T. rex was closer to a bird than a crocodile in body temperature? New fossil tooth study reveals how the dinosaur survived Arctic winters and hunted across North America

Scientists have been trying for years to determine whether Tyrannosaurus rex had a physiology akin to that of cold-blooded creatures such as today’s crocodile or had the ability to regulate its own body heat, much like a bird or mammal.

Fossil evidence found in the northern areas, such as Alaska, hinted that the massive dinosaur could live in places where today's reptiles would find it hard to exist.

Now there is more accurate evidence to determine this question.


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The researchers calculated the average body temperature of the pre-historic creature at around 97.3 degrees Fahrenheit or 36.3 degrees Celsius. It means that the dinosaur had a higher body temperature compared to crocodiles and other reptiles.

Scientists arrived at their conclusion by analyzing the chemical signatures in the dinosaur’s tooth enamel. This research was published in Science Advances.

How T. rex survived in northern climates

The temperature measurement also allows scientists to understand why the fossils of T. Rex are found throughout a vast territory of North America.

At that time in late Cretaceous, North America was warmer than today. However, in the north, there were seasonal colds and some areas of ancient Alaska had periods of limited light.

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Having a warm body temperature would allow the animal to rely less on sunshine and function at lower temperatures. It might have helped the tyrannosaurs survive in northern areas where many cold-blooded reptiles could not live.

However, the results obtained cannot be used to describe every dinosaur automatically since scientists increasingly believe that dinosaurs use various metabolic methods.

Now, researchers want to examine other types of dinosaurs such as Triceratops, Stegosaurus, and long necked sauropods.

For the time being, T. Rex appears to be a warm-blooded predator whose temperature is similar to human ones.

What a warm-bodied T. rex could do

Such a body temperature level would affect all aspects of T. rex biology, including the ability to hunt and move as well as feeding requirements.

Generally, warm-blooded animals require more energy than cold-blooded species. More energy makes an organism more active but also increases the need for food.

Thus, for T. rex, maintaining such an elevated temperature level would imply constant feeding or hunting for big preys. For instance, compared to a cold-blooded predator of similar size, the dino would be able to remain active longer.

The research does not confirm how fast T. rex was able to run. Warm blood does not mean the dino was a fast runner. Nevertheless, warm blood helped it maintain energetic efficiency even without heating up from the outside.

Such an effect is called gigantothermy, and it probably existed along with quite active metabolism of T. rex.

In general, all the above features made the dino a formidable hunter that could operate under a variety of conditions.

A dinosaur with a human-like body temperature

The calculated temperature would put the Tyrannosaurus rex somewhere between today's reptiles and birds.

"Poikilotherms" or "ectotherms," as cold-blooded animals are called, need plenty of external warmth. Snakes, crocodiles, and many lizards become more active with increasing external warmth and tend to be inactive during low temperatures.

"Endotherms" or "warm-blooded animals" make their own body heat metabolically. Mammals and birds are examples of such animals, though there are differences between them. For instance, some mammals' body temperatures are close to 90 F, while many birds can function with temperatures over 104 F or 40 C.

Tyrannosaurus rex seems to be warmer than most crocodiles, but colder than many of today's birds at the 36 C point.

However, the research does not imply that the animal was a bird; it was actually a big egg-laying dinosaur. Nonetheless, birds came out of theropod dinosaurs, which include tyrannosaurs. Its body temperature gives another clue about the evolution of metabolic system of some dinosaurs into that of today's birds.

This discovery refutes the perception of T. rex as a slow reptile, which requires sun warmth for activity.

Fossil teeth revealed the dinosaur’s temperature

They analyzed small samples from T. Rex teeth. Two were from the skeleton referred to as Thomas that was stored at the Natural History Museum of Los Angeles County. They required just milligrams of enamel for their work.

The technique involves the use of rare types of carbon and oxygen molecules called isotopes that bond with each other in specific proportions depending on the temperature at which they form.

The specific bond forms more frequently under low temperatures than in high temperatures. Scientists analyze these bonds to determine the temperature of enamel formation.

Clumped isotope analysis, as the technique is called, works like taking temperature of the tooth.

The tooth enamel is good material for analysis since it is highly resistant. In contrast to the bones, which can be remodeled during an organism’s lifetime and even after death, tooth enamel can store chemical information for millions of years.

For over ten years the team had been developing the technique.

Scientists have also analyzed the teeth of fossil crocodilians that existed in the same geological formation in Montana. The results showed that their average body temperature was about 87.6 F (30.9 C).

Frequently asked questions

1. What was the body temperature of T. rex?

The body temperature of T. rex was calculated to be about 97.3 F, which equals 36.3 C.

2. How was its temperature determined?

Scientists measured the carbon and oxygen isotopic bonds in the tooth enamel of the fossils of T. rex. They form in a different way at different temperatures.

3. Was T. rex hotter than a crocodile?

Yes. Crocodilians’ teeth from the same location revealed a temperature of about 87.6 F, while the temperature of T. rex was approximately 97.3 F.

4. Does this mean all dinosaurs were warm-blooded?

No. This research proves only the case of T. rex. Other dinosaur species might have a completely different metabolism system and must be tested separately.