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Two species of pterosaurs, Arambourgiania philadelphiae and Inabatin alarabia, had different flight styles

NEWS - Scientists confirm the flight capabilities of giants in the ancient skies, with some pterosaur species flapping their wings while others soared like vultures. New finds include a new pterosaur with a wingspan of 5 meters (16 feet) and one of the most complete pterosaurs ever discovered from Afro-Arabia.

Two species of pterosaurs, Arambourgiania philadelphiae and Inabatin alarabia, had different flight styles

Scientists have long debated whether the largest pterosaurs could fly at all. But extraordinary and rare three-dimensional fossils of two species of large-bodied azhdarchoid pterosaurs have led scientists to hypothesize that the largest pterosaurs not only could fly, but that their flight styles may have been different.

Kierstin Rosenbach of the University of Michigan in Ann Arbor and her team detail the fossils from the late Cretaceous period (72-66 million years ago) that are remarkably preserved in three dimensions at two different sites in coastal environments on the edge of Afro-Arabia, an ancient landmass that included Africa and the Arabian Peninsula.

“The excavation team was surprised to find a pterosaur bone preserved in three dimensions, which is a very rare occurrence because pterosaur bones are hollow, very fragile and more likely to be found flattened like a pancake,” Rosenbach said.

“Because 3D preservation is so rare, we don’t have much information about what pterosaur bones look like inside, so I wanted to CT scan them. It’s very possible that there’s nothing preserved inside or that the CT scanner isn’t sensitive enough to distinguish the fossil bone tissue from the surrounding matrix,” Rosenbach said.

The new specimen was collected from a giant pterosaur already known, Arambourgiania philadelphiae with a wingspan of 10 meters (33 feet), and provides the first details about the bone’s structure. CT images reveal that the interior of the humerus is hollow and contains a series of ridges that spiral up and down the bone.

The fossil resembles the structure on the inside of the wing bones of vultures. The spiral ridges are hypothesized to have supported the torsional loads associated with high-altitude or sustained powered flight that requires launching and flapping.

Another specimen is a new genus and species, Inabtanin alarabia, which had a wingspan of 5 metres. Inabtanin is one of the most complete pterosaurs ever found from Afro-Arabia and CT scans reveal a completely different flight bone structure from Arambourgiania.

The inner wing bones are crisscrossed with the same arrangement of struts as in the wing bones of modern flapping birds. These bones are adapted to withstand the bending loads associated with flapping. It is likely that Inabtanin flew by flapping its wings.

“The struts in Inabtanin are very interesting to look at, although unusual. The ridges in Arambourgiania are completely unexpected. To see a complete 3D model of the humerus of Arambourgiania covered in helical ridges is really exciting,” says Rosenbach.

The diverse flight styles of these different-sized pterosaurs provide a window into how they lived and raises interesting questions, such as to what extent flight style correlated with body size and which flight styles were more common among pterosaurs.

"If we look at the 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 wing flapping and maintain a flight position," Rosenbach said.

"Flapping flight is the default state, and soaring flight may have evolved later if it was advantageous for pterosaur populations in a particular environment; in this case, the open ocean," Rosenbach said.

The specimens were discovered by Jeff Wilson Mantilla, a curator at the University of Michigan Museum of Paleontology and Department of Earth and Environmental Sciences in Ann Arbor, in 2007 in northern and southern Jordan. The bone variations likely reflect responses to mechanical forces on pterosaur wings during flight.

"Pterosaurs were the earliest and largest vertebrates to evolve powered flight, but they are the only major extinct group of volants. Efforts to understand them so far have relied on aerodynamic principles and analogies with birds and bats," Rosenbach said.

"This study provides a framework for further investigation of the correlation between internal bone structure, flight capacity and behavior that will hopefully lead to a broader sampling of flight bone structures in pterosaur specimens," Rosenbach said.

Original research

Rosenbach, K. L., Goodvin, D. M., Albshysh, M. G., Azzam, H. A., Smadi, A. A., Mustafa, H. A., … Wilson Mantilla, J. A. (2024). New pterosaur remains from the Late Cretaceous of Afro-Arabia provide insight into flight capacity of large pterosaurs. Journal of Vertebrate Paleontology, DOI:10.1080/02724634.2024.2385068

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