‘Some pterosaurs flapped their wings, others glide’: New study confirms the flying ability of these giants of the skies

Some species of pterosaurs flew by flapping their wings while others soared like vultures, a new study published in the journal Science shows. Journal of Vertebrate Paleontology.

It has long been debated whether the largest pterosaurs could actually fly.

However, “remarkable” and “rare” three-dimensional fossils of two different species of large azhdarchoid pterosaurs, one of which is new to science, have led scientists to hypothesize that not only could larger pterosaurs take to the air, but their flight styles might also differ.

The new findings are led by experts from the University of Michigan in the United States, the Natural Resources Authority and Yarmouk University in Jordan, and the Saudi Geological Survey in Saudi Arabia.

Their paper details how these fossils, which date back to the late Cretaceous period (about 72 to 66 million years ago), were remarkably preserved in three dimensions at the two different sites that preserve a coastal environment on the margin of Afro-Arabia, an ancient landmass that included both Africa and the Arabian Peninsula.

The research team used high-resolution CT scans to analyze the internal structure of the wing bones.

“The excavation team was extremely surprised to find pterosaur bones preserved in three dimensions. This is a very rare phenomenon,” said lead author Dr. Kierstin Rosenbach of the University of Michigan’s Department of Earth and Environmental Sciences.

“Because pterosaur bones are hollow, they are very fragile and are more likely to be found flattened like a pancake, if preserved.

“Because 3D preservation is so rare, we don’t have much information about the insides of pterosaur bones, so I wanted to scan them.

“It is entirely possible that nothing was preserved inside, or that the scanners were not sensitive enough to differentiate the fossil bone tissue from the surrounding matrix.”

Fortunately, what the team discovered was “remarkable,” with “exciting internal structures not only preserved, but visible on CT scans.”

CT scans show one rising, the other spreading

Newly collected specimens of the already known giant pterosaur, Arambourgiania philadelphiae, confirm its 10-meter wingspan and provide the first details of its bone structure. CT scans revealed that the inside of its humerus, which is hollow, contains a series of ridges that spiral up and down the length of the bone.

These structures resemble those inside the wing bones of vultures. The spiral ridges are thought to resist the torsional loads associated with gliding (sustained powered flight that requires launching and flapping of the wings for maintenance).

The other specimen analyzed was the Inabtanin alarabia, a specimen unknown to scientists, which had a wingspan of five meters. The team named it after the place where it was exhumed, near a large grape-colored hill, called Tal Inab. The generic name combines the Arabic words “inab,” for grape, and “tannin,” for dragon. “Alarabia” refers to the Arabian Peninsula.

Inabtanin is one of the most complete pterosaurs ever recovered from Afro-Arabia, and CT scans revealed that the structure of its flight bones was completely different from that of Arambourgiania.

The interior of the flight bones was intersected by an arrangement of struts that match those found in the wing bones of modern birds.

This indicates that it was adapted to withstand the bending loads associated with flapping flight, and so it is likely that Inabtanin flew in this way, although this does not preclude the occasional use of other flight styles as well.

“The struts found in Inabtanin were interesting to see, but not unusual,” says Dr. Rosenbach. “The ridges in Arambourgiania were completely unexpected; we weren’t sure what we were seeing at first. Being able to see the full 3D model of the Arambourgiania humerus lined with helical ridges was just thrilling.”

What explains this difference?

The discovery of different flight styles in pterosaurs of different sizes is “exciting,” experts say, because it provides a window into how these animals lived. It also raises interesting questions, such as how flight style correlates with body size and which flight style is most common among pterosaurs.

“Information about the internal bone structure of pterosaurs over time is so limited that it is difficult to say with certainty which flight style emerged first,” adds Dr. Rosenbach. “If we look at other groups of flying vertebrates, birds and bats, we can see that wing flapping is by far the most common flight behavior. Even birds that glide or fly need wing flapping to gain lift and maintain flight.”

“This leads me to believe that flapping flight is the default condition, and that gliding behavior might evolve later if it was advantageous to the pterosaur population in a specific environment; in this case, the open ocean.”

Co-author Professor Jeff Wilson Mantilla, curator at the Michigan Museum of Paleontology, and Dr. Iyad Zalmout of the Saudi Geological Survey discovered the specimens in 2007 at sites in northern and southern Jordan.

According to Professor Jeff Wilson Mantilla, “the variations likely reflect responses to mechanical forces applied to the pterosaur wings during flight.”

To enable a more in-depth study of vertebrate flight

In conclusion, Dr. Rosenbach says: “Pterosaurs were the first and largest vertebrates to develop powered flight, but they are the only large flying group to have become extinct. Attempts to understand their flight mechanics have relied on aerodynamic principles and analogies with living birds and bats.

“This study provides a framework for further investigation of the correlation between internal bone structure and flight ability and behavior, and will hopefully lead to broader sampling of flight bone structure in pterosaur specimens.”