Flying Dino Too Weak to Lift Off?

Quetzalcoatlus demonstrates the so-called "quad launch" in this illustration. Click to enlarge this image. Mark Witton
Mark Witton

These pterodactyls had the wingspan of a F-16 fighter, but they may have been too out of shape to fly.

Bad news dragon riders: Your dragon can't take off.

A new analysis of the largest of pterodactyls suggests they were too big and their muscles too weak to vault into the air and fly. Instead, they were right at the upper limit of animal flight and needed a hill or stiff breeze so they could soar like hang gliders.

The new analysis was done on the enormous pterosaur Quetzalcoatlus from Late Cretaceous rocks of Big Bend, Texas. Quetzalcoatlus had a wingspan of about 35 feet (10.6 meters), or about the wingspan of a F-16 fighter. It was among the last pterodactyls to look down on dinosaurs 65 million years ago.

The new study, presented on Nov. 7 at the meeting of the Geological Society of America in Charlotte, N.C., puts the mass of the flying reptile at around 155 pounds (70 kilograms). That's near the upper limit of what flesh and bone can support in flight, according to paleontologist Sankar Chatterjee of Texas Tech University in Lubbock.

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Chatterjee was spurred to do the research by claims from other researchers that Quetzalcoatlus weighed a great deal more -- up to 440 pounds (200 kilograms) -- and took off by jumping from all fours into the air (called "quad launch").

The claims got a lot of attention, but concerned Chatterjee. So he put Quetzalcoatlus through aeronautical computer simulation that he has used on other pterosaurs to see what would work.

"There's no way this animal could take off from the ground," said Chatterjee of the quad launch, especially of a more massive animal. "There is no way it could fly."

At least not by jumping directly into the air and taking flight, he said. As for the greater weight suggested by others, that doesn't work in his model either. Despite the fact that Quetzalcoatlus was as large as a giraffe, it could not have weighed more than a medium-sized adult human, he said.

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"This is the upper limit for any flying animal," said Chatterjee. "This is really the highest limit for there to be able to fly. Above that, they can't even flap." The only way they were able to make Quetzalcoatlus fly at all, he said, was by employing a hand glider approach to take offs.

Other researchers, however, are sticking to their quad launch hypothesis, partly because they can't see how Quetzalcoatlus could weigh as little as 70 kilograms.

"These animals have 2.5- to three-meter-long (8.2- to 9.8-feet-long) heads, three-meter necks, torsos as large as an adult man and walking limbs that were 2.5 meters long," said paleontologist Mark Witton of the University of Portsmouth in the United Kingdom. Quetzalcoatlus skeletons alone weigh 20 kilograms (44 pounds), leaving 50 kilograms (110 pounds) of soft-tissue to cover a giraffe sized skeleton. "(That) leads to one atrophied pterosaur!"

A number of researchers using different techniques are now arguing that 200 kilograms or more is a realistic mass for these giant animals, Witton told Discovery News. That's still very light for an animal of those proportions, he said. But it gives it enough muscle to match its skeleton.

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Another clue they might have quad launched is Quetzalcoatlus' unusually thick forelimb bones, said Witton. These suggest the front limbs were used to launch into the air, Witton said.

So could dragons fly? It's clear more work will have to be done to find out for sure.