It was like nothing anyone had ever seen: a tiny, desiccated creature found behind a church in an abandoned desert town in Chile.

With a huge, misshapen skull that ended in a point and slanted eye sockets, it looked like an alien. But with limbs, ribs and a spine, it also looked human -- and yet not human at all.

Though the mummy was the size of a fetus – only 13 centimetres long -- its fully hardened bones and teeth suggested it couldn't be.

Was it a mummified alien? An ancient non-human primate?

A team of scientists from Stanford University and at UC San Francisco says they now have the answers – at least most of them.

The mummy was discovered more than 10 years ago and dubbed “Ata,” after the Atacama Desert of Chile where it was found. After changing hands on the archeological finds black market, the specimen ended up in promotional photos for an upcoming documentary on UFOs.

That’s how Garry P. Nolan, an immunologist at Stanford University, first learned of it.

“I had heard about this specimen through a friend of mine, and I managed to get a picture of it,” Nolan said in Stanford announcement.

“You can’t look at this specimen and not think it’s interesting; it’s quite dramatic.”

He contacted the movie directors to offer to do a genetic sequencing of the mummy.

With the help of Stanford radiology professor Dr. Ralph Lachman, and Dr. Atul Butte, director of the Institute for Computational Health Sciences at the University of California-San Francisco, the team began an analysis, which they detail in a new report in the journal Genome Research.

Their first finding: the mummy was definitely human, definitely female, and most likely a miscarried fetus or stillbirth.

But what accounted for the child’s bizarre features, its fully formed bones, its 13-centimetre length, and the 10 sets of ribs instead of the usual 12?

Over four years, Butte and a team conducted a thorough genomic evaluation of the mummy. They learned the child had a mix of genetic mutations that combined to cause a disorder never before documented in humans -- and one that likely led to the child’s death.

The mummy’s DNA showed mutations in seven genes that separately or in combination cause various bone deformities, including dwarfism and facial malformations.

Some of the mutations had never before been associated with bone growth disorders, although they had been known to cause disease.

The researchers believe the mutations caused the child’s skeleton to mature quickly, yet fail to grow to normal size, and that it was the disorder that caused the child to be miscarried or stillborn.

With the mystery solved, Nolan hopes that Ata can now be given a proper burial.

Ata’s genome showed she likely died no more than 40 years ago and has the genetics of the Chilote Indians of Chile’s Andean mountains.

“We now know that it’s a child, and probably either a pre- or post-term birth and death,” he said in a UCSF statement.

“I think it should be returned to the country of origin and buried according to the customs of the local people.”