DavidKeys.com

For more than a century, scientists have debated whether Tyrannosaurus rex was a cold-blooded reptile or a warm-blooded, highly active predator. Now, researchers have taken what may be the clearest look yet at the dinosaur’s internal temperature—and the result is surprisingly familiar.

A new study published in Science Advances indicates that Tyrannosaurus rex had an average body temperature of about 97.3 degrees Fahrenheit (36.3 degrees Celsius), remarkably close to the temperature of a modern human.

The finding provides direct evidence supporting the idea that T. rex was warm-blooded, or endothermic, rather than relying primarily on its surroundings to regulate its body temperature.

Scientists Finally Put a Number on T. Rex’s Temperature

Researchers have suspected for decades that T. rex had a relatively high metabolism. Fossil evidence, growth patterns, anatomy and the discovery of tyrannosaurs in northern regions have all contributed to the argument that these dinosaurs were more physiologically active than modern reptiles.

However, scientists had never been able to determine the dinosaur’s actual body temperature with this level of precision.

That changed when researchers developed a way to use fossilized dinosaur teeth as a prehistoric thermometer.

The team analyzed the chemical composition of enamel from several T. rex teeth. The technique examines the way certain carbon and oxygen isotopes are bonded together in the mineral structure of the enamel. Because those chemical relationships are influenced by temperature when the enamel forms, they can preserve a record of the animal’s internal temperature.

The researchers examined teeth from T. rex specimens, including teeth from “Thomas,” a remarkably complete T. rex skeleton housed at the Natural History Museum of Los Angeles County.

The resulting estimate was approximately 36.3°C (97.3°F).

What Does “Warm-Blooded” Mean?

The terms “warm-blooded” and “cold-blooded” are commonly used, but scientists more precisely refer to endothermy and ectothermy.

Warm-blooded animals, such as humans and birds, generate much of their body heat internally through metabolism. They can maintain relatively stable internal temperatures even when the surrounding environment changes.

Cold-blooded, or ectothermic, animals depend much more heavily on environmental heat. Modern crocodiles, for example, can experience substantial changes in body temperature depending on their surroundings.

The new T. rex measurement is considerably warmer than typical temperatures measured in modern reptiles and falls within the range associated with large warm-blooded animals. UCLA researchers noted that modern reptiles generally operate around 28–30°C (82–86°F), while many birds have considerably higher body temperatures.

This places T. rex in an interesting position: its body temperature was similar to humans and large mammals, although still below that of many modern birds.

A More Active T. Rex

The findings have important implications for how scientists understand the famous predator.

A warm-blooded metabolism requires considerable energy. Maintaining a relatively high and stable body temperature means an animal needs a steady supply of fuel.

For T. rex, that likely meant consuming substantial amounts of food to support its metabolism.

The research therefore supports a picture of T. rex as an active predator or scavenger, rather than a sluggish reptile that spent much of its time basking in the sun to warm itself.

Warm-blooded physiology could also have helped T. rex remain active when temperatures dropped.

How Could T. Rex Live in Cold Regions?

One of the most intriguing aspects of the discovery involves the geographic range of T. rex.

Tyrannosaurus fossils have been found across western North America, including evidence from areas as far north as Alaska. That has long raised questions about how these enormous animals could survive in environments that experienced much colder conditions than the tropical or subtropical environments often associated with dinosaurs.

A warm-blooded metabolism provides part of the explanation.

Because T. rex could generate substantial body heat internally, it would have been less dependent on warm environmental temperatures. Researchers say the findings help explain how the species could inhabit a broad range extending from areas corresponding to modern Mexico to Alaska during the Late Cretaceous.

This does not mean Alaska was necessarily a comfortable environment. Instead, the ability to maintain its internal temperature would have given T. rex an advantage in climates where a strongly ectothermic animal might have struggled.

This Isn’t the First Evidence of Warm-Blooded Dinosaurs

The latest research is significant because it provides an actual temperature measurement, but the idea that dinosaurs could regulate their body temperatures isn’t new.

Scientists have been finding evidence of elevated dinosaur metabolism for decades.

A 1994 study examining oxygen isotopes in T. rex bone suggested that the species maintained relatively stable body temperatures, with less than 4°C of variation in the measurements analyzed. The researchers argued that this homeothermy was consistent with a relatively high metabolic rate.

Other research has also found evidence that dinosaurs had metabolic characteristics more similar to mammals and birds than to modern reptiles.

The new study builds on that history by providing a specific estimate for T. rex.

Why the Teeth Were So Important

Studying dinosaur physiology is difficult because the animals disappeared approximately 66 million years ago.

Scientists obviously cannot directly measure the temperature of a living T. rex.

Fossil bones can provide clues, but the amount of material traditionally required for some chemical analyses can be substantial. Museums are understandably reluctant to sacrifice large pieces of rare fossils.

The UCLA research team spent years refining its technique. According to UCLA, the new approach reduced the amount of fossil material required for dental analysis by roughly 90%, making it possible to study precious dinosaur specimens while removing only very small portions of their teeth.

That development could be important well beyond T. rex.

A New Tool for Studying Dinosaurs

Researchers now have an opportunity to apply the same approach to other dinosaur species.

That could help scientists determine whether warm-blooded metabolism was widespread among dinosaurs or whether different groups evolved different strategies for regulating body temperature.

It could also help answer questions about dinosaur evolution.

Birds are the living descendants of dinosaurs, and modern birds are highly endothermic. Understanding when and how different dinosaur groups developed increasingly sophisticated methods of regulating body temperature could provide another piece of the evolutionary puzzle connecting ancient dinosaurs with today’s birds.

What This Tells Us About the “King of the Dinosaurs”

The new research adds another dimension to our understanding of T. rex.

It wasn’t simply a gigantic animal with enormous jaws and powerful legs. Its body appears to have been equipped with a metabolic system capable of maintaining an internal temperature remarkably close to that of humans.

At approximately 97.3°F, T. rex was substantially warmer than typical modern reptiles and considerably closer to mammals in terms of body temperature.

That physiology may have helped the dinosaur remain active, hunt or scavenge for food and occupy environments across a huge portion of Late Cretaceous North America.

The T. Rex May Have Been More Like Us Than We Thought

For generations, the image of T. rex was shaped by the idea of a giant reptile—perhaps powerful, but dependent on external heat to get moving.

The emerging scientific picture is very different.

The latest evidence indicates that Tyrannosaurus rex maintained a body temperature of roughly 97°F, making it one of the most remarkable examples of dinosaur physiology ever measured.

That doesn’t make T. rex a mammal. It remained a dinosaur, an egg-laying animal covered in scales and closely related to the evolutionary lineage that eventually produced birds.

But its internal temperature suggests that the “King of the Dinosaurs” was also a highly regulated, metabolically active animal.

And that could change how scientists think about where T. rex lived, how it behaved and how it survived in the changing environments of prehistoric North America.

Key Takeaways

• Tyrannosaurus rex had an estimated body temperature of about 97.3°F (36.3°C).
• The temperature is remarkably close to that of modern humans.
• Chemical analysis of fossilized T. rex teeth provided the measurement.
• The findings support the conclusion that T. rex was warm-blooded or endothermic.
• Warm-blooded physiology could have helped T. rex remain active in cooler environments.
• The research may provide a new method for determining the body temperatures of other extinct dinosaurs.
• The discovery adds to decades of evidence that many dinosaurs were much more metabolically active than modern reptiles.