T. rex had a giant air conditioner in its noggin

Sept. 6 (UPI) -- To keep cool, Tyrannosaurus rex, one of the largest carnivores to ever roam the planet, deployed an air-conditioning-like system of blood vessels inside its head.

Paleontologists knew there was something unique about the top of T. rex's head. The top of the dinosaur's skull hosts a pair of large holes, the dorsotemporal fenestra.

Prior to the latest study, scientists assumed muscles filled the cavities. When earlier researchers reconstructed the anatomy of T. rex's head, they looped the temporal muscles up to the top of the skull.

Something about those early reconstructions didn't sit right with Casey Holliday, a professor of anatomy at the University of Missouri. Holliday and his research partners took a closer look.

"After careful study we found that jaw muscles couldn't really work right if they attached in this particular spot, and instead blood vessels probably excavated the space," he told UPI in an email.

To better understand what purpose a knot of blood vessels at the top of the dinosaur's head might serve, the team of researchers, which included scientists from Ohio University and the University of Florida, turned their attention to alligators, which also boast a pair of holes in the top of their skull.

"Alligators are close relatives of dinosaurs like birds and the T. rex, and share many of the same anatomical features," Holliday said.

Scientists trained thermal imaging cameras on alligators as they went about their day, tracking the movement of heat in and out of their bodies. During the coolest parts of the day, the images showed the top of the alligators head, near the dorsotemporal fenestra, turned red, indicating an influx of heat. During the hottest parts of the day, midday, the holes appeared dark blue, indicating a cooling function.

Researchers concluded that T. rex, like alligators, deployed a cross-current circulatory system in the top of it's head to help warm up and cool down. Holliday and his colleagues shared their conclusions in the journal The Anatomical Record.

According to the study's authors, T. rex and alligators aren't alone in their deployment of unique temperature-regulating vascular systems.

"Even though T. rex is getting all the focus, we found that most dinosaurs, crocodilians, birds and other fossil archosaurs have similar vascular structures, all of which probably affect the physiology of the animals," Holliday said. "These same blood vessels supply the frills of Ceratopsian dinosaurs, crests of pterosaurs, and skull roofs of weird crocodiles like Aegisuchus, and fleshy display structures of birds like turkeys and vultures. The feature is quite ubiquitous among archosaurs."

Earlier this week, scientists reported the discovery of a unusual maze of blood vessels in the heads of blue-banded sea snakes. The structure helps the marine snake absorb oxygen from the water while diving.

"I think we're just beginning to appreciate all the complicated physiological structures reptiles employ to control body temperature, besides just hanging out in the sun or shade," Holliday said.