The largest flying bird in history had a 24 feet wingspan - more than twice that of the biggest living albatross - and dined on fish probably caught in mid-flight over the open ocean, a study has found.
Fossilised remains of the extinct species were first unearthed in 1983 during the building excavations for a new terminal at Charleston airport in South Carolina, but the latest analysis of the paper thin bones of its skeleton revealed the giant wingspan, scientists said.
The bird, named Pelagornis sandersi, lived about 25 million or 28 million years ago. Its long, slender wings suggest that it could glide for long periods with minimal energy, although its huge size suggests that it may have had trouble taking off and landing without the help of air currents or a downhill slope to run, they said.
Its wingspan would have been greater than the wingspans of the giant condor and the royal albatross combined. Computer models of the wing bones and flight feathers of living birds suggest that Pelagornis was a very efficient glider capable of taking it out to sea for longer periods of time without landing.
An array of small, tooth-like spikes in its upper and lower jaw means that it is possible that the bird fed on fish, squid, eels and other soft-bodied prey, probably caught while it was gliding over the ocean as its large size indicates it was mathematically impossible to take off from the sea surface simply by flapping is wings.
"Pelagornis sandersi could have travelled for extreme distances while crossing ocean waters in search of prey. That's important in the ocean where food is patchy," said Dan Ksepka, formerly of the US National Evolutionary Synthesis Centre in Durham, North Carolina and now curator of science at the Bruce Museum in Greenwich, Connecticut.
A comparative wingspan line drawing of the world's largest-ever flying bird, Pelagornis sandersi. At bottom left is a California condor, and at bottom right is a Royal albatross.
The bird's bony, teeth-like projections and other anatomical details of its well preserved skeleton indicate that it belonged to the Pelagornithidae: an extinct group of giant seabird that lived during this period 25 million years ago, long after the dinosaurs had died out but long before the rise of humans.
"Pelagornithids were like creatures out of a fantasy novel. There is simply nothing like them around today....The upper wing bone alone was longer than my arm," Dr Ksepka said.
Pelagornis may have lived much like modern day albatrosses, soaring high into the sky and riding on air currents for long periods without flapping their wings to preserve energy, occasionally swooping down to the sea surface to feed on soft-bodied prey.
Pelagornithids were found all over the world and survived for tens of millions of years before becoming extinct in the Pliocene about three million years ago: their sudden disappearance remains a mystery.
The latest study naming and describing Pelagornis sandersi is published in the journal Proceedings of the National Academy of Sciences. The species may eventually prove to have had the longest wingspan in the 140 million year history of the bird, being at the theoretical upper size limits for powered flight.
The species was named after Albert Sanders, the Charleston Museum curator who led the fossil's excavation.