Customs agents have seized fossilized dinosaur eggs believed to have been smuggled illegally from China and auctioned for $420,000, officials said Thursday.

The 22 eggs, each 65 million years old, were so well-preserved that embryonic raptors are visible inside 19 of them. They were seized late last week from the Bonhams & Butterfields auction house in Los Angeles.

The eggs were auctioned in December to an undisclosed buyer, but the transaction was scrubbed before money changed hands after concerns were raised about the legality of their export.

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"That sale was canceled and the property turned over to the U.S. government," said Levi Morgan, a spokesman for the auction house in San Francisco.

The eggs were found in China's Guangdong province in 1984, shipped to Taiwan and in 2004 to an American collector in Florida, according to a customs agent's affidavit filed last month in federal court.

Authorities found that the shipper in Taiwan had no paperwork to prove the fossil was legally transferred from China, and that an invoice falsely described the items as being from Taiwan and worth only about $500, according to U.S. Immigration and Customs Enforcement.

Morgan said the auction house essentially had to trust that the American seller had the legal right to consign the eggs, because it isn't able to verify export documents.

No arrests have been made, but the auction house is cooperating with the investigation.

Customs agents are holding the eggs as evidence, but "the goal is to return them to China," spokeswoman Virginia Kice said.