An artist’s drawing of the newly named species Pelagornis sandersi shows the discovered bone fragments in white. The strikingly well-preserved specimen consisted of multiple wing and leg bones and a complete skull. (Liz Bradford)

When South Carolina construction workers came across the giant, winged fossil at the Charleston airport in 1983, they had to use a backhoe to pull the bird, which lived about 25 million years ago, up from the earth.

But if the bird was actually a brand-new species, researchers faced a big question: Could such a large bird, with a wingspan of 20 to 24 feet, actually get off the ground? After all, the larger the bird, the less likely its wings are able to lift it unaided.

The answer came from Dan Ksepka, paleontologist and science curator at the Bruce Museum in Greenwich, Conn.

He modeled a probable method of flight for the long-extinct bird, named as a new species this week in the Proceedings of the National Academy of Sciences. If Ksepka’s simulations are correct, Pelagornis sandersi would be the largest airborne bird ever discovered.

Pelagornis sandersi relied on the ocean to keep it aloft. Similar in many ways to a modern-day albatross — although with at least twice the wingspan and very different in appearance, Ksepka said — the bird probably needed a lot of help to fly. It had to run downhill into a head wind, catching the air like a hang glider. Once airborne, it relied on air currents rising from the ocean to keep it gliding.

Paleontologist Dan Ksepka examines the fossilized skull of what may be the biggest flying bird ever found. Its telltale beak allowed Ksepka to identify the find as a previously unknown species of pelagornithid, an extinct group of giant seabirds known for bony, toothlike spikes that lined their upper and lower jaws. (Courtesy of Dan Ksepka)

Like the albatross, Pelagornis sandersi spent much of its time over water.

“It was a bit warmer 25 million years ago,” Ksepka said, “and the sea level was higher. So even though the Charleston airport, where the fossil was found, is on dry land today, it used to be an ocean.”

An in­cred­ibly efficient glider, Pelagornis sandersi could probably soar for miles and miles over the sea, swooping down to catch its prey in the waves.

To snap up its meals, the bird used pseudo-teeth — a characteristic that Ksepka found just as fascinating as the bird’s massive wingspan. These teeth, Ksepka said, are not anything like our own.

“They don’t have enamel, they don’t grow in sockets, and they aren’t lost and replaced throughout the creature’s life span,” he said. “Instead, the bone just extends from the jaw.”

There were bigger flying creatures than Pelagornis sandersi. Some of the largest pterodactyls had wingspans of up to 35 feet. But they were flying reptiles, not the dinosaurs that birds descended from.

The previous record holder for largest flying bird, Argentavis magnificens, lived only 6 million years ago and hailed from Argentina. It was probably heavier than the new bird — something researchers know because of the size of their hind legs, which had to support their weight.

An illustration of the newly confirmed species Pelagornis sandersi shows its wingspan. The species may be the biggest flying bird ever found. (Liz Bradford)

The only way to directly compare the two species is the upper wing bone.

It is hard to use that as a direct scale between the two, Ksepka said, but “when the difference is 940 millimeters in sandersi and 570 in magnificens, you can’t reasonably create a skeleton where the sandersi doesn’t have a bigger wingspan.”

All of this is based on computer simulation, he said. By comparing bone sizes and proportions to modern birds, researchers can estimate size and mass. And complex computer modeling uses these and other factors to determine whether flight could be possible, and how.

“It’s not like a modern bird, where you can put it into a wind tunnel, or sit on a beach with binoculars and watch it,” Ksepka said. He added that while it is not possible to know everything about the ancient creature from one skeleton, he is quite certain about one thing:

“This is pushing the boundary of what we know about avian size, and I’m very confident that the wingspan is the largest we’ve seen in a bird capable of flight.”