences. 100: 227–242. doi:10.1016/j.jafrearsci.2014.07.001. ISSN 1464-343X.
  8. ^ a b Oliver, Day, Michael (2014-03-04). Middle Permian continental biodiversity changes as reflected in the Beaufort Group of South Africa: a bio-and lithostratigraphic review of the Eodicynodon, Tapinocephalus and Pristerognathus assemblage zones (Ph.D thesis). Johannesburg: University of Witwatersrand.{{cite thesis}}: CS1 maint: multiple names: authors list (link)
  9. ^ Day, Michael O.; Ramezani, Jahandar; Bowring, Samuel A.; Sadler, Peter M.; Erwin, Douglas H.; Abdala, Fernando; Rubidge, Bruce S. (2015-07-22). "When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa". Proc. R. Soc. B. 282 (1811): 20150834. doi:10.1098/rspb.2015.0834. ISSN 0962-8452. PMC 4528552. PMID 26156768.
  10. ^ 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. doi:10.1016/S0899-5362(01)00081-1. ISSN 1464-343X.
  11. ^ Lucas, Spencer G.; Zeigler, Kate E. (2005). The Nonmarine Permian: Bulletin 30. New Mexico Museum of Natural History and Science.
  12. ^ Day, Mike; Rubidge, Bruce; Almond, John; Jirah, Sifelani (January 2013). "Biostratigraphic correlation in the Karoo: The case of the Middle Permian parareptile Eunotosaurus". South African Journal of Science. 109 (3–4): 4. doi:10.1590/sajs.2013/20120030. ISSN 0038-2353.
  13. ^ Lyson, Tyler R.; Bever, Gabe S.; Scheyer, Torsten M.; Hsiang, Allison Y.; Gauthier, Jacques A. (2013-06-17). "Evolutionary Origin of the Turtle Shell". Current Biology. 23 (12): 1113–1119. doi:10.1016/j.cub.2013.05.003. ISSN 0960-9822. PMID 23727095.
  14. ^ Botha-Brink, Jennifer; Modesto, Sean P. (2007-11-22). "A mixed-age classed 'pelycosaur' aggregation from South Africa: earliest evidence of parental care in amniotes?". Proceedings of the Royal Society of London B: Biological Sciences. 274 (1627): 2829–2834. doi:10.1098/rspb.2007.0803. ISSN 0962-8452. PMC 2288685. PMID 17848370.
  15. ^ Botha-Brink, Jennifer; Modesto, Sean P. (2009-06-12). "Anatomy and relationships of the Middle Permian varanopidHeleosaurus scholtzibased on a social aggregation from the Karoo Basin of South Africa". Journal of Vertebrate Paleontology. 29 (2): 389–400. doi:10.1671/039.029.0209. ISSN 0272-4634. S2CID 84703110.
  16. ^ Modesto, Sean P.; Smith, Roger M. H.; Campione, Nicolás E.; Reisz, Robert R. (2011-10-19). "The last "pelycosaur": a varanopid synapsid from the Pristerognathus Assemblage Zone, Middle Permian of South Africa". Naturwissenschaften. 98 (12): 1027–1034. doi:10.1007/s00114-011-0856-2. ISSN 0028-1042. PMID 22009069. S2CID 27865550.
  17. ^ a b Sidor, Christian (2015-04-09). "The first biarmosuchian from the upper Madumabisa Mudstone Formation (Luangwa Basin) of Zambia". Palaeontologia Africana. 49: 1–7.
  18. ^ Kammerer, Christian F.; Smith, Roger M. H.; Day, Michael O.; Rubidge, Bruce S. (2015-02-16). "New information on the morphology and stratigraphic range of the mid-Permian gorgonopsianEriphostoma microdonBroom, 1911". Papers in Palaeontology. 1 (2): 201–221. doi:10.1002/spp2.1012. ISSN 2056-2802. S2CID 128762256.
  19. ^ Damiani, Ross J. (2004-01-01). "Temnospondyls from the Beaufort Group (Karoo Basin) of South Africa and Their Biostratigraphy". Gondwana Research. 7 (1): 165–173. doi:10.1016/S1342-937X(05)70315-4. ISSN 1342-937X.
  20. ^ Cisneros, Juan Carlos; Abdala, Fernando; Jashashvili, Tea; Bueno, Ana de Oliveira; Dentzien-Dias, Paula (2015-07-01). "Tiarajudens eccentricus and Anomocephalus africanus, two bizarre anomodonts (Synapsida, Therapsida) with dental occlusion from the Permian of Gondwana". Royal Society Open Science. 2 (7): 150090. doi:10.1098/rsos.150090. ISSN 2054-5703. PMC 4632579. PMID 26587266.
  21. ^ Kemp, Thomas Stainforth; Kemp, T. S. (2005). The Origin and Evolution of Mammals. OUP Oxford. ISBN 9780198507611.
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