Flight is a rare skill in the animal world. Among vertebrates, it evolved only three times: in bats, birds, and the long-extinct pterosaurs. Pterosaurs were the first to master the skies more than 220 million years ago, long before early bird relatives such as Archaeopteryx appeared. Scientists have pieced together a detailed fossil record showing how birds’ brains adapted for flight, but the neurological origins of pterosaur flight have remained far less clear.
A new study published in , co-authored by Ƶ researcher Lawrence Witmer, as well as with researchers from all over the world, now sheds light on how pterosaurs evolved the neurological structures required for powered flight. For Witmer, the project represents a return to a research path he helped define more than two decades ago, when his 2003 Nature study revealed the complex brain and inner-ear structures that enabled pterosaurs to maneuver in the air. This latest work builds on those early discoveries and provides the clearest view yet of how these remarkable reptiles evolved the neural “flight equipment” that powered their airborne lifestyle.
“We’ve had abundant information about early birds and knew they inherited their basic brain layout from their theropod dinosaur ancestors,” said Witmer, a professor of anatomy at the Ƶ Heritage College of Osteopathic Medicine. “But pterosaur brains seemed to appear out of nowhere. Now, with our first glimpse of an early pterosaur relative, we see that pterosaurs essentially built their own ‘flight computers’ from scratch.”
“The breakthrough was the discovery of an ancient pterosaur relative, a small lagerpetid archosaur named Ixalerpeton from 233-million-year-old Triassic rocks in Brazil,” Mario Bronzati, an Alexander von Humboldt fellow at the University of Tübingen in Germany and lead author of the study, said.
To piece together this evolutionary story, the researchers used high-resolution 3D imaging techniques, including microCT scanning, to reconstruct brain shapes from more than three dozen species. These included pterosaurs, their close relatives like Ixalerpeton, early dinosaurs and bird precursors, modern crocodiles and birds, and a wide range of Triassic archosaurs, the larger group that includes all these animals.
“Then, using statistical analysis of the size and 3D shape of their cranial endocasts, we were able to map the stepwise changes in brain anatomy that accompanied the evolution of flight,” said coauthor Akinobu Watanabe, associate professor of anatomy at the New York Institute of Technology College of Osteopathic Medicine.
Flight is a physiologically demanding form of locomotion and has long been assumed to require major neurological adaptations including enlargement of the brain to coordinate the complicated sensory and motor information required for powered flight. Previous studies of pterosaur brain structure had shown that they indeed shared some neurological similarities with bird precursors like Archaeopteryx, such as some enlargement of brain regions like the cerebrum and cerebellum involved with sensorimotor integration, as well as enlargement of visual centers like the optic lobes.
Ixalerpeton, the lagerpetid close relative of pterosaurs showed some but not all neurological traits of pterosaurs. For example, as Bronzati notes, “lagerpetids were probably tree-dwellers, and their brains already show features linked to improved vision, such as an enlarged optic lobe, an adaptation that may have later helped their pterosaur relatives take to the skies, but they still lacked key neurological traits of pterosaurs.”
Lagerpetids like Ixalerpeton had brains intermediate in shape between more primitive archosaurs and pterosaurs but retain greater similarity to early dinosaurs. Other than the enlarged optic lobe that occupies a position in the brain similar to that in pterosaurs and birds and their close theropod relatives, there is little in Ixalerpeton that indicates what was to come in pterosaurs. A unique feature of the brain of pterosaurs is a greatly enlarged flocculus, a structure of the cerebellum likely involved in processing sensory information from their membranous wings to keep their eyes fixed on a target while in flight. The flocculus in Ixalerpeton wasn’t expanded like pterosaurs, instead resembling the modest flocculus of other archosaurs, including early birds and their close nonavian theropod relatives.
Likewise, the new analyses show that pterosaurs retained modest brain sizes.
“While there are some similarities between pterosaurs and birds, their brains were actually quite different, especially in size,” said coauthor Matteo Fabbri, assistant professor of Functional Anatomy and Evolution at the Johns Hopkins University School of Medicine. “Pterosaurs had much smaller brains than birds, which shows that you may not need a big brain to fly.”
Surprisingly, the overall brain shape of pterosaurs most closely resembled that of small, bird-like dinosaurs such as troodontids and dromaeosaurids, animals that had little or no powered flight ability. Yet pterosaurs and birds still represent two entirely independent experiments in the evolution of flight. Birds inherited a brain already adapted from their non-flying dinosaur ancestors, while pterosaurs evolved their flight-ready brains at the same time they developed their wings.
Birds’ notably large brains, the authors note, likely came later and were tied more to increasing intelligence and complex behaviors rather than the act of flying itself. A key takeaway from the study is that, according to Witmer, “it apparently doesn’t take a large brain to get into the air, and the later brain expansion in both birds and pterosaurs was likely more about enhancing cognition than about flying itself.”
Another important takeaway is that paleontological fieldwork remains an engine for new breakthroughs.
“Discoveries from southern Brazil have given us remarkable new insights into the origins of major animal groups like dinosaurs and pterosaurs,” coauthor Rodrigo Temp Müller, a paleontologist at Universidade Federal de Santa Maria, Brazil, noted. “With every new fossil and study, we’re getting a clearer picture of what the early relatives of these groups were like, something that would have been almost unimaginable just a few years ago.”
The full list of coauthors includes: Mario Bronzati, Akinobu Watanabe, Roger B. J. Benson, Rodrigo T. Müller, Lawrence M. Witmer, Martín D. Ezcurra, Felipe C. Montefeltro, M. Belén von Baczko, Bhart-Anjan S. Bhullar, Julia B. Desojo, Fabien Knoll, Max C. Langer, Stephan Lautenschlager, Michelle R. Stocker, Alan H. Turner, Ingmar Werneburg, Sterling J. Nesbitt, and Matteo Fabbri.
The research was funded by the Alexander von Humboldt Foundation, Germany; Financiadora de Estudos e Projetos - Brazilian Federal Government; a Sepkoski Grant of the Paleontological Society; Agencia Nacional de Promoción Científica; Conselho Nacional de Desenvolvimento Científico e Tecnológico; INCT Paleovert’ European Union NextGeneration; the U.S. National Science Foundation; and the Swedish Research Council.