TUCSON, Ariz. (Map, News) - More than two years after federal authorities seized four tons of rare fossils illegally imported for sale at the Tucson Gem and Mineral Show, the relics were returned to Argentina on Thursday.

U.S. Customs and Immigration Enforcement agents seized the fossilized relics early in 2006, acting on a tip from Interpol that a vendor at the show might be selling smuggled goods. The vendor represented the Rhodo Co., an Argentine corporation that mines rhodochrosite.

ICE undercover agents posed as prospective buyers and conducted surveillance, taking photos of suspicious specimens, agency officials said.

Using that evidence, ICE agents sought and obtained a federal warrant to seize numerous pallets and barrels of fossils the vendor had at the show. They also found and seized additional specimens belonging to the vendor at a nearby warehouse.

Lisa Fairchild, the ICE supervisory special agent who headed the initial investigation, said at the time that the agency considered the fossils priceless.

"It's the property of another government and it can't be replaced," Fairchild said.

ICE said in a statement Thursday that the investigation is continuing.

ICE Assistant Secretary Julie Myers returned more than 8,100 pounds of antiquities during a cultural repatriation ceremony in Buenos Aires to the Argentine minister of culture and the head of the Museum of Geological and Paleontological Artifacts.

The fossils, including an unspecified number of dinosaur eggs, shell fragments, petrified pine cones and fossils prehistoric crabs, date from 251 million years ago, when the Mesozoic era started, to about 65 million years ago, the beginning of the Cenozoic era, experts say.

"We think these historical artifacts rightly belong to the people of Argentina, so I'm very proud to be able to formally hand them back," Myers said earlier this week when she arrived in Buenas Aires. The fossils, she said, were "pieces of a country's history that people are trying to put up for sale."