Level 1 — Absolute Beginner

Tyrannosaurus rex was a very big dinosaur. People call it T. rex. It lived millions of years ago and had huge teeth.

Scientists wanted to know one thing. Was the body of T. rex warm or cold? Nobody could measure it, because the animal died long ago.

Now scientists have an answer. They looked at three old T. rex teeth. Inside the hard part of a tooth, tiny pieces sit in different ways when the body is warm or cold.

The answer is about 36 degrees Celsius. That is almost the same as a human body. So T. rex was a warm animal, and it could move and hunt even when the weather was cold.

dinosaur

A very large animal that lived on Earth millions of years ago.

tooth

A hard white part in the mouth used for biting and eating.

warm

Having some heat, not cold.

body

The whole physical form of a person or an animal.

measure

To find out how big, how hot or how heavy something is.

scientist

A person who studies the natural world to learn how it works.

degree

A unit used to say how hot or cold something is.

hunt

To chase and catch animals for food.

Level 2 — Elementary

Scientists have taken the body temperature of a Tyrannosaurus rex for the first time. The study was published in the journal Science Advances in September 2026, and the answer is about 36 degrees Celsius, roughly the same as a human being.

The method is clever. The hard outer layer of a tooth is called enamel. Inside enamel, certain atoms join together in different patterns depending on how warm the animal's body was when the tooth formed. Those patterns stay locked in the fossil for millions of years.

To read them, researchers used a dental drill to take a small amount of fossilised enamel from three T. rex teeth. They dissolved the powder in phosphoric acid, which released carbon dioxide gas. A machine called a mass spectrometer then measured the exact mix of atoms in that gas.

For decades scientists have argued about whether large dinosaurs were warm-blooded like birds and mammals, or cold-blooded like modern reptiles. This result supports the warm-blooded side, and it suggests T. rex could keep an active life even in a cold climate.

journal

A regular publication where scientists share new research.

enamel

The hard outer layer that covers the surface of a tooth.

atom

One of the extremely small units that all matter is built from.

fossil

The preserved remains of an animal or plant from long ago.

dissolve

To mix a solid into a liquid until the solid disappears into it.

acid

A chemical that can break down other substances.

warm-blooded

Able to keep a steady body temperature regardless of the surroundings.

reptile

A cold-blooded animal with scales, such as a lizard or a crocodile.

Level 3 — Intermediate

For the first time, researchers have produced a direct estimate of the body temperature of Tyrannosaurus rex, and the figure is startlingly familiar: roughly 36 degrees Celsius, almost exactly human. The finding, published in Science Advances in September 2026, rests not on inference from bone growth rings or body size but on a chemical record preserved inside the animal's own teeth.

The technique exploits a subtle property of mineral chemistry. When enamel forms, certain heavy isotopes of carbon and oxygen bond to one another, and the frequency with which they do so depends on temperature. Cooler conditions favour more of these clumped bonds, warmer conditions fewer. Because the ratio is fixed at the moment of formation and is insensitive to the chemistry of the surrounding water, it functions as a thermometer that keeps reading long after the animal has died.

Recovering it is delicate work. The team drilled a small quantity of fossilised enamel from three T. rex teeth, dissolved the powder in phosphoric acid to liberate carbon dioxide, and passed the resulting gas through a mass spectrometer to count the isotopic combinations precisely. Enamel was chosen over bone deliberately, since it is dense, slow to exchange material with its environment and therefore far less prone to chemical alteration during fossilisation.

The result feeds into a long-running dispute about dinosaur physiology. Cold-blooded animals depend on external heat and slow down when the environment cools, while warm-blooded animals generate their own heat and pay for it with a much higher appetite. A temperature of 36 degrees implies the latter, which in turn implies an animal that could hunt through cool seasons and at high latitudes, and that needed to eat a great deal to do so.

estimate

A calculated judgement of a value that cannot be measured directly.

inference

A conclusion reached from evidence rather than from direct observation.

isotope

A version of a chemical element with a different number of neutrons.

ratio

The relationship between two quantities, expressed as a comparison.

liberate

To release something that was held or bound inside.

alteration

A change made to the original state or composition of something.

physiology

The study of how the bodies of living things function.

latitude

How far north or south of the equator a place lies.

Level 4 — Advanced

Palaeontology has argued about dinosaur metabolism for the better part of a century, largely because the central quantity, body temperature, seemed permanently out of reach. A study published in Science Advances in September 2026 closes part of that gap, reporting a direct thermal estimate for Tyrannosaurus rex of approximately 36 degrees Celsius. The number is unremarkable in itself and remarkable in its provenance: it was read not from morphology or analogy with living animals, but from the chemistry of the animal's own enamel.

The method is clumped isotope thermometry, and its appeal lies in what it does not require. Conventional stable isotope palaeothermometry must assume a composition for the ancient water an animal drank, an assumption that has quietly weakened many published results. Clumped isotope analysis instead counts how often rare heavy isotopes of carbon and oxygen bond to each other within the same carbonate group. That ordering is thermodynamically governed and temperature dependent, so the abundance of clumped bonds yields a temperature without reference to any external baseline.

Execution imposes its own constraints. The team drilled enamel from three T. rex teeth, dissolved the powder in phosphoric acid to evolve carbon dioxide, and quantified the isotopologues by mass spectrometry. Enamel is the correct substrate precisely because its low porosity and large crystallite size make it resistant to diagenetic resetting, the post-burial exchange that can silently overwrite a bone's original chemistry. A sample of three is small, and the authors present the figure as the first direct estimate rather than a settled constant.

The implication is physiological and ecological at once. Endothermy of the kind a 36 degree set point implies would have given T. rex a sustained aerobic capacity independent of ambient conditions, consistent with tyrannosaur remains recovered from high-latitude Cretaceous deposits where seasonal cold was significant. It also carries a bill. Maintaining such a temperature in a multi-tonne body demands a caloric intake far above that of an equivalently sized ectotherm, which constrains how much prey the surrounding ecosystem must have supported and, by extension, how abundant such predators could ever have been.

metabolism

The chemical processes by which an organism converts food into energy.

provenance

The origin of something and the record of where it came from.

morphology

The study of the form and structure of organisms.

thermodynamically

In a way governed by the physical laws relating heat, energy and order.

baseline

A reference value against which other measurements are compared.

diagenetic

Relating to the chemical and physical changes a buried remain undergoes over time.

endothermy

The ability of an animal to generate and regulate its own internal body heat.