a) Isotopic dinosaur body temperature determinations plotted versus compilations of modern mammal, bird and ectotherm body temperatures and body masses ( Supplementary Tables 5 and 6). Error bars on dinosaur body temperature estimates represent two s.e. Clumped isotope-based temperature determinations from teeth of Jurassic Camarasaurus and Giraffatitan plotted alongside determinations from titanosaurid eggshells from Auca Mahuevo, Argentina, and oviraptorid eggshells from Ukhaa Tolgod, Mongolia. Modern ectotherm data points are calculated mean values with measured upper and lower limits indicated by grey bars ( 18 Supplementary Table 6). Clumped isotope estimates of oviraptorid dinosaur body temperatures are lower than all modern birds and most modern mammals, but are comparable to a minority of modern mammals. Isotopic estimates of oviraptorid dinosaur body temperatures are higher than most calculated mean ectotherm body temperatures but fall within the range exhibited by many ectotherms, including those of similar mass. Sauropod dinosaur (that is, titanosaurid, Camarasaurus, Giraffatitan) body temperatures are higher than the mean and range exhibited by the majority modern reptiles in this compilation. ( b) Clumped isotope-based temperature determinations for both modern eggshells and dinosaur fossils. Monitor lizard eggshell isotope data with high error is excluded from this figure.