What lurks inside a dinosaur's nose?

In one of the more bizarre research crazes these days, scientists are racing each other to look up the nostrils of extinct beasts. Their quarry: a set of delicate bones that can tell whether an animal was warm-blooded (endothermic) or cold-blooded (ectothermic).

The current nasal fetish stems from an ongoing debate about dinosaurs. Although paleontologists once saw them as sluggish ectotherms, many now envision dinosaurs as endotherms. The debate rages on for lack of definitive evidence.

Enter respiratory turbinates. These thin, scroll-shaped bones or cartilage appear in the nasal passages of almost all modern endotherms, according to physiologists John A. Ruben of Oregon State University in Corvallis and Willem J. Hillenius of the University of California, Los Angeles. Covered with a moist membrane, turbinates humidify and warm air going into the lungs and dehumidify air on its way out, thus cutting down on water loss. Their presence in a fossil animal signals endothermy, say the researchers (SN: 5/14/94, p.312).

But computerized tomography (CT) scans of several theropod dinosaurs showed no evidence of respiratory turbinates in these active predators, reports Ruben. That puts a chill on the idea of endothermic dinosaurs.

Defenders of the warm-blooded theory thought they might get support from paleontologist John R. Horner of the Museum of the Rockies in Bozeman, Mont. Horner reported finding some unusual nasal structures on CT scans of a duck-billed dinosaur. But he eventually agreed with Ruben that the bones are not respiratory turbinates.