The research adds to a decade of evidence suggesting many dinosaur lineages were not strictly cold-blooded and points to a broader trend of elevated metabolism in dinosaur ancestors that led to birds.

This work provides the first relatively direct, thermodynamically grounded measurement of a dinosaur’s body temperature, reinforcing the idea that meat-eating dinosaurs had endothermic metabolisms with variation across species.

The study is published in Science Advances.

Co-author Robert Eagle notes this offers a direct measurement of physiology that was previously unavailable.

Researchers will continue analyzing the tooth before returning it to the museum, underscoring the ongoing value of natural history specimens for revealing physiology.

A UCLA-led study measuring tooth enamel isotopes on Thomas the T. rex finds a body temperature around 36.3°C (97°F), indicating Tyrannosaurus rex was warm-blooded with a human-like core temperature range.

The study builds on prior evidence like bone growth rates and predator-prey dynamics that also indicate high metabolic demands for this apex predator.

The findings align with observations of T. rex’s behavior and ecology, providing a coherent explanation for its widespread fossil distribution across diverse climates.

Tooth enamel was used because its durable crystal structure resists diagenesis, enabling reliable isotope readings to infer ancient temperatures, a method also used for other predators like the megalodon.

Led by Aradhna Tripati and Robert Eagle from UCLA, this work marks about 15 years of development of the technique and its first exact body temperature determination for T. rex.

Researchers used a refined chemical technique to measure blood temperature from fossilized tooth enamel by analyzing carbon–oxygen bonds, relying on tooth enamel rather than larger bone fragments.

The technique analyzes isotopic bonds in CO2 released from dissolved enamel and requires only milligrams of material, enabling study with much smaller samples than before.