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Pterosaurs, which dominated the skies of the Triassic, Jurassic and Cretaceous periods, first evolved to take to the air in warm and humid conditions during the Late Triassic, a new study suggests.

In a paper published in Nature Ecology & Evolution, a research team—including academics from the University of Birmingham, University College London and Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany—has combined data on the distribution of fossils in the Triassic period with information on the ancient climate in the same areas.

The team focused on the distribution of two closely related groups, pterosaurs and lagerpetids. Living approximately 240–201 million years ago, lagerpetids were a group of relatively small (rat-to-dog-sized) land- and tree-dwelling active reptiles. These small land-based reptiles are now considered the closest relatives to pterosaurs, the study reveals, and were able to tolerate a wider range of climate conditions than their close flying kin, including the arid areas of the ancient landmass Pangea. This broad tolerance resulted in a widespread distribution of this group.

Pterosaurs, meanwhile, appear to have been at first confined to the more humid conditions found in smaller areas of the ancient world, based on fossils found in modern-day Italy and Austria, and the southwestern U.S.A., all regions that at the time were close to the equator.

During the Late Triassic, climatic conditions changed across the globe, leading to a general increase in warm and humid conditions outside the equatorial belt. This became an opportunity that allowed the flying reptiles to rapidly spread across the globe, including to high-latitude areas such as what is now Greenland and South America.

Dr. Davide Foffa from the University of Birmingham, and corresponding author of the paper, said, "Pterosaurs capture the imagination, with the idea of terrifying reptiles dominating the air at the time while dinosaurs were roaming the world. However, pterosaur origins are still wrapped in mystery. Our study adds new information to this puzzle, suggesting that their early evolution during the Triassic period into a dominant group may have been favored by changing climates and environments."

Dr. Emma Dunne, from Friedrich-Alexander-Universität Erlangen-Nürnberg, and a co-author of the paper, added, "Climate change is a leading cause of biodiversity change, both in the present day and the geological past. However, it is only in the last few years [with advances in modeling methods] that paleontologists are getting to grips with how climate change impacted the biodiversity of prominent fossil groups like the pterosaurs."

Dr. Alessandro Chiarenza, from University College London, and co-leading author of the paper, noted, "Taken together, ecological models and fossil data paint a coherent picture of early pterosaur evolution. Lagerpetids thrived as generalists, while pterosaurs, initially confined to humid tropical niches and perhaps limited flight performance, occupied equatorial treetops."

When global climates shifted and forested corridors opened, those same wings catapulted them into every corner of the planet and ultimately carried them through one of Earth's greatest extinctions. What began as a tale of missing fossils is becoming a textbook example of how paleoclimate, paleoecology and evolutionary innovation intertwine to illuminate a patchy history that has intrigued paleontologists for two centuries.