U.S. Attorney's Office

This photo, attached as an exhibit to the complaint filed by federal attorneys, shows the tyrannosaur skeleton that has stirred up an international legal dispute.

Federal attorneys today filed a civil lawsuit that seeks to wrest a tyrannosaur skeleton valued at more than $1 million away from its sellers and return it to the Mongolian government.

The skeleton was sold at a New York auction last month for $1.05 million to an unidentified buyer, even though a federal district judge in Texas issued a restraining order to hold up the sale. The auction house behind the offering, Texas-based Heritage Auctions, made the sale contingent on the outcome of Mongolia's court challenge — and since then, the skeleton has been held in legal limbo.

Earlier this month, a panel of paleontologists declared that the skeleton represented a Tyrannosaurus bataar, also known as a Tarbosaurus bataar, which was probably smuggled out of Mongolia sometime in the past 15 years or so. Today's complaint, filed by the U.S. attorney for Manhattan in New York federal district court, follows up on that determination and lays out the authorities' version of a tangled tyrannosaur tale.

"The skeletal remains of this dinosaur are of tremendous cultural and historical significance to the people of Mongolia, and provide a connection to the country's prehistoric past," Manhattan U.S. Attorney Preet Bharara said in a statement. "When the skeleton was allegedly looted, a piece of the country's natural history was stolen with it, and we look forward to returning it to its rightful place."

Mongolia has had laws on the books forbidding the export of dinosaur fossils since 1924. The complaint says the nearly complete skeleton was brought into the United States illegally, and thus should be forfeited by the sellers and returned to Mongolia.

James Hayes, a special agent-in-charge for the U.S. Immigration and Customs Enforcement's Homeland Security Investigations, said the complaint alleges that "criminal smugglers misrepresented this fossil to customs officials."

When the skeleton was imported into the United States from Britain in 2010, the country of origin was listed as Britain — even though, according to the paleontologists, nearly complete tyrannosaur skeletons of this type have been found only in Mongolia. The experts cited a dozen features of the bones, as well as their light color and even the dirt stuck in the cracks in the fossils, as characteristic of Tyrannosaurus bataar rather than the larger T. rex or other members of the tyrannosaur tribe.

Federal attorneys said that the importers set the skeleton's value at $15,000, but that a value of $950,000 to $1.5 million was listed in this year's auction catalog. They also said the 8-foot-tall (2.4-meter-tall), 24-foot-long (7.3-meter-long) skeleton was incorrectly listed on customs forms as consisting of assorted fossilized reptiles and skulls.

The complaint names Florida Fossils as the ultimate consignee for the imported goods, and notes that the company was owned at the time of importation by Eric Prokopi. The skeleton was shipped from Florida to Texas, and then on to New York in preparation for the May 20 sale. Soon after word spread that a million-dollar tyrannosaur was coming up for auction, representatives of the Mongolian government became interested and sought unsuccessfully to stop the sale.

The dinosaur skeleton is currently in the custody of Cadogan Tate Fine Art in Sunnyside, N.Y. In the weeks since the controversial sale took place, the auction house has let paleontologists and representatives of the Mongolian government examine the fossil.

"I thank and applaud the United States Attorney's office in this action to recover the Tyrannosaurus bataar, an important piece of the cultural heritage of the Mongolian people," Mongolian President Tsakhia Elbegdorj was quoted as saying in the U.S. government's news release about the case. "Cultural looting and profiteering cannot be tolerated anywhere, and this cooperation between our governments is a large step forward to stopping it."

My efforts to contact Prokopi today were unsuccessful, but representatives of Heritage Auctions issued this statement from the company's co-chairman, Jim Halperin:

"We auctioned the Tyrannosaurus bataar conditionally, subject to future court rulings, so this matter is now in the hands of lawyers and politicians. We believe our consignor purchased fossils in good faith, then spent a year of his life and considerable expense identifying, restoring, mounting and preparing what had previously been a much less valuable matrix of unassembled, underlying bones. We sincerely hope there will be a just and fair outcome for all parties."

More about the tyrannosaur:

• May 18: Auction stirs up a tussle over tyrannosaur
• May 21: Despite challenge, fossil sells for $1 million
• May 24: Auctioned dino skeleton believed to be smuggled
• June 8: Experts say tyrannosaur is definitely from Mongolia

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.