Noses show dinosaurs were cold-blooded.

The long, sometimes heated debate about whether dinosaurs were warm- or cold-blooded may be about over, a new study suggests. The verdict is that they were cold-blooded, just like most scientists believed all along and modern reptiles are today. Moreover, despite a scary, but erroneous, scene from the movie "Jurassic Park," their breath was not so hot it would have steamed up a window.

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. "With extinct animals, it's always difficult to say things with absolute certainty," notes John Ruben, professor of zoology, Oregon State University, Corvallis. "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. if dinosaurs were cold-blooded, it is likely they would not have been able to run at fast speeds for extended times or distances, but that doesn't mean they necessarily were 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 points out. 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...