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The Recovery of Terrestrial Vertebrate Diversity in the South African Karoo Basin After the End-Permian Extinction

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The Recovery of Terrestrial Vertebrate Diversity in the South African Karoo Basin After the End-Permian Extinction C. R. Palevol 4 (2005) 555–568 http://france.elsevier.com/direct/PALEVO/ Systematic Palaeontology (Vertebrate Palaeontology) The recovery of terrestrial vertebrate diversity in the South African Karoo Basin after the end-Permian extinction Roger Smith *, Jennifer Botha Department of Karoo Palaeontology, Iziko South African Museum, Box 61, Cape Town, 8000, South Africa Received 30 August 2004; accepted after revision 8 July 2005 Available online 25 August 2005 Written on invitation of the Editorial Board Abstract The southern half of the main Karoo Basin in South Africa contains an almost continuous stratigraphic record of terrestrial sedimentation through the Permo-Triassic boundary (PTB). Detailed logging of multiple sections through the boundary sequence has defined the end-Permian mass extinction event using vertebrate fossils as well as a synchronous change in fluvial style reflecting a rapid aridification of climate. Field data demonstrates a 69% mass extinction of Late Permian terrestrial vertebrates lasting some 300 kyr terminating at the PTB, followed by a lesser extinction event (31%) approximately 160 kyr later involving four survivor taxa that crossed the PTB. The Early Triassic recovery fauna comprises proterosuchian archosauromorphs (Prot- erosuchus), small amphibians (Micropholis, Lydekkerina), small procolophonoids (‘Owenetta’ kitchingorum, Procolophon), medium-sized dicynodonts (Lystrosaurus) and small insectivorous cynodonts (Progalesaurus, Galesaurus, Thrinaxodon). Tapho- nomic bias towards preferential preservation of drought accumulations in the Early Triassic has probably over-emphasized the abundance and diversity of semi aquatic and burrowing animals. To cite this article: R. Smith, J. Botha, C. R. Palevol 4 (2005). © 2005 Académie des sciences. Published by Elsevier SAS. All rights reserved. Résumé La restauration de la diversité des Vertébrés terrestres dans le bassin du Karoo d’Afrique du Sud, après la crise biologique de la fin du Permien. Un enregistrement stratigraphique presque continu de la sédimentation terrestre du passage Permien–Trias (PTB), se trouve exposé dans la moitié méridionale du principal bassin du Karoo, en Afrique du Sud. Des relevés lithologiques détaillés de nombreux affleurements, englobant la séquence PTB, ont permis de définir l’événement des extinc- tions en masse de la fin du Permien à partir des vertébrés fossiles ainsi qu’à travers un changement contemporain du régime fluviatile, traduisant une rapide aridification du climat. Les données de terrain révèlent qu’une extinction en masse affecte 69 % des vertébrés terrestres à la fin du Permien, la durée de l’événement s’étalant sur environ 300 000 ans avant la PTB. Elle est suivie par un événement de moindre ampleur, avec un taux d’extinction de 39 %, survenant approximativement 160 000 ans plus * Corresponding author. E-mail address: [email protected] (R. Smith). 1631-0683/$ - see front matter © 2005 Académie des sciences. Published by Elsevier SAS. All rights reserved. doi:10.1016/j.crpv.2005.07.005 556 R. Smith, J. Botha / C. R. Palevol 4 (2005) 555–568 tard et comportant quatre taxons survivant au passage de la PTB. Les faunes de la reconquête du Trias inférieur comprennent des archosauromorphes protérosuchiens (Proterosuchus), de petits amphibiens (Micropholis, Lyddekerina), de petits procolo- phonidés (« Owenetta » kitchingorum, Procolophon), des dicynodontes de taille moyenne (Lystrosaurus) et de petits cynodon- tes insectivores (Progalesaurus, Galesaurus, Thrinaxodon). Les distorsions taphonomiques, en privilégiant la préservation des fossiles dans les mares en voie d’assèchement du début du Trias, ont probablement fait surestimer l’abondance et la diversité des animaux amphibies ou fouisseurs. Pour citer cet article : R. Smith, J. Botha, C. R. Palevol 4 (2005). © 2005 Académie des sciences. Published by Elsevier SAS. All rights reserved. Keywords: Terrestrial vertebrates; Mass extinction; Recovery; Permo-Triassic boundary (PTB); Karoo Basin; South Africa Mots clés : Vertébrés terrestres ; Extinction en masse ; Reconquête ; Limite Permien-Trias ; Bassin du Karoo ; Afrique du Sud 1. Introduction restrial vertebrate communities after the end-Permian mass extinction. The end-Permian mass extinction that occurred at approximately 251 Ma [8] is generally regarded as the most catastrophic of the five major Phanerozoic mass 2. Palaeoenvironment extinctions. An estimated 90% of all marine species (e.g. [5,17,33,50]) and 70% of all terrestrial vertebrate The Karoo Supergroup is a thick succession of sedi- families [34,35] disappeared within 165 kyr [8] and per- mentary rocks that