New research using advanced fossil imaging shows that early pterosaurs – the first flying reptiles – may have mastered flight almost immediately upon their appearance, without needing a large brain like birds.
New research using advanced fossil imaging shows that ancient pterosaurs – the first flying reptiles – may have mastered flight almost immediately upon their appearance, without needing a large brain like that of birds.
A team of researchers examining ancient fossils, led by an evolutionary biologist at Johns Hopkins Medicine, reports that a lineage of large reptiles that lived as early as 220 million years ago may have acquired the ability to fly early in their existence. This idea runs counter to what is commonly thought about the ancient relatives of modern birds, which seem to have adopted flight gradually, along with an increase in brain size.
Details of the study, which used advanced imaging techniques to examine the brain cavities of pterosaur fossils, were published in the journal Current Biology. The study was supported in part by the National Science Foundation (NSF).
According to Dr. Matteo Fabbri, an associate professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine, the findings strengthen the assumption that the enlarged brains of modern birds – which we thought their ancient ancestors also shared – were not a necessary condition that allowed pterosaurs to fly.
"Our study shows that pterosaurs developed flight early in their existence, and that they did so with a smaller brain, similar to that of true, non-flying dinosaurs," says Fabry.
He adds that pterosaurs were powerful fliers during the dinosaur era. Some species weighed up to 500 pounds, or 230 kilograms, and their wingspan (and spread) reached about 30 feet—about 9 meters—from wingtip to wingtip. Pterosaurs are considered the earliest of the three groups of flying vertebrates to independently develop active flight: pterosaurs, birds, and bats.
To test whether pterosaurs evolved flight in a different way than birds and bats, the researchers traced their evolutionary history and tracked changes in brain shape and size over time. They focused specifically on the visual cortex, the part of the brain responsible for processing visual information, whose expansion is thought to be linked to the development of flight capabilities.
Using CT scans and imaging software that allowed researchers to extract information about the nervous system from the fossils, the team focused on the closest relative of pterosaurs, first described in 2016: the flightless lagereptid, which lived in trees during the Triassic period 242 to 212 million years ago. In 2020, another study showed the close relationship between lagereptids and pterosaurs.
"The lagereptid brain already showed features related to improved vision, including an enlarged visual lobe. This may have been an adaptation that later helped their pterosaur relatives conquer the skies," says the paper's lead researcher, Dr. Mario Bronzati of the University of Tübingen in Germany.
Fabry notes that a larger visual lobe also appeared in pterosaurs themselves. However, he says, there is little other similarity in brain shape and size between pterosaurs and their flightless relatives, the legerptids.
"The few similarities we do see suggest that the flying pterosaurs, which appeared very shortly after the legraptiids, probably acquired the ability to fly all at once early in their evolution," says Fabry. "In other words, the pterosaur brain changed rapidly, and early in their evolution they were equipped with everything they needed to take off."
Modern birds, by contrast, are thought to have evolved flight in a more gradual, step-by-step process. They inherited traits from their ancient relatives such as an enlarged forebrain (cerebrum), a large cerebellum (cerebellum) and well-developed visual lobes, and later adapted these traits to support flight, says Fabry. This view is also supported by findings from 2024 from the lab of Dr. Amy Balanoff, a professor of functional anatomy and evolution at Johns Hopkins Medicine, who showed that the expansion of the cerebellum is key to birds' ability to fly. The cerebellum, located at the back of the brain, is responsible, among other things, for regulating and controlling muscle movement.
"Any information that fills the gaps in our knowledge about the brains of dinosaurs and birds is important for understanding flight and sensory-neuronal evolution in the pterosaur and bird lineages," says Blanoff.
In the next step, the scientists compared the brain cavities in fossils of ancient crocodilians and extinct ancient birds, and also compared them to the brain cavities in fossil pterosaurs.
They found that pterosaur brains had moderately enlarged hemispheres, similar in size to those found in other dinosaurs. Examples include the bipedal, bird-like dinosaurs of the troodontid family, which lived from the Late Jurassic to the Late Cretaceous, about 163 to 66 million years ago, and the oldest known bird, Archaeopteryx lithographica, which lived about 150.8 to 125.45 million years ago. All of these differed from the brains of modern birds.
Fabry says that in the future, understanding how the internal structure of pterosaur brains – and not just their size and shape – enabled flight will be the most important step towards deriving biological “fundamental laws” of flight.
More of the topic in Hayadan:
