Full Breakdown
T. rex’s Body Temperature Measured Directly for the First Time
By Drooid · · How we work
Core Findings
On September 16, researchers published a study in *Science Advances* reporting that the body temperature of a Tyrannosaurus rex was 97.3 °F (36.3 °C), with a margin of error of ± 4.5 °F. The estimate comes from isotopic analysis of three teeth belonging to the specimen “Thomas” from the Natural History Museum of Los Angeles County. The temperature is comparable to modern humans and elephants, and higher than the 87.6 °F (30.9 °C) recorded for contemporaneous crocodile teeth from the same Hell Creek Formation.
Background & Context
For decades paleontologists have debated whether large theropods were ectothermic like modern reptiles or endothermic like birds and mammals. Indirect evidence—bone histology, growth rates, and earlier isotope work—has increasingly favored warm-bloodedness, but no direct temperature measurement existed. The new study builds on a decade-long refinement of a “clumped-isotope” thermometer that reads the temperature at which tooth enamel formed.
Methodology & Data
The team drilled away about five milligrams of enamel from each tooth, dissolved the powder in phosphoric acid, and measured the resulting carbon-dioxide gas with a mass spectrometer. The abundance of carbon-13–oxygen-18 bonds decreases with higher formation temperatures, allowing a temperature estimate. Applying the same technique to five crocodile teeth from the same strata confirmed that the method distinguishes a warm-blooded signal from ambient environmental temperatures. The resulting T. rex range of 33.8 °C to 38.8 °C overlaps large mammals and flightless birds such as ostriches.
Why It Matters
A thermoregulated T. rex implies a high metabolic rate, requiring more food but enabling sustained activity and migration across diverse climates. Climate-model reconstructions suggest the dinosaur could have inhabited a continent-spanning range from present-day Mexico to Alaska. The finding narrows the physiological gap between non-avian dinosaurs and their avian descendants, providing a concrete data point for models of dinosaurian evolution.
Official Statements & Responses
Museum curator Luis Chiappe noted that sacrificing tiny portions of two teeth was “definitely worth the trade-off” for the knowledge gained.
Conflicting Reports & Gaps
Some researchers, such as Robert Eagle, warned that higher metabolic rates entail higher food requirements, a factor that remains difficult to quantify for extinct ecosystems.
Verbatim Quotes
- “We can't just use a thermometer to do that,” — Jasmina Wiemann, Johns Hopkins University
- “That’s the basis of using the isotopes as a thermometer,” — Robert Eagle, UCLA
- “This was a warm-bodied organism, which really places new constraints on its behavior, its physiology, how it interacted with other species and how much food it needed, for example,” — Robert Eagle, UCLA