Scientists have identified the largest flying bird known to have ever lived - an extinct giant with a wingspan of up to 24 foot, more than twice the size of the largest living flying bird.
The creature 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 findings show that the creature was an extremely efficient glider, with long slender wings that helped it stay aloft despite its enormous size.
The fossil was first unearthed in 1983 near Charleston, South Carolina. The specimen was so big they had to dig it out with a backhoe.
"The upper wing bone alone was longer than my arm," said author Dan Ksepka of the National Evolutionary Synthesis Center in Durham, North Carolina.
Now in the collections at the Charleston Museum, the strikingly well-preserved specimen consisted of multiple wing and leg bones and a complete skull.
Its sheer size and telltale beak allowed Ksepka to identify the find as a previously unknown species of pelagornithid, an extinct group of giant seabirds known for bony tooth-like spikes that lined their upper and lower jaws.
Named 'Pelagornis sandersi', the bird lived 25 to 28 million years ago - after the dinosaurs died out but long before the first humans arrived in the area.
Researchers have no doubt that P sandersi flew. It's paper-thin hollow bones, stumpy legs and giant wings would have made it at home in the air but awkward on land.
But because it exceeded what some mathematical models say is the maximum body size possible for flying birds, what was less clear was how it managed to take off and stay aloft despite its massive size.
To find out, Ksepka fed the fossil data into a computer programme designed to predict flight performance given various estimates of mass, wingspan and wing shape.
P sandersi was probably too big to take off simply by flapping its wings and launching itself into the air from a standstill.
Like Argentavis, P 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.
Once airborne, Ksepka's simulations suggest 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, P sandersi 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, now Curator at the Bruce Museum in Connecticut.
Researchers hope the find will help shed light on why the family of birds that P sandersi belonged to eventually died out.
The finding was published in the journal PNAS.
