Army ants, groups of ants that sweep along in massive, voracious groups, evolved just once -- contrary to common scientific belief -- a Cornell University researcher reports.

Entomologist Sean Brady studied the DNA of 30 army ant species from across the world and concluded that they all had the same point of origin.

Brady's findings, scheduled for next week's online edition of Proceedings of the National Academy of Sciences, were being released early, the academy said Tuesday.

Scientists have thought that army ants originated separately on different continents over millions of years.

But Brady's findings indicate that these ants have been around 100 million years -- since the reign of dinosaurs -- and haven't changed.

"I didn't think they'd be that old ... it's kind of amazing that for tens of millions of years they were engaged in their hunting parties when dinosaurs were walking all over them," Brady said.

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