Ankylosaur noses were cool
Or rather, their brains were cool thanks to their noses.
The latest work from my dissertation has recently hit the net newswire. This time it's
about ankylosaurs and their crazy long airways. We've known that ankylosaurs had crazy convoluted nasal passages since Witmer and Ridgely uncovered this in 2008. In that paper and subsequent talks it was hypothesized that this extreme elongation may have come about as a means of enhancing the thermoregulatory capacity of the nose by providing more room for heat exchange to occur. I decided to functionally test this hypothesis using the computational fluid dynamic (CFD) techniques I have developed over the years. I performed a "simple" steady-state analysis of airflow during inspiration and expiration in the two ankylosaur taxa from Witmer and Ridgely 2008 (Panoplosaurus mirus and Euoplocephalus tutus). I looked at the heat transfer across the nasal passage during inspiration and during expiration. I also took the initial segmentation results from Witmer and Ridgely 2008 and incorporated missing soft-tissue (dramatically shrinking the calibre of the airway). These data were presented at the 74th annual meeting of the Society of Vertebrate Paleontology in Berlin, Germany. My results indicate that both dinosaurs were quite good at warming inspired air (I had the dinosaurs raise inspired air temperature from 15°C to 35°C at 50% relative humidity) and cooling it back down upon expiration. I also found that the larger E. tutus was slightly better and warming air than P. mirus. This was not too surprising as E. tutus has a noticeably more convoluted nasal passage. I suspect that the larger size of E. tutus was the driving force behind the more convoluted airway and more efficient heat exchanger. Larger animals have bigger heat loads to deal with. Not only would both dinosaurs be good at warming up inspired air, but it would come at the cost of cooler leaving the nasal passage. My colleague, Ruger Porter, found that these nasal vessels would have headed to the brain. Thus it seems that ankylosaurs had developed an efficient means of cooling down their brains. It was likely that having a source of cooled blood was necessary for keeping the brain from boiling inside the head. We know that many extant animals use this oronasal pathway to keep their brains from overheating (this is why dogs pant on hot days), but this was the first time that we were able to show that dinosaurs also took advantage of this pathway, or at least had the potential to.
All that said it is important to keep in mind that these results are still preliminary. The paper is currently in the works. We still need to test the effects of relative humidity on the efficiency, as well as the range of air flow velocities in which this ability holds up. So there is still a fair amount of work to do before we can say anything definitive about these airways. Nonetheless, these preliminary data do seem to indicate that ankylosaurs found a functional alternative to the respiratory turbinates we see in most mammals and birds. That in itself is very interesting.
Stay tuned for more.