T. rex body temperature estimated at 36.3 °C via tooth analysis

Geochemists from the University of California, Los Angeles (UCLA) have achieved the first direct measurement of the body temperature of a Tyrannosaurus rex. By analyzing fossilized teeth from the Hell Creek Formation in Montana, researchers determined that the T. rex had an average body temperature of 36.3 ± 2.5 °C.

This temperature is significantly higher than estimated environmental conditions and is closer to the body temperature of modern large mammals, such as elephants, than to contemporary reptiles. This finding supports the theory that the T. rex possessed internal heat production, or endothermy, which would have allowed it to survive in various climates.

The study, published in Science Advances, utilized a novel method to bypass the limitations of previous bone-based studies. While oxygen isotopes in bones can be influenced by an animal's water balance—a variable unknown for extinct species—the researchers focused on the chemical bonds of rare isotopes, carbon-13 and oxygen-18, within tooth enamel. Because enamel forms within the organism and is less prone to the continuous remodeling seen in bone, it acts as a molecular thermometer that preserves the chemical conditions present during the animal's life.