How large dinosaurs kept cool heads

Jason Bourke
Jason Bourke

In what is now the Southern United States 110 million years ago, a titanic predatory dinosaur prowled. Its name was Acrocanthosaurus and it was the top predator of its day. From afar it would have looked similar to its more famous cousin Tyrannosaurus. Despite this impressive status, Acrocanthosaurus had a problem. It was a problem shared by all large dinosaurs. Its brain was under constant heat stress. Acrocanthosaurus was the size of a large dump truck, but its brain could fit in the palm of your hand.

Heat moves slower in larger bodies than smaller ones. That’s why hamsters constantly shiver while zoo elephants can roam outside during the winter. However, this means that under high temperatures, large animals run the risk of overheating since their bodies can’t release excess heat fast enough. Brains are not very tolerant of temperature swings, and high temperatures cause permanent damage and eventually brain death. The small brains of dinosaurs, encased inside their enormous bodies, were at constant risk of overheating. Dinosaurs had to have some way of keeping their brains cool.

Modern-day animals (including humans) use their noses to dump heat from the body into the air. This cools our blood as it goes to the head, creating a thermal buffer between our brains and the heat coming from our body’s core. The skulls of most large dinosaurs show that their noses expanded as body size increased, suggesting that they probably used their noses as air conditioners too. Strangely, Acrocanthosaurus and its relatives don’t show this trend. They retained fairly simple noses regardless of body size. So how did Acrocanthosaurus keep its brain from frying?

To answer this question I am studying the skull of an Acrocanthosaurus. The North Carolina Museum of Natural Sciences houses the most complete Acrocanthosaurus skull ever discovered. Using CT scanning technology, I am digitally reconstructing its nose. With powerful computers, I can simulate air movement through this reconstructed nose. These simulations show me firsthand how effective the nose of Acrocanthosaurus was at cooling its blood. By finding where the nose fails I can search for other regions of the head that could have compensated for it. By testing brain cooling efficiency in Acrocanthosaurus, I can start addressing questions of how active it was. Together this provides a clearer picture of how Acrocanthosaurus and other dinosaurs lived in their environments so long ago.

Jason Bourke is a postdoctoral researcher in the North Carolina Museum of Natural Sciences’ Paleontology Research Lab