The fossil remains of a 50-million-year-old bird with a six-metre wingspan have been found in Antarctica.

Paleontologists at a natural history museum in Argentina said they had identified the pelagornithid, or bony-toothed bird, nearly three years after its fossilised bones were first found at an Argentine research base on the Antarctic island of Marambio.

"Almost three years ago, remains began to appear of what we believed could be this bird.

Then we found a bone that confirmed that it was a pelagornithid," an extinct family of enormous seabirds, said Carolina Acosta Hospitaleche, a researcher on the project.

The bird's wings, fully extended, spanned more than 6.4 metres.

This is twice as big as the albatross, the largest flying bird alive today, which has a wingspan of 3.3 metres.

Ms Acosta Hospitaleche's colleague Marcos Cenizo, the director of the Natural Sciences Museum of La Pampa, said the bird was the largest pelagornithid specimen ever found.

"The shape of their wings allowed them to glide and cross large distances across the oceans," he said.

Antarctica specialists say there were two kinds of pelagornithid on the continent, one that reached up to five metres tall, with a similar wingspan, and another that stood more than seven metres.

The birds likely developed to their monstrous size some 50 million years ago, when warming ocean temperatures would have given them an abundance of food to thrive on, the researchers said.

But the recently identified specimen would have been quite light despite its stature, at 30 to 35 kilograms —"almost like a feather," Mr Cenizo said.

The researchers published the find in the Journal of Paleontology.

AFP/ABC