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The tail's anatomy enabled the scientists to rule out that it belonged to a bird because it was long and flexible and lacked a pygostyle, fused vertebrae that in birds support the tail feathers.

"We can be sure of the source because the vertebrae are not fused into a rod or pygostyle as in modern birds and their closest relatives," he explained.

Turning a pygostyle back into a long tail requires learning how the pygostyle evolved in the first place.

Instead, they have a complicated appendage called a pygostyle, with short, fused vertebrae and connected muscles that allow them to control and fan out their tail feathers.

Pygostyle, pī′gō-stīl, n. the vomer or ploughshare bone of a bird's tail.—adj.