Using chemical clues in Tyrannosaurus rex teeth, scientists have shown that this massive predator was warm-blooded - with a body temperature close to that of a person - in a finding they said should prompt a fundamental change in the perception of the celebrity dinosaur.
The chemical makeup of the enamel in three T. rex teeth unearthed in Montana indicated that the dinosaur had a body temperature of 97.3 degrees Fahrenheit (36.3 degrees Celsius), plus or minus 4.5 F (2.5 C), the researchers found. For humans, the average body temperature is 98.6 F (37 C).
More apt comparisons may be the average body temperature of the elephant, the most massive extant land animal, of around 97 F (36 C), and the ostrich, the largest extant bird, at roughly 102 F (39 C). Tyrannosaurus was among the most massive meat-eating dinosaurs.
The new study's evidence that Tyrannosaurus was warm-blooded rebuts the obsolete notion of a sluggish brute.
"It stops being a reptile in the way people picture reptiles. An animal at 36 degrees Celsius is not waiting for the sun to warm up. It is thermally independent of its surroundings, and in that respect closer to an elephant or an ostrich than to a crocodile," said UCLA geoscientist Aradhna Tripati, senior author of the research published on Wednesday in the journal Science Advances.
Tyrannosaurus roamed western North America during the Cretaceous Period about 66 million years ago at the end of the age of dinosaurs. Its fossils are known from as far north as the Canadian provinces of Alberta and Saskatchewan, then south through the U.S. states of Montana, Wyoming and the Dakotas, and into New Mexico and Texas.
Tripati said climate modeling indicates Tyrannosaurus would have been able to inhabit most of the continent, "including cold environments where it would have experienced freezing. That is a far more mobile and adaptable animal than the one people picture."
'Significantly more food'
Warm-bloodedness, also called endothermy, involves the ability of an animal to generate and conserve internal metabolic heat. This provides certain physiological advantages such as sustained energy and stamina, as well as the ability to thrive in warm and cold climes. Cold-bloodedness, or ectothermy, makes animals dependent upon external heat sources to warm up their bodies, like crocs and snakes.
"Endothermy is common in large animals and even some fish. It comes at a cost, though," UCLA geobiologist and study co-author Robert Eagle said.
"Higher metabolic rates mean higher food requirements and potentially more active hunting to acquire it. An endothermic T. rex would have had to acquire significantly more food to sustain its higher metabolic rate, but would also be capable of more sustained activity to find food and migrate, and live in colder environments," Eagle said.
Birds and mammals are endotherms. All meat-eating dinosaurs are part of a lineage called theropods. Birds are part of this lineage, having evolved from small feathered dinosaurs. Small flying birds today have a body temperature around 107 F (42 C).
"Our temperature for T. rex sits at the low end of the endotherm range," Tripati said.
Teeth were the key to the study.
"Tooth enamel forms inside the animal at body temperature, so the enamel chemistry is a thermometer," Tripati said.
The ratio of certain forms, or isotopes, of carbon and oxygen present in the enamel can reveal body temperature, through a method called "clumped isotopes."
The researchers used a minimally destructive technique using a low-speed rotary drill with a tungsten carbide bit to take about 5 milligrams of enamel powder, less than a pinch of salt, from each tooth.
The Natural History Museum of Los Angeles County provided the teeth, two from a well-preserved young adult specimen nicknamed Thomas and the other an isolated partial tooth from a second Tyrannosaurus, both from the same locale in Montana's Carter County.
The researchers also applied the technique to five similarly old crocodilian teeth from the same rock formation, finding average body temperatures of 87.6 F (30.9 C), in line with modern crocs and lower than in Tyrannosaurus.
"It's thought that many dinosaurs, but not necessarily all, were warm-blooded," Eagle said. "However even amongst warm-blooded organisms, there are questions of the degree. They can be warm-blooded like sloths or anteaters, with low-level endothermy; modern large mammals; or avian (bird) endotherms, which typically have higher metabolic rates than mammals."
"On other dinosaurs, I would be cautious about generalizing," Tripati said, regarding endothermy. "This is one species, and the evidence across dinosaurs points to a range of strategies rather than a single answer." – Reuters
