Matheus Fernandes
A new study reveals how pterosaurs—long-extinct reptiles—evolved the neurological structures required for powered flight. The study, published recently in Current Biology by an international team led by the University of Tübingen in Germany, is based on the discovery of an ancient pterosaur relative, a small lagerpetid archosaur named Ixalerpeton, from 233-million-year-old Triassic rocks in Brazil.
Flight has evolved only two other times in vertebrates—in bats and birds. Pterosaurs were the first to achieve this feat, taking to the skies more than 220 million years ago, tens of millions of years before early bird relatives appeared.
“Scientists have come to know a lot about how the flight-ready brain of birds evolved by examining the rich fossil record of closely related dinosaurs, but the evolutionary story of pterosaur brains has remained elusive until now because it wasn’t clear who the ancestors of pterosaurs were until very recently,” said Akinobu Watanabe, associate professor of anatomy at the New York Institute of Technology and a research associate in the Museum’s Division of Paleontology.
The researchers used high-resolution 3D imaging techniques to reconstruct the shape of the brain cavity in more than three dozen species of pterosaurs and other extinct species, including close relatives of pterosaurs, early dinosaurs and bird precursors, modern crocodiles and birds. They then mapped the changes in brain anatomy that accompanied the evolution of flight, using statistical analysis.
Flight has long been assumed to require major neurological adaptations including enlargement of the brain. Previous studies of pterosaur brain structure had shown that they shared some similarities with early birds like Archaeopteryx, such as some enlargement of brain regions like the cerebrum, cerebellum, and the optic lobes.
But the new analyses show that, despite the enlargement of certain regions, pterosaurs retained modest brain sizes overall, smaller than those of living birds.
“While there are some similarities between pterosaurs and birds,” said coauthor Matteo Fabbri, assistant professor of Functional Anatomy and Evolution at the Johns Hopkins University School of Medicine, “their brains were actually quite different, especially in size. 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. But pterosaurs and birds still represent two 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.
Ixalerpeton, the newly discovered pterosaur relative, had a brain intermediate in shape between more primitive archosaurs and pterosaurs, with greater similarity to early dinosaurs. Likely tree-dwellers, Ixalerpeton already had features linked to improved vision, such as an enlarged optic lobe, but they still lacked key neurological traits of pterosaurs, including an enlarged flocculus, a structure of the cerebellum that was probably involved in processing sensory information.
“Pterosaurs are some of the most inspiring extinct groups, because they were the first vertebrates to evolve flight. But many aspects of their biology and evolution remain mysterious,” said study co-author Roger Benson, the Museum’s Macaulay Curator of Dinosaur Paleobiology. “It’s exciting to see how the brain evolved in some ways similar to birds, but in other ways very different”