Ankylosaurs had long nasal passages

With their heavy armour and club tails, ankylosaurs were among the most rugged of dinosaurs, but it seems they also had another less obvious survival mechanism.

Their “insanely long nasal passages” acted like air conditioners to help keep their brains cool under the Cretaceous sun, according to a study by a team from Arkansas State University and Ohio University in the US.

And it’s possible, the researchers suggest, that this natural engineering feat allowed for the evolution of many large dinosaurs.

In a paper published in the journal PLOS ONE, they describe using CT scanning and computational fluid dynamics to simulate how air moved through the nasal passages of two ankylosaur species – the hippo-sized Panoplosaurus and the larger, rhino-sized Euoplocephalus.

When they compared their findings to data from living animals, they discovered that the dinosaurs’ noses were just as efficient at warming and cooling respired air. 

To test if nasal passage length was the reason for this efficiency, they ran alternative models with shorter, simpler nasal passages that ran directly from the nostril to the throat, as in most other animals. The results clearly showed that nose length was the key to their air-conditioning ability.

“When we stuck a short, simple nose in their snouts, heat-transfer rates dropped over 50% in both dinosaurs,” says lead author Jason Bourke. “They were less efficient and didn’t work very well.”

Further evidence came from analyses of blood flow. “When we reconstructed the blood vessels, based on bony grooves and canals, we found a rich blood supply running right next to these convoluted nasal passages,” says co-author Ruger Porter.

“Hot blood from the body core would travel through these blood vessels and transfer their heat to the incoming air. Simultaneously, evaporation of moisture in the long nasal passages cooled the venous blood destined for the brain.”

The researchers found that larger dinosaur species have the most elaborate noses, suggesting that the physiological stresses of large body size may have spurred some of these anatomical novelties.

The next step is to examine other dinosaurs to determine when this nasal enlargement happened.

“We know that large dinosaurs had these crazy airways, but at exactly what size did this happen?” Bourke asks.

“Was this elaboration gradual as body size increased, or is there a threshold size where a run-of-the-mill nose can no longer do the job? We just don’t know yet.”