T. Rex Was Warm-Blooded, Fossil Tooth Analysis Confirms

Clamped-Isotope Analysis of Prehistoric Teeth

To measure the internal warmth of the extinct predator, scientists utilized two small portions of teeth from “Thomas,” a roughly 70% complete skeleton housed at the Natural History Museum of Los Angeles County, as reported in the study. Researchers drilled a few milligrams of enamel from teeth not currently on public display. According to UCLA climate scientist and senior study author Aradhna Tripati, the enamel chemistry recorded the temperature at which it formed 66 million years ago.

The team spent more than a decade refining the method to make the measurement possible on rare specimens. By reducing the required sample size by roughly 90%, the technique allowed scientists to bypass institutional reluctance over damaging valuable fossils. Inside the tooth enamel, researchers measured carbon and oxygen isotopes. These atoms form chemical bonds at rates dictated by temperature—cooler conditions produce more bonds, while warmer conditions yield fewer. After dissolving the enamel in phosphoric acid and analyzing the resulting carbon dioxide with a mass spectrometer, the team calculated the 97-degree Fahrenheit (36-degree Celsius) reading.

Metabolism and Range Across Prehistoric North America

The 97-degree Fahrenheit finding places T. rex between modern cold-blooded reptiles, which typically register between 82 and 86 degrees Fahrenheit, and modern birds, which can exceed 104 degrees Fahrenheit. According to study co-author and UCLA geobiologist Robert Eagle, this elevated, regulated body temperature provided the energy needed to sustain an active metabolism over longer periods than a cold-blooded animal could manage.

This physiological trait supports the suspicion that tyrannosaurs were active predators. Furthermore, a warm-bodied physiology explains how the species successfully colonized cold environments. According to paleoclimate models reconstructing North America during the late Cretaceous period, a warm-blooded T. rex could inhabit a broad range stretching from modern-day Mexico all the way to Alaska, surviving in high-latitude regions where cold-blooded reptiles could not endure.

Comparing T. rex to Modern and Ancient Species

University of Maryland principal lecturer in the department of geology Thomas Holtz Jr., who was not involved in the research, noted that comparing the T. rex’s body temperature to contemporaneous cold-blooded crocodiles and clams from the same fossil sites gives high confidence in the accuracy of the new data. Holtz pointed out that while previous studies relied on bone and biomechanics, the isotope method provides direct chemical confirmation of endothermy.

Researchers plan to apply the same technique to other dinosaurs, such as Triceratops, Stegosaurus, and Brachiosaurus. Testing these groups will help paleontologists determine whether warm-bloodedness was universal among dinosaurs or if certain lineages maintained cooler metabolisms.

Frequently Asked Questions

Was T. rex definitely warm-blooded?

According to the Science Advances study, chemical analysis of tooth enamel confirms T. rex maintained an internal body temperature of about 97 degrees Fahrenheit, supporting decades of research indicating the dinosaur was warm-blooded.

How did scientists measure a dinosaur’s body temperature?

Researchers used isotope analysis on fossilized tooth enamel. By measuring the chemical bonds between carbon and oxygen isotopes formed at specific temperatures, scientists used the teeth as a prehistoric thermometer.

What does a warm-blooded T. rex mean for its behavior?

A higher internal temperature indicates a faster metabolism, allowing the predator to maintain high energy levels, hunt actively, and survive in cold environments like ancient Alaska.