Fossil teeth analysis strengthens case for warm-blooded T. rex dinosaur

A new analysis of fossilized Tyrannosaurus rex teeth has provided the clearest estimate yet of the dinosaur’s body temperature. Researchers found that the giant predator likely maintained an internal temperature of about 97 degrees Fahrenheit, strengthening evidence that it was a warm-blooded animal.

Ancient dental remains provide fresh insights into T. rex physiology

For decades, paleontologists have debated whether Tyrannosaurus rex should be considered a warm-blooded dinosaur capable of regulating its internal temperature or an animal whose body temperature was largely determined by its surroundings.

That question has been difficult to answer because body temperature does not survive directly in a fossil. Scientists have instead relied on indirect evidence, including growth patterns in bones, anatomy, activity levels and the environments in which dinosaurs lived.

A fresh study published in Science Advances proposes a distinct methodology. Investigators examined chemical markers retained within the enamel of T. rex teeth to approximate the thermal conditions under which that enamel originally crystallized.

The outcome reached roughly 97 degrees Fahrenheit, which translates to 36 degrees Celsius.

That figure places T. rex within the general range of many modern warm-blooded animals and considerably above the typical body temperatures associated with modern cold-blooded reptiles. The measurement does not by itself answer every question about dinosaur metabolism, but researchers say it provides an important physical constraint on how the animal functioned.

Robert Eagle, a geobiologist, associate professor at the University of California, Los Angeles, and coauthor of the research, characterized this measurement as one of the most direct evaluations scientists have managed to secure regarding the body temperature of a T. rex.

The discovery holds immense weight since the controversy surrounding dinosaur metabolism has persisted for decades. For close to 60 years, researchers have theorized that tyrannosaurs and various other dinosaurs might have been equipped to produce and sustain significant levels of internal warmth.

Evidence from the fossil record has gradually strengthened that interpretation. The discovery of a T. rex footprint in Alaska in 2022 was particularly relevant because it showed that the species could occupy environments that experienced very cold conditions.

The new temperature estimate adds another piece to that picture. Rather than relying solely on the animal’s anatomy or the environment in which its fossils were found, researchers can now examine a chemical record preserved directly inside its teeth.

That evidence indicates that T. rex was not merely a cold-blooded reptile whose temperature rose alongside the ambient surroundings. Instead, it sustained a thermal baseline considerably above its external environment.

How researchers converted T. rex teeth into an ancient thermometer

The research relied upon a comparatively limited quantity of fossil specimens, a crucial factor whenever paleontologists analyze one of the most precious and iconic dinosaurs ever unearthed.

The team examined two tiny sections taken from teeth belonging to a specimen known as Thomas the T. rex. The skeleton is approximately 70% complete and is housed at the Natural History Museum of Los Angeles County.

Researchers managed to work with just a few milligrams of enamel since the analytical technique had undergone refinement across more than ten years. Previous iterations of the process demanded significantly greater quantities of fossil material. Slashing the required volume by about 90% enabled experts to examine specimens safely, bypassing the need to extract large or aesthetically disruptive portions from valuable fossils.

The approach focuses on isotopes, which are different forms of chemical elements. Carbon and oxygen occur in several isotopic forms, and certain combinations of these isotopes can form bonds in tooth enamel at rates that depend on temperature.

In simple terms, the chemical structure of the enamel retains information about the conditions that existed when it formed.

The researchers measured these isotope bonds in tiny samples from the T. rex teeth. By examining their abundance and arrangement, they were able to calculate the temperature associated with enamel formation.

That made the teeth function much like a geological thermometer.

The selection of teeth mattered as well. Enamel ranks among the toughest biological substances, capable of preserving chemical data remarkably well across geological epochs. Even though fossilization alters biological specimens, enamel remains relatively resilient against shifts that might otherwise wipe out the original temperature signature.

Aradhna Tripati, a climate scientist and UCLA professor of geochemistry who was a senior author of the study, emphasized that the ability to work with such small samples was essential for studying a specimen as valuable as T. rex.

For decades, researchers had estimates about dinosaur metabolism based on bones and biomechanics, but they lacked a direct measurement of body temperature. The chemical composition of the enamel provided an opportunity to approach that question from another direction.

