U.S. researchers said Monday they have identified the fossilized remains of an extinct giant bird that could be the biggest flying bird ever found.

With a wingspan of 20 to 24 feet (6.1 to 7.3 meters), Pelagornis sandersi surpassed size estimates based on wing bones from the previous record holder -- a long-extinct bird named Argentavis magnificens -- and was twice as big as the Royal Albatross, the largest flying bird today.

The enormous wingspan places the new species above some theoretical upper limits for powered flight in animals, but nonetheless model results suggest that the bird was a masterful flyer, according to the researchers' paper, which appeared online in the journal Proceedings of the National Academy of Sciences.

The birds "were like creatures out of a fantasy novel -- there is simply nothing like them around today," study author Daniel Ksepka of the National Evolutionary Synthesis Center in Durham, North Carolina, said in a statement.

The new fossil was first unearthed in 1983 near Charleston, South Carolina, when construction workers began excavations for a new terminal at the Charleston International Airport.

The strikingly well-preserved specimen consisted of multiple wing and leg bones and a complete skull. Its sheer size and the presence of bony tooth-like spikes in the jaw allowed Ksepka to identify the bird as a previously unknown species of the Pelagornithidae, an extinct group of giant seabirds.

The researchers believed the bird lived 25 to 28 million years ago, after the dinosaurs died out but long before the first humans arrived in the area.

According to the researchers, the bird's paper-thin hollow bones, stumpy legs and giant wings would have made it at home in the air but awkward on land.

They also used computer model based on the fossil data to predict how the bird managed to take off and stay aloft despite its massive size, since it exceeded what some mathematical models say is the maximum body size possible for flying birds.

The bird was probably too big to take off simply by flapping its wings and launching itself into the air from a standstill, the researchers said.

Like Argentavis, the previous record holder, Pelagornis sandersi may have gotten off the ground by running downhill into a headwind or taking advantage of air gusts to get aloft, much like a hang glider, they said.

Once it was airborne, Ksepka's simulations suggested that the bird's long, slender wings made it an incredibly efficient glider. By riding on air currents that rise up from the ocean's surface, the bird was able to soar for miles over the open ocean without flapping its wings, occasionally swooping down to the water to feed on soft-bodied prey like squid and eels.

"That's important in the ocean, where food is patchy," said Ksepka, who is now Curator of Science at the Bruce Museum in Greenwich, Connecticut.

The researchers hoped the find will help shed light on why the family of birds that Pelagornis sandersi belonged to eventually died out, and add to our understanding of how the giants of the skies managed to fly.

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