A Florida fossils dealer has admitted smuggling dinosaur bones into the US, 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 $1m (£600,000).
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 by authorities 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 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 imprisonment when he is sentenced in April.
US Attorney Preet Bharara said authorities would now begin the process of returning the fossils to their countries of origin.
"Fossils and ancient skeletal remains are part of the fabric of a country's natural history and cultural heritage, and black marketers like Prokopi who illegally export and sell these wonders, steal a slice of that history," he said.
Mongolia has been seeking the return of the Tyrannosaurus skeleton - which it says was stolen from the Gobi desert - through the US courts.
In court on Thursday, Assistant US Attorney Martin Bell read out a list of the dinosaurs that he said Prokopi had illegally imported.
"It's among the larger dinosaur shopping lists you'll see today," he told Magistrate Judge Ronald Ellis.
He said 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 residential dwelling in Florida.
One of the Saurolophus skeletons was sold at an auction in California for $75,000 but later confiscated by authorities.
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.
Prokopi was described as a commercial palaeontologist who sold coral, fossils and other items over the internet.