Paleontologists have found that the thin neck vertebrae of the azhdarchid pterosaurs got their strength from an intricate internal structure.
Pterosaurs — flying reptiles of the Mesozoic era – made their first appearance in the fossil record in the Late Triassic and survived until the end of the Cretaceous approximately 66 million years ago.
Although some pterosaurs were small, with wingspans of less than 1 m, members of the enigmatic pterosaur family Azhdarchidae achieved wingspans of up to 10 m, possibly even as high as 12 m.
The azhdarchids are notable for elongation of the neck as a result of hyper-elongation of their cervical vertebrae.
“These animals had ridiculously long necks,” said Cariad Williams, a Ph.D. candidate at the University of Illinois at Urbana-Champaign.
“In some species, the fifth 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.”
Williams and colleagues investigated the internal micro-architecture of a well-preserved cervical vertebra from the Cretaceous azhdarchid pterosaur Alanqa sp. found in the Kem Kem Group of Morocco.
“One of our most important findings is the arrangement of cross-struts within the vertebral centrum,” said Dr. Dave Martill, a paleontologist at the University of Portsmouth.
“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.”
The team’s analysis suggests that as few as 50 of the spoke-like trabeculae increased the amount of weight azhdarchid necks could carry without buckling by 90%.
Together with the basic tube-within-a-tube structure, it explains how the relatively light-weight animals could capture and carry heavy prey items 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 m — on necks longer than that of the modern-day giraffe, all whilst retaining the ability of powered flight,” Dr. Martill said.
“While pterosaurs are sometimes thought of as evolutionary dead ends, the new findings reveal them as fantastically complex and sophisticated. Their bones and skeletons were marvels of biology — extremely light yet strong and durable,” the paleontologists said.
“There’s still much to learn in future work about pterosaurs, including seemingly basic questions about their flight abilities and feeding ecology.”
The findings appear in the journal iScience.
Cariad J. Williams et al. Helically arranged cross struts in azhdarchid pterosaur cervical vertebrae and their biomechanical implications. iScience, published online April 14, 2021; doi: 10.1016/j.isci.2021.102338
Fossil of New Crested Pterosaur Discovered in Australia
Pterosaurs were highly successful reptiles (not dinosaurs, as they’re commonly mislabeled) that lived between 210 and 65 million years ago.
Some pterosaurs, such as the giant azhdarchids, were the largest flying animals of all time, with wingspans exceeding 9 m (30 feet) and standing heights comparable to modern giraffes.
Pterosaur fossils from Australia are exceptionally rare, comprising fragmentary and predominately isolated bones from the Cretaceous of Queensland, New South Wales, Victoria and Western Australia.
Since the discovery of the first Australian pterosaur fossils almost four decades ago, fewer than 20 specimens have been described.
From these, only three species have been named: Mythunga camara, Aussiedraco molnari, and Ferrodraco lentoni. They come from the mid-Cretaceous rocks of the Rolling Downs Group, part of the Eromanga Basin in Queensland.
“The new pterosaur, which we named Thapunngaka shawi, would have been a fearsome beast, with a spear-like mouth and a wingspan around 7 m,” said Tim Richards, a Ph.D. candidate at the University of Queensland.
“It was essentially just a skull with a long neck, bolted on a pair of long wings.”
“This thing would have been quite savage. It would have cast a great shadow over some quivering little dinosaur that wouldn’t have heard it until it was too late.”
Thapunngaka shawi belongs to a group of crested pterosaurs known as Anhangueridae.
“What was particularly striking about this new species of anhanguerian was the massive size of the bony crest on its lower jaw, which it presumably had on the upper jaw as well,” said Dr. Steve Salisbury, also from the University of Queensland.
“These crests probably played a role in the flight dynamics of these creatures, and hopefully future research will deliver more definitive answers.”
A partial mandible of Thapunngaka shawi was found by local fossicker Len Shaw in June 2011 at a site known as the ‘water pond’ near Richmond, North West Queensland, Australia.
Originally developed as a quarry for road dressing, this site exposes a heavily weathered 4-5 m (13-16-foot) thick sequence of marls and coquinas of the Toolebuc Formation.
“It’s quite amazing fossils of these animals exist at all,” Richards said.
“By world standards, the Australian pterosaur record is poor, but the discovery of Thapunngaka shawi contributes greatly to our understanding of Australian pterosaur diversity.”
“It is only the third species of anhanguerian pterosaur known from Australia, with all three species hailing from western Queensland.”
The discovery of Thapunngaka shawi is described in a paper published today in the Journal of Vertebrate Paleontology.
Timothy M. Richards et al. A new species of crested pterosaur (Pterodactyloidea, Anhangueridae) from the Lower Cretaceous (upper Albian) of Richmond, North West Queensland, Australia. Journal of Vertebrate Paleontology, published online August 9, 2021; doi: 10.1080/02724634.2021.1946068