Recent research involving fossilized teeth belonging to the Tyrannosaurus rex has yielded the most precise calculation to date regarding the body temperature of this dinosaur. Scientists discovered that the colossal carnivore probably kept a core temperature hovering around 97 degrees Fahrenheit, thereby reinforcing the data supporting its classification as an endothermic creature.
Fossil teeth offer a new clue about 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 new study published in Science Advances offers a different approach. Researchers analyzed chemical signatures preserved in the enamel of T. rex teeth and used them to estimate the temperature at which the enamel formed.
The result was approximately 97 degrees Fahrenheit, or 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.
Data gathered from fossils has steadily reinforced that view. A notable turning point occurred in 2022 with the unearthing of a T. rex footprint in Alaska, which effectively demonstrated that these animals were capable of thriving in fiercely frigid habitats.
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 suggests that T. rex was not simply a reptile that became warm when the surrounding environment warmed. It maintained a body temperature significantly higher than the conditions around it.
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 were able to use only a few milligrams of enamel because the analytical technique had been refined over more than a decade. Earlier versions of the method required substantially more fossil material. Reducing the amount needed by roughly 90% made it possible to study specimens without removing large or visually significant sections from important fossils.
The method centers on isotopes, which represent alternative variations of chemical elements. Both carbon and oxygen manifest in multiple isotopic states, and specific pairings of these isotopes can forge bonds within tooth enamel at speeds influenced by 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 choice of teeth was also important. Tooth enamel is among the most durable biological materials and can preserve chemical information exceptionally well over geological timescales. Although fossilization can alter biological remains, enamel is comparatively resistant to the changes that could erase the original temperature signal.
Aradhna Tripati, a climate scientist and UCLA geochemistry professor who served as a senior author for the research, underscored that the capacity to handle such tiny samples proved vital when analyzing a specimen as precious 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 warm-blooded animals, on the other hand, typically preserve fairly constant internal temperatures via metabolic reactions. Such a capacity demands substantial energy while simultaneously enabling these creatures to stay active throughout a broader spectrum of external conditions.
The new estimate places T. rex closer to the warm-bodied end of that spectrum.
That does not imply that the physiological makeup of the dinosaur was identical to that of a contemporary bird or mammal. Dinosaurs held a distinct evolutionary placement, meaning their metabolic rates cannot be directly equated with those of extant 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 commonly have body temperatures closer to the low-to-mid 80s Fahrenheit, although the exact figure varies according to species and environmental conditions.
The distinction is significant since core body temperature remains intimately linked to physical movement and caloric expenditure.
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 mean T. rex was a fast sprinter. Researchers emphasize that the temperature estimate should not be interpreted as proof that the dinosaur could run continuously at high speed.
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.
During the late Cretaceous epoch, Alaska was distinct from today’s polar landscape, yet it still endured extended stretches of darkness alongside freezing temperatures. Any major carnivore inhabiting that region would have confronted physiological hurdles that a heavily ectothermic creature could scarcely surmount.
A cozy indoor atmosphere would have altered those limitations.
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 analysis suggested that the dinosaur could have occupied a broad geographic area stretching from what is now Mexico 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 based at the University of Maryland who remained unconnected to the research, noted that an endothermic T. rex probably would have demanded a greater supply of food than a similarly proportioned cold-blooded creature.
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 help scientists examine their interactions with other large animals living in the same 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 finding could help resolve a much older dinosaur debate
The question of dinosaur metabolism is nearly as ancient as the scientific study of dinosaurs themselves.
In 1842, British anatomist Richard Owen coined the term Dinosauria while outlining the traits that set dinosaurs apart from alternative reptiles. Ever since, scholars have continually argued over whether dinosaurs ought to be understood mainly through the physiological lens of present-day reptiles or treated as creatures possessing significantly higher metabolic rates.
Over the following decades, evidence accumulated suggesting that at least some dinosaurs were endothermic or had metabolic systems capable of generating substantial 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 technique to animals such as Triceratops, Stegosaurus and Brachiosaurus could provide valuable comparisons. If those species also show relatively high body temperatures, it could suggest that warm-bodied physiology was widespread among dinosaurs.
If their temperatures were substantially different, the results could point to greater metabolic diversity than previously assumed.
This approach could likewise be applied outside the realm of 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 changes farther back in time could help scientists understand when and how the ability to regulate internal temperature became established.
A clearer picture of how T. rex lived
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 research illustrates how even minute pieces of fossilized remains can retain details concerning creatures that vanished 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 outcome points toward a creature that was capable of maintaining a high internal temperature and sustaining significant physiological activity.
That discovery introduces a fresh layer to the portrait of the renowned carnivore. Far from being merely a massive reptile suited for balmy climates, T. rex seems to have been equipped with a metabolic rate that granted it enhanced resilience against ambient thermal conditions.
Its ability to remain warm may have helped it occupy a vast portion of North America, from relatively warm southern regions to much colder northern landscapes.
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.
