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 Dynamics of the oxygen, carbon dioxide, and water interaction across the insect spiracle(Hindawi Publishing Corporation, 2014-09-03) Simelane, S.M.; Abelman, S.; Duncan, F.D.This paper explores the dynamics of respiratory gases interactions which are accompanied by the loss of water through an insect's spiracle. Here we investigate and analyze this interaction by deriving a system of ordinary differential equations for oxygen, carbon dioxide, and water vapor. The analysis is carried out in continuous time. The purpose of the research is to determine bounds for the gas volumes and to discuss the complexity and stability of the equilibria. Numerical simulations also demonstrate the dynamics of our model utilizing the new conditions for stability and instability.