Eodicynodon Assemblage Zone

Eodicynodon Assemblage Zone
Stratigraphic range: Middle Permian
Eodicynodon oosthuizeni
Type	Biozone
Unit of	Abrahamskraal Formation of the Beaufort Group
Underlies	Tapinocephalus Assemblage Zone
Overlies	Ecca Group
Thickness	up to 2,034.12 feet (620 m)
Location
Region	Northern & Western Cape
Country	South Africa
Extent	Karoo Basin
Type section
Named for	Eodicynodon
Named by	Harry Govier Seeley (1892) Robert Broom (1906, 1909)

The Eodicynodon Assemblage Zone is a tetrapod assemblage zone or biozone which correlates to the Abrahamskraal Formation, Adelaide Subgroup of the Beaufort Group, a fossiliferous and geologically important geological Group of the Karoo Supergroup in South Africa.^[1] The thickest outcrops, reaching approximately 620 metres (2,030 ft), occur south-east of Sutherland, north of Prince Albert, and south-east of Beaufort West. The Eodicynodon Assemblage Zone is the lowermost biozone of the Beaufort Group.^[2][3][4]

The name of the biozone refers to Eodicynodon oosthuizeni, a small to medium-sized herbivorous dicynodont therapsid. It is characterized by the presence of this dicynodont genus along with the Nyaphulia, and the dinocephalian Tapinocaninus pamelae.^[5][6]

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.^[7] 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,^[8] which he named (from oldest to youngest):

• Zone of "Pareiasaurians"
• Zone of "Dicynodonts"
• Zone of "highly specialized group of theriodonts"

These proposed biozones Seeley named were subdivided further by Robert Broom between 1906 and 1909.^[9] Broom proposed the following biozones (from oldest to youngest):

• Pareiasaurus beds
• Endothiodon beds
• Kistecephalus beds
• Lystrosaurus beds
• Procolophon beds
• Cynognathus beds

These biozone divisions were approved by paleontologists of the time and were left largely unchanged for several decades.^[10] The rocks composing the current Eodicynodon Assemblage Zone were previously included in the upper Waterford Formation of the underlying Ecca Group.^[11] This was due to prior observations of the biozone rock colours not being consistent with the known reddish to purple colours that are diagnostic of the Beaufort Group. After further stratigraphic reorganization of the Beaufort Group was conducted from the 1970s,^{[12][13][14][15][16][17]} it was discovered that the Eodicynodon Assemblage Zone correlated with the lower Abrahamskraal Formation, the lowermost geological formation of the Beaufort Group, and that the fossils of Eodicynodon sp. were only known from these specific rocks.^[18] The Eodicynodon Assemblage Zone is currently accepted as the oldest biozone of the Beaufort Group.^{[19][20][21][22][23]}

Lithology

The Eodicynodon Assemblage Zone correlates with the lower Abrahamskraal Formation, Adelaide Subgroup of the Beaufort Group.Outcrops of this biozone are only known from the south-western margins of the Abrahamskraal Formation and is considered to be Middle Permian (Guadalupian) in age.

The rocks of the Eodicynodon Assemblage Zone comprise mudstones, siltstones, and fine-grained, siliceous sandstone. The mudstones are olive green to moderate yellowish brown in colour and contain thinner light reddish-brown layers. The reddish-brown layers frequently contain calcareous nodules. Desiccation cracks - indicative of seasonal dry periods - and raindrop impressions are sometimes found in the mudstone layers. Argillaceous layers are also common. The siltstones are extremely fine-grained, often containing ripple marks from being deposited in low energy streams, and vary from being dark grey, greenish-grey, and blueish-grey in colour. Thin sheets of chert occur in the mudstone and less commonly in the siltstone layers. The sandstones are fine-grained and vary from being greyish olive green to dark yellowish brown. Some sandstone layers either contain or are capped by pebble-sized mudstone-clast conglomerates. These conglomerates also contain isolated fossils in some localities. The sandstones are more common and at their thickest towards the upper sections of the biozone. The rocks of this biozone were likely deposited in a subaerial deltaic environment which included floodplains. The presence of calcareous nodules also indicates that the environment was warm with seasonal dry periods.^[24][25][26]

