NEW YORK, NY.- In May 2022, Jason Cooper, a commercial paleontologist, went for a walk around his property near the aptly named Colorado town of Dinosaur with a friend and found a bit of femur protruding from some rock.

That femur led to a stegosaurus fossil, among the largest and most complete ever found, which has subsequently been nicknamed “Apex.” In July the Sotheby’s auction house will sell Apex at auction at an estimated value of $4 million to $6 million, making the skeleton the latest flashpoint in a long-running debate about the private fossil trade.

Dinosaur fossils have fetched escalating prices at auction houses since 1997, when Sotheby’s sold “Sue” the Tyrannosaurus rex to the Field Museum in Chicago for $8.36 million. In 2020, “Stan,” another largely complete T. rex skeleton, sold at Christie’s for $31.8 million.

Such pricing has raised serious concerns among academic paleontologists, said Stuart Sumida, vice president of the Society of Vertebrate Paleontology. Many of them have watched fossils that may unlock scientific mysteries get steered into the hands of wealthy private collectors rather than toward research institutions in recent decades.

Cooper and his colleagues unearthed the Sotheby’s-bound stegosaurus in 2023. Digs on his property have yielded a number of Jurassic period dinosaurs, several of which Cooper has donated to institutions including the Brigham Young University Museum of Paleontology in Provo, Utah, and the Frost Museum of Science in Miami.

Cooper described the Apex stegosaurus as a unique and scientifically important specimen. Skeletons — even partial ones — of the plate-backed, spike-tailed herbivore are rare. The skeletal mount contains material from about 70% of the animal’s bones. At 11 feet tall and over 20 feet long, Apex is double the size of “Sophie,” the most intact stegosaurus specimen known, and has unusual proportions, remarkably long legs and square-bottom plates.

The specimen was also discovered with skin impressions, possibly from the neck, which will be offered as part of the sale.

Cooper supervised the preparation and mounting of the stegosaurus, 3D-scanning the existing bones and mirroring elements of the specimen to fill in the gaps. The team also collected extensive contextual data, which they think could be attractive to prospective buyers. The information includes a detailed site survey, quarry maps and other documentation.

Cooper also invited several paleontologists to examine the specimen.

“If you combine size, completeness and bone preservation, it is the best stegosaurus I’ve seen,” said Rod Scheetz, curator at the Brigham Young University Museum of Paleontology, who inspected it at Cooper’s property.

Cassandra Hatton, the head of Sotheby’s science and popular culture department, said the auction house worked closely with Cooper to reinforce the scientific legitimacy of this privately sold dinosaur mount, aiming to create a model for future auctions.

“This is the first time a specimen has been auctioned where we’ve been working together from the time it was excavated,” she said. “This is the most transparent sale of a dinosaur to have ever occurred.”

But Jim Kirkland, the state paleontologist of Utah, declined to endorse the stegosaurus when he was invited by Cooper. “It looks pretty interesting,” he wrote in an email, “but I will not promote something going to auction. I would have hooked him up with museums directly but not this.”

While anything can happen at a public auction, Cooper and Hatton both expressed their hopes that Apex will ultimately land at a scientific institution — whether through direct purchase or by donation from a private collector. The team gathered the data and documentation not just to reassure potential purchasers of the specimens’ authenticity but also to help museums smoothly integrate such a specimen into a research collection.

“Whoever purchases this also has the right to come to my property and collect contextual information,” Cooper said. “A private collector might not give a stego spike about that, but for a museum, that’d be really cool.”

However, the stegosaurus’s potential price tag could be out of reach for many institutions, Sumida said. He said that the costs of studying an already mounted and reconstructed specimen can be higher than just the purchase price. Reconstructing and mounting fossils is as much art as science — and specific choices can be used to hoodwink the uninitiated by blurring the lines on what parts of any given bone are real.

“If the specimen is as scientifically important as it’s purported, then they’re going about it entirely the wrong way,” Sumida said.

Cary Woodruff, curator of vertebrate paleontology at the Frost Museum of Science in Miami, agreed that public auctions were often “scientific abbatoirs.” But Woodruff — who also examined the specimen before the auction agreement — suggested that compiling detailed records, pictures and digital scans of commercially sold fossils is something other sellers should emulate. That way, “at least a vestige of the scientific data can exist if the specimen does not end up in the public trust,” he said.

Ultimately, however, Woodruff concurred that the public trust is where such fossils belong.

“If a wealthy person were interested in how they could work with a scientific institution to make a contribution to scientific knowledge and advancement,” he said, “then I hope such specimens would attract their attention.”

This article originally appeared in The New York Times.