Ankylosaurs are the group of herbivorous ornithischians that looked like armoured-rhinos. Renowned for being covered in thick bony plates for protection against predators, many also wielded dangerous clubs on their tails – even lending some the nickname ‘destroyer of shins’ as a result.
But, as Ace Ventura let us know oh too well, it sure does get kinda hot in these rhinos. So, imagine for a second what it might be like for a rhino covered in armour plates.
Well, was it the same for ankylosaurs? A new study shows that ankylosaurs were able to regulate their body temperature using a system of nasal passages that allowed for more efficient exchange between the air and the body. This is similar to the process that some modern mammals and birds use, whereby air is warmed as it is inhaled, and cooled as it exhales to reduce heat loss.
Such a suggestion linking form and function has been proposed before for ankylosaurs, with research dating back to the 1970s. But one of the cool things about much of modern Paleontology is that it is about looking at old questions using new techniques. So while much of this discovery is largely thanks to a wave of new ankylosaur discoveries, often with exquisite, three-dimensional preservation, much is also down to modern digitisation and imaging techniques. These are opening up new dimensions into how researchers can reconstruct and analyse extinct animals, and bring Paleontology into the digital 21st century of research.
What the researchers were able to do is construct 3D digital reconstructions of the fossilised nasal passages from two ankylosaur species, Panoplosaurus mirus and Euoplocephalus tutus. From this, they applied computational fluid dynamic analyses, the sort of tests designed for aeronautical or automotive engineering, to simulate airflow and heat transfer during a simulation of breathing.
By doing this, they were able to quantify just how much heat energy would be preserved, estimating it to be between 65% and 84% per breath. This is comparable to many modern mammals that live on land, and also would have helped to save on energy bills. When you take in between 34-64 litres of air in each breath, as the researchers estimated, this equates to quite a bit of heat energy being conserved.
Lead author of the study, Jason Bourke said: “The large body sizes of dinosaurs like ankylosaurs, would have worked great for retaining heat, but they would also have put the small brains of these dinosaurs at a constant risk of overheating. Ankylosaurs appear to have solved this problem by greatly stretching out and coiling their nasal passages within their skull, allowing them to cool down blood destined for the brain and providing an effective air conditioner for their heads.”
It seems that by having a complex maze of air passages, ankylosaurs were able to therefore regulate their body temperatures much more efficiently. By coiling into a labyrinthine fleshy network, this helped to increase the relative surface area to volume to allow much more efficient transfer of heat during breathing. Evolution, you so crazy.
Bourke JM, Porter WR, Witmer LM (2018) Convoluted nasal passages function as efficient heat exchangers in ankylosaurs (Dinosauria: Ornithischia: Thyreophora). PLoS ONE 13(12): e0207381. https://doi.org/10.1371/journal.pone.0207381