The dreaded Tyrannosaurus rex -- one of the largest meat-eating dinosaurs on the planet -- had an air conditioner in its head, according to a study that challenges over a century of previous beliefs.
Scientists previously believed that two large holes in the roof of a T rex's skull -- called the dorsotemporal fenestra -- were filled with muscles that assist with jaw movements, according to the study published in The Anatomical Record journal.
"It's really weird for a muscle to come up from the jaw, make a 90-degree turn, and go along the roof of the skull," said Casey Holliday, a professor at the University of Missouri in the US.
"Yet, we now have a lot of compelling evidence for blood vessels in this area, based on our work with alligators and other reptiles," Holliday said.
Using thermal imaging -- devices that translate heat into visible light -- researchers examined alligators at the St Augustine Alligator Farm Zoological Park in Florida, US.
They believe their evidence offers a new theory and insight into the anatomy of a T rex's head.
"An alligator's body heat depends on its environment," said Kent Vliet, coordinator of laboratories at the University of Florida in the US.
"Therefore, we noticed when it was cooler and the alligators are trying to warm up, our thermal imaging showed big hot spots in these holes in the roof of their skull, indicating a rise in temperature," Vliet said.
"Yet, later in the day when it's warmer, the holes appear dark, like they were turned off to keep cool. This is consistent with prior evidence that alligators have a cross-current circulatory system -- or an internal thermostat, so to speak," he said.
Holliday and his team took their thermal imaging data and examined fossilised remains of dinosaurs and crocodiles to see how this hole in the skull changed over time.
"We know that, similarly to the T rex, alligators have holes on the roof of their skulls, and they are filled with blood vessels," said Larry Witmer, a professor at Ohio University in the US.
"Yet, for over 100 years we've been putting muscles into a similar space with dinosaurs. By using some anatomy and physiology of current animals, we can show that we can overturn those early hypotheses about the anatomy of this part of the T rex's skull," Witmer said.