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If you looked up at Cretaceous skies in what is now Texas, you might have seen an imposing creature that might have convinced you dragons are real.
Azhdarchid pterosaurs could somehow take off even though their necks were outlandishly long (not unlike the way many dragons are drawn). How they managed flight without those necks buckling remained a mystery until now. New research has revealed that trabeculae, connective bone structures inside their neck vertebrae, were arranged like the spokes of a bicycle wheel, even crossing over each other. These trabeculae strengthened the neck enough to stay aloft without adding much weight. Pterosaurs had hollow bones, but nothing like azhdarchids.
Fossilized remains of azhdarchids, like Quetzalcoatlus, that have been preserved well enough to study are rare. Most have succumbed to the ravages of time. When a team of paleontologists including Cariad Williams, Roy Smith and David Martill of the University of Portsmouth ran X-ray CT (XCT) scans of azhdarchid neck vertebrae—something they almost passed up because they only wanted a surface scan—what they found was astonishing.
“Our research demonstrates that pterosaurs were continuously coming up with new and innovative ways of lengthening and strengthening their skeletons,” Wiliams, who led a study recently published in iScience, along with co-authors Smith and Martill, told SYFY WIRE. “Pterosaurs were continually evolving right up to the moment they became extinct.”
Quetzalcoatlus was an almost mythical beast. Thought to be one of the largest animals to ever take flight, and maybe the closest thing to a dragon that actually existed, it could probably take a human for an epic ride like Drogon soared with Daenerys on his back in Game of Thrones. The largest specimen found, though incomplete, is believed to have had a 40-foot wingspan that would have cast an intimidating shadow. It was named after the “feathered serpent” Aztec god Quetzalcoatl for a reason. The only thing it couldn’t do was breathe fire.
No other animal, extant or extinct, has ever been found to have bones like this, but you need all the support you can get when your neck is longer than a giraffe’s and you need to take to the air. There was an optimal number of trabeculae that would stabilize the the necks of these pterosaurs from buckling or fracturing and keep them stable in flight. The neural tube that ran through their vertebrae, extended through their backs, and continued to the spinal cord and brain was connected to the inner walls of the vertebrae by an intricate arrangement of trabeculae.
“Subsuming the neural canal into the vertebrae into a central position provides an internal structural element that does not need to be large,” said the researchers. “A benefit of this is that the spinal cord is even better protected.”
There are pterydactyloid certain neck features that azhdarchids evolved without. The absence of pneumatic foramina, or air sacs in the bones, actually gave their bizarre necks an advantage because it meant the walls of their already thin-walled vertebrae were stronger. Having a reduced neural spine allowed each vertebra to take on a nearly circular shape that added strength and would not have been possible if the neural spine was more prominent. Another thing that gave these pterosaurs a flight boost was having a neural tube that ran through the centers of their vertebrae, which allowed for spinal cord protection without bulk that would have weighed them down.
How and why pterosaurs like Quetzalcoatlus and Hatzegopteryx evolved this way remains something of a mystery, though Williams, Smith and Martill have some ideas.
“A long neck would enable them to reach further from the bank of a river or lake to feed,” they said. “Alternatively, as they are very large animals with long wings, this meant that their bodies were in an upright position when they were walking on all fours, so they would need to reach the ground if they were feeding on small mammals and lizards.”
There has been some debate about how azhdarchids fed. Though snapping up fish on the wing was a popular hypothesis for a while, the only known fossils of these creatures have surfaced hundreds of miles from any area that was once a Cretaceous shore. The drag would have also been too intense for them to endure. Another theory tried to argue that they were scavengers, but there was no way their beak or neck structure would have allowed for that. They most likely stalked prey on land, using their wings as forelegs to wade through the ancient swampland and waiting for the opportune moment to snatch unwary small vertebrates.
Williams and her team were also able to figure out how much weight in prey an azhdarchid could safely carry. Though their feeding habits are still somewhat mysterious, it is possible that they could have flown away after catching something so no other hungry predator would try to steal their dinner. Long necks would be useful in surveying their surroundings for any threats or competition. They might have also been used in displays similar to the neck-bashing that giraffes do to look impressive for a potential mate or decide who is their territory’s overlord. The Portsmouth team is looking to demystify everything they can about these fascinatingly unusual pterosaurs.
“We will continue to investigate how these animals 'engineered' their skeletons to make them ever light, stronger and bigger,” the researchers said. “We are desperate to find articulated, complete examples of azhdarchids, and we also want to take a look at how they micro-engineer their bones.”
Azhdarchids like Quetzalcoatlus really do make it seem as if, in some way, dragons did exist.