Scientists say the fossils of an extinct flightless bird that once lived in Jamaica, show that its wings evolved into clubs.
The heavy, flailing bludgeons allowed the bird to fight rivals and predators.
The bird, Xenicibis xympithecus may have lived until about 10,000 years ago.
A member of the ibis family, it was probably about the size of a chicken.
Writing in the Royal Society journal Proceedings B, researchers say its club-like wings were an adaptation unique among birds and unlike anything in mammals, reptiles or amphibians.
Dr Nicholas Longrich, from Yale University told BBC News:
"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."
Xenicibis xympithecus was first identified in the 1970s by Storrs Olson from the Smithsonian Institution, a colleague of Dr Longrich in this research.
