Massive flying pterosaurs had spoked vertebrae to support especially long necks

April 14 (UPI) -- With wingspans of nearly 40 feet, the biggest azhdarchid pterosaur species were the largest animals to ever take to the skies. Even more impressive, the largest species boasted necks as long as eight feet and heads stretching nearly five feet -- like a big-headed giraffe with wings.

Until now, scientists weren't sure how exactly the vertebrae of these flying reptiles were able to support such long necks and large heads.

According to a new paper, published Wednesday in the journal iScience, azhdarchid pterosaurs and their hollow bones -- necessary for flying -- were only able to support such heavy necks and heads thanks to a unique structure hidden inside their vertebrae.

While investigating the range of motion afforded by the vertebrae of flying reptiles, scientists discovered rod-like trabeculae hidden inside each vertebra.

Researchers determined the trabeculae, positioned like bicycle spokes, allowed the animals and their vertebrae to support more weight without buckling.

"One of our most important findings is the arrangement of cross-struts within the vertebral centrum," study co-author Dave Martill said in a press release.

"It is unlike anything seen previously in a vertebra of any animal," said Martill, a paleontologist at the University of Portsmouth in Britain.

"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," Martill said. "They even cross over like the spokes of a bicycle wheel. Evolution shaped these creatures into awesome, breathtakingly efficient flyers."

Though scientists had long been perplexed by the size and anatomical proportions of azhdarchid pterosaurs, the authors of the new paper didn't set out to study the vertebrae's load-bearing capabilities.

They just wanted to understand how it moved.

"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," Martill said.

Remarkably, the Moroccan pterosaur bones they were studying were impeccably preserved internally. The CT scans revealed an array of spoke-like trabeculae connecting the inner neural tube and the external walls of the vertebrae.

The team of paleontologists recruited the help of engineers to determine the load-bearing advantages provided by the unique internal structure.

Engineers determined just 50 trabeculae would be enough to boost the vertebrae's load-bearing capacity by up to 90 percent.

The findings help explain how these massive flying reptiles were able to get airborne while still supporting large amounts of weight in the head and neck.

Like their cousins, the dinosaurs, azhdarchid pterosaurs disappeared at the end of the Cretaceous Period.

But despite their reputation as an evolutionary dead end, the latest research suggests azhdarchid pterosaurs were able to evolve a tremendous complex and strong skeletal structure.

"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 ... on necks longer than the modern-day giraffe, all whilst retaining the ability of powered flight," Martill said.