The metabolic functioning of hadrosaurs can be examined using oxygen isotope ratios from structural bone carbonate. The temperature dependant fractionation of oxygen isotopes during bone apatite deposition allows variations in d¹⁸O values to be used as a proxy for variations in an individual's body temperature during growth. After removing diagenetic components and accounting for environmental factors that may affect the oxygen isotope compositions of metabolic water, it was determined that original isotope signatures can be obtained from structural bone carbonate. Using both Micromass gas source continuous flow and dual inlet IsoPrime mass spectrometers, extremely small sample sizes (~0.5-1 mg) could be measured to high precision (+/-0.4‰), therefore eliminating the need for excessive destruction of bone samples. The oxygen isotope compositions of bone carbonate samples from both genera ranged between -11.8 to -13.5‰, with an average of -12.8‰ vs. V-PDB. Examination of Hypacrosaurus and Maiasaura individuals suggests that these two genera share a similar metabolic strategy. Their cladistic relationship to each other allows the further conclusion that this strategy may represent the basal condition for the Hadrosauridae family. Comparison of juvenile and adult hadrosaurs suggests that these dinosaurs were homeotherms. However, actual body temperatures and method of temperature regulation remain to be determined.