Fig. 1.

Shark teeth from various Miocene (triangle) and Pliocene (circle) localities provide phosphate oxygen isotope compositions (δ¹⁸O_p) that reveal thermal physiology with temperature differences among sampled taxa. (A) The five localities provide context for Otodus (red) with comparisons to ectothermic (blue) sharks, predicted or known (yellow and orange based on extant Isurus oxyrinchus and Carcharodon carcharias, respectively) regionally endothermic (r. endothermic) sharks, and endothermic marine mammals (dark red). (B) Based on these δ¹⁸O_p values, a Bayesian model correctly predicts body temperatures of endothermic marine mammals (dark red), distinguishes thermal differences among ectothermic (blue) and regionally endothermic (yellow and orange) sharks, and indicates elevated body temperatures in Otodus (red) similar to or beyond the extant C. carcharias. The Bayesian δ¹⁸O_p–based temperature model is described in the Materials and Methods section briefly with greater detail in SI Appendix, Text.