Dinosaurs may have been heavy, wet breathers

© Corbis

Illustration of the Cretaceous pachycephalosaur Stegoceras.

The first ever reconstruction of how dinosaurs breathed finds that these long-extinct animals used each heavy, mucous-moistened breath to smell their surroundings and to cool their brains.

The study, published in the , helps to explain why most non-avian dinosaurs had such long snouts. It also adds another dimension of life to these prehistoric animals, the last of which took its final breath around 65 million years ago.

Lead author Jason Bourke and his team used plant-eating Stegoceras as a model dinosaur since it had a particularly bony skull with fossilized bones in its nasal region still in place.

"The biggest difference between Stegoceras and us (in terms of breathing) is that it would have breathed more like a bird or reptile in that it probably took longer, deeper breaths," Bourke, an Ohio University doctoral student, told .

Another major difference is that humans and other mammals have hairs in their nose to help block debris from going into the body. Dinosaurs did not have nose hairs, so they relied on something functional, but messy.

"Mucous was probably the number one defender of unwanted particles in the nose," Bourke said. "This mucous would be constantly flowing towards the nostril, creating a slow-moving conveyor belt that removed unwanted items from getting trapped in the nose. A good sneeze, now and then, would speed up the process."

The researchers analyzed dinosaur skull anatomy while also drawing from a branch of engineering called computational fluid dynamics that is commonly used in the aerospace industry and medicine. In this case, the scientists applied the process to modeling how air flows through the noses of modern day dinosaur relatives, such as ostriches and alligators, and then to Stegoceras.

Bourke explained that with each dinosaur breath, air would have moved from the nostrils through the internal structure of the dino's nasal passage. Some air entered a "dead end" spot at the back of the interior snout where much of the sense of smell was located. This is called the olfactory region.

© WitmerLab at Ohio University

Airflow modeled through the nasal cavity of the Cretaceous pachycephalosaur Stegoceras based on restoration of nasal soft tissues and Computation Fluid Dynamics of nasal airflow.

The rest of the air would then exit the snout at the back of the throat and continue down the trachea to the lungs where gas exchange would occur, releasing oxygen and picking up carbon dioxide. Upon expiration, air would follow the same path, but in reverse.

Senior author Lawrence Witmer, a professor in the Ohio University Heritage of Osteopathic Medicine, explained that nasal "turbinates" -- scrolls of cartilage­ -- were key to understanding the process. Turbinates were likely in the front, respiratory part of the dinosaur's nasal cavity, increasing surface area and helping to direct air flow.

As for what the dinosaurs were doing with all of that air, co-author Ruger Porter said that it helped to cool blood, which circulated around the brain, essentially preventing the brain from cooking.

Porter said, "Overheating would be a major problem for most dinosaurs, simply because they were so huge. The hot blood from the body could easily fry the brain if physiological mechanisms aren't in place to cool that blood down."

Seven-foot-long Stegoceras was relatively small for a dinosaur, but the researchers still think that brain cooling via breathing took place.

In terms of smelling, Bourke said, "Stegoceras was no bloodhound, but it could do alright." The dinosaur spent much of its time sniffing out predators, potential mates, food and other things in its environment.

Witmer, Bourke and their colleagues next hope "to breathe life" back into a variety of other dinosaurs with even greater detail.

As Witmer said, "We've already got some other dinosaurs in our sights that have some pretty crazy noses."