Secret of Sustained Pterosaur Flight Found in Its Unique Bone Structure, Study Finds

(CN) --- Scientists have finally uncovered the secret of how Azhdarchid pterosaurs, ancient creatures known for being the largest animal to take flight during the time of dinosaurs, were able to hold their massive bodies aloft in the sky.

With an astonishing wingspan that could stretch up to 39 feet, the flying reptile’s oldest fossils date back 225 million years ago during the Late Triassic period up to 66 million years ago when the Cretaceous period ended. 

While the creatures were known for having lengthy necks that could measure more than 6 feet long, a new study published Wednesday in the journal iScience revealed they were able to support their necks thanks to spoked vertebrae.

"One of our most important findings is the arrangement of cross-struts within the vertebral centrum," said Dave Martill, of the University of Portsmouth in the U.K., in a statement. "It is unlike anything seen previously in a vertebra of any animal. 

“The neural tube is placed centrally within the vertebra and is connected to the external wall via a number of thin rod-like trabeculae, radially arranged like the spokes of a bicycle wheel and helically arranged along the length of the vertebra. They even cross over like the spokes of a bicycle wheel. Evolution shaped these creatures into awesome, breathtakingly efficient flyers."

Though scientists have long thought the neck contained a tube-within-tube structure, it didn’t explain how the creatures were able to support their bodies in flight with such thin-walled bones.

Cariad Williams, the study’s first author and a PhD student at the University of Illinois at Urbana-Champaign, said she stumbled upon the answer while studying the degree of movement between the vertebrae in the pterosaur’s neck.

"These animals have ridiculously long necks," Williams said. "It makes a giraffe look perfectly normal. We wanted to know a bit about how this incredibly long neck functioned, as it seems to have very little mobility between each vertebra."

The fossils, recovered in Morocco, were well preserved but the researchers didn’t get a clear view of how the neck worked until it was placed in a CT scanner.

"We did not originally CT scan it to learn about the inside; we wanted a very detailed image of the outside surface," Martill said. "We could have got this by ordinary surface scanning, but we had an opportunity to put some specimens in a CT scanner, and it seemed churlish to turn the offer down. We were simply trying to model the degree of movement between all the vertebrae to see how the neck might perform in life."

"What was utterly remarkable was that the internal structure was perfectly preserved --- so too was the microhistology when we made some petrographic sections through the bone. As soon as we saw the intricate pattern of radial trabeculae, we realized there was something special going on. As we looked closer, we could see that they were arranged in a helix traveling up and down the vertebral tube and crossing each other like bicycle wheel spokes,” he added.

The research team called in engineers to help determine the biomechanics of the neck. Their research found that as little as 50 of the spoked trabeculae allowed the neck to increase the amount of weight it could carry by 90%, allowing the creatures to fly, hunt and carry prey without straining their bodies.

"It appears that this structure of extremely thin cervical vertebrae and added helically arranged cross-struts resolved many concerns about the biomechanics of how these creatures were able to support massive heads--longer than 1.5 meters--on necks longer than the modern-day giraffe, all whilst retaining the ability of powered flight," Martill said.

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