This technique has already been utilized for other vanished species, such as dinosaurs, woolly mammoths, and the colossal prehistoric shark megalodon. Every single application provides researchers with an alternative approach to reconstruct the ways ancient organisms adapted to the environmental conditions of their respective eras.

A temperature between reptiles and birds

At around 36 degrees Celsius, the estimated temperature of T. rex is considerably warmer than that of many modern reptiles but does not reach the upper range observed in some birds.

Modern reptiles are generally described as ectothermic, meaning they depend heavily on external sources of heat to regulate their body temperature. A crocodile, for example, can become warmer by moving into the sun and cooler by seeking shade or entering water.

Birds and mammals, by contrast, generally maintain relatively stable internal temperatures through metabolic processes. This ability requires considerable energy but also allows them to remain active across a wider range of environmental conditions.

The recent calculation positions T. rex closer to the end-member of that range characterized by warm-blooded physiology.

That does not mean the dinosaur’s physiology was identical to that of a modern mammal or bird. Dinosaurs occupied a different evolutionary position, and their metabolism cannot simply be equated with that of living species.

Nevertheless, the temperature provides useful information about how much energy T. rex may have been able to produce and sustain.

Robert Eagle noted that some modern mammals, including sloths and anteaters, can have body temperatures in the low 90s Fahrenheit, while some birds can exceed 104 degrees Fahrenheit, or 40 degrees Celsius.

Modern cold-blooded reptiles generally maintain internal temperatures hovering around the low-to-mid 80s Fahrenheit, though the precise reading fluctuates depending on the species and ambient surroundings.

The difference matters because body temperature is closely connected to activity and energy use.

An animal capable of maintaining a high internal temperature can potentially sustain physiological activity for longer periods than an ectothermic animal whose performance is strongly dependent on its surroundings.

That does not necessarily imply that T. rex functioned as a rapid sprinter. Experts stress that this thermal calculation ought not to be misconstrued as definitive evidence confirming the dinosaur possessed the capacity for sustained high-speed locomotion.

Instead, a warm-bodied metabolism could have supported prolonged activity and helped the animal remain physiologically active under conditions that would have been more challenging for an ectothermic predator.

The distinction is important. Crocodiles, for example, can move rapidly for short bursts but cannot maintain intense activity indefinitely. A warm-bodied T. rex may have had greater capacity for sustained physical performance.

The Arctic may have been within T. rex’s range

One of the most interesting implications of the temperature estimate concerns where T. rex could have lived.

The unearthing of tyrannosaur tracks and bones in far northern regions has previously proven that these creatures could thrive in habitats vastly distinct from the tropical settings commonly linked to prehistoric reptiles.

Alaska during the late Cretaceous was not identical to the Arctic environment of today, but it still experienced long periods of darkness and cold conditions. A large predator living there would have faced physiological challenges that would be difficult for a strongly ectothermic animal to overcome.

A warm internal temperature would have changed those constraints.

Employing paleoclimatic simulations, the scientific team reconstructed temperatures throughout North America roughly 66 million years ago, close to the close of the Cretaceous Period. Subsequently, those ecological parameters were contrasted against the calculated internal temperature of T. rex.

Their findings indicated that this dinosaur might have inhabited a vast regional expanse reaching from present-day Mexico all the way to Alaska.

That possibility changes the way scientists can think about the animal’s ecology.

A predator that relied heavily on sunlight to warm its body would have been more restricted by climate and season. A warm-bodied T. rex, however, could have remained active even when environmental temperatures dropped significantly.

Tripati described the distinction as an important one. If T. rex maintained a body temperature substantially higher than its surroundings, it would have been capable of living in places that would be less accessible to an animal dependent primarily on external heat.

The Alaskan evidence therefore fits with the chemical data rather than standing alone.

Together, the results back the concept that tyrannosaurs possessed the physiological capacity to operate across numerous continental habitats.

A warmer body also meant higher energy demands

Sustaining an elevated core temperature entails a price.

Warm-blooded creatures typically require a continuous energy supply to keep their metabolism running. Consequently, T. rex must have secured ample nourishment, not merely to power its locomotion, development, and breeding, but also to maintain its core body temperature.

Thomas Holtz Jr., a vertebrate paleontologist at the University of Maryland who was not involved in the study, pointed out that a warm-bodied T. rex would likely have required more food than a comparably sized ectothermic animal.

