Stratigraphic ranges of Tapinocephalus Rossouw & De Villiers (1953)) and dinocephalians are completely absent in the uppermost unit. Keyser & Smith Assemblage Zone dicynodonts: (1977/78) refined this by providing stratigraphic ranges of implications for middle Permian certain taxa. They also subdivided the Tapinocephalus Zone of Boonstra into a lower Dinocephalian Assemblage continental biostratigraphy Zone, and an upper Pristerognathus Assemblage Zone and mapped out these units in the area West of longitude Bruce Rubidge1 & Ken Angielczyk2 26 degrees east. Loock et al. (1994), after extensive 1Bernard Price Institute for Palaeontological Research, University of the biostratigraphic and lithostratigraphic research in the Witwatersrand, Private Bag 3, WITS, 2050 South Africa Moordenaars Karoo, were able to corroborate the three E-mail: [email protected] units of Boonstra and correlated these with lithostrati- 2Department of Geology, The Field Museum, 1400 South Lake Shore Drive, Chicago, IL 60605, U.S.A. graphic units. Rubidge (1990, 1995) recognized the presence of a new biozone, the Eodicynodon Assemblage Zone The rocks of the Karoo Supergroup of South Africa below the Tapinocephalus Assemblage Zone. Fossil collect- preserve the world’s best record of continental Permian to ing in the lowermost Beaufort over the past two decades Jurassic faunal biodiversity. The long temporal range of with a view to biostratigraphic refinement has shown that the rocks of the Supergroup, and their rich fossil record, the Beaufort–Ecca contact is diachronous (Rubidge 2005), has enabled studies of biodiversity over this extended with the earliest terrestrially deposited rocks of the Beau- time, particularly in relation to the Permo-Triassic mass fort Group being limited to the area between Rietbron and extinction event (e.g. Smith & Ward 2001; Retallack et al. Laingsburg in the southwestern part of the basin. 2003), and enhanced understanding of the evolution of In the lower Beaufort, herbivorous dinocephalians, important tetrapod lineages, particularly reptiles and dicynodonts and pareiasaurs are the most abundant synapsids. A rich tetrapod record has allowed biostrati- tetrapod fossils and offer the best possibility as biozone graphic subdivision of these rocks into seven Permian and indicators. However, the large size of dinocephalians and two Triassic biozones (Rubidge 1995) which have served pareiasaurs, and the fact that they are less abundant than as the basis for global correlation of Permian–Triassic dicynodonts, make the latter the best possibility. In addi- continental sedimentary deposits. In the absence of tion recent taxonomic refinement of lower Beaufort reliable radiometric dates for the Beaufort Group, recent dicynodonts (Cluver & Hotton 1981; Cluver & King 1983; enhanced basin development models for the Karoo have Keyser 1993; King & Rubidge 1993) and the recent descrip- been reliant on biostratigraphic refinements. tion of several new genera (Modesto et al. 2002, 2003) has While much recent research has been undertaken on facilitated use of dicynodonts as biostratigraphic indicator refining the biostratigraphic ranges in the Middle (Botha genera. & Smith 2006) and Upper (Hancox 2001; Neveling et al. Ongoing stratigraphic collecting in the lower Beaufort 2005) Beaufort Group, biostratigraphic refinement of the and the inclusion of reliably identified dicynodonts on Lower Beaufort has been more difficult. This is because of stratigraphic sections has led to the recognition of trends the relative paucity of tetrapod fossils in the lowermost in the stratigraphic distribution of certain dicynodont Beaufort Group, the difficulty in extracting them from genera. In addition, the recent production of a GIS data- very hard matrix, and the complex nature of the folding of base of all fossil tetrapods of the Beaufort Group (Nicolas these rocks in the southern Karoo. 2007) has further facilitated understanding of the geo- With the recognition of an extinction in the marine graphic distribution of different dicynodont genera. realm at the end of the Guadalupian, we aim to determine The following distribution of dicynodonts has been whether an equivalent occurred in the terrestrial realm. observed immediately above the Ecca-Beaufort contact As the lower Beaufort Group is one of the few fossil- around the basin: Eodicynodon is geographically restricted bearing terrestrial depositional basins which has the to the southwestern part of the Beaufort Group; further possibility of recording this event, an understanding of northwards, five specimens of Colobodectes have been lithostratigraphy and the biostratigraphic ranges of tetra- found between Sutherland and Carnavon, while still pods in this stratigraphic interval is critical. Lithostrati- further northwards Robertia is present as far as Phillipolis. graphic subdivision of the lower Beaufort has been the Following Walther’s Law the same stratigraphic pattern subject of several publications (e.g. Stear 1980; Le Roux would be expected in the southern Karoo where the most 1985; Jordaan 1990; Loock et al. 1994) but the complex complete stratigraphic succession of the Tapinocephalus nature of the folding as well as lateral facies changes have Assemblage Zone is present. Eodicynodon is restricted to made lithostratigraphy difficult to apply. It is thus essen- the lower 1100 m of the Beaufort Group in the southern tial to develop a reliable biostratigraphic scheme. Karoo (Jinnah & Rubidge 2006), but so far no Colobodectes Boonstra (1969) tabulated the relative numbers of lower specimens have been reported from this area. Robertia first Beaufort tetrapod families and their biostratigraphic appears after the last occurrence of Eodicynodon, and ranges, suggesting that the Tapinocephalus Zone could be occurs upwards into the Pristerognathus Assemblage divided into a lower, middle and upper unit. He pointed Zone. The stratigraphic range of Diictodon begins about out that the lower unit has a relative abundance of 1900 m from the base of the Beaufort, overlaps with the dinocephalians relative to dicynodonts, whereas the reverse upper range of Robertia and continues up to the end of the applies to middle unit (corroborating the observation of Dicynodon Assemblage Zone.

