A Florida fossils dealer has admitted smuggling dinosaur bones into the United States, including those of a 70-million-year-old Tyrannosaurus bataar from Mongolia.
A court in New York heard that Eric Prokopi sold the skeleton at auction in May for more than $US1 million.
In June, US officials seized the bones after Mongolia said they were stolen.
In a plea bargain, Prokopi gave up any claim to the skeleton as well as to others seized in the case, which included remains from China.
He also admitted illegally importing a Chinese flying dinosaur, two oviraptors and a duckbilled creature known as a Saurolophus.
The BBC reports the court heard that Prokopi, 38, was arrested in October as a lorry arrived at his home loaded with fossils.
He faces a maximum of 17 years in prison when he is sentenced in April.
Mongolia has been seeking the return of the Tyrannosaurus skeleton - which it says was stolen from the Gobi desert - through the courts.
US Attorney Preet Bharara said the fossils would be returned to their countries of origin.
In court on Thursday, Assistant US Attorney Martin Bell read a list of the dinosaurs that he said Prokopi had illegally imported.
He told Magistrate Judge Ronald Ellis that a second, almost complete, Tyrannosaurus skeleton had been found at Prokopi's home in Gainsville, Florida.
Mr Bell said one oviraptor skeleton was found at Prokopi's home and the other at another house in Florida.
One of the Saurolophus skeletons was sold at an auction in California for $US75,000 but was later confiscated.
Prokopi admitted illegally importing skeletons from Mongolia and China.
Heritage Auctions in New York, which sold the Tyrannosaurus skeleton in May, said Prokopi had spent a year restoring and remounting what had been a loose collection of bones.