Faculty of Science
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Item Oxygen isotopes suggest elevated thermometabolism within multiple permo-triassic therapsid clades(eLife Sciences Publications Ltd, 2017-07) Rey, K.; Amiot, R.; Fourel, F.; Abdala, F.; Fluteau, F.; Jalil, N.-E.; Liu, J.; Rubidge, B.S.; Smith, R.M.H.; Steyer, J.S.; Viglietti, P.A.; Wang, X.; Lécuyer, C.The only true living endothermic vertebrates are birds and mammals, which produce and regulate their internal temperature quite independently from their surroundings. For mammal ancestors, anatomical clues suggest that endothermy originated during the Permian or Triassic. Here we investigate the origin of mammalian thermoregulation by analysing apatite stable oxygen isotope compositions (d18Op) of some of their Permo-Triassic therapsid relatives. Comparing of the d18Op values of therapsid bone and tooth apatites to those of co-existing non-therapsid tetrapods, demonstrates different body temperatures and thermoregulatory strategies. It is proposed that cynodonts and dicynodonts independently acquired constant elevated thermometabolism, respectively within the Eucynodontia and Lystrosauridae + Kannemeyeriiformes clades. We conclude that mammalian endothermy originated in the Epicynodontia during the middle-late Permian. Major global climatic and environmental fluctuations were the most likely selective pressures on the success of such elevated thermometabolism.Item Leachability of metals from gold tailings by rainwater: An experimental and geochemical modelling approach.(South African Water Research Commission, 2016-01) Grover, B.P.C.; Johnson, R.H.; Tutu, H.Mine leachates from gold tailings impoundments usually contain elevated concentrations of metals and sulphates that impact negatively on water quality. This study was aimed at assessing the leachability of such metals from tailings by rainwater. Oxidised and unoxidised tailings were leached experimentally and through simulations using the PHREEQC geochemical modelling code. The results revealed that the majority of readily leachable metals were held in secondary mineral phases, mainly sulphates. A good agreement between experimental and modelling techniques was obtained, indicating the potential use of geochemical modelling in future metal release studies for the site. A list of reactive minerals for the tailings material was compiled. These minerals may or may not be present in the tailings; however, the list provides a means of estimating future reactivity or bulk metal release from the tailings.