ABDALA Nestor Fernando
congresos y reuniones científicas
Gondwanan Middle Permian synapsid radiations.
RUBIDGE, B.S.; ANGIELCZYK, K. A.; DE KLERK, W.; ABDALA, F.
Conferencia; 69th Meeting of the Society of Vertebrate Paleontology; 2009
SOCIETY OF VERTEBRATE PALEONTOLOGY
The South African Karoo preserves the best unbroken record of continental Permian to Jurassic biotas, enabling extended studies tracking changes in the biodiversity, particularly in relation to the P-T event. Although much research has been undertaken on biostratigraphic ranges in the Middle and Upper Beaufort Group, biostratigraphic refinement of the Lower Beaufort is more difficult because of the relative paucity of tetrapod fossils, outdated taxonomy of the tetrapods represented, and the complex folded nature of the rocks in the southern Karoo. The end Guadalupian extinction event is well documented in the marine realm, but not yet understood in the terrestrial realm. As the lower Beaufort Group is one of the few fossil-bearing terrestrial depositional basins which has the possibility of recording this event, an understanding of lithostratigraphy and the biostratigraphic ranges of tetrapods in this stratigraphic interval is critical. Synapsids in the lower Beaufort are represented by varanopids, biarmosuchians, gorgonopsians, therocephalians, dinocephalians and dicynodonts. Long term stratigraphic collecting has led to the recognition of trends in the geographic and stratigraphic distribution of synapsid genera. Along the Ecca-Beaufort contact Eodicynodon is restricted to the southwestern Beaufort; further northwards Robertia is present as far as Phillipolis. Following Walther?s Law, the same stratigraphic pattern exists in the southernmost Karoo where Eodicynodon is restricted to the lowermost Beaufort Group, followed by Robertia, and finally Diictodon. Dateable volcanic ash layers in the lower Beaufort offer additional opportunities for correlating fossils in the lower Beaufort and providing insight on the rate of evolution of the earliest therapsids as well as faunal turnover and diversity pulses in the Middle Permian.