Large armoured dinosaurs kept cool by using an air conditioning system built into their noses, scientists have discovered.
The heavily armoured, club-tailed ankylosaurs are thought to have stopped themselves from overheating in the Cretaceous sun by using their long and twisting nasal passages.
These acted as radiators, transferring heat from the body to the inhaled air and cooling blood on its way to the brain.
Ruger Porter, one of the study's co-authors, said: "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.
"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."
Researchers from Ohio University and the New York Institute of Technology College of Osteopathic Medicine published their findings in the journal PLOS ONE.
They used CT scanning and engineering to simulate how air moved through the nasal passages of two different ankylosaur species, the hippo-sized Panoplosaurus and larger rhino-sized Euoplocephalus.
Ankylosaurs were good at retaining heat but struggled to shed it, putting them at risk of overheating even on cloudy days.
The results "clearly showed" that nose length was key to their air-conditioning ability, with heat-transfer rates dropping more than 50 per cent when a shorter nose model was tested.
This natural engineering feat "may have allowed the evolution of the great sizes of so many dinosaurs", they believe.
The most elaborate noses were found in the larger dinosaur species, suggesting they may have evolved as a response to the "physiological stresses of large body size".
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