Recent advances in mass spectrometry techniques have resulted in new applications to the fiel d of dinosaur paleontology. Specifically, oxygen isotope signatures from the bone phosphate can be used as proxies for metabolic functioning. Oxygen isotopes fractionate according to the temperature at which the bones mineralize. Skeletal isotopic variati ons are utilized to distinguish temperature differences within an animal’s body. This study consists of an isotopic examination of Acrocanthosaurus atokensis, a large theropod dinosaur from the Aptian-Albian of south-central North America. This dinosaur’s large size and potentially active lifestyle during a hot house climate leads to the hypothesis that supplementary thermoregulatory mechanisms were necessary to prevent overheating. Temperature differences within the Acrocanthosaurusbody, as suggested by delta¹⁸O values, are compared with those of modern animals representing a range from ectothermic heterothermy to endothermic homeothermy. The possibilities of heat loss through panting or oral gaping and dissipation fro m a sail-like structure on the back are tested through examination of the palatal bones and neural spine oxygen isotopic signatures in relation to core body temperature. These comparisons are suspected to support the hypothesis that Acrocanthosaurusmaintained a moderate to high level of homeothermy supplemented by the aforementioned heat regulatory mechanisms.