Oxygen and carbon isotope compositions of middle Cretaceous vertebrates from North Africa and Brazil: Ecological and environmental significance
Résumé
In order to investigate mid-Cretaceous terrestrial climates of low paleolatitudes, Moroccan, Tunisian and Brazilian vertebrate apatites have been analyzed for their oxygen and carbon isotope compositions of phosphates (delta(18)O(p)) and carbonates (delta(18)O(c), delta(18)C(c)). At each site, coexisting theropod dinosaurs, titanosaurid sauropods, pterosaurs, crocodilians, turtles and fish have distinct delta(18)O(p) and delta(18)C(c) values reflecting their ecologies, diets and foraging environments. Oxygen isotope compositions of surface waters (delta(18)O(w)) estimated from turtle and crocodile delta(18)O(p) values range from -5.0 +/- 1.0 parts per thousand to -2.4 +/- 1.0 parts per thousand, which do not differ from mean annual rainwater values occurring today under inter-tropical sub-arid to arid climates. High water temperatures ranging from 21 +/- 6 degrees C to 34 +/- 2 degrees C deduced from fish delta(18)O(p) values are in agreement with those published for mid-Cretaceous low latitudes. Temporary or seasonal droughts are inferred from high delta(18)O(p) values of lungfish teeth, even though lower reptile delta(18)O(p) values suggest the use of distinct and most likely larger or regularly renewed bodies of water. Environmental conditions of the studied low latitude regions during the Aptian-Cenomanian interval were somewhat similar to those experienced today under semi-arid to arid tropical or equatorial climates, but with higher mean surface temperatures than present-day ones