T. rex teeth indicate it ran as warm as an elephant

Researchers measured T. rex body temperature by analyzing its teeth, finding a reading of about 36° Celsius, comparable to a modern elephant. This research utilizes clumped isotope thermometry, which measures the clumping of heavy carbon and oxygen isotopes in tooth enamel to determine formation temperature, independent of water content. Previously, debates on dinosaur endothermy relied on indirect evidence from bone structure and growth rates. Earlier attempts using oxygen isotopes in bones and teeth were limited because the isotopic ratios depend on unknown water composition. The new technique bypasses this limitation by utilizing the thermal signature recorded in the mineral structure itself.

The shift from relying on indirect paleontological evidence to direct geochemical thermometry illustrates a crucial evolution in scientific inquiry: moving from inference based on morphology to measurement based on physical chemistry. The limitations of earlier attempts highlight how context—specifically the composition of the surrounding medium—can introduce confounding variables into measurements concerning extinct life. The introduction of clumped isotope thermometry represents an advancement where the chosen methodology directly isolates the target variable (temperature) by using a stable, internal chemical process (isotope clumping) within the sample itself, rather than relying on external assumptions about the organism’s environment or physiology. This challenges the entrenched argument that thermal strategies for extinct organisms must be inferred from indirect biological structures alone. The implication is that establishing endothermy in dinosaurs requires methodology that is robust against environmental ambiguities, demanding a skepticism toward any conclusion derived solely from suggestive physical evidence without rigorous methodological control.