Study picks new site for dinosaur nostrils.

An innovative analysis of fossils and living animals suggests that most dinosaurs' nostrils occurred at locations toward the tip of their snout rather than farther up on their face.

Precisely where a dinosaur's nostrils were located on its head has implications beyond building models for theme parks and movies. The size and shape of air passages through an animal's nose affect many aspects of its physiology, including how well it breathes, smells, and regulates its body temperature, says Lawrence M. Witmer, an evolutionary biologist at Ohio University in Athens.

The bony opening behind an animal's nose is often much larger than the nostrils. Although soft tissue, such as a nose, doesn't typically fossilize, the paths of nerves and blood vessels through or over the surface of bones sometimes remain apparent on well-preserved fossils.

With these clues, as well as bone scars that reveal where cartilage grew, paleontologists can infer what the missing soft tissue looked like and thus where the air flowed in, says Witmer. After a detailed reanalysis of a variety of previously discovered fossils, he concludes that the nostrils of most dinosaurs should be placed at the forward end of the nasal opening.

Witmer's study of the nostril placement in living animals backs up this idea. Among 45 species of birds, crocodiles, and lizards--the dinosaurs' closest living relatives--the nostrils are almost always at the extreme forward end of the nasal opening. Although seemingly as obvious as the noses on the animals' faces, this consistency in nostril position in this group of animals hadn't been reported before, Witmer says. This contrasts with whales and dolphins, for example, whose nostrils emerge on top of their head.

The traditional placement of dinosaur nostrils is more a matter of history than biology, says Witmer. In the late 1800s, many new dinosaurs were unearthed, including massive, long-necked sauropods. Paleontologists held that these dinosaurs spent much of their time in shallow water, which buoyed their weight. The bony nasal openings high on the skulls of dinosaurs such as Diplodocus were interpreted as snorkels used in deep water.

Scientists therefore placed the nostrils, even of terrestrial dinosaurs, far back along the skull's nasal opening. Eventually, paleontologists rejected the idea of such snorkeling because they found that the deep water's pressure would have compressed a dinosaur's throat, cutting off the oxygen supply. But they never reconsidered the placement of the animal's nostrils, Witmer says.

He notes that dinosaurs often had extensive nasal cavities jam-packed with intricate networks of large blood vessels. In modern animals, such networks often serve as heat-exchange devices, warming the inhaled air and cooling the brain. If a dinosaur's nostril had been placed far back along the nasal opening, such a process probably wouldn't have been as efficient, Witmer notes.

Dinosaur imagery is frequently embellished with odd anatomical structures, such as frills and wattles, that go beyond the fossil evidence. By sticking to the detailed anatomy of fossils, as Witmer is doing, paleontologists can get a more accurate idea of what dinosaurs looked like, says Scott D. Sampson, a vertebrate paleontologist at the University of Utah. Only then, he contends, should they go farther and speculate about dinosaur physiology and behavior.