Lung structure challenges dinosaur-bird theory.

Paleontologists at Oregon State University, Corvallis, have discovered evidence that theropod--meat-eating--dinosaurs were cold-blooded and that the first birds probably did not, as long has been believed, evolve from known dinosaurs. The conclusions largely are based on examination of lung structure and ventilation in modern mammals, birds, and reptiles, which were used as models to understand similar functions in dinosaurs and prehistoric birds.

"Our analysis suggests that it was a physiological impossibility for the lungs of birds to have evolved from the lungs of the theropod dinosaurs, as has been the conventional wisdom for decades," indicates professor of zoology John Ruben, an expert on dinosaur and avian evolution. "For this to have happened, the lungs of such dinosaurs could not have functioned in any normal way. Such an animal probably wouldn't have been active enough to even catch its own food, and there isn't much evolutionary or survival value to that." This suggests birds did not evolve from known dinosaurs, but does not provide solid conclusions about where they did come from. It is possible that some pre-dinosaurian reptile or early dinosaur that predated the known dinosaurs may have been the ancestor of birds.

In recent years, Ruben and graduate students Nicholas Geist and Terry Jones have done studies on dinosaur evolution and metabolism that provided some of the first concrete evidence about the physiology of these ancient reptiles. CAT scans of dinosaur nasal structure clearly suggested that dinosaurs were not warm-blooded, since they lacked the nasal turbinates that warm-blooded animals use to prevent excess heat and water loss white breathing.

In the latest study, they looked at lungs. Living reptiles have septate lungs that are like a pair of flabby, compartmentalized air...