Ankylosaur Nasal Air Conditioning

Lawrence M. Witmer, PhD
Professor of Anatomy
Chang Professor of Paleontology

Dept. of Biomedical Sciences
Heritage College of Osteopathic Medicine
Life Science Building, Rm 123
Ohio University
Athens, Ohio 45701 USA

Email: witmerL@ohio.edu

Nasal air conditioning helped dinosaurs keep a cool head

Common Language Summary
Nasal air conditioners helped armored dinosaurs keep a cool head. A decade ago, Ohio University researchers discovered that armored ankylosaurian dinosaurs had long, convoluted nasal passages. Now, new research from Ohio University, drawing on advanced imaging, engineering-based computer modeling, and anatomy, has shed light on these features, suggesting that these large-bodied dinosaurs had elaborate “krazy-straw” nasal passages that functioned as efficient air conditioners to cool blood that was shunted to the brain cavity to help maintain brain temperatures within safe limits, helping the animals avoid heat stress. Large-bodied animals, such as the two 75-million-year-old ankylosaurs—Euoplocephalus and Panoplosaurus—that were the focus of the study, face thermal challenges in that they tend to retain heat and are at risk of heat stroke, because the hot blood from the body core can damage the delicate brain tissues. Simulations of nasal airflow revealed that the dinosaurs’ long tortuous nasal passages functioned as efficient heat exchangers, warming and humidifying the air on its way to the lungs. Analysis of CT scans revealed large canals for blood vessels running next to the nasal passages that led to the bony brain cavity. As the animals breathed, evaporation of moisture would have cooled the venous blood in these canals, providing a mechanism to cool the brain even as their bodies heated up in the Cretaceous sun. To test if the long, “krazy-straw” airway was the key to evolving this efficient air conditioner, the researchers modeled a short and simple airway (like ours) as well as a long but straight airway (no twisting). In both cases, the efficiency dropped dramatically, suggesting that indeed both the length and convolutions evolved to enhance physiological efficiency. The researchers are now exploring whether other large-bodied dinosaurs had similar mechanisms. This research was funded by grants from the National Science Foundation.

A technical article was published on 19 December 2018 in PLOS ONE.

• Download a PDF of the published article:
Bourke, J. M., W. R. Porter, and L. M. Witmer. 2018. Convoluted nasal passages function as efficient heat exchangers in ankylosaurs (Dinosauria: Ornithischia: Thyreophora). PLOS ONE 13(12): e0207381.

• Download a PDF with key facts about the study, as well as links to and captions for all the graphics below

Scroll down to read the Ohio University press release

Graphics & Animations

Heat exchange through the highly convoluted nasal passages of the Cretaceous ankylosaurian dinosaur Euoplocephalus not only efficiently warmed and humidified the inspired air on its way to the lungs but also cooled the blood running through the nasal veins, much of which was destined for the brain. In this way, the brain was protected from the high temperatures of the hot arterial blood coming from the body core. Courtesy of WitmerLab at Ohio University. (Silhouettes: Marmelad - CC-BY-SA-2.5)

This study of dinosaur thermal physiology focused on the Cretaceous ankylosaurian dinosaur Euoplocephalus (illustrated here), as well another less specialized ankylosaur called Panoplosaurus. Both dinosaurs were found in Late Cretaceous fossil deposits of Alberta, Canada. The research team used CT scanning, soft-tissue reconstruction, and engineering analyses (computational fluid dynamics) to simulate air and blood flow and calculate heat exchange in the nasal passages. Courtesy of WitmerLab at Ohio University. (Silhouettes: Marmelad - CC-BY-SA-2.5)

The skulls of the two ankylosaurian dinosaurs—Panoplosaurus and Euoplocephalus—that were the focus of the research. The skulls are rendered semitransparent, revealing the convoluted “krazy-straw” nasal passages coiled within their snouts. Colors within the nasal passages show the heat exchange modeled by the computational fluid dynamics analysis. The heat exchange allowed efficient warming and humidification of the inspired air. The more elaborately coiled nasal passages of Euoplocephalus were more efficient than the simpler ones of Panoplosaurus. Courtesy of WitmerLab at Ohio University.

The Late Cretaceous armored dinosaur Euoplocephalus (center) had a long, highly convoluted nasal passage coiled up in its snout. The physiological efficiency of heat exchange was tested by computational fluid dynamics analyses that compared the (top left) “bony bounded” airway (i.e., as preserved in the fossil), (top right) the “soft tissue” airway (closer to real life due to restored nasal mucous membrane), (top middle) the “basic airway” (short and simple, as in many animals, including humans), and (bottom) the “straightened airway” (same length as bony-bounded and soft-tissue airways but without convolutions). The basic airway is the least efficient, and the long convoluted soft-tissue air is the most efficient as well as the most realistic. The long straight airway was also very efficient but less so than the convoluted airway, indicating that the twists and turns contribute significantly, probably due to the increased vorticity that slowed down the airstream and increased the chance for heat transfer. Courtesy of WitmerLab at Ohio University.

The skull of the Late Cretaceous armored dinosaur Euoplocephalus that was used in the study.

