A team of researchers led by the University of Tokyo has found that the living warm-blooded descendants of theropod dinosaurs have evolved a more efficient nasal cooling system aided by larger nasal cavities than their cold-blooded counterparts in order to cool off their heat-sensitive brains.
While cold-blooded animals such as reptiles (ectotherms) use external heat sources to keep warm, warm-blooded animals such as birds and mammals (endotherms) are able to maintain their high body temperature through internal heat sources. However, scientists have long pondered how endotherms manage to prevent overheating.
By analyzing the head specimens of 51 modern endotherms and ectotherms, as well as the skull of a theropod dinosaur called Velociraptor mongoliensis using computer tomography, the researchers discovered that endotherms’ noses are not only used for olfaction, but also contribute to heat exchange due to small undulating scroll-shaped structures called respiratory turbinates. These structures consist of bone and cartilage tissue and help moisten the inhaled air, and exchange heat from the circulating blood, thus cooling their brains.
Compared to ectotherms, endotherms have well-developed turbinates and a relatively larger nasal cavity compared to their head size. By contrast, V. mongoliensis had a smaller nasal cavity and most probably could not regulate temperature as efficiently as its modern-day descendants, suggesting that it had a less developed brain which did not need such efficient cooling. According to the experts, living endotherms’ nasal cooling system has likely co-evolved with changes in their skull structure.
“Our findings highlight the importance of the nose in inferring the physiology of fossil forms such as dinosaurs and enable us to study the evolution of drastic skull modification from the nonflying theropod dinosaurs to modern birds from a new angle,” concluded lead author Seishiro Tada, a doctoral student in Earth and Planetary Sciences at the University of Tokyo.
The study is published in the journal Royal Society Open Science.
By Andrei Ionescu, Earth.com Staff Writer
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