Everyone expected the auction of the T-Rex skeleton to go peacefully. But they were wrong.

On the fourth floor of an airy gallery building in Chelsea on Sunday afternoon, a small group of private collectors and natural history enthusiasts gathered to witness the historic auction of a 24-foot-long, museum-quality Tyrannosaurus bataar skeleton, which was expected to bring up to $1.5 M. After a couple hours of uneventful sales of things like fine gemstones and amber-trapped insects, the marquee object came up.

The centerpiece auction was abruptly interrupted.

Before bidding on the skeleton began, the auctioneer announced that the sale would be “contingent upon a court proceeding dealing with this matter.” Almost immediately, Robert Painter, a lawyer representing Elbegdorj Tsakhia, the president of Mongolia, stood up with a cell phone held to his ear and yelled, “I’m sorry, I need to interrupt this auction. I have a judge on the phone.”

A loud whistle rang out, and Heritage Auctions president Greg Rohan, along with a group of security guards, gathered around Mr. Painter. They urged him to a corner of the room, past a massive cast of a sabre-tooth tiger and a glass case full of meteorite chunks.

In the past week, many prominent paleontologists have taken issue with the provenance of the skeleton and the legality with which it ended up at the Heritage auction. News of the sale eventually reached the Mongolian head-of-state, and Mr. Painter says he was contacted by President Elbegdorj’s office “Friday after 5 PM” to see what he could do to postpone the auction.

The next day, Mr. Painter told The Observer, he filed a lawsuit against Heritage Auctions in Dallas, Texas (the headquarters of the auction house), alleging the skeleton was taken from Mongolia, and that, under Mongolian criminal law, “the export of dinosaur bones and fossils is a criminal offense.”

Mr. Painter also got a temporary restraining order signed by district court judge Carlos Cortez, who he had on the phone during the auction, which was intended to prevent the sale and transfer of possession of the skeleton. (Mr. Painter provided us copies of both.)

“I was quite surprised and disappointed that Heritage Auctions chose knowingly to ignore a court order that the auction could not proceed,” Mr. Painter said.

Despite the ruckus, the auction continued, and the considerable artifact sold for $1,052,500, to an unidentified phone bidder. The small audience, slightly confused, applauded.

After being escorted from the building, Mr. Painter stood with a small gathering of protestors—one of them wearing a traditional Mongolian hat and jacket—who were distributing fliers on the sidewalk. They held a sign that read, rather dispassionately, “It’s a national treasure of Mongolia. Return our stolen treasure.” Also among them was prominent Mongolian paleontologist Bolortsetseg Minjin, a representative of the Mongolian Academy of Sciences and the director of the Institute for the Study of Mongolian Dinosaurs, and Ann Altman, of Connecticut, who represented of one of the Mongolian president’s advisors.

Ms. Altman explained, “We wanted postponement and clarification [of the provenance of the skeleton]. The president has made this his personal mission. He personally has stepped in to protect the patrimony of the country.”

The protestors had learned of the sale only days prior, in an article in the Daily Mail, which states the origin of the skeleton was Mongolia.

Mark Norell, the chairman and curator of the division of paleontology at the American Museum of Natural History wrote a letter in support of the Mongolians, included in Mr. Painter’s affidavit, which says the skeleton “clearly [was] excavated in Mongolia as this is the only locality in the world where these dinosaurs are known,” and that the specimen was “undoubtedly looted from Mongolia.”

But the auction catalog provided by Heritage Auctions does not so clearly state the origin of the skeleton. It notes that the skeleton is from “Central Asia” and that the Tyrannosaurus bataar lived in what is now the Gobi Desert (half of which lies in Mongolia), but does not provide further information.

In a brief interview, Mr. Rohan, the president of Heritage Auctions, told The Observer he was confident that the transport of the skeleton to the U.S. was legal. “We and our counsel are not aware of any treaties under which the sale would be illegal,” Mr. Rohan said.

An updated press release on the Heritage Auction website noted that Heritage Auctions

fully appreciate[s] the widespread concerns relating to the Tyrannosaurus, but our conclusion is that no impropriety exists to prevent its sale at auction. Our consignor is an individual with a good reputation who has warrantied in writing to us that he holds clear title to the specimen. We’ve seen no evidence even suggesting that the fossils were collected illegally.

Mr. Rohan also discussed the complex patrimony issues that arise when dealing artifacts. “In a perfect world, the scientific community would like the sale of fossils to be illegal, and they would all be in museums. But the fact is it is legal to sell fossils. We as the auction house remain neutral [on this issue]. We represent the consignor, who in this case spent a year of his life repairing the skeleton,” Mr. Rohan said.

He also said he felt that the negative attention in the press had “kept bidders away.”

In the hours after the auction, Heritage posted another press release to its website, maintaining that the skeleton was acquired legally and denying Mongolia’s claims to the artifact:

As far as we know, the Mongolian government has not produced any evidence that the piece originated in its territory, but the final determination will be up to the American legal system.

Mr. Painter plans to ask the judge for a shortened discovery period, with the hope that it will take a week rather than the typical month to get this ironed out.

“I feel comfortable that the Tyrannosaurus skeleton is safe. Once we get the ownership identified, if we’re correct and this is the property of the Mongolian nation, this will not go back to the consignor—it will be returned to the Mongolian people. That’s our goal,” he said.

The buyer of the bones bid by phone, and his or her name was not disclosed by the auction house.