To ward off overheating, large animals such as elephants and rhinos had to evolve strategies to keep cool. Dinosaurs like Tyrannosaurus rex likely faced the same problem—and new research finds that the huge carnivores solved it by developing giant air conditioners in their heads.

Researchers led by Casey Holliday looked at large holes in the tops of carnivorous dinosaur skulls called dorsotemporal fenestrae. Careful anatomical study revealed that the cavities probably contained tissue rich with fat and blood vessels.

These structures may have been useful for dumping heat into the environment when dinosaurs were running too hot and absorbing heat when they got cold, the team reports in the journal The Anatomical Record.

“We found that the big theropod dinosaurs—and even