Preserved fossils reveal how dinosaur-era reptiles flew

Well-preserved fossils of large ancient reptiles called pterosaurs revealed that some species flew by flapping their wings, while others glided like vultures, according to a new study published Friday (6).

Pterosaurs ruled the skies during the dinosaur era, and they met the same fate 66 million years ago after an asteroid impact triggered a mass extinction event. Some of the largest pterosaur species were giants that grew to the size of small airplanes and were as tall as giraffes, leading researchers to question whether pterosaurs were truly capable of flight.

The newly discovered fossils have preserved three-dimensional structures inside the delicate wing bones, which are usually found flattened like pancakes in rock layers.

CT scans of the fossils have provided a rare glimpse inside wing bones belonging to two pterosaur species, including one new to science.

The research results, published in the Journal of Vertebrate Paleontologyshed light on a remarkable and unexpected discovery: not only could giant pterosaurs fly, but different species adapted varying styles of flight.

Intact fossils offer a window into the past

The fossils date back 66 million to 72 million years, to the late Cretaceous period. The team initially found the specimens in 2007 at two sites in the north and south of what is now Jordan, buried in deposits of an ancient landmass called Afro-Arabia, which once included Africa and the Arabian Peninsula.

After realizing that the hollow bones still contained their original structures, the research team was eager to analyze them using high-resolution CT scans, said study lead author Kierstin Rosenbach, a paleontologist and researcher in the department of Earth and environmental sciences at the University of Michigan in Ann Arbor.

Some of the fossils belonged to a giant pterosaur known as Arambourgiania philadelphiae and provided a first look at its bone structure, as well as confirmation that it had a wingspan of 10 meters. The team observed a series of ridges that spiraled up and down the hollow humerus bone.

The remaining fossils were part of a pterosaur new to science called Inabtanin alarabia. It was named after a large grape-colored hill, Tal Inab, where it was discovered. The name combines the Arabic words “inab,” for grape, and “tanin,” for dragon, while “Alarabia” refers to the Arabian Peninsula.

According to researchers, the Inabtanin alarabia is one of the most complete pterosaur fossils ever found in this region. The reptile was smaller than the Arambourgianiawith a wingspan of 5 meters.

When researchers scanned the flight bones, they realized they were looking at a completely different structure than the Arambourgiania.

The flight bones of Inabtanin included an internal structure of stilts, or reinforcing rods, that aided flight. These are not unlike those found in the wing bones of modern birds that flap their wings to fly, Rosenbach said.

In contrast, the spiral ridges within the wing bones of the Arambourgiania resembled the interiors of vulture wing bones, which are believed to resist the forces associated with gliding flight.

“The stakes found in the Inabtanin were cool to see, though not unusual,” Rosenbach said in a statement. “The ridges on the Arambourgiania were completely unexpected, we weren’t sure what we were seeing at first.”

A diversity of flight among pterosaurs

The largest modern flying bird is the Andean condor, which has a wingspan of 9 feet (2.8 meters). But pterosaurs had massive wingspans that could reach 16 to 40 feet (5 to 12 meters).

“They represent the largest animals with the ability to fly,” Rosenbach said of the extinct reptiles.

Discovering that pterosaurs adapted different flight styles is exciting because it provides insights into the behaviors and lifestyles of these ancient reptiles, the researchers said.

“I think they would look noticeably different if we could see them flying side by side,” Rosenbach said.Inabtanin would have flapped its wings in a similar way to modern birds, but the Arambourgiania would probably have glided with some flapping of its wings, much like a vulture or pelagic seabird.”

The fossils did not reveal any insight into how pterosaurs took off from the ground, but the team is using their findings to determine how these varied flight styles evolved.

“The variation in internal structure likely reflects the response of the bones to the mechanical forces applied to pterosaur wings,” said study co-author Jeff Wilson Mantilla, a curator and professor at the University of Michigan Museum of Paleontology.

Researchers can’t say for sure which style came first, though when looking at birds and bats, flapping is the most common, Rosenbach said. And even birds that glide or glide need to flap their wings to take off and maintain flight.

Flight styles likely evolved due to a combination of factors, such as the pterosaurs’ environment, their body shape and size, and how they hunted prey, the authors said.

Scientists found both fossils in areas where a large shallow sea once existed, so each species may have adapted different behaviors to forage in the same environment, Rosenbach said.

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

An evolutionary look at ancient flight

Pterosaur wing bones had to handle the stress of flight while remaining lightweight, which is why hollow bones show different reinforcing structures within their walls, said Michael Benton, a professor of vertebrate paleontology at the University of Bristol in the United Kingdom.

“This is a nice study of the structure of the vertebrae of two large pterosaurs, one large and one huge,” said Benton, who was not involved in the research. “It has always been a mystery how pterosaurs could be light enough and yet strong enough to fly, especially the many examples that were much larger than any known bird. This paper helps provide the answer.”

The study authors believe their findings provide new evidence to the ongoing debate among paleontologists about whether the most massive pterosaurs could fly.

“The internal bone structure of these fossils suggests that they experienced the mechanical forces associated with flight,” Rosenbach said. “We can think of these discoveries as one piece of the puzzle of growing evidence that large pterosaurs retained the ability to fly at extremely large body sizes.”

The research team is eager to see more scans of pterosaur bones and determine how the newly discovered pterosaur *Inabtanin* relates to the rest of the ancient reptiles.

“There is increasing evidence that pterosaurs were more diverse approaching the great Cretaceous-Paleogene extinction event than we previously thought,” Rosenbach said in an email, referring to the mass extinction of dinosaurs and most life on Earth. “This indicates that the extinction was catastrophic, rather than a slow process of extinction for large reptiles.”

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This content was originally published in Preserved fossils reveal how reptiles from the time of dinosaurs flew on the CNN Brasil website.

Source: CNN Brasil