Pterosaurs With Necks Like Giraffes Survived Flight Thanks To Spoke-Like Vertebrae

Strong giraffe necks come in handy when bothering The Missing Link. Image creit: Davide Bonadonna

The genetic makeup of a gannet is arguably one of evolution’s finest creations. It gives rise to a body plan that is aerodynamic enough to fly, hydrodynamic enough to dive, and strong enough to survive plummeting into the ocean’s surface at speeds upwards of 50 mph. The same cannot be said of azhdarchid pterosaurs, the largest flying vertebrates. These enormous flying reptiles had necks longer than those of giraffes, which have puzzled paleontologists. How do you fly with such a thing, and without breaking your neck? New research published in the journal iScience believes the remarkably strong vertebrae may have survived such pressure thanks to an internal structure that looks a bit like part of a bicycle.

"One of our most important findings is the arrangement of cross-struts within the vertebral centrum," said Dave Martill of the University of Portsmouth, UK, 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."

pterosaur neck flight
The pterosaur vertebra had a bicycle wheel-like spoke arrangement inside. Image credit: Williams et al

The champions of the air were cruising the skies of the Late Triassic around 225 million years ago, helped on their way by a 12-meter (39.4 foot) wingspan. Airborne giants need light internal structures if they’re going to take flight, as is seen in many extant birds who have pneumatic bones. But for a neck of the azhdarchid pterosaurs’ length, it didn’t make sense, as something so fragile surely wouldn’t survive the pressures of aerial living. Add into the equation that azhdarchids were fierce predators, scooping up large prey, and the body plan makes even less sense.

Solving this paleontological puzzle was something of an accident, as the study’s first author Cariad Williams actually set about scanning these vertebrae as a means of better understanding their flexibility, which seemed pretty limited. "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."

Using a CT scanner, they were able to peek inside the vertebrae and were surprised to find their internal structure was perfectly preserved. The radial trabeculae were arranged in a helix that crossed over, looking a bit like the spokes of a bike wheel. They called in some engineers who were better able to translate the biomechanics of the strange structure. Their analyses revealed 50 of these spoke-like trabeculae almost doubled the weight azhdarchids could tolerate without their necks buckling.

"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,” Martill said, “all whilst retaining the ability of powered flight.”

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