The depositional environment of the Eodicynodon Assemblage Zone was formed by sedimentary material being deposited in the Karoo Basin - a retro-arc foreland basin - by vast, low-energy alluvial plains flowing northwards from a southerly source area in the rising the Gondwanide mountains. The Gondwanides were the result of crustal uplift that had previously begun to take course due to subduction of the Palaeo-pacific plate beneath the Gondwanan Plate. Orogenic pulses from the growing Gondwanides mountain chain and associated subduction created accommodation space for sedimentation in the Karoo Basin where the deposits of the Eodicynodon Assemblage zone, and all other succeeding assemblage zones, were deposited over millions of years.^[27][28][29]

Paleontology

The Eodicynodon Assemblage Zone is characterized by the presence of the dicynodont species Eodicynodon and the dinocephalian Tapinocaninus pamelae.^[30][31][32] The biozone is not especially fossiliferous with the fossils of dicynodonts Eodicynodon sp. and the dinocephalians Tapinocaninus and Australosyodon nyaphuli being most commonly found. The preservation of these fossil taxa are good with the majority of fossils being found in the mudstone layers. This is especially true of the reddish-brown mudstones containing calcareous nodules. Interestingly, dinocephalian fossils have been more commonly found in the sandstones, and fossil fragments have been found in the mudstone-clast conglomerates.^[33] However, tantalizing remains of more numerous fossil species have been found to date, hinting at the true level of fossil diversity that could be discovered in the future. The fragmented material includes the scales of the fish Namaichthys digitata^[34], species of temnospondyl amphibians,^[35] and skull material of gorgonopsids.^[36] Rarer fossils encountered in this biozone include skull material of therocephalians,^[37] various anomodonts such as Patranomodon nyaphulii,^[38][39][40] trace fossils of planolites and arthropod trackways, molluscs, and the plant remains of Glossopteris symmetrifolia, Equisetum modderdriftensis, and Schizoneura africana.^[41]

The following faunal list follows Rubidge and Day 2020^[42] unless noted otherwise.

Synapsids

• Australosyodon nyaphuli
• Eodicynodon oosthuizeni
• Eutheriodon vandenheeveri (includes Glanosuchus macrops and Ictidosuchus angusticeps of Rubidge & Day, 2020)
• Nyaphulia oelofseni (formerly "Eodicynodon" oosthuizeni)
• Patranomodon nyaphuli
• Tapinocaninus pamelae
• Gorgonopsia indet.

Temnospondyls

• Temnospondyl indet.

Fish

• Namaichthys digitata

Mollusks

• cf. Palaeanodonta

Plants

• Glossopteris sp.
• Schizoneura sp.

