Oxygen isotope variability in juvenile dinosaurs ( Hypacrosaurus ): evidence for thermoregulation

Small terrestrial vertebrates are not capable of maintaining a constant body temperature (±2°C) without a relatively high metabolism. The amount of temperature variability during bone growth can be determined using oxygen isotopes from bone phosphate because fractionation of oxygen isotopes between body fluid and bone phosphate is dependent upon temperature. Fluctuation of body temperature during the early phase of growth in juvenile ectotherms should result in high intra- and interbone isotopic variability, whereas juvenile endotherms should have low isotopic variability resulting from the maintenance of homeothermy. Analyses of juvenile Hypacrosaurus individuals indicate a pattern of low isotopic heterogeneity suggestive of endothermy.