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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