Nearly two decades ago, the rumors began: In the Atacama Desert of northern Chile, someone had discovered a tiny mummified alien.

An amateur collector exploring a ghost town was said to have come across a white cloth in a leather pouch. Unwrapping it, he found a six-inch-long skeleton.

Despite its size, the skeleton was remarkably complete. It even had hardened teeth. And yet there were striking anomalies: it had 10 ribs instead of the usual 12, giant eye sockets and a long skull that ended in a point.

Ata, as the remains came to be known, ended up in a private collection, but the rumors continued, fueled in part by a U.F.O. documentary in 2013 that featured the skeleton. On Thursday, a team of scientists presented a very different explanation for Ata — one without aliens, but intriguing in its own way.