134 ISSN 0078-8554 Palaeont. afr. (December 2009) 44: 134–135 Our recent discovery of dateable volcanic ash layers in LE ROUX, J.P.1985. Palaeochannels and uranium mineralisation in the Main Karoo Basin of South Africa. Unpublished Ph.D. thesis, University of the lower Beaufort as well as the application of palaeo- Port Elizabeth, South Africa. magnetic dating in these rocks offers additional opportu- LOOCK, J.C., BRYNARD, H.G., HEARD, R.G., KITCHING, J.W. & nities for correlating fossils in the lower Beaufort and RUBIDGE, B.S. 1994. The stratigraphy of the lower Beaufort Group in an area north of Laingsburg, South Africa. Journal of African Earth providing insight on the rate of evolution of the earliest Sciences 18(3), 185–195. therapsids as well as faunal turnover and diversity pulses MODESTO, S.P.,RUBIDGE, B.S. & WELMAN, J. 2002. A new dicynodont in the Middle Permian. therapsid from the lowermost Beaufort Group, Upper Permian of South Africa. Canadian Journal of Earth Sciences 39, 1755–1765. MODESTO, S.P., RUBIDGE, B., VISSER, I. & WELMAN, J. 2003. A new REFERENCES basal dicynodont from the Upper Permian of South Africa. Palaeontol- BOONSTRA, L.D. 1969. The fauna of the Tapinocephalus Zone (Beaufort ogy 46, 211–223. beds of South Africa). Annals of South African Museum 56, 1–73. NEVELING, J., HANCOX, P.J.& RUBIDGE, B.S. 2005. Biostratigraphy of BOTHA, J. & SMITH, R.M.H. 2006. Rapid vertebrate recuperation in the the lower Burgersdorp Formation (Beaufort Group; Karoo Super- Karoo Basin of South Africa following the End-Permian extinction. group) of South Africa – implications for the stratigraphic ranges of Journal of African Earth Sciences 45, 502–514. early Triassic tetrapods. Palaeontologia africana 41, 81–88. CLUVER, M.A. & HOTTON, N., III. 1981. The genera Dicynodon and NICOLAS, M.V. 2007. Tetrapod biodiversity through the Permo-Triassic Diictodon and their bearing on the classification of the Dicynodontia Beaufort Group (Karoo Supergroup) of South Africa. Unpublished Ph.D. (Reptilia, Therapsida). Annals of the South African Museum 83, 99–146. thesis, University of the Witwatersrand, Johannesburg, South Africa. CLUVER, M.A. & KING, G.M. 1983. A reassessment of the relationships RETALLACK, G.J., SMITH, R.M.H. & WARD, P.D. 2003. Vertebrate of the Permian Dicynodontia (Reptilia, Therapsida) and a new classifi- extinction across the Permian-Triassic boundary in the Karoo Basin, cation of dicynodonts. Annals of the South African Museum 91, 195–273. South Africa. Geological Society of America Bulletin 115, 1133–1152. HANCOX, P.J. 1998. A Stratigraphic, Sedimentological and Palaeonviron- ROSSOUW,P.J.& DE VILLIERS, J. 1953. The geology of the Merweville area, mental synthesis of the Beaufort–Molteno contact in the Karoo Basin. Cape Province. Explanation Sheet 198, The Geological Survey of South Unpublished Ph.D. thesis, University of the Witwatersrand, Johannes- Africa, 93 pp. burg, South Africa. RUBIDGE, B.S. 1990. A new vertebrate biozone at the base of the Beaufort JINNAH, Z.A. & RUBIDGE, B.S. 2007. A double-tusked dicynodont and group, Karoo sequence (South Africa). Palaeontologia africana 27, 17–20. its biostratigraphic significance. South African Journal of Science 103, RUBIDGE, B.S. (ed.) 1995. Reptilian Biostratigraphy of the Permo-Triassic 51–53. Beaufort Group (Karoo Supergroup) Biostratigraphy of the Beaufort Group JORDAAN, M.J. 1990. Basin analysis of the Beaufort Group in the western part (Karoo Supergroup). South African Committee for Stratigraphy, of the Karoo Basin. Unpublished Ph.D. thesis, University of the Orange Biostratigraphic Series 1. Free State, Bloemfontein, South Africa. RUBIDGE, B.S. 2005. Re-uniting lost continents – Fossil reptiles from the KEYSER, A.W. 1993. A re-evaluation of the smaller endothiodontidae. ancient Karoo and their wanderlust. South African Journal of Geology Geological Survey of South Africa Memoir 82, 1–53. 108, 135–172. KEYSER, A.W. & SMITH, R.M.H. 1977/78. Vertebrate biozonation of SMITH, R.M.H. & WARD, P.D. 2001. Pattern of vertebrate extinctions the Beaufort group with special reference to the Western Karoo Basin. across an event bed at the Permian-Triassic boundary in the Karoo Annals of the Geological Survey of South Africa 12, 1–36. Basin of South Africa. Geology 29(12), 1147–1150. KING, G.M. & RUBIDGE, B.S. 1993. A taxonomic revision of small STEAR, W.M. 1980. The sedimentary environment of the Beaufort Group dicynodonts with post-canine teeth. Zoological Journal of the Linnean uranium province in the vicinity of Beaufort West. Unpublished Ph.D. Society 107, 131–54. thesis, University of Port Elizabeth, Port Elizabeth, South Africa.

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