This illustration reveals an artist’s making of a pterosaur (Alanqa saharica). Credit: Davide Bonadonna
Little is understood about azhdarchid pterosaurs, massive flying reptiles with outstanding wingspans of approximately 12 meters. Cousins of dinosaurs and the biggest animals ever to fly, they initially appeared in the fossil record in the Late Triassic about 225 million years back and vanished once again at the end of the Cretaceous duration about 66 million years back. One of their most noteworthy functions for such a big flighted animal was a neck longer than that of a giraffe. Now, scientists report an unforeseen discovery in the journal iScience on April 14, 2021: their thin neck vertebrae got their strength from a complex internal structure, unlike anything that’s been seen prior to.
“One of our most important findings is the arrangement of cross-struts within the vertebral centrum,” states Dave Martill of the University of Portsmouth, UK. “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.”
This picture of a pterosaur vertebra reveals the bike wheel-like spoke plan. Credit: Williams et al.
Scientists formerly believed the pterosaur’s neck had an easier tube-within-a-tube structure, he describes. But it raised a crucial concern: how could their thin-walled bones, required to minimize weight in the flying reptiles, still support their bodies and permit them to catch and consume heavy victim animals?
Cariad Williams, the research study’s very first author, hadn’t set out to respond to that concern. She wished to analyze the degree of motion in between each vertebra of the pterosaur’s neck.
“These animals have ridiculously long necks,” Williams states, including that, in some types, the 5th vertebra of the neck from the head end is as long as the animal’s body. “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.”
While the Moroccan pterosaur bones they study are well maintained in 3 measurements, the scientists still hadn’t anticipated the scans to provide such a clear view of the vertebra’s complex internal structure.
“We did not originally CT scan it to learn about the inside; we wanted a very detailed image of the outside surface,” Martill states. “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.”
He includes, “What was utterly remarkable was that the internal structure was perfectly preserved — so too was the microhistology when we made some petrographic sections through the bone. As soon as we saw the intricate pattern of radial trabeculae, we realized there was something special going on. As we looked closer, we could see that they were arranged in a helix traveling up and down the vertebral tube and crossing each other like bicycle wheel spokes.”
His group understood instantly that they required to generate engineers to comprehend how the biomechanics of this uncommon neck would have worked. Those analyses recommend that as couple of as 50 of the spoke-like trabeculae increased the quantity of weight their necks might bring without buckling by 90%. Together with the fundamental tube-within-a-tube structure, it describes how the reasonably light-weight animals might catch and bring heavy victim products without breaking their necks.
“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, all whilst retaining the ability of powered flight,” Martill states.
While pterosaurs are in some cases considered evolutionary dead ends, Martill and associates state the brand-new findings expose them as “fantastically complex and sophisticated.” Their bones and skeletons were marvels of biology — incredibly light yet strong and resilient.
The scientists state there’s still much to discover in future work about pterosaurs, consisting of relatively fundamental concerns about their flight capabilities and feeding ecology.
Reference: “Helically arranged cross struts in azhdarchid pterosaur cervical vertebrae and their biomechanical implications” by Williams et al., 14 April 2021, iScience.
DOI: 10.1016/j.isci.2021.102338
