A clutch of fossilised bones uncovered during the expansion of an airport terminal in the US may belong to the largest flying bird ever found.

The prehistoric creature had a wingspan of between 6.1 and 7.4 metres and could glide for long distances over the oceans as it searched for fish 25m years ago, according to scientists writing in the Proceedings of the National Academy of Sciences.

Its wingspan was double that of the royal albatross, the largest flying bird alive, and challenges the wingspan of Argentavis magnificens, a prehistoric bird that lived six million years ago and had a wingspan between 5.5 and 7 metres.

The bird, named Pelagornis sandersi, had short, stumpy legs and likely took to the air by hopping off cliff edges or making short runs into the wind to take off from the ground or sea. In flight it reached speeds of up to 60 km/h.

Skeletal reconstruction of P sandersi with a California condor (lower left) and royal albatross (lower right) for scale. Illustration: Liz Bradford/PNAS

"This was a remarkable fossil, almost like something out of Game of Thrones," said Daniel Ksepka at North Carolina State University. Its mouth was filled with bony spikes that gave it the menacing look of a dragon, he added.

The remains of the bird, including its skull, shoulder blade, and hollow leg and wing bones, were dug from rock near Charleston airport in 1983, but the full significance of the fossils had not been realised before.

Though no feathers survived, Ksepka extrapolated the mass, wingspan and wing shape from the fossilised bones and fed them into a computer to estimate how the bird might fly. A conservative estimate put the wingspan of P. sandersi at around 6.4 metres.

The computer model showed that like the modern albatross, the prehistoric bird was an extremely efficient glider and barely needed to flap to cover ground. "It could probably travel for extreme distances using a very, very small amount of energy," said Ksepka. If the bird was caught on low ground in bad wind conditions, it may have become fatally stuck.

The Charleston specimen likely died at sea, as the excavation site was a prehistoric seabed. Remains of archaic rays, skates, and even a toothed whale have been unearthed at the site in the past. There are no obvious breaks in the bird's bones that point to a particularly violent death, Ksepka said.

Robert Nudds at Manchester University said the bird's dimensions were "guesstimates instead of estimates", but said the bird would have had a similar flying style to the albatross. "It would flap its wings rarely and use wind profiles above the waves to carry it," he said.

Ksepka said the remains of larger flying birds may yet be found. "I wouldn't be surprised if something a little bit larger was found some time down the line. I don't think we'll be pushing 10-metre wingspans, but a little bit bigger," he said.