Scientists have directly estimated Tyrannosaurus rex's body temperature at approximately 97 degrees Fahrenheit using chemical analysis of fossilized tooth enamel, confirming decades of suspicions that the predator was warm-blooded. The technique, which measures isotope bonds in tooth enamel, reveals that T. rex maintained an active metabolism comparable to modern humans, positioning it between cold-blooded reptiles and warm-blooded birds. This finding provides new insights into the dinosaur's behavior, physiology, and ecological role 66 to 69 million years ago.