This movie is associated with an article published in PLOS ONE on 19 December 2018 (http://bit.ly/2rzFudE) by Jason Bourke, Ruger Porter, and Lawrence Witmer. Nasal airflow was modeled using Computational Fluid Dynamics analyses for two Late Cretaceous ankylosaurian dinosaurs, Panoplosaurus and Euoplocephalus. The video demonstrates how the highly convoluted nasal cavity in both species warms the inhaled air on its way to the lung and then cools the exhaled air, resulting in a highly efficient system of air conditioning that conserves both heat and water. For more in this project, visit the WitmerLab project page: http://bit.ly/2EwOzMO.
• Download a 48 MB QuickTime version (HD: 1920x1080)
• Download a 22 MB QuickTime version (1280x720)
• Download a 12 MB QuickTime version (853x480)
• Download an 8 MB QuickTime version (640x360)

Animated GIF (640x360, 10 MB): Heat exchange of inspired air as it passes through the tortuous nasal cavity of the Late Cretaceous ankylosaur Euoplocephalus. The computational fluid dynamics analysis shows the flow of air during inhalation, with color—i.e., gray to red to orange to yellow—indicating progressively warmer temperatures. Euoplocephalus has a very efficient nasal cavity, fully warming and humidifying the inspired air before it reaches the lungs. Panoplosaurus, with its simpler nose is somewhat less efficient but still impressive. Likewise, on exhalation, the long convoluted airways cool the expired air, saving heat and energy. Courtesy of WitmerLab at Ohio University.
• Right-click or CTRL-click (Mac) to save the GIF; also can be copied-and-pasted into social media posts or websites
• To view, copy, and/or save a 1280x720 (36 MB) version of this GIF, click here.

Authors of the article investigate key features in the skulls of ankylosaurian dinosaurs in WitmerLab at Ohio University. From left: Jason Bourke, Ruger Porter, and Lawrence Witmer. Courtesy of WitmerLab at Ohio University.

3D-PDF of the skull and nasal passages of the ankylosaurian dinosaurs Euoplocephalus and Panoplosaurus, showing the four different shapes of the airways tested: “bony bounded” airway (as preserved in the fossil), “soft tissue” airway (closer to real life due to restored nasal mucous membrane), “basic airway” (short and simple, as in many animals, including humans), and “straightened airway” (same length as bony-bounded and soft-tissue airways but without convolutions). 3D-PDF files should be saved and then run on your computer; they will not run in a browser window. Courtesy of WitmerLab at Ohio University.

Skulls of the Late Cretaceous armored dinosaur Euoplocephalus represented as a solid skull (left) and as a transparent skull, revealing the long convoluted nasal cavity within the snout.

Ohio University News Release

EMBARGOED FOR RELEASE WEDNESDAY, 19 DECEMBER 2018, 2 PM EST

Breathing study shows huge armored dinosaurs battled overheating with nasal air-conditioning
Researchers use 3D computer modeling to simulate heat exchange in dinosaurs

ATHENS, Ohio (Dec. 19, 2018) – Being a gigantic dinosaur presented some challenges, such as overheating in the Cretaceous sun and frying your brain. Researchers from Ohio University 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.

“The huge bodies that we see in most dinosaurs must have gotten really hot in warm Mesozoic climates,” 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. “Brains don’t 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.”

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.

“A decade ago, my colleague Ryan Ridgely and I published the discovery that ankylosaurs had insanely long nasal passages coiled up in their snouts,” said study co-author Lawrence Witmer, professor at the Ohio University Heritage College of Osteopathic Medicine. “These convoluted airways looked like a kid’s ‘krazy-straw!’ 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.”

“This 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,” said Kathy Dickson, a program officer at the National Science Foundation that funded the research. “From these new images and models, fossils can provide further insight into extinct organisms like the ankylosaur – in this case, offering an explanation of how unusual features actually function physiologically.”

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. “Ankylosaurs didn’t have turbinates, but instead made their noses very long and twisty,” said Bourke.

When the researchers compared their findings to data from living animals, they discovered that the dinosaurs’ noses were just as efficient at warming and cooling respired air. “This was a case of nature finding a different solution to the same problem,” 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’re 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. “When 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’t work very well,” said Bourke.

Another line of evidence that these noses were air conditioners that helped cool the brain 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,” said Ruger Porter, lecturer at the Ohio University Heritage College of Osteopathic Medicine and one of the study’s co-authors. “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.”

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.

“Sure, their brains were almost comically small,” Bourke said. “But they’re still their brains and needed protection.”

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.

“When 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,” Witmer said.

The next step for the researchers 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 said. “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.”

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 Ohio University Heritage College of Osteopathic Medicine.

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Editors:
• Advance copy can be downloaded here: https://people.ohio.edu/witmerl/Downloads/Bourke_et_al-Ankylosaur_MS_PLOS_ONE_Revisions-3.pdf
• Related images and animations can be downloaded from the WitmerLab site: https://people.ohio.edu/witmerl/ankylosaur_brain-AC.htm
• A fact sheet can be accessed here: https://people.ohio.edu/witmerl/Downloads/Dinosaur_nasal_air-conditioning_Fact_Sheet.pdf

Contacts (all Eastern Daylight Time):
1. Jason Bourke, 740-818-7503, jbourke@nyit.edu [lead author]
2. Lawrence Witmer, 740-591-7712, witmerL@ohio.edu [co-author]
3. Jim Sabin, 740-593-0858, sabin@ohio.edu [Ohio University Communications and Marketing]
4. Kim Tucker, 516-686-4013, kimberly.tucker@nyit.edu [NYITCOM External Relations & Marketing]

This website provides supplementary information as an adjunct to the published paper. Witmer, with the skilled assistance of Ryan Ridgely, is responsible for the content of the website. Content provided here is for educational and research purposes only, and may not be used for any commercial purpose without the permission of L. M. Witmer and other relevant parties.

This project was funded by grants from the National Science Foundation.