Dinosaur Brain-Cooling Strategies

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

Dinosaurs used different strategies to keep a cool head

Common Language Summary
Keeping a cool head – Different dinosaurs evolved different cooling strategies. For more than a decade, a team of Ohio University researchers has been studying how large-bodied dinosaurs survived potentially fatal overheating. New research from this team, drawing on advanced imaging techniques and sophisticated quantitative analyses, has discovered evidence of often vast networks of blood vessels in the skulls of dinosaurs that were likely used to cool blood destined for the brain. It turns out that different groups of large dinosaurs emphasized different sites of evaporative cooling in the head. For example, armored ankylosaurs like Euoplocephalus used the nasal cavity as an air conditioner, whereas long-necked sauropods like Diplodocus and Camarasaurus also used the mouth to cool blood, probably through panting. The predatory theropod dinosaurs, such as T. rex and Majungasaurus, however, evolved a very different brain-cooling strategy, involving a highly vascular air sinus in the snout through which air was pumped by movements of the jaws. The famously huge body sizes of different dinosaur groups evolved independently from smaller-bodied ancestors. Thus, the picture that emerges is that different gigantic dinosaurs solved the problem of overheating in different ways by using different sites of evaporative cooling and different sets of blood vessels. The researchers are now exploring similar kinds of thermal physiological strategies to control brain temperatures in other groups of large dinosaurs such as horned ceratopsians like Triceratops and duck-billed hadrosaurs. This research was funded by grants from the National Science Foundation.

A technical article was first published online on 16 October 2019 in Anatomical Record.

• Download a PDF of the published article:
Porter, W. R., and L. M. Witmer. 2020. Vascular patterns in the heads of dinosaurs: evidence for blood vessels, sites of thermal exchange, and their role in physiological thermoregulatory strategies. Anatomical Record 303(4):1075–1103. https://doi.org/10.1002/ar.24234

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Graphics & Animations

Gigantic dinosaurs like the sauropod Diplodocus, which weighed over 15 tons and was longer than an 18-wheeler truck, would have had problems with potentially lethal overheating. Hot blood from the body core would have been pumped to the head, damaging the delicate brain. New research shows that in sauropods, evaporation of moisture in the nose and mouth would have cooled extensive networks of venous blood destined for the brain. Other large dinosaurs evolved different brain-cooling mechanisms, but all involving evaporative cooling of blood in different regions of the head. Life restoration by Michael Skrepnick. Courtesy of WitmerLab at Ohio University.

Gigantic dinosaurs like the sauropod Diplodocus would have had problems with potentially lethal overheating. New research shows that in sauropods, evaporation of moisture in the nose and mouth would have cooled extensive networks of venous blood destined for the brain. Other large dinosaurs evolved different brain-cooling mechanisms, but all involving evaporative cooling of blood in different regions of the head. Life restoration by Michael Skrepnick. Courtesy of WitmerLab at Ohio University.

Different kinds of dinosaurs had different physiological strategies for dealing with the problem of overheating. Small dinosaurs like Stegoceras could cool down by simply running into the shade and so they lacked elaborate cooling mechanisms in the head. Gigantic dinosaurs, however, were so large that their bodies remained hot and continuously pumped hot blood to the head, potentially damaging the delicate brain. New research shows that different kinds of large dinosaurs evolved different brain-cooling mechanisms, but all involving evaporative cooling of blood in different regions of the head. The ankylosaur Euoplocephalus emphasized its convoluted nasal region as a cooling site, whereas huge sauropods like Camarasaurus used not only its nose as a cooling site, but also its mouth. Theropods like Majungasaurus evolved a different strategy, increasing the blood supply to a large air sinus in its snout through which air was pumped by movements of the jaws. Courtesy of WitmerLab at Ohio University.

The bipedal predatory theropod dinosaurs, such as T. rex, Allosaurus, and Majungasaurus evolved a brain-cooling strategy involving a highly vascular air sinus in the snout through which air was pumped by movements of the jaws. Gigantic theropods like T. rex would have had major problems with overheating and had extensive air sinuses, many of which show signs of enhanced blood flow. As Allosaurus shows, the opening and closing of the jaws caused air to move in and out of the air sinus, ventilating the sinus like an old-fashioned bellows pump. Blood surrounding the sinus, as shown in Majungasaurus would have been cooled by evaporation of moisture in the sinus and directed to the brain to help moderate temperatures. Courtesy of WitmerLab at Ohio University.