That has implications for the dinosaur’s role within its ecosystem.

T. rex was already an enormous predator, with a powerful skull and teeth capable of processing large prey. A high metabolic demand would have added another factor to its ecological requirements.

Researchers can use this information to develop better models of how much food tyrannosaurs needed and how frequently they may have hunted or fed.

It could also assist researchers in evaluating how they interact with other massive wildlife inhabiting identical ecosystems.

The question extends beyond individual behavior. Metabolism affects growth rates, reproduction, movement, activity patterns and the amount of energy an animal needs to survive.

Consequently, determining the approximate body temperature of T. rex provides a foundation for investigating many other aspects of its biology.

The measurement does not establish precisely how fast the dinosaur grew, how frequently it hunted or how much food it consumed. Those questions require additional evidence. But having an estimated body temperature gives researchers a parameter that can be incorporated into future models.

The discovery might help settle an even older dinosaur controversy

The question of dinosaur metabolism is nearly as ancient as the scientific study of dinosaurs themselves.

In 1842, British anatomist Richard Owen introduced the term Dinosauria and discussed characteristics that distinguished dinosaurs from other reptiles. Since then, researchers have repeatedly debated whether dinosaurs should be viewed primarily through the physiological framework of modern reptiles or as animals with much more active metabolisms.

Over the following decades, accumulated evidence suggested that at least a portion of dinosaurs were endothermic or possessed metabolic systems capable of producing significant internal heat.

Bone microstructure, growth patterns, posture, activity levels and discoveries from high-latitude environments have all contributed to that discussion.

The new chemical technique does not replace those lines of evidence. Instead, it provides another independent method for examining the question.

Holtz said the comparison between T. rex and animals such as crocodiles and mollusks from similar periods and locations gives researchers additional confidence that the high temperature measured in the tyrannosaur represents a genuine biological signal rather than simply reflecting the surrounding environment.

The next step will be to determine whether similar temperatures were characteristic of other dinosaurs.

Not every dinosaur occupied the same ecological niche, and there has been considerable debate about whether different dinosaur groups had different metabolic strategies.

Applying the method to creatures like Triceratops, Stegosaurus and Brachiosaurus might yield insightful comparisons. Should these animals similarly exhibit comparatively elevated core temperatures, researchers could infer that endothermic traits were prevalent across the dinosaur lineage.

If their temperatures were substantially different, the results could point to greater metabolic diversity than previously assumed.

The method could also be used beyond dinosaurs.

Researchers are interested in applying it to ancient relatives of mammals, particularly species living during periods when the evolutionary transition toward modern warm-blooded physiology was taking place.

Tracing those modifications further back in time might help researchers comprehend when and how the capacity to regulate internal temperature originated.

A better understanding of the lifestyle of T. rex

The estimated 97-degree-Fahrenheit body temperature does not answer every question about Tyrannosaurus rex, but it provides a significant new piece of information about the animal’s physiology.

The chemical evidence from its teeth supports decades of research suggesting that tyrannosaurs were more metabolically active than modern cold-blooded reptiles. It also helps explain how such a large predator could inhabit environments that included relatively cold regions of ancient North America.

More broadly, the study demonstrates how even tiny fragments of fossil material can preserve information about animals that disappeared tens of millions of years ago.

The enamel of a T. rex tooth may look like an ordinary piece of fossilized tissue, but its microscopic chemistry contains clues about the conditions under which it formed. By developing techniques sensitive enough to read those signals without requiring large portions of a specimen, researchers can investigate questions that were once considered nearly impossible to answer.

For T. rex, the result points toward an animal that was capable of maintaining a high internal temperature and sustaining significant physiological activity.

That finding adds another dimension to the image of the famous predator. Rather than simply being a giant reptile adapted to warm environments, T. rex appears to have possessed a metabolism that gave it greater independence from external temperatures.

Its capacity for maintaining warmth may have allowed it to inhabit a massive expanse of North America, stretching from comparatively mild southern territories to significantly chillier northern environments.

Future measurements from other dinosaurs will determine how widespread that physiology was. For now, however, the chemistry locked inside two small pieces of T. rex tooth enamel has provided scientists with one of the most direct estimates yet of the animal’s internal temperature, offering a new window into how the predator lived roughly 66 to 69 million years ago.