For more than a century, scientists have tried to reconstruct the biology of Tyrannosaurus rex from bones, teeth, footprints, and other traces left behind more than 60 million years ago. Fossils discovered as far north as Alaska have suggested that T. rex could tolerate cold conditions, adding to evidence that the giant dinosaur was moving away from the cold-blooded physiology of many reptiles and toward the warm-blooded metabolism seen in birds. Now scientists have done something that once seemed impossible: they have effectively taken T. rex's temperature.
Researchers at UCLA developed a method for estimating body temperature from fossilized teeth and applied it to specimens held by the Natural History Museum of Los Angeles County. Their results indicate that T. rex maintained a body temperature of about 97 degrees Fahrenheit, remarkably close to that of humans. The finding supports the picture of T. rex as an active predator or scavenger with a relatively fast metabolism rather than a sluggish animal that depended heavily on basking in the sun.
Its ability to generate and regulate internal heat may also help explain how tyrannosaurs survived in colder regions that were inhospitable to many other reptiles. A Fossil Thermometer Refined Over a Decade UCLA researchers first developed their prehistoric thermometer method about a decade ago. The technique used skeletal material to investigate whether extinct animals were warm-blooded or cold-blooded.
Applying it to T. rex initially posed a major problem. The early version of the method required more fossil material than a museum would reasonably sacrifice from such an important and irreplaceable specimen. Over the following decade, however, the UCLA team dramatically improved the technique.
Researchers reduced the amount of material needed for testing ancient teeth by roughly 90%. That improvement persuaded L.A.'s Natural History Museum to provide tiny portions of two teeth belonging to Thomas the T. rex, the most complete of the towering tyrannosaur skeletons displayed in the museum's dinosaur hall. Although other lines of evidence have increasingly suggested that T. rex was warm-blooded, the study, published Sept. 16 in Science Advances, provides the first actual temperature measurement for the animal.
"No one's been able to make a temperature measurement like this before," UCLA geobiologist and study co-author Robert Eagle said. "We found T. rex was 36 Celsius (97 Fahrenheit), about the same as humans. The temperature is about what I would have guessed -- higher than a reptile or a slow mammal like a sloth, but lower than an avian." T. rex was still a scaly, egg-laying reptile, but its 36 C body temperature was much closer to that of a warm-blooded mammal than a modern reptile.
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