The evidence comes (as so much evidence does) from the bowels of a museum collection. At the turn of the 20th century, Dragutin Gorjanović-Kramberger excavated a site full of human and animal remains in what is now Croatia. The site held nearly a thousand human bones and several thousand animal bones, along with at least a thousand tools, all from 120,000 to 130,000 years ago.
Gorjanović-Kramberger used very modern techniques to keep track of where he found each specimen, but the researcher missed something that now seems obvious.
"He found these eagle talons and sent them to a bird specialist in Budapest," said David Frayer of the University of Kansas, one of the authors of the new study. "But ironically, even though he was the first person to identify cut marks on human bones, he missed these really obvious signs of cut marks and manipulation on the eagle talons."
So did the bird specialist in Budapest. And the museum curators who then stored the specimens.
A year and a half ago, Frayer said, a colleague of his took over as a curator of the Croatian Natural History Museum and gave the talons a second look. She contacted him when she suspected they'd been manipulated by the Neanderthals who'd been found with them.
"When I saw them, my jaw dropped," he said. "The talons were so complete and so beautiful, and the cut marks were so obvious."
This is important, he said, because of their age: 120,000 or 130,000 years ago, there were only Neanderthals in Croatia. No modern humans were around.
"People often argue that Neanderthals were mimicking modern humans instead of coming up with ornamental things on their own," Frayer said. "In this case, there's no doubt: There were only Neanderthals there, and only Neanderthal tools."
Based on the wear of the talons, Frayer and his colleagues believe that they were strung together and worn around the neck, where sweat and other body fluids caused polishing seen on similarly made shell bead necklaces.
And because eagles would have been rare -- and vicious -- in that environment, Frayer thinks the find suggests the Neanderthals were skilled hunters.
"There are talons from three or four different eagles here, and that represents a lot of planning and skill," he said. "They're big birds, and they're vicious when caught."
He also thinks the talons' use as ornamentation -- if that's indeed what they were for -- speaks to some impressive levels of abstract thought.
"When you catch the most powerful aerial predator in your environment and wear it around your neck, that suggests some kind of attempt to get its power," he said.