Stable isotope analyses (δ18OPO4, δ18OCO3, and δ13C) are reported for the first time on crocodilian, theropod, and sauropod teeth from two stratigraphic levels (G1 and G2) from the late Campanian–early Maastrichtian “Lo Hueco” fossil site (Cuenca, Spain) in order to better understand paleoclimatic and paleoenvironmental conditions existing in the Iberian Peninsula during the Late Cretaceous. Diagenetic alteration was evaluated using three tests: (1) consistent differences in enamel and dentine δ18OPO4 values, (2) crocodilian δ18OPO4 values consistently lower than dinosaur δ18OPO4 values in agreement with the proposed latitudinal distribution between ectotherms and endotherms, and (3) a Δδ18OCO3-PO4 value of 9.1 ± 1.7‰ for dinosaurs in accordance with the expected equilibrium fractionation between carbonate and phosphate in unaltered modern mammalian bioapatite. Calculated δ18OH2O values are slightly higher in crocodilians compared to dinosaurs since semiaquatic ectothermic taxa δ18OH2O represents local meteoric waters in a brief window of time when the conditions are favorable for apatite synthesis, whereas terrestrial endothermic taxa δ18OH2O records ingested water year-round. Mean air temperature calculated using crocodilian and dinosaur δ18OH2O values shows an increase between G1 and G2, which may be related to differences in the sedimentological setting and/or to a shift toward warmer conditions over time. Finally, the sauropod mean δ13C value (−11.1 ± 0.2‰, VPDB) is in the predicted range for C3 vegetation.

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