Dinosaur vascular anatomy & thermal physiology by WitmerLab at Ohio University on Sketchfab

Recent research by Porter & Witmer (2019: http://bit.ly/2AWXMKS) has shown that different dinosaur groups had different thermal physiological strategies to help moderate brain temperatures in the face of high heat loads. Evaporatively cooled blood in different sites of heat exchange was shuttled to the brain region to help moderate brain temperatures. This 3D model generated by Ryan Ridgely replicates the content of Figure 1 of Porter & Witmer (2019). Small-bodied dinosaurs like Stegoceras had a balanced pattern of blood supply with no particular emphasis on any one site of heat exchange whereas larger-bodied dinosaurs had a more focused thermal strategy, emphasizing blood flow to the nasal region (Euoplocephalus), oral & nasal regions (Camarasaurus), or the antorbital air sinus (Majungasaurus). Development of focused thermal strategies is associated with the evolution of large body sizes. Courtesy of WitmerLab at Ohio University.
Here is a link to the animation on Sketchfab's site: https://sketchfab.com/3d-models/ce6163daf99c4947956386049416fe67.

Recent research by Porter & Witmer (2019: http://bit.ly/2AWXMKS) has shown that different dinosaur groups had different thermal physiological strategies to help moderate brain temperatures in the face of high heat loads. The predatory theropod dinosaurs, such as T. rex, Allosaurus, and Majungasaurus evolved a brain-cooling strategy involving a highly vascular air sinus in the snout through which air was pumped by movements of the jaws. This video was generated by Ryan Ridgely in WitmerLab and shows the bellows-pump-like action of the jaws to move air in and out of the air sinus. Blood surrounding the sinus would have been cooled and directed to the brain to help moderate temperatures. See WitmerLab Project Page for more information: http://bit.ly/2p5ybwB. Courtesy of WitmerLab at Ohio University.
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The two authors of the new dinosaur brain-cooling study—Ruger Porter, PhD (left) and Lawrence M. Witmer, PhD (right)—surrounded by skulls of some of the dinosaurs studied in the new research: clockwise from top right, Majungasaurus, Tyrannosaurus rex, Diplodocus, Ankylosaurus, Stegoceras, Allosaurus, and Camarasaurus. Courtesy of WitmerLab at Ohio University.

Ohio University News Release

EMBARGOED FOR RELEASE WEDNESDAY, 16 OCTOBER 2019, 2 PM EDT

New study shows huge dinosaurs evolved different cooling systems to combat heat stroke
Researchers use 3D imaging to discover multiple heat exchangers in dinosaur heads

ATHENS, Ohio (Oct. 16, 2019) – Different dinosaur groups independently evolved gigantic body sizes, but they all faced the same problems of overheating and damaging their brains. Researchers from Ohio University’s Heritage College of Osteopathic Medicine show in a new article in the Anatomical Record that different giant dinosaurs solved the problem in different ways, evolving different cooling systems in different parts of the head.

“The brain and sense organs like the eye are very sensitive to temperature,” said Ruger Porter, Assistant Professor of Anatomical Instruction and lead author of the study. “Animals today often have elaborate thermoregulatory strategies to protect these tissues by shuttling hot and cool blood around various networks of blood vessels. We wanted to see if dinosaurs were doing the same things.”

Many of the famous gigantic dinosaurs — such as the long-necked sauropods or armored ankylosaurs—actually evolved those big bodies independently from smaller-bodied ancestors. “Small dinosaurs could have just run into the shade to cool off,” said study co-author Professor Lawrence Witmer, “but for those giant dinosaurs, the potential for overheating was literally inescapable. They must have had special mechanisms to control brain temperature, but what were they?”

The answer turned out to be based in physics, but still part of our everyday experience. “One of the best ways to cool things down is with evaporation,” Porter said. “The air-conditioning units in buildings and cars use evaporation, and it’s the evaporative cooling of sweat that keeps us comfortable in summer. To cool the brain, we looked to the anatomical places where there’s moisture to allow evaporative cooling, such as the eyes and especially the nasal cavity and mouth.”

To test that idea, the team looked to the modern-day relatives of dinosaurs — birds and reptiles — where studies indeed showed that evaporation of moisture in the nose, mouth, and eyes cooled the blood on its way to the brain.

Porter and Witmer obtained carcasses of birds and reptiles that had died of natural causes from zoos and wildlife rehabilitation facilities. Using a technique developed in Witmer’s lab that allows arteries and veins to show up in CT scans, they were able to trace blood flow from the sites of evaporative cooling to the brain. They also precisely measured the bony canals and grooves that conveyed the blood vessels.

