Unlike their peers, the pterodactyls, the azhdarchid pterosaurs aren't a familiar part of the pop culture lexicon. Yet these Cretaceous-era reptiles are similar in appearance to the pterodactyls from the "Jurassic Park" series: the massive wings, the large jaws, the clawed feet, the long neck.
Azhdarchid pterosaurs looked like that except, well, bigger. They flew over modern North Africa roughly 100 million years ago, with wingspans that reached up to 33 feet and necks longer than those of modern giraffes. And they are believed to be the largest animals to ever fly.
That raises some interesting physics questions, not all of which have been solved. After all, in order for such a large animal to fly, they would require very light-weight bones that were at once very strong. How could an animal so massive feed itself without breaking its neck?
A group of scientists recently published an article in the journal iScience with a tantalizing hypothesis that may answer that mystery. Their finding was done with fossilized materials under a CT scan, as Cariad Williams — a Ph.D. student at the University of Illinois at Urbana-Champaign who co-authored the paper — told Salon.
Williams described the moment of discovery as "incredible."
"I put them straight into my computer and I literally went to my friend, who was also a co-author of the paper, Roy Smith," Williams recalled. "'You have to come and see this.' Then I went straight to Dave [Martill]'s office and said to David, 'You have to come to my office right now and have a look at this.' And we spent the entire day just talking about what we could do next with this study."
Their scans reveal that the azhdarchid pterosaur was utterly unique. And in order to fly and eat while supporting such a heavy frame, the azhdarchid pterosaur evolved to have a neck unlike anything else known in the animal kingdom.
"There's between seven and nine cervical vertebrae, and that's neck vertebrae. Inside each vertebra, it basically looks like a tube within a tube that's connected by very thin bones," Williams explained. She added that the bones were organized helically, comparing it to the spokes on a bicycle wheel.
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The bizarre and highly tensile structure of their bones allowed pterosaurs to be both very strong and very light-weight.
"It explains that the pterosaur was able to actually carry a greater load than what we once thought, like prey items," Williams told Salon. "It was able to carry larger prey by the support of its neck... It actually distributed this stress along the spokes inside the vertebrae." This meant that the ancient beast actually would have been able to capture larger prey without hurting or even breaking its neck.
Dr. David M. Martill, a professor of paleobiology at the University of Portsmouth, told Salon by email that while this discovery does not change anything we know about the outward appearance of the pterosaurs, it has possible applications not only for what we know about how they carried their prey, but how they handled "being buffeted by strong winds for example."
He added, "It was always a surprise when you found a broken pterosaur vertebrae as to how incredibly thin the bone was, even in the gigantic pterosaurs. Now we know how they got away with it."
Yet the researchers' work is not without its critics. Paleontologist Rodrigo Pêgas of Brazil's Federal University of ABC–São Bernardo told Science Magazine that he wished the team which scanned fossils of an azhdarchid's neck had done the same thing with other pterosaurs to see if the structure is unique to them.
Alexander Kellner, a paleontologist and director of the National Museum at the Federal University of Rio de Janeiro, told the publication that he is "not very impressed" because "I think you should have more specimens to really make a claim."
"Pêgas has a point, we should look at a range of pterosaurs," Martill told to Salon. "But herein lies a problem. We were specifically looking at the hyper-long necked pterosaurs called azhdarchids (like Quetzalcoatlus, Hatzegopterus, Arabourgiania), not the 'ordinary pterosaurs'. And for our study we needed well preserved 3D material that would scan well in the CT scanner. There are very few places in the world where you can get this material."
The researchers wound up using material from the Kem Kem beds of Morocco, where "it is easy to extract from the rock, it is uncrushed, and so the interior is intact," as Martill explained. This, he said, makes for them ideal for CT scans.
"We would love to go to Russia to see their material, and maybe one day that will happen," he added.
Martill said that the researchers hope to expand their work to other pterosaurs, adding that there is pterosaur vertebrae in Brazil that could be studied in this fashion. "I am very surprised that Kellner has not done so, as the material is just begging to be studied in this way," he noted.
In an email to Salon, Pêgas explained that "I think the methods and the results that these authors presented are very interesting and well-done, but the conclusions need further support from the comparisons with 'ordinary pterosaurs.'" He argued that the researchers need to differentiate between azhdarchids and other pterosaurs in order "to demonstrate that the biomechanical properties of azhdarchids are 'unordinary.'" He also claimed that "there is plenty of well-preserved material that belong to 'ordinary pterosaurs' that can be used in a CT scan, including tapejarids and anhanguerids in the State Museum of Natural History of Karlsruhe (Germany)." He concluded that it is acceptable for the authors to not proceed with analyzing other pterosaurs, but that "their claims will remain unresolved until someone else does so. I am looking forward to see someone proceeding with such analyses, as I do think they have great potential to corroborate the new claims!"
Updated April 15 to include an additional quote from Dr. Rodrigo Pêgas.