Scientists Reconstructed a Dinosaur’s Pea-Sized Brain

The brain is larger relative to the dinosaur’s body size than brontosaurus’ tennis ball-sized brain

An artist's rendition of Buriolestes schultzi next to a labeled diagram of its brain, including its cerebellum, cerebrum and olfactory bulb
Buriolestes schultzi was about the size of a fox and had a pea-sized brain. Courtesy of UFSM / Márcio L. Castro

A dinosaur fossil with an unusually well-preserved skull has given scientists the opportunity to reconstruct its brain in incredible detail, Veronique Greenwood reports for the New York Times.

The skull belonged to a dinosaur called Buriolestes schultzi, a fox-sized carnivore that lived in what’s now Brazil about 230 million years ago. Because the skull’s braincase was still intact, researchers at the Universidade Federal de Santa Maria in Brazil used computed tomography (CT) scanning to map its shape and figure out how the brain would have fit inside. Details of the skull’s shape provided hints as to the sizes of different brain structures.

Overall, the Buriolestes’ brain had a similar structure to that of a crocodile, says paleontologist and study co-author Rodrigo Müller to the U.K.-based South West News Service (SWNS). The brain committed a lot of energy to regions committed to vision processing, but relatively little to the sense of smell. A full description of the dinosaur’s brain is published in the Journal of Anatomy on November 2.

“The study of the brain of dinosaurs is booming as it is now easier than ever to reconstruct the brain morphology thanks to digital technology,” says Dinopolis Foundation paleontologist Fabien Knoll to the New York Times. “However, information about the brain in early dinosaurs is hampered by a lack of quality fossils. So I’d say that it is important to keep digging in those sites in Brazil, Argentina and elsewhere that are likely to provide well-preserved very early dinosaurs.”

Most dinosaur fossils either don’t include skulls or the skulls are broken, so the discovery of such a well-preserved dinosaur skull is exciting—even more so because it belongs one of the earliest known dinosaurs. Brains are soft tissue, so they are very unlikely to fossilize—the first fragment of fossilized dinosaur brain was discovered in 2016, Jason Daley wrote for Smithsonian at the time. Lacking the actual ancient brains, researchers rely on the cavity of the skull to work backwards and decode the brain’s shape.

According to the new study, Buriolestes schultzi’s brain had an elongated shape and weighed about 1.5 grams, as much as a pea, Tibi Puiu writes for ZME Science. That’s pretty small for an animal. For comparison, a similarly-sized fox has a 53 gram brain. But relative to its body size, Buriolestes had more brain power than its descendants.

Over the course of about 50 million years spanning the late Triassic period and the early Jurassic Epoch, the two-legged, carnivorous Buriolestes’ lineage evolved into gigantic, four-legged, plant-eating sauropods. While the dinosaurs grew bigger, their brains didn’t keep up. By the time the sauropods, like brontosaurus, reached 100 tons and 110 feet long, their brains were only the size of tennis balls.

Thi sfeature is strange because usually, evolution favors larger brains over time. The new study revealed other changes in the brain structure between Buriolestes and sauropods, too. While the early dinosaur had small olfactory bulbs, sauropods had large ones, meaning their sense of smell improved over time, Müller tells SWNS.

“The development of a high sense of smell could be related to the acquisition of a more complex social behavior – seen in several vertebrate groups,” says Müller to SWNS. “Alternatively, it has also been observed high olfactory capabilities played an important role in foraging – helping animals to better discriminate between digestible and indigestible plants,” and avoiding predators along the way.

The researchers suspect that vision processing was very important to a hunter like Buriolestes as it tracked its prey and avoided larger carnivores higher in the food chain, but less important to ponderous sauropods that ate only plants. And later carnivorous dinosaurs, like velociraptors and the famous Tyrannosaurus rex, had larger brains than Buriolestes.

The new study is intriguing, says Ohio University paleontologist Lawrence Witmer, who specializes in sauropods and wasn’t involved in the study, to the New York Times.

“It gives us a window into the earliest evolution of the brain and sensory systems of the largest animals ever to walk on land," says Witmer.