Pterosaurs prove big brains are not needed to fly — in contrast to modern bird ancestors

For more than a hundred years, scientists believed flying reptiles called pterosaurs took to the air with birdlike brains. Old fossils seemed to show it. Hard stone casts inside skulls hinted at big vision centers, short smell regions, and strong balance controls, much like birds.

Those clues tied flight to a special brain design. Bigger brains, the thinking went, meant better control in the sky. Birds helped cement the idea. Many birds have large brains for their size, and some rival primates. It felt simple. Smart brain equals smooth flight.

New research now tells a different story, and it is far more surprising.

A team led by Matteo Fabbri at Johns Hopkins Medicine used high-resolution CT scans to peer inside ancient skulls. Their work appeared in Current Biology and received support from the National Science Foundation. The scientists compared flying reptiles with birds and their kin. They also studied a small, tree-dwelling reptile that lived long before flight.

The results upend the old belief. Pterosaurs did not wait for a big bird brain to fly. They took off with a smaller brain, closer to other reptiles.

“Our study shows that pterosaurs evolved flight early on in their existence and that they did so with a smaller brain similar to true non-flying dinosaurs,” Fabbri says.

The turning point came from a fossil of Ixalerpeton polesinensis. This tiny animal lived more than 230 million years ago. It scurried in trees and likely hunted insects. Researchers consider it one of the closest known relatives of pterosaurs.

At last, a nearly complete brain cast from this species gave a clear picture. The brain was long and narrow. Smell took up about half its length. The thinking centers were small. By contrast, pterosaurs and birds have wider forebrains and shorter smell regions.

Yet one feature stood out. The vision center was already large and pushed to the side. That shift likely helped life in the branches, where sharp sight keeps you alive.

“The lagerpetid's brain already showed features linked to improved vision, including an enlarged optic lobe, an adaptation that may have later helped their pterosaur relatives take to the skies,” says Mario Bronzati of the University of Tübingen in Germany.

When pterosaurs later appeared in the fossil record, their brains changed quickly. Other traits fell into place in what looks like a rapid leap into flight.

“The few similarities suggest that flying pterosaurs, which appeared very soon after the lagerpetid, likely acquired flight in a burst at their origin,” Fabbri says. “Essentially, pterosaur brains quickly transformed acquiring all they needed to take flight from the beginning.”

Pterosaurs also carried a strange hallmark. A small region called the floccular lobe ballooned in size. This area helps steady the eyes and head. In some pterosaurs, it even exceeded the vision center.

No other animal, living or extinct, shows this extreme growth.

Why would that happen? Pterosaurs flew with skin membranes, not feathers. Those membranes were filled with nerves. They sent constant signals from wing to brain. Managing that flood of information likely demanded extra brain power.

Some once argued the fossil space might reflect blood vessels, not nerves. But scans of modern birds show the space mostly holds nerve tissue. That strengthens the case that the region was truly large.

A simple rule of biology helps here. When a brain area grows, it works hard. In pterosaurs, balance and visual control took center stage.

The team used 3D tools to compare shapes across species. Two measures explained most differences. One tracked how curved the brain was. The other measured forebrain growth.

Pterosaurs clustered near early birds like Archaeopteryx. Their brains curved in similar ways, with big vision areas and wider forebrains. Evolution reached a similar shape through a different route.

One species, Anhanguera santanae, even matched modern birds more closely than some living species such as the kiwi. That finding stunned the researchers.

Still, a key contrast remained. Pterosaurs had smaller brains for their size. When compared using thigh bone length, they resembled other reptiles more than birds. Flight did not demand a giant brain.

Birds followed another path. Their bodies shrank after dinosaurs died out. Only then did brains grow larger. In birds, flight came first. Brain boom came later.

A 2024 study by Amy Balanoff at Johns Hopkins Medicine supports that story. Her lab found growth in the cerebellum, a movement control center, played a role in bird flight.

“Any information that can fill in the gaps of what we don’t know about dinosaur and bird brains is important in understanding flight and neurosensory evolution within pterosaur and bird lineages,” Balanoff says.

Both groups flew. They just did it with different plans.

Pterosaurs launched with compact brains tuned for balance and sight. Birds took off with dinosaur brains and remodeled them over time. Each solved the riddle of flight in its own way.

Pterosaurs were no feathered copy. Some weighed hundreds of pounds and spanned nearly 30 feet from tip to tip. They ruled the skies long before birds.

The new work shows flight can rise from more than one blueprint. Nature can reach the same goal by different roads.

Fabbri sees the next step as even bigger. He hopes to link brain wiring, shape, and behavior to the physics of flight. That could reveal basic rules that guide how animals conquer the air.

These findings reshape how scientists think about flight, not just in fossils but in living animals and machines. By showing that large brains are not required for flight, the research frees engineers from one narrow model.

Designers of drones and robotic wings may look to pterosaurs for ideas about control systems that rely on fast sensory feedback rather than heavy processing. The study also sharpens how doctors and biologists link brain regions to function, which can inform care for balance and vision disorders.

Most of all, the work highlights evolution’s flexibility, a lesson that can guide future studies across biology and technology.

Research findings are available online in the journal Current Biology.

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