Pterosaur Precursors Found to Fill Gap in Early Evolutionary History

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(CN) — For 150 million years, pterosaurs reigned as the only creatures in the skies, their broad wings and elongated skulls creating a unique silhouette that has captured human imagination since their discovery in the 19th century.

But details of their evolution and ability to fly have remained a mystery to scientists — until now: Virginia Tech researchers Sterling Nesbitt and Michelle Stocker have found pterosaurs’ closest relatives, a group of “dinosaur precursors” called lagerpetids.

“’Where did pterosaurs come from?’ is one of the most outstanding questions in reptile evolution,” said Nesbitt, associate professor of geosciences and an affiliated faculty member of the Fralin Life Sciences Institute and the Global Change Center. “We think we now have an answer.”

Analyzing newly discovered skulls and skeletons unearthed in North America, Brazil, Argentina and Madagascar, researchers were able to fill gaps in the pterosaurs’ evolutionary record with fossils of Dromomeron gregorii, a species of lagerpetid that had been misidentified since its discovery in Texas in the 1930s. Of particular interest was a well-preserved skull and braincase revealing that these reptiles had good equilibrium and were likely agile, according to findings published in the journal Nature.

With additional fossil evidence from more lagerpetid species in South America, paleontologists began to create a picture of the small, wingless reptiles that lived across Pangea during much of the Triassic Period.

For decades, paleontologists recognized that the length and shape of lagerpetids bones were similar to those of pterosaurs and dinosaurs. But considering how different the two species appeared, it’s easy to understand how paleontologists mischaracterized the significance of lagerpetids — which seemed closer to dinosaurs than their flying reptile relatives. This gap in knowledge led paleontologists to attribute extremely fast evolution for the pterosaurs’ acquisition of wings and other unique features.

More recent lagerpetid fossils, however, displayed pterosaur features too similar to ignore. So researchers used micro-computed tomographic (CT) scanning to reconstruct their brains and sensory systems within the recently discovered skulls, allowing paleontologists to striking imilarities with those of pterosaurs.

“CT data has been revolutionary for paleontology,” noted Stocker, an assistant professor of vertebrate paleontology. “Some of these delicate fossils were collected nearly 80 years ago, and rather than destructively cutting into this first known skull of Dromomeron, we were able to use this technology to carefully reconstruct the brain and inner ear anatomy of these small fossils to help determine the early relatives of pterosaurs.”

In light of this new knowledge, paleontologists think pterosaurs evolved at the same rate as other major reptile groups.

“Flight is such a fascinating behavior, and it evolved multiple times during Earth’s history,” said Serjoscha W. Evers of the University of Fribourg in Switzerland. “Proposing a new hypothesis of their relationships with other extinct animals is a major step forward in understanding the origins of pterosaur flight.”

Remarkably, flightless lagerpetids had already evolved some of the neuroanatomical features that allowed pterosaurs to fly. But they lacked the most obvious flight characteristic: wings.

“We are still missing lots of information about the earliest pterosaurs, and we still don’t know how their skeletons transformed into an animal that was capable of flight,” said Nesbitt.

Virginia Tech researchers hope their study helps bridge the anatomical and evolutionary between pterosaurs and other reptiles, creating a new framework for studying flying reptiles.

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