Dinosaur Noses Are Cool

Nearly a century ago, while working in the 75 million year old rock of Alberta, Canada, the professional fossil-hunter George Sternberg found a stunning skeleton. The remains belonged to a six-foot-long “bonehead” dinosaur named Stegoceras, and, best of all, the dinosaur’s frame included a complete skull – a rarity for these animals. More often than not, a rough geological afterlife has reduced these boneheads – technically known as pachycephalosaurs – to little more than their sturdy skull domes. Stegoceras is an exception.

The dense mounds of skull bones, bordered by spiky tonsures, are what have traditionally transfixed paleontologists. And given that Sternberg’s Stegoceras has an exquisite skull, it has been central to ongoing investigations about whether these dinosaurs were butting heads, showing off, or both. But the importance of Stegoceras goes beyond the way dinosaurs – and paleontologists – tussle with each other. Deep inside the skull, Ohio University paleobiologist Jason Bourke and colleagues have found delicate structures that are relevant to different dinosaur mysteries.

The skull of Stegoceras. Courtesy of WitmerLab at Ohio University.
The skull of Stegoceras. Courtesy of WitmerLab at Ohio University.

Next time you’re at a museum and have the right vantage point, look inside a dinosaur’s nose. Provided that the skull has been fully prepared, you’re probably not going to see anything but a void bounded by bone. Yet, in cases of exceptional preservation, paleontologists have found intricate structures inside a few dinosaur noses called turbinates. Many tetrapods have turbinates – including us – and, in life, these scrolls of bone are covered by a soft mucosa called concha. These curious structures not only direct airflow through the nose, but often have other physiological duties like cooling blood or preventing water loss.

So when Bourke and colleagues working with Ohio University’s Witmer Lab CT scanned the classic Stegoceras skull, they found another case of dinosaur turbinates. Even better, scans of domes from another pachycephalosaur called Sphaerotholus revealed turbinates in that taxon, too. Pachycephalosaur noses weren’t just open vestibules. They had additional anatomy that altered airflow.

But how? To answer that question, Bourke and colleagues borrowed a modeling method often used in engineering called fluid dynamics. Given that we can never observe a living Stegoceras breathing, the researchers’ efforts to run virtual air through a 3D model of the dinosaur’s nose is the closest thing to seeing the extinct critter actually inspire air.

As an initial test, Bourke and colleagues ran air through the nose without any turbinates in place. The air didn’t blow by the dinosaur’s olfactory centers. This didn’t make sense. The researchers knew that the brain of Stegoceras had relatively large olfactory lobes, meaning that the dinosaur had a good sense of smell. Air had to come in contact with that sensory system.

Turbinates were the solution. Even though the actual, fossil turbinates couldn’t be teased out and reconstructed in their true form, Bourke and colleagues fashioned four models with different turbinate and concha anatomy based upon what’s seen in living birds, crocodiles, and lizards. And sure enough, with the turbinates in place the air was properly directed back to where the scents of the air could be picked up by the brain.

Of course, noses aren’t only for sniffing. In reconstructing the blood vessels around the dinosaur’s nose, Bourke and colleagues found that the turbinates probably acted as a cooling system, too. As the dinosaur breathed in and air passed over the turbinates, the researchers propose, the air would cool the warm blood inside before the vital fluid continued on to the brain. This arrangement would have allowed Stegoceras to remain literally cool-headed while running away from a tyrannosaur, or any other activity that would have generated a great deal of heat.

Diagram of bloodflow through the nasal region of Stegoceras. Courtesy of WitmerLab at Ohio University.
Diagram of bloodflow through the nasal region of Stegoceras. Courtesy of WitmerLab at Ohio University.

How other dinosaur noses worked, and what effect they had on dinosaur physiology, is largely unknown. The highly-armored ankylosaurs, for example, have confounded paleontologists with their  strangely circuitous nasal passages, and they had turbinates, too. And how turbinates affected the ability of tyrannosaurs to sniff out prey and regulate their brain temperature is an open question. That’s all just for starters. In time, more research like the Stegoceras study will uncover more details of prehistoric biology and show that a promising way to get to know a dinosaur is to look it in the nose.

Reference:

Bourke, J., Porter, W., Ridgely, R., Lyson, T., Schachner, E., Bell, P., Witmer, L. 2014. Breathing life into dinosaurs: tackling challenges of soft-tissue restoration and nasal airflow in extinct species. Anatomical Record. 297: 2148-2186.

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