accumulated in a large, intracra- haps as little as 10 kyr [56,60]. Research to date on the tonic, retroarc foreland basin in southwestern Gond- Permo-Triassic boundary (PTB) has focused more on wana. The strata record more than 100 Ma of almost patterns of taxon extinctions and possible causes for continuous sediment accumulation from the Permo- the extinction event (e.g., [2,3,22,24,47,60]) rather than Carboniferous (300 Ma) through to the Early Jurassic on the recovery of biodiversity during the Early Trias- (190 Ma) under a range of climatic regimes and within sic. Numerous marine PTB sections have provided a several tectonically controlled sub-basins. broad indication of the devastation of marine life From the Middle Permian onwards, some 4000 m [22,24,25,36,60]. However, the details of the effect of of vertebrate-fossil-bearing fluvio-lacustrine sedi- the end-Permian extinction on the terrestrial ecosys- ments that make up the Beaufort Group dominate the tems of Pangaea remain poorly understood. World- Karoo Supergroup succession. The PTB occurs in the wide there are very few stratigraphic sequences that are middle of the Beaufort Group succession and is not only complete enough to preserve the terrestrial end-Permian marked by a major extinction episode, recorded in the mass extinction and the succeeding Early Triassic fossil record by the ‘Glossopteris-Dicroidium floral suc- recovery. One of these rare locations is the South Afri- cession’and the therapsid fauna, but also coincides with can Karoo Basin, where recent work has revealed a a major change in fluvial style. complete terrestrial sequence from the Permian to the Triassic, containing abundant fossils that record changes 2.1. Sedimentology of the PTB sequence in floral and vertebrate taxa across the PTB and subse- quent recovery of the southern Gondwanan ecosys- The main extinction zone is approximately 40 m tems in the Early Triassic [52,53]. thick at both the Bethulie and the Graaff-Reinet sec- Over the past ten years, 225 in situ vertebrate fossils tions and is stratigraphically positioned in the lower have been systematically collected from the PTB strata of the Palingkloof Member at the top of the Bal- sequences in the Bethulie and the Graaff-Reinet dis- four Formation (Fig. 1). Detailed sedimentological logs tricts of the southern and central Karoo Basin (Fig. 1). compiled from several sections at each locality show Here, we present a compilation of the latest palaeoen- that the facies sequences in the boundary beds are vironmental and biostratigraphic data collected from remarkably similar (Fig. 2). The overall lithological these sections with particular emphasis on the nature transitions are from drab greenish grey and blue-grey and the controls of the recovery of Early Triassic ter- thickly-bedded and pedogenically modified massive R. Smith, J. Botha / C. R. Palevol 4 (2005) 555–568 557 Fig. 1. (A) Map of South Africa, showing the location of Bethulie and Graaff-Reinet districts where detailed lithostratigraphical sections were conducted. (B) Summary of the litho- and biostratigraphy for the southern and central Karoo Basin indicating the stratigraphic positions of the PTB described in this report. Abbreviations: C.T., Cape Town; D, Durban; JHB, Johannesburg; SACS, South African Committee for Stratigra- phy. Fig. 1. (A) Carte d’Afrique du Sud localisant les districts de Bethulie et de Graaff-Reinet, où des coupes lithostratigraphiques détaillées ont été relevées. (B) Synthèse des données litho- et biostratigraphiques des parties méridionales et centrale du bassin du Karoo, indiquant les positions stratigraphiques de la PTB décrites dans cet article. Abréviations : C.T., Le Cap; D, Durban; JHB, Johannesburg; SACS, Comité sud-africain de stratigraphie. siltstone beds with interbedded, laterally-accreted fine glomeratic sandstone-dominated succession – the grained sandstone bodies grading upwards into progres- Katberg Formation. sively more maroon coloured siltstone beds interbed- ded with vertically accreted sandstones with distinc- 2.1.1. Massive dark grey mudrock tive gullied basal scours and include a regionally In the drab-coloured dark grey (5Y 4/1) and olive extensive interval of maroon coloured thinly bedded grey (5Y5/2) mudrocks below the PTB, large dark laminites. The PTB sequence is capped by a thick con- brown weathering calcareous nodules and claystone 558 R. Smith, J. Botha / C. R. Palevol 4 (2005) 555–568 Fig. 2. Summary sedimentological log of the PTB sequence compiled from the study sections in the Bethulie District with interpreted palaeo- landscape reconstructions. Vertical scale in metres. Fig. 2. Profil sédimentologique synthétique de la séquence de la PTB, d’après les coupes étudiées dans le district de Bethulie et interprétations des paysages correspondants. Échelle verticale en mètres. lined-root channels as well as Planolites and Taenidium disarticulated postcranial
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