Breathing study shows huge armored dinosaurs battled overheating with nasal air-conditioning
Photo courtesy of: WitmerLabAuthors of the article investigate key features in the skulls of ankylosaurian dinosaurs in WitmerLab at 91探花. From left: Jason Bourke, Ruger Porter, and Lawrence Witmer.
Being a gigantic dinosaur presented some challenges, such as overheating in the Cretaceous sun and frying your brain. Researchers from 91探花 and NYITCOM at Arkansas State show in a new article in PLOS ONE that the heavily armored, club-tailed ankylosaurs had a built-in air conditioner in their snouts.
鈥淭he huge bodies that we see in most dinosaurs must have gotten really hot in warm Mesozoic climates,鈥 said Jason Bourke, Assistant Professor at the New York Institute of Technology College of Osteopathic Medicine at Arkansas State and lead author of the study. 鈥淏rains don鈥檛 like that, so we wanted to see if there were ways to protect the brain from cooking. It turns out the nose may be the key.鈥
Bourke and the team used CT scanning and a powerful engineering approach called computational fluid dynamics to simulate how air moved through the nasal passages of two different ankylosaur species, the hippo-sized Panoplosaurus and larger rhino-sized Euoplocephalus, to test how well ankylosaur noses transferred heat from the body to the inhaled air.
鈥淎 decade ago, my colleague Ryan Ridgely and I published the discovery that ankylosaurs had insanely long nasal passages coiled up in their snouts,鈥 said study co-author Lawrence Witmer, professor at the 91探花 Heritage College of Osteopathic Medicine. 鈥淭hese convoluted airways looked like a kid鈥檚 鈥榗razy-straw!鈥 It was completely unexpected and cried out for explanation. I was thrilled when Jason took up the problem as part of his doctoral research in our lab.鈥
鈥淭his project is an excellent example of how advances in CT scanning, 3-D reconstruction, imaging, and computational fluid dynamics modeling can be used in biological research to test long-standing hypotheses,鈥 said Kathy Dickson, a program officer at the National Science Foundation that funded the research. 鈥淔rom these new images and models, fossils can provide further insight into extinct organisms like the ankylosaur 鈥 in this case, offering an explanation of how unusual features actually function physiologically.鈥
Smell may be a primary function of the nose, but noses are also heat exchangers, making sure that air is warmed and humidified before it reaches our delicate lungs. To accomplish this effective air conditioning, birds and mammals, including humans, rely on thin curls of bone and cartilage within their nasal cavities called turbinates, which increase the surface area, allowing for air to come into contact with more of the nasal walls. 鈥淎nkylosaurs didn鈥檛 have turbinates, but instead made their noses very long and twisty,鈥 said Bourke.
When the researchers compared their findings to data from living animals, they discovered that the dinosaurs鈥 noses were just as efficient at warming and cooling respired air. 鈥淭his was a case of nature finding a different solution to the same problem,鈥 said Bourke.
Just how long were these nasal passages? In Panoplosaurus, they were a bit longer than the skull itself and in Euoplocephalus they were almost twice as long as the skull, which is why they鈥檙e coiled up in the snout. To see if nasal passage length was the reason for this efficiency, Bourke 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 indeed the key to their air-conditioning ability. 鈥淲hen we stuck a short, simple nose in their snouts, heat-transfer rates dropped over 50 percent in both dinosaurs. They were less efficient and didn鈥檛 work very well,鈥 said Bourke.
Another line of evidence that these noses were air conditioners that helped cool the brain came from analyses of blood flow.
鈥淲hen 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,鈥 said Ruger Porter, lecturer at the 91探花 Heritage College of Osteopathic Medicine and one of the study鈥檚 co-authors. 鈥淗ot 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.鈥
So why the need for such effective heat exchangers? The large bodies of Panoplosaurus and Euoplocephalus were really good at retaining heat, which is good for staying warm, but bad when the animals need to cool off. This heat-shedding problem would have put them at risk of overheating even on cloudy days. In the absence of some protective mechanism, the delicate neural tissue of the brain could be damaged by the hot blood from the body core.
鈥淪ure, their brains were almost comically small,鈥 Bourke said. 鈥淏ut they鈥檙e still their brains and needed protection.鈥
The complicated nasal airways of these dinosaurs were acting as radiators to cool down the brain with a constant flow of cooled venous blood, allowing them to keep a cool head at all times. This natural engineering feat also may have allowed the evolution of the great sizes of so many dinosaurs.
鈥淲hen we look at the nasal cavity and airway in dinosaurs, we find that the most elaborate noses are found in the large dinosaur species, which suggests that the physiological stresses of large body size may have spurred some of these anatomical novelties to help regulate brain temperatures,鈥 Witmer said.
The next step for the researchers is to examine other dinosaurs to determine when this nasal enlargement happened.
鈥淲e know that large dinosaurs had these crazy airways, but at exactly what size did this happen?鈥 Bourke said. 鈥淲as 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鈥檛 know yet.鈥
The research was funded by National Science Foundation (NSF) grants to Witmer (part of the Visible Interactive Dinosaur Project) and an NSF fellowship to Bourke, as well as by the 91探花 Heritage College of Osteopathic Medicine.