The pterosaur rapidly evolved flight abilities, in contrast to modern bird ancestors, new study suggests

(Press-News.org) In a study of fossils, a research team led by an evolutionary biologist at Johns Hopkins Medicine suggests that a group of giant reptiles alive up to 220 million years ago may have acquired the ability to fly when the animal first appeared, in contrast to prehistoric ancestors of modern birds that developed flight more gradually and with a bigger brain.

A report on the study, which used advanced imaging tools to study the brain cavities of pterosaur fossils, and was funded in part by the National Science Foundation, was published Nov. 26 in Current Biology.

The findings add to evidence that enlarged brains seen in modern birds and presumably in their prehistoric ancestors were not the driver of pterosaurs’ ability to achieve flight, says Matteo Fabbri, Ph.D., assistant professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine. 

“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.

Fabbri says the pterosaur was a force to be reckoned with in dinosaur skies, weighing up to 500 pounds and with a wingspan of up to 30 feet in some species. It is known to be the oldest of three groups of flying vertebrates (in addition to birds and bats) that independently evolved self-powered flight.

To learn whether pterosaurs acquired flight differently than birds and bats, the scientists studied the reptile’s evolutionary tree to pinpoint the evolution of pterosaur brain shape and size, looking for clues that may have led to the development of flight. They focused particularly on the area involved in vision, the optic lobe, the growth of which is thought to be associated with flying abilities.

Using CT scans and imaging software that allowed the scientists to extract information about the nervous systems of fossils, the researchers honed in on the pterosaur’s closest relative initially described by a team of researchers in 2016, the flightless, tree-dwelling lagerpetid that originated during the Triassic period 242 to 212 million years ago. In 2020, another group of scientists characterized the lagerpetid’s close relation to the pterosaur.

“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 corresponding author Mario Bronzati, a researcher at University of Tübingen, Germany.      

A larger optic lobe was also present in pterosaurs, Fabbri says. However, he says there were otherwise very few similarities in the shape and size of pterosaur brains and that of the flying reptile’s closest relative, the lagerpetid.

“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.”

By contrast, modern birds are believed to have acquired flight in a step-by-step, more gradual process, inheriting certain features, such as an enlarged cerebrum, cerebellum and optic lobes from their prehistoric relatives, and later adapting them to enable flight, says Fabbri. This theory is supported by 2024 findings from the lab of Amy Balanoff, Ph.D., assistant professor of functional anatomy and evolution at Johns Hopkins Medicine, that point to the expansion of the brain’s cerebellum as a key to bird flight. The cerebellum, located at the back of the brain, regulates and controls muscle movement among other activities.

“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.

In further studies, the scientists analyzed brain cavities of fossils from crococdylians (crocodile ancestors) and early, extinct birds, and compared these with pterosaur brain cavities.

They determined that the pterosaur's brain had moderately enlarged hemispheres, similar in size to other dinosaurs—including two-legged bird-like troodontids living during the Late Jurassic to the Late Cretaceous periods 163 to 66 million years ago, and the oldest-known bird, Archaeopteryx lithographica from 150.8 million to 125.45 million years ago—compared with the brain cavities of modern birds.

In the future, Fabbri says that better understanding how the structure of the pterosaur brain, in addition to the size and shape, enabled flight will be the most important step to better infer the basic biological laws of flight. 

Funding support for this research was provided by the Alexander von Humboldt Foundation, Brazilian Federal Government, The Paleontological Society, Agencia Nacional de Promoción Científica y Técnica, Conselho Nacional de Desenvolvimento Científico e Tecnológico, the European Union NextGeneration EU/PRTR, the National Science Foundation ( NSF DEB 1754596, NSF IOB-0517257, IOS-1050154, IOS-1456503), and the Swedish Research Council

In addition to Fabbri and Bronzati, other scientists who contributed to this research are Akinobu Watanabe from New York Institute of Technology, Roger Benson from the American Museum of Natural History, Rodrigo Müller from Federal University of Santa Maria, Brazil, Lawrence Witmer from the University of Ohio, Martín Ezcurra and  M. Belén von Baczko from Bernardino Rivadavia Museum of Natural Science, Felipe Montefeltro from São Paulo State University; Bhart-Anjan Bhullar from Yale University; Julia Desojo from Universidad Nacional de La Plata, Argentina; Fabien Knoll from Museo Nacional de Ciencias Naturales, Spain; Max Langer from Universidade de São Paulo, Brazil; Stephan Lautenschlager from University of Birmingham; Michelle Stocker and Sterling Nesbitt from from Virginia Tech; Alan Turner from Stony Brook University; and Ingmar Werneburg from Eberhard Karls University of Tübingen.

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