By Stephen Beech via SWNS
Some flying dinosaurs flapped their wings while others would soar like vultures, according to a new study.
It has previously been debated whether the largest pterosaurs could fly at all.
But “remarkable” and “rare” three-dimensional fossils of two different large-bodied azhdarchoid pterosaur species – including one new-to-science – have enabled scientists to work out that not only could the largest pterosaurs take to the air, but their flight styles differed too.
They describe how the fossils, dating back to the latest Cretaceous period around 72 to 66 million years ago, were remarkably three-dimensionally preserved within the different sites on the margin of Afro-Arabia, an ancient landmass that included both Africa and the Arabian Peninsula.
The research, published in the Journal of Vertebrate Paleontology, was conducted by scientists from the University of Michigan, the Natural Resources Authority and Yarmouk University in Jordan, and the Saudi Geological Survey in Saudi Arabia.
The specimens were found at sites in the north and south of Jordan by co-author Dr. Jeff Wilson, curator of Michigan’s Museum of Paleontology, and Dr. Iyad Zalmout, from the Saudi Geological Survey, in 2007.
The team used high-resolution CT scans to analyze the internal structure of the wing bones.
Study lead author Dr. Kierstin Rosenbach, of the University of Michigan, said: “The dig team was extremely surprised to find three-dimensionally preserved pterosaur bones, this is a very rare occurrence.
“Since pterosaur bones are hollow, they are very fragile and are more likely to be found flattened like a pancake, if they are preserved at all.
“With 3D preservation being so rare, we do not have a lot of information about what pterosaur bones look like on the inside, so I wanted to CT scan them.
“It was entirely possible that nothing was preserved inside, or that CT scanners were not sensitive enough to differentiate fossil bone tissue from the surrounding matrix.”
But she said that what the team uncovered was “remarkable,” via “exciting internal structures not only preserved but visible in the CT scanner”.
Newly collected specimens of the already-known giant pterosaur, Arambourgiania philadelphiae, confirmed its 10-metre (33ft) wingspan and provided the first details of its bone structure.
CT images revealed that the interior of its humerus, which is hollow, contains a series of ridges that spiral up and down the bone.
The researchers said that it resembles structures in the interior of wing bones of vultures.
They believe the spiral ridges resist the torsional loadings associated with soaring – a sustained powered flight that requires launch and maintenance flapping.
The other specimen analyzed was the previously Inabtanin alarabia, which had a five-meter (16.5ft) wingspan.
The team named it after the place where it was excavated – near a large grape-colored hill, called Tal Inab. The generic name combines the Arabic words “inab,” for grape, and “tanin” for dragon. ‘Alarabia’ refers to the Arabian Peninsula.
Inabtanin is one of the most complete pterosaurs ever recovered in the region.
CT scans revealed the structure of its flight bones was completely different from that of Arambourgiania.
The interior of the flight bones was criss-crossed by an arrangement with struts that match those found in the wing bones of modern flapping birds.
The researchers say that indicates it was adapted to resist bending loads associated with flapping flight, and so it is likely that Inabtanin flew that way.
Dr. Rosenbach said: “The struts found in Inabtanin were cool to see, though not unusual.
“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 Arambourgiania’s humerus lined with helical ridges was just so exciting.”
She said the discovery of diverse flight styles in differently-sized pterosaurs is “exciting” as it opens a window into how they lived.
Dr. Rosenbach said: “There is such limited information on the internal bone structure of pterosaurs across time, it is difficult to say with certainty which flight style came first.
“If we look to other flying vertebrate groups, birds and bats, we can see that flapping is by far the most common flight behavior.
“Even birds that soar or glide require some flapping to get in the air and maintain flight.
“This leads me to believe that flapping flight is the default condition and that the behavior of soaring would perhaps evolve later if it were advantageous for the pterosaur population in a specific environment; in this case the open ocean.”
Dr. Wilson says the variations “likely reflect responses to mechanical forces applied on the pterosaurs’ wings during flight”.
Dr. Rosenbach added: “Pterosaurs were the earliest and largest vertebrates to evolve powered flight, but they are the only major volant group that has gone extinct.
“Attempts to-date to understand their flight mechanics have relied on aerodynamic principles and analogy with extant birds and bats.
“This study provides a framework for further investigation of the correlation between internal bone structure and flight capacity and behavior, and will hopefully lead to broader sampling of flight bone structure in pterosaur specimens.”
