HONG KONG – Christie’s said on Sunday it was withdrawing a Tyrannosaurus rex skeleton that it had been planning to auction in November in Hong Kong, where it was initially expected to fetch between US$15 million (S$21 million) and US$25 million, after questions were raised about the number of replica bones used in the specimen and the way it was described in marketing materials.

“After consultation with the consignor of the Tyrannosaurus rex scheduled for sale on Nov 30 in Hong Kong, Christie’s has decided to withdraw the lot,” a spokesman for Christie’s, Mr Edward Lewine, said in a statement. “The consignor has now decided to loan the specimen to a museum for public display.”

Asked about the reason for the withdrawal, Mr Lewine said the auction house believes the specimen would “benefit from further study”.

The news came 10 days before the scheduled sale.

The T. rex, which the auction house called Shen, had been billed as the first skeleton of its species to appear at auction in Asia. A Christie’s news release touted the specimen as “museum standard” and “a world-class specimen”.

But questions about the fossil were raised in recent weeks, when a lawyer for the Black Hills Institute of Geological Research, a fossil company in South Dakota, reached out to Christie’s about similarities between Shen and another T. rex skeleton, named Stan, which Christie’s sold in 2020 for a record US$31.8 million.

Although Stan was auctioned off, the Black Hills Institute retained intellectual property rights on the specimen, allowing it to continue selling painted polyurethane casts of the skeleton, which are currently priced at US$120,000 each.

Mr Peter Larson, the company’s president, said in an interview that when he first saw a photo of Shen, the skeleton Christie’s was preparing to auction in Hong Kong, he noticed that the skull looked similar to Stan’s skull, including holes in the lower left jaw that Mr Larson said were unique to Stan.

Mr Larson and his colleagues at Black Hills examined the particularities of Stan’s bones over three decades after excavating the specimen starting in 1992.

Mr Larson said it appeared to him that the owner of Shen – who was not identified by Christie’s – bought a cast of Stan from Black Hills to supplement the original bones.

“They’re using Stan to sell a dinosaur that’s not Stan,” Mr Larson said in an interview with The New York Times a few days before the sale was called off. “It’s very misleading.”

On Sunday, after the decision was made to withdraw the skeleton, Mr Larson said, “Christie’s did the right thing”.

After a lawyer for Mr Larson’s company, Mr Luke Santangelo, contacted Christie’s this fall with concerns that the online auction materials did not make clear to the public that the specimen included casts of Stan, the auction house added a note to its online auction materials.

“Replica bones that were added to original bones (referred to as STAN™ elements) were created by, and purchased from, Black Hills Institute of Geological Research, Inc.,” read a note added to the bottom of a web page advertising the specimen.

The auction house’s catalogue confirmed that none of Shen’s teeth are original.

Excavated from Montana in 2020, the bones were described in the catalogue as “well-preserved and quite solid”, and with pathologies that included bite marks and osteoarthritis.

How much was original?

Fossil auction sales have been booming in recent years, and earlier in 2022, Christie’s sold the remains of a raptor for US$12.4 million, more than double the auction house’s high estimate.

The withdrawal is a significant loss for the auction house, which made Shen the headliner of its weeklong sales in Hong Kong that begin next week.

Nearly all dinosaur skeletons are incomplete, requiring casts of other specimen’s bones or reconstructed additions to appear whole. How much of a skeleton is fake depends on the amount of original bone.

Christie’s said in its marketing materials that Shen was “54 per cent represented by bone density”, a measure that some fossil experts questioned.

The auction house’s catalogue notes that the Shen specimen has about 79 original bones; the total bone count for a T. rex is not known with certainty and can vary depending on how they are counted, but some scientists have estimated that they contain 300, and others 380.

In comparison, Stan, the specimen sold in 2020, has 190 original bones, according to research on the specimen. And Sue, the famous T. rex that was also excavated by Black Hills and auctioned off to the Field Museum of Natural History, in Chicago, has 250, the museum said, a figure that includes a set of rib-like bones across the belly that are sometimes not included in total bone counts.

Mr Santangelo, the lawyer, said he urged Christie’s to alter any descriptions that were “potentially misleading the public” about Shen, including its claim that the dinosaur was “54 per cent represented by bone density”.

Fossil experts have questioned the meaning of that figure, which Christie’s earlier explained as helping to provide more weight to, for example, a massive femur bone compared to a tiny ear bone.

“Bone density has no scientific meaning whatsoever” in this context, said Ms Margaret Lewis, president of the Society of Vertebrate Paleontology, a professional group that vocally opposed the auction of Stan in 2020.

Auctions like this one have drawn criticism from palaeontologists at museums and universities, who fear that scientifically important specimens could end up privately owned and out of the reach of researchers.

‘It’s pretty obvious’

Dr John R. Nudds, one of the researchers credited with having studied Shen and a central figure in the auction house’s advertisements, acknowledged in an interview before the withdrawal that by bone count, roughly three-quarters of the original bones in the specimen were casts of Stan.

Dr Nudds, who said he retired as a lecturer in palaeontology at the University of Manchester in 2020, said he did not think the existence of cast elements in Shen was obscured.

“I don’t think that’s ever been hidden,” said Dr Nudds, who added that he consulted on the specimen for the private owner, not Christie’s. “I think it’s pretty obvious that if a skeleton is 54 per cent by bone density, then 46 per cent by bone density has got to be cast – there’s no other way around it.”

Stan’s buyer was anonymous. But earlier in 2022, National Geographic reported that the dinosaur would be featured in a developing natural history museum in the United Arab Emirates.

Mr Larson’s company has sold about 100 casts of Stan, including to the Smithsonian National Museum of Natural History, providing a significant portion of its income. He said he has been concerned that any buyer of Shen would assume the right to make and sell their own copies.

“It was jeopardising our copyright and our trademark,” he said.

As the company’s lawyer negotiated with Christie’s over the past several weeks, some information in the auction house’s online materials was modified.

A line in the news release about Shen being “auctioned with full rights and all soft assets relating to it” disappeared. And the US$15 million to US$25 million estimate was altered, reading only, “estimate on request”.

Then, on Sunday, the sale was called off. NYTIMES