CORVALLIS, Ore. - The long, sometimes heated debate about whether dinosaurs were warm or cold-blooded may be about over, a new study suggests.
The verdict: they were cold-blooded, just like most scientists believed all along and modern reptiles are today.
And with apology to a scary but erroneous scene from Jurassic Park, no, their breath was not so hot it would have steamed up the window.
In research to be reported Friday in the journal Science, sophisticated CAT scans of the nasal bones from three species of dinosaurs provides some of the first clear, causal evidence that these ancient reptiles were cold-blooded - quick, agile and sometimes deadly, perhaps - but still cold-blooded.
"With extinct animals it's always difficult to say things with absolute certainty," said John Ruben, a professor of zoology at Oregon State University and lead author of the publication. "But this is the most powerful evidence we have so far about the metabolic status of the dinosaurs."
Aside from settling arguments among paleontologists, such information will help researchers better understand how dinosaurs may have lived, fed and reproduced, Ruben said.
If dinosaurs were cold-blooded it does suggest they would not have been able to run at fast speeds for extended time or distances, he said, but it doesn't mean they were necessarily sluggish or slow.
Many biologists who never study reptiles outside of temperate zones are surprised at the speed and agility of their tropical counterparts, Ruben said. In a short burst of energy, the present-day Komodo dragon of Indonesia can run down and kill a deer.
The newest evidence in this scientific debate evolved from several years of study of the nasal bones and structure of dinosaurs - in this particular project, those of a duckbill, a tyrannosaurid and an ostrich-like dinosaur.
According to the researchers, there is a clear correlation between the volume of nasal passages, the presence of respiratory "turbinate" bones and warm or cold-bloodedness. Larger nasal structures and turbinate bones serve to limit bodily heat and water loss in steamy, fast-metabolizing, warm-blooded animals, they say.
This mechanism is so essential to the function and survival of warm-blooded creatures that it has evolved similarly in separate animal classes such as mammals and birds, the study said. Metabolic and lung ventilation rates in cold-blooded animals are only about 5 percent of a similarly sized warm-blooded animal.
But the dinosaur fossils examined in this research had no respiratory turbinate bones and comparatively narrow nasal passages that would not have been large enough to contain them, the scientists concluded.
They most closely resembled the nasal passages of modern crocodiles or lizards, the researchers said - which are cold-blooded reptiles.
"The nasal structures we saw in dinosaur fossils simply would not have been able to accommodate the higher lung ventilation rates that dinosaurs would have had if they were warm-blooded," Ruben said.
Continued findings such as this have greatly reduced any debate over whether dinosaurs were cold-blooded creatures, Ruben said.
Most previous speculation that they may have been warm-blooded, he said, was based on less definitive factors such as posture, lifestyle, growth rates, or nesting behavior, he said.