If you gaze up at the sky in the Late Cretaceous Period, you can catch a glimpse of surreal, wing-span flying giants that rival small planes. Known as the azhdarchids, this oversized group of pterosaurs included species that measured 33 feet between their wing tips, making them the largest animals ever to take to the air.
The Azhdarchid’s extreme dimensions raise tantalizing questions, such as how they carried large prey without breaking their long necks, or how animals the size of giraffes hovered effortlessly over their dinosaur relatives on the ground.
Cariad Williams, Ph.D. The student at the University of Illinois at Urbana-Champaign hoped to shed some light on these questions with the help of an Azhdarchid specimen from the fossil Kem Kem beds in Morocco. She used a CT scan to examine fossils from the animal’s neck.
“We just couldn’t believe the structure we found inside,” said Ms. Williams.
The results, published Wednesday in iScience magazine, stunned Ms. Williams and her colleagues. The animal’s neck was shown to be armored by a unique and complex network of screw struts that connected a central neural tube to the vertebral wall like the spokes of a bicycle. It was a structure that has no parallel anywhere else in the animal kingdom.
This unprecedented look into an Azhdarchid throat helps fill some of the lingering gaps in our knowledge of their anatomy and behavior. Pterosaurs, like birds, developed extremely fragile and lightweight skeletons in order to optimize their flight skills. These properties also mean that they are underrepresented in the fossil record because their bones break apart easily.
The Kem Kem site is one of the few places in the world where relatively intact Azhdarchid fossils can be found. The Moroccan fossil beds preserve a lush river system that existed about 100 million years ago and which attracts chalk sharks, large predatory dinosaurs such as Spinosaurus and Carcharodontosaurus, and Azhdarchids.
Ms. Williams and her colleagues tentatively identified their specimen as an Alanqa pterosaur. While it’s difficult to gauge the exact dimensions, the Azhdarchid likely had a five-foot neck and a wingspan of 20 to 26 feet.
Biomechanical analysis of the intricate structure of the neck revealed that the spoke-like filaments supported the vertebrae against the pressure of catching and carrying heavy prey. According to the team’s calculations, adding just 50 struts increased the weight they could carry without kinking by 90 percent, allowing this particular specimen to carry loads of up to 24 pounds, which Ms. Williams described as “really impressive.”
“They used less energy to optimize their neck strength and lift the prey,” she said.
The unusual adaptation can have functions that go beyond hunting and feeding, e.g. on the ground, ”according to the study. Ms. Williams and her colleagues plan to follow up on their findings by scanning other Azhdarchid vertebrae to see if the spoke structure is widespread.
David Hone, a paleontologist at the University of London’s Queen Mary, who was not involved in the study, said the new research provided “nice confirmation” of the mechanical solidity of azhdarchid vertebrae.
“It is a very nice finding that there is this strange arrangement of struts and that this is about the minimum that is possible to strengthen the bone,” he said. “But it comes as no great surprise, as we know that Azhdarchids had incredibly reduced bones and were extremely light for their size.”
“What we really need for Azhdarchids is a well-preserved 3-D skeleton,” concluded Dr. Hone. “We either work with flattened fossils or with very incomplete specimens, which makes it difficult to do a lot of the basics yourself.”