Study Paints New Picture of Dinosaur's Nose
for National Geographic News
|August 2, 2001|
A new study suggests that anyone who sits down to draw a detailed picture of what dinosaurs may have looked like will have to tweak the nose a bit to get it right.
Usually the flesh-covered nasal passages of dinosaurs are shown toward the back of the openings in the nose bone.
But Lawrence Witmer, a paleontologist at Ohio University in Athens, Ohio, says that's wrong, and the nostrils were really much closer to the front, just above the mouth, and were larger than thought.
The finding, which Witmer reported in the August 3 issue of Science, is significant not just because it changes our idea of what dinosaurs looked like. It also has implications for how dinosaurs breathed, smelled, and regulated their body temperature and water loss.
"I don't know why we got it wrong for so long," said Witmer. "In general, the fleshy nostrilthe opening into the nasal cavityhas escaped scientific inquiry."
People have relatively small bony nostrils, so there's little doubt about where the flesh-covered nasal passages can be located to effectively do their job. The bony noses of dinosaurs, however, could have been more than two feet (0.6 meters) long, which leaves the placement of the fleshy nostrils open to interpretation.
Witmer said traditional views of the nostril placement are probably rooted in a historical belief that the huge, long-necked sauropod dinosaurs were amphibious. In that case, nasal passages positioned further back on the head would have worked like a snorkel.
Evidence uncovered in the 1970s suggested that sauropods were not aquatic, but landlubbers. Yet for some reason, the early depictions of sauropods with nostrils further back on the head didn't change, and that position was also picked up in renderings of other dinosaurs.
Witmer undertook the study because he is interested in the overall physiology of dinosaurs. He was curious about why the fleshy nostrils of dinosaurs were shown where they are, but he couldn't find an explanation.
So he set out to get a more accurate idea of just where a dinosaur's nose was probably positioned. He did X-ray examinations of living birds, crocodiles, and lizards, which are thought to be surviving relatives of dinosaurs.
He painted the fleshy nostrils of the animals with latex and sprinkled the painted parts with barium sulfate so they could be seen on X-ray film. This allowed him to examine the position of the fleshy nostrils in relation to the bony nose structure.
To his surprise, almost all the animals had nostrils that were perched toward the front of the heads, close to the upper margin of the mouth (known as a "rostral" position).
Witmer then examined turtles and mammals, and found that those animals also had frontal nostrils.
"There seems to be a consistent rule about where nostrils are placed," said Jack Hayes, program director for ecological and evolutionary physiology at the National Science Foundation in Arlington, Virginia.
To confirm the finding, Witmer examined grooves and pits within the bony nostril, which are the mark of an intricate network of blood vessels in the region of the flesh-covered nasal passages.
By comparing these signature markings in the nose bones of modern-day animals with similar markings on dinosaur skulls, Witmer was able to map the likely position of cartilage, blood vessels, and other soft tissues that made up the nasal cavity of dinosaurs.
"We had two independent lines of evidence that converged on dinosaurs having their nostrils parked out front, which is a departure from what we had known in the past," he said.
Where the fleshy nostril is positioned in relation to the nose bone influences how air passes through the nasal passages, Hayes explained. The air can flow in greater volume if the nasal passages are positioned toward the front.
Maximizing the flow of air would have enabled a dinosaur to benefit in a number of ways, such as controlling the humidity of the air it breathed, filtering out particles, and even regulating brain and body temperatures, said Witmer.
"Another thing is it makes a lot of sense in terms of smelling," he noted. Smell is important in a broad range of behaviors, from feeding to detection of predators to finding a potential mate.
Witmer plans to do similar analysis of dinosaurs' jaws and limbswork that could further change scientists' and society's perception of what dinosaurs looked like.
"This work shows that you can look at modern animals and clues from fossils and reconstruct some soft tissue if there is some consistent rule," said Hayes.
Additional dinosaur resources from National Geographic:
Paul Sereno: NG Explorer-in-Residence and dinosaur hunter
Destinations: Dinosaur National Monument
Educational Video: Dinosaurs on Earth: Then and Now
Children's Pop-up Book: Dinosaur Babies
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