Latitudinal temperature gradient during the Cretaceous Upper Campanian–Middle Maastrichtian: δ18O record of continental vertebrates

Latitudinal variations in model biogenic apatite δ18O values were calculated using fractionation equations of vertebrates and weighted rainfall δ18O values along with mean annual air temperatures provided by IAEA–WMO meteorological stations. The reference equation obtained was used to compute a continental temperature gradient for the Late Campanian–Middle Maastrichtian interval by using published and new δ18O values of phosphate from vertebrates. Samples are mainly tooth enamel from crocodilians and dinosaurs that lived at paleolatitudes ranging from 83−9+4°N (Alaska) to 32±3°S (Madagascar). The temperature gradient was less steep (0.4±0.1 °C/°latitude) than the present-day one (0.6 °C/°latitude) with temperatures that decreased from about 30 °C near the equator to about −5 °C at the poles. Above 30° of paleolatitude, air temperatures were higher than at present. The validity of these results is discussed by comparison with climatic criteria inferred from paleontological, paleobotanical and sedimentological data. The latitudinal distribution of oxygen isotope compositions of continental vertebrates is potentially a powerful tool for quantifying Mesozoic terrestrial climates.