Ethiopia ? After 3.2 million years in East Africa, one of the world’s most famous set of fossils was quietly flown out of Ethiopia overnight for a U.S. tour that some experts say is a dangerous gamble with an irreplaceable relic.

Although the fossil known as Lucy had been expected to leave the Ethiopian Natural History Museum this month, some in the nation’s capital were surprised the departure took place under cover of darkness with no fanfare Sunday.

The Smithsonian Institution has objected to the six-year tour because museum experts do not believe the fragile remains should travel. Even in Ethiopia, the public has seen the real Lucy fossil only twice. The Lucy exhibition at the Ethiopian Natural History Museum is a replica, and the real remains are usually locked in a vault to protect them.