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A 2026 study in Science Advances estimates that Tyrannosaurus rex maintained a body temperature of about 36.3 °C (97.3 °F), close to the human average. The estimate comes from chemical signatures preserved in fossil tooth enamel, not from a thermometer placed on a living animal, and it rests on a small sample of three teeth. Those limits matter, but the result is a clear, measurable signal that T. rex was warm-blooded in a way that set it apart from the crocodilian reptiles that lived alongside it.
What the study measured
The team, led by Randy Flores with co-author Robert Eagle and senior author Aradhna Tripati at UCLA, analyzed three T. rex teeth from the Late Cretaceous Hell Creek Formation in Montana. They averaged the results to an estimated body temperature of 36.3 ± 2.5 °C. The “± 2.5” is a standard error (1 SE), a measure of how precisely the average is pinned down given the small number of teeth.
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To check whether the result reflected the rocks rather than the animal, the authors also measured five crocodilian teeth from the same formation. Those teeth averaged 30.9 ± 2.6 °C (1 SE), and the paper reports that the T. rex and crocodilian estimates differ significantly. Because both groups were buried in the same setting, a shared geological alteration would be expected to affect both, which makes the gap between them more informative than either number alone.
The two estimates side by side
| Group | Teeth analyzed | Source setting | Mean estimated temperature | Uncertainty (1 SE) |
|---|---|---|---|---|
| Tyrannosaurus rex | 3 | Hell Creek Formation, Montana (Late Cretaceous) | 36.3 °C | ± 2.5 °C |
| Crocodilians | 5 | Same formation | 30.9 °C | ± 2.6 °C |
Both values are isotope-derived temperature estimates from the same type of tissue and the same method, so they are directly comparable. What they are not is a measurement of living body temperature taken under the same conditions as a modern animal’s.
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How clumped-isotope thermometry works in a tooth
The method relies on rare, heavy forms of carbon and oxygen in the mineral carbonate of enamel. These heavy isotopes tend to bond with one another (“clump”) more often at lower temperatures, so the abundance of clumped bonds records the temperature at which the enamel formed. The researchers used enamel because its crystal structure resists chemical change better than many other skeletal materials, which helps preserve the original signal over tens of millions of years.
The procedure, as UCLA describes it, runs in four stages:
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- A dental drill removes a small amount of enamel powder from the tooth.
- The powder is dissolved in phosphoric acid, which releases carbon dioxide gas.
- A mass spectrometer measures the ratios of the rare isotopes in that gas.
- The clumped-isotope abundance is converted into a formation temperature using the calibrated relationship the authors describe in the paper.
A practical advance here is sample size. UCLA reports that the team refined the method so it works with a few milligrams of enamel. That allowed destructive sampling of museum-held teeth without requiring large pieces of the fossil.
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What the sample can and cannot support
Three teeth are a narrow base. Two of them were associated with the museum specimen LACM 150167, nicknamed “Thomas,” and the third was a partial isolated tooth. The estimate therefore describes these individuals, not every T. rex across its life span, sex, or range, and it says nothing direct about other dinosaur species.
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The AP report, which quoted outside paleobiologist Jasmina Wiemann of Johns Hopkins University, makes the same point from another angle: “We can’t just use a thermometer to do that.” The method has to be applied to more specimens, and to other dinosaurs, before broader claims can be tested.
The authors also combined the temperature estimate with paleoclimate proxies and climate model simulations to infer where T. rex could plausibly have lived across the North American paleocontinent, including colder and higher latitudes. That is a modeled implication built on the temperature result, not a fossil record of the animal’s actual range.
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Warm-blooded, and how warm compared with humans
An estimated body temperature of about 36 °C sits above the Hell Creek crocodilian values and well above what a cold-blooded reptile would be expected to maintain relative to its surroundings. The authors describe the figure as comparable to modern endotherms, meaning animals that generate and regulate their own heat.
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The human comparison is useful for scale, but it should be read loosely. The T. rex value is an inference from enamel chemistry, while human temperatures are direct clinical measurements from living people. The two numbers are close, but they do not come from identical measurement methods or reference populations.
Key takeaways
- Three T. rex teeth from Hell Creek yielded a mean estimated body temperature of 36.3 ± 2.5 °C (1 SE), according to the 2026 Science Advances paper.
- Five crocodilian teeth from the same formation averaged 30.9 ± 2.6 °C (1 SE), and the difference between the groups is reported as significant.
- The result supports warm-blooded physiology in T. rex. It does not, on its own, settle every question about dinosaur metabolism or show that all dinosaurs were warm-blooded in the same way.
- The range implications come from climate modeling layered on the temperature estimate, not from direct observation of the animal’s full geographic distribution.
Sources for these findings are the study authors’ paper in Science Advances (2026), the UCLA press account of the work, and the Associated Press report that included Wiemann’s comments.
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