“The handy thing about blood vessels is that they basically write their presence into the bones,” Porter said. “The bony canals and grooves that we see in modern-day birds and reptiles are our link to the dinosaur fossils. We can use this bony evidence to restore the patterns of blood flow in extinct dinosaurs and hopefully get a glimpse into their thermal physiology and how they dealt with heat.”

“The discovery that different dinosaurs cooled their brains in a variety of ways not only provides a window into the everyday life of dinosaurs, it also serves as an exemplar of how the physical constraints imposed by specific environmental conditions have shaped the evolution of this diverse and unique group,” said Sharon Swartz, a program director at the National Science Foundation, which funded the research. “Using a combination of technological innovation and biological expertise, these researchers were able to take a direct reading from the fossil record that provides new clues about how dinosaur skeletal form and function evolved.”

This team of current and former members of WitmerLab at Ohio University has previously looked at other cases of dinosaur physiology. In 2014 and 2018, former doctoral student Jason Bourke led projects involving Porter and Witmer on breathing and heat exchange in pachycephalosaurs (http://bit.ly/2JI6RLn) and ankylosaurs (http://bit.ly/2EwOzMO), respectively. Most recently, former lab doctoral student Casey Holliday led a project with Porter and Witmer (http://bit.ly/2kzvKjP) that explored blood vessels on the skull roof of T. rex and other dinosaurs that also might have had a thermoregulatory function.

The new study by Porter and Witmer is a more expansive, quantitative study that shows that “one size didn’t fit all” with regard to how large-bodied dinosaurs kept their brains cool. That is, they had different thermoregulatory strategies. The researchers looked at bony canal sizes in the dinosaurs to assess the relative importance of the different sites of evaporative cooling based on how much blood was flowing through them.

A key factor turned out to be body size. Smaller dinosaurs such as the goat-sized pachycephalosaur Stegoceras had a very balanced vascular pattern with no single cooling region being particularly emphasized. “That makes physiological sense because smaller dinosaurs have less of a problem with overheating,” Porter said. “But giants like sauropods and ankylosaurs increased blood flow to particular cooling regions of the head far beyond what was necessary to simply nourish the tissues.” This unbalanced vascular pattern allowed the thermal strategies of large dinosaurs to be more focused, emphasizing one or more cooling regions.

But although sauropods like Diplodocus and Camarasaurus and ankylosaurs like Euoplocephalus all had unbalanced vascular patterns emphasizing certain cooling regions, they still differed. Sauropods emphasized both the nasal cavity and mouth as cooling regions whereas ankylosaurs only emphasized the nose. “It’s possible that sauropods were so large — often weighing dozens of tons — that they needed to recruit the mouth as a cooling region in times of heat stress,” Porter said. “Panting sauropods may have been a common sight!”

One problem that the researchers encountered was that many of the theropod dinosaurs — such as the 10-ton T. rex — were also gigantic, but the quantitative analysis showed that they had a balanced vascular pattern, like the small-bodied dinosaurs.

“This finding had us scratching our heads until we noticed the obvious difference—theropods like Majungasaurus and T. rex had a huge air sinus in their snouts,” Witmer said. Looking closer, the researchers discovered bony evidence that this antorbital air sinus was richly supplied with blood vessels. Witmer had previously shown that air circulated through the antorbital air sinus like a bellows pump every time the animal opened and closed its mouth. “Boom! An actively ventilated, highly vascular sinus meant that we had another potential cooling region. Theropod dinosaurs solved the same problem…but in a different way,” concluded Witmer.

The researchers are now expanding the project to include other dinosaur groups such as duck-billed hadrosaurs and horned ceratopsians like Triceratops to explore how thermoregulatory strategies varied among other dinosaurs and how these strategies may have influenced their behavior and even their preferred habitats.

The research was funded by National Science Foundation (NSF) grants to Witmer (part of the Visible Interactive Dinosaur Project), 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/2019_Porter_&_Witmer_dinosaur_cooling_strategies.pdf
• Related images and animations can be downloaded from the WitmerLab site: https://people.ohio.edu/witmerl/dinosaur_brain-cooling_strategies.htm
• A fact sheet can be accessed here: https://people.ohio.edu/witmerl/Downloads/Dinosaur_brain-cooling_strategies_Fact-Sheet.pdf

Contacts (all Eastern Daylight Time):
1. Ruger Porter, porterw1@ohio.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]

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.