The giant pterosaur Quetzalcoatlus needed to taxi down a slope to take off, new research shows.
It weighed about 155 pounds and had a 34-foot wingspan, making it not far off the size of an F-16 fighter jet. It's the largest flying animal ever discovered - any larger, and it would have had to walk.
Researchers couldn't help but wonder how such a heavy animal, with relatively flimsy wings to boot, became airborne. Professor Sankar Chatterjee of Texas Tech University used a computer simulation to find out.
"This animal probably flew like an albatross or a frigate bird in that it could soar and glide very well. It spent most of its time in the air. But when it comes to takeoff and landing, they're so awkward that they had to run," says Chatterjee.
"If it were taking off from a cliff, then it was OK. But if Quetzalcoatlus were on the ground, it probably had to find a sloping area like a river bank, and then run quickly on four feet, then two to pick up enough power to get into the air. It needed an area to taxi."
There's been speculation about what the animal actually looked like, with some researchers suggesting recently that it could have used its forelimbs as a sort of catapult for a standing takeoff, in the same way as a common vampire bat.
However, Chatterjee says computer modeling shows this was impossible, as flight performance seems to degrade systematically with body size. Above a particular size, there's just not enough power, and flapping flight isn't possible.
"Its enormous wings must have been difficult to manage," says Chatterjee . "Each wing had at least a 16-foot span, so during its full downstroke it would smash its wing resulting in crash landing. A standing takeoff of flying of such a heavy animal violates the laws of physics."
Like today's condors and other large birds, Quetzalcoatlus probably relied on updraft to remain in the air. As a result, it had long, narrow, flat and pointed wings like those of modern seabirds - but these were structurally weak for vigorous flapping, causing the pterosaur difficulty during ground takeoff.
"Sooner or later the animal would come to the ground, especially during foraging and nesting," says Chatterjee.
"Like albatrosses and the Great Kori bustards, which weigh 20 to 40 pounds, ground takeoff was agonizing and embarrassing for Quetzalcoatlus. With a slight headwind and as little as a 10-degree downhill slope, an adult would be able to take off in a bipedal running start to pick up flying speed, just like a hang glider pilot."