People look at the fossilized remains of dinosaur skeletons on display during a repatriation ceremony at the United States Attorney's Office of the Southern District of New York on Thursday. US authorities agreed to ship the remains of 18 dinosaurs back to Mongolia after finding the smuggled fossils during a criminal investigation. Eduardo Munoz / Reuters

US officials on Thursday turned over to the Mongolian government enough 80 million-year-old dinosaur skeletons to stock a museum, including two relics of a kind of dinosaur that a prosecutor said "memorably stampeded" in a Hollywood movie.

US Attorney Preet Bharara said the fossilized remains of more than 18 dinosaurs recovered by US federal authorities were transferred after a ceremony attended by Mongolia's ambassador to the United Nations.

"This is a historic event for the US attorney's office, in addition to being a pre-historic event," Bharara joked at the gathering.

James T. Hayes, special agent in charge of the New York office of US Homeland Security Investigations, said at least 31 fossilized dinosaur remains will eventually be returned to Mongolian authorities, after it was determined that they were illegally poached and smuggled out of the Asian country between 2005 and 2012.

Hayes said the effort to intercept illegal shipments of dinosaur bones shows the US "will not allow the illicit greed of some to trump the cultural history of an entire nation".

He said the bones will be displayed at a national museum in Mongolia.

The bones were recovered after US Immigration and Customs Enforcement agents discovered illegal shipments of mislabeled bones were being made to the US.

Hayes said Eric Prokopi, a commercial paleontologist from Virginia, who pleaded guilty to federal charges, had disassembled some chunks of bones from a Tyrannosaurus bataar skeleton to sneak them into the country, knowing he could easily put them together. Once assembled, the skeleton was sold at auction for more than a million dollars before federal authorities seized it and returned it to Mongolia last year.

Prokopi, 39, who cooperated extensively and alerted authorities to many skeletons they did not know about, was ordered at a Manhattan court proceeding last month to serve three months in prison.

Bharara said the dinosaurs returned to Mongolia on Thursday included two Tyrannosaurus bataar skeletons, a dinosaur egg and two skeletons of Gallimimus, "the dinosaurs that memorably stampeded in one scene" of the movie Jurassic Park.