Smuggled dinosaur fossils headed home to Mongolia from New York
The dinosaur remains, all between 68 million and 80 million years old, were looted from sites in the Gobi desert.
Their repatriation comes a month after paleontologist Eric Prokopi was sentenced to three months in prison for his involvement in a smuggling scheme.
"This is a historic moment for the US Attorney's office, in addition to being a prehistoric event," said Manhattan US Attorney Preet Bharara, who displayed some of the bones during a repatriation ceremony in Manhattan.
"A recovery of this sort is really without precedent."
Mongolia is constructing a new natural history museum where the fossils may be displayed, Bharara said.
The remains include two Tyrannosaurus bataar skeletons, a fossilized egg and a well-preserved 'nest' of several Oviraptor skeletons.
All told, the investigation by federal prosecutors and customs agents has yielded remains from 31 dinosaurs, officials said.
A Tyrannosaurus bataar skeleton was sent back to Mongolia last year.
"Fossil looting is a huge problem worldwide," Mark Norell, curator-in-charge of the paleontology division of the American Museum of Natural History, said at the ceremony.
Prokopi pleaded guilty in 2012 to three felony counts and cooperated with prosecutors in recovering fossils, including some that were previously unknown to authorities.
The probe has led to other investigations into possibly illegally imported fossils in Wyoming, California and New York, prosecutors said at his sentencing in June.