Evrim Yazgin
Cosmos science journalist
Pterosaurs were the largest creatures to ever take flight. How they did so has long been subject to debate. Research on new fossils from the Arabian Peninsula provides fresh answers.
During the “Age of Dinosaurs”, large reptiles called pterosaurs soared through the skies.
These animals were wiped out 66 million years ago when an asteroid impact led to a mass extinction which saw roughly 75% of species disappear.
Among pterosaurs were creatures as small as pigeons. But on the other end were species such as Quetzalcoatlus northropi and Hatzegopteryx thambema. Both giants are part of a group of pterosaurs called azhdarchids.
These were the largest animals ever to fly. They had wingspans of more than 10m – about the size of a biplane – and would have stood as tall as a giraffe when on the ground.
How could giraffe-sized reptiles even get off the ground and fly? Answering this question has been difficult from sparse fossil remains of pterosaurs.
The new study – published in the Journal of Vertebrate Paleontology – uses “remarkable” and “rare” pterosaur fossils to give some insights. The authors suggest that there isn’t one answer, but two: some pterosaurs flew by flapping their wings while others soared like modern-day vultures.
“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,” says lead author Kierstin Rosenbach from the University of Michigan in the US.
Rosenbach and her team were surprised to find three-dimensionally preserved pterosaur bones dating to 72–66 million years ago at the end of the Cretaceous period. Both were found in a region which, at the end of the Cretaceous, would have been a coastal environment on the edge of an ancient landmass referred to as Afro-Arabia.
One of the specimens was from the already known giant azhdarchid pterosaur Arambourgiania philadelphiae found in Jordan.
The other fossil is from a species which is described for the first time in the new paper.
Inabtanin alarabia was also found in Jordan at a hill called Tal Inab, 34km north of the border with Saudi Arabia. The specimen is from an adult pterosaur with a wingspan of about 5m.
Rosenbach CT scanned the fossils and was excited to find that internal structures not only preserved, but visible in the CT scanner.
The CT scans revealed that Inabtanin bone structure was completely different to that of Arambourgiania.
Inabtanin’s flight bones were criss-crossed with struts like those found in the wing bones of flapping birds today. Scientists think these struts help resist bending of the bone during flapping flight. This, however, doesn’t preclude that the animal used other flight styles too.
The interior of an Arambourgiania humerus, on the other hand, showed ridges spiralling up and down the bone. These resemble structures in the wing bones of vultures. It’s believed these spiral ridges help the animal resist twisting during soaring.
The fossils give a glimpse into the different flying styles of different pterosaurs.
“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,” Rosenbach says.
“If we look to other flying vertebrate groups, birds and bats, we can see that flapping is by far the most common flight behaviour. 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 behaviour of soaring would perhaps evolve later if it were advantageous for the pterosaur population in a specific environment; in this case the open ocean.”