Ichnofossils

• Planolites
• Umfolozia

See also

• List of synapsids

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. S, Rubidge, Bruce (1990). "A new vertebrate biozone at the base of the Beaufort Group, Karoo sequence (South Africa)". Palaeontologia Africana. ISSN 0078-8554.
3. Cole, D.I.; Johnson, M.R.; Day, M.O. (June 2016). "Lithostratigraphy of the Abrahamskraal Formation (Karoo Supergroup), South Africa". South African Journal of Geology. 119 (2): 415–424. doi:10.2113/gssajg.119.2.415. ISSN 1012-0750.
4. Jirah, Sifelani; Rubidge, Bruce S. (2014-12-01). "Refined stratigraphy of the Middle Permian Abrahamskraal Formation (Beaufort Group) in the southern Karoo Basin". Journal of African Earth Sciences. 100: 121–135. doi:10.1016/j.jafrearsci.2014.06.014. ISSN 1464-343X.
5. Rubidge, B.S.; King, G.M.; Hancox, P.J. (1994). "The posteranial skeleton of the earliest dicynodont synapsid Eodicynodon from the Upper Permian of South Africa". Palaeontology. 37 (2): 397–408.
6. Rubidge, B.S.; Modesto, S.; Sidor, C.; Welman, J. (1999). "Eunotosaurus africanus from the Ecca-Beaufort contact in Northern Cape Province, South Africa-implications for Karoo basin development". South African Journal of Science. 95 (11/12): 553–554.
7. 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.
8. 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.
9. 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.
10. 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. doi:10.1017/S001675680019675X. ISSN 1469-5081. S2CID 130747924.
11. S, Rubidge, Bruce (1990). "A new vertebrate biozone at the base of the Beaufort Group, Karoo sequence (South Africa)". Palaeontologia Africana. ISSN 0078-8554.
12. 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)
13. "Inside front cover". South African Journal of Science. 75 (2). 1979-02-01. ISSN 0038-2353.
14. Keyser, A.W. and 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. Kitching, J.W. (1984). "A reassessment of the biozonation of the Beaufort Group". Paleo News. 4 (1): 12–13.
17. 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.
18. S, Rubidge, Bruce (1990). "A new vertebrate biozone at the base of the Beaufort Group, Karoo sequence (South Africa)". Palaeontologia Africana. ISSN 0078-8554.
19. Rubidge, B. S. (ed.) 1995b. Biostratigraphy of the Beaufort Group (Karoo Supergroup). South African Committee of Stratigraphy. Biostratigraphic Series 1. Pretoria, Council for Geoscience.
20. van der Walt, M., Day, M., Rubidge, B., Cooper, A.K. and Netterberg, I., 2010. A new GIS-based biozone map of the Beaufort Group (Karoo Supergroup), South Africa.
21. 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.
22. 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". {{cite journal}}: Cite journal requires |journal= (help)
23. Cole, D.I.; Johnson, M.R.; Day, M.O. (June 2016). "Lithostratigraphy of the Abrahamskraal Formation (Karoo Supergroup), South Africa". South African Journal of Geology. 119 (2): 415–424. doi:10.2113/gssajg.119.2.415. ISSN 1012-0750.
24. Rubidge, B. S. (ed.) 1995b. Biostratigraphy of the Beaufort Group (Karoo Supergroup). South African Committee of Stratigraphy. Biostratigraphic Series 1. Pretoria, Council for Geoscience.
25. S, Rubidge, Bruce (1990). "A new vertebrate biozone at the base of the Beaufort Group, Karoo sequence (South Africa)". Palaeontologia Africana. ISSN 0078-8554.
26. Cole, D.I.; Johnson, M.R.; Day, M.O. (June 2016). "Lithostratigraphy of the Abrahamskraal Formation (Karoo Supergroup), South Africa". South African Journal of Geology. 119 (2): 415–424. doi:10.2113/gssajg.119.2.415. ISSN 1012-0750.
27. Catuneanu, O.; Hancox, P.J.; Rubidge, B.S. (1998-12-01). "Reciprocal flexural behaviour and contrasting stratigraphies: a new basin development model for the Karoo retroarc foreland system, South Africa". Basin Research. 10 (4): 417–439. doi:10.1046/j.1365-2117.1998.00078.x. ISSN 1365-2117. S2CID 56420970.
28. Catuneanu, O.; Wopfner, H.; Eriksson, P.G.; Cairncross, B.; Rubidge, B.S.; Smith, R.M.H.; Hancox, P.J. (2005-10-01). "The Karoo basins of south-central Africa". Journal of African Earth Sciences. 43 (1–3): 211–253. doi:10.1016/j.jafrearsci.2005.07.007. ISSN 1464-343X.
29. 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
30. S, Rubidge, Bruce (1990). "A new vertebrate biozone at the base of the Beaufort Group, Karoo sequence (South Africa)". Palaeontologia Africana. ISSN 0078-8554.
31. J., Hancox, P.; S., Rubidge, B. (1997). "The role of fossils in interpreting the development of the Karoo Basin". Palaeontologia Africana. ISSN 0078-8554. Archived from the original on 2018-05-28. Retrieved 2018-09-17.
32. 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.
33. Cole, D.I.; Johnson, M.R.; Day, M.O. (June 2016). "Lithostratigraphy of the Abrahamskraal Formation (Karoo Supergroup), South Africa". South African Journal of Geology. 119 (2): 415–424. doi:10.2113/gssajg.119.2.415. ISSN 1012-0750.
34. PA, Bender (2016-09-22). "Late Permian actinopterygian (Palaeoniscid) fishes from the Lower Beaufort Group, South Africa". {{cite journal}}: Cite journal requires |journal= (help)
35. 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.
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40. 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.
41. N.F.H. (November 1984). "J. M. Anderson & H. M. Anderson 1983. Palaeoflora of Southern Africa. Molteno Formation (Triassic). Volume 1. Part 1. Introduction; Part 2, Dicroidium. ix + 227 pp. Rotterdam: A. A. Balkema. Price Dfl. 135.00, £31.40. ISBN 90 6191 283 0 (for complete set of six volumes ISBN 90 6191 282 2)". Geological Magazine. 121 (6): 659–660. doi:10.1017/s0016756800030880. ISSN 0016-7568.
42. Rubidge, B.S.; Day, M.O. (2020). "Biostratigraphy of the Eodicynodon Assemblage Zone (Beaufort Group, Karoo Supergroup), South Africa". South African Journal of Geology. 123 (2): 141–148. doi:10.25131/sajg.123.0010. S2CID 242275064.