T. Rex Was Warm-Blooded: Fossil Tooth Reveals Human-Like Body Temperature

New research published in Science Advances has provided the first direct estimate of the body temperature of a Tyrannosaurus rex, establishing that the predator maintained an internal temperature of about 36 °C. Led by University of California, Los Angeles (UCLA) scientists using isotopic analysis of fossilized tooth enamel, the findings offer physiological data on how the extinct dinosaur regulated its core warmth between 69 million and 66 million years ago.

Decoding the Prehistoric Thermal Engine

For nearly six decades, scientists have suspected that the Tyrannosaurus rex was warm-blooded. The discovery of a fossilized T. rex footprint in Alaska back in 2022 added momentum to theories that these predators could prosper in freezing environments where the majority of cold-blooded reptiles could not. However, hard thermal metrics remained absent until UCLA researchers successfully applied a specialized chemical technique to dental fragments.

The team analyzed tiny portions of teeth sourced from “Thomas”—a T. rex specimen housed at the Natural History Museum of County Los Angeles that is complete in approximately 70 %. According to UCLA geobiologist and co-author Robert Eagle, the resulting 36 °C reading provides the most direct and least complicated constraint established so far regarding the actual internal temperature of a T. rex.

Inside the Isotopic Tooth Thermometer

Measuring the thermal history of a 66-million-year-old animal required refining analytical methods over more than a decade. The research team successfully reduced the required fossil material mass by approximately 90 %, enabling the museum to release microscopic samples from two teeth kept off-exhibit. Aradhna Tripati, a UCLA climate scientist, professor of geochemistry, and lead author of the study, noted that despite the fame of the animal, direct data on its underlying biology was historically missing.

“The chemistry of the enamel registered the temperature at which it formed and, 66 million years later, we can read it,” Tripati explained via email, emphasizing that previous metabolic assessments relied primarily on skeletal structures and biomechanical inferences.

The technique relies on examining isotopes—specifically, how carbon and oxygen atoms form chemical bonds within dental enamel. Lower temperatures produce more bonds, allowing scientists to calculate the formation environment.

Evolutionary Placement Between Reptiles and Birds

While dinosaurs are classified as reptiles, they share an evolutionary link with modern birds. The newly established 36 °C mark places the T. rex between the two groups. It was hotter than reptiles, yet cooler than modern birds.

Photo: es-us.noticias.yahoo.com

This thermal profile gives researchers new constraints for modeling the creature’s daily existence. Being a warm-bodied organism influenced its behavior, physiology, how it interacted with other species, and its food requirements. The method itself has been used in a few ancient species, including woolly mammoths, megalodons, and other dinosaurs, gradually building a clearer picture of thermoregulation across ancient climates.