An extinct flightless bird from Jamaica fought rivals and predators using wings evolved into clubs, scientists suggest.
The boney bludgeons carried by Xenicibis xympithecus are unlike anything else known in the bird world - or in mammals, reptiles or amphibians.
Writing in the Royal Society journal Proceedings B, the scientists report finding bones that had apparently been broken by another bird's club.
The species may have survived until less than 10,000 years ago.
A member of the ibis family, it was probably about the size of a chicken, but with an infinitely more robust armoury.
Fossils show that the metacarpus - one of the "hand" bones - was elongated and much bigger than in related species, with very thick walls.
This allowed the wings to function "in combat as a jointed club or flail", the researchers write.
"We don't really know how they would have used these clubs, but we do know that modern ibises grab each other by the beak and pound away with their wings," said Nicholas Longrich, from Yale University in the US.
"And we analysed two bones that had been broken during fighting, including a humerus (upper arm bone) that had been snapped in half - it had started to re-heal, although the two ends hadn't knitted together," he told BBC News.
Dr Longrich's colleague in this research, Storrs Olson from the Smithsonian Institution, was one of the scientists who first identified Xenicibis xympithecus back in the 1970s.
A number of other birds are known to fight by whacking each other with their wings - including swans, who will also protect their young this way.
Some, including screamers, lapwings and and spur-winged goose, have evolved spurs to increase the damage they can wreak.
The extinct solitaire from the Indian Ocean island of Rodrigues - a cousin of the dodo - had bony growths colloquially known as "musketballs" on their wings, which appear to have served the same purpose.
"But among vertebrates - there's no animal of any sort that has anything like a limb modified as a club," noted Dr Longrich.
Julian Hume, an avian palaeontologist with London's Natural History Museum who was not involved in the research, noted that unlike most flightless birds, Xenicibis retained long wings, possibly making its flailing more powerful.
"Ibis young stay in the nest for a relatively long time," he said.
"So if they retained that feature, that suggests they needed it for defence against predators - and there were quite a few on Jamaica."
However, ibises also tend to be intensely territorial, so the flailing clubs may also - or alternatively - have found employment in disputes between individuals, probably with both sexes involved.
By Richard Black
Environment correspondent, BBC News
http://www.bbc.co.uk/news/science-environment-12115776
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