Largest stegosaurus fossil ever found to be auctioned by Sotheby's in New York

The largest stegosaurus fossil ever found is heading to auction next month with an estimated value of up to $6 million.

The specimen, known as "Apex," was excavated near Colorado's Morrison Formation, close to the town of Dinosaur, in 2023, according to the Sotheby's auction house.

A part of the armored dinosaur was first discovered on the nearby property of commercial paleontologist Jason Cooper, according to the auction house. In total, it measures 11 feet tall and 20 feet long and includes 247 fossil bones. The dinosaur is believed to be between 146 million and 161 million years old.

Cassandra Hatton, Sotheby's senior vice president and global head of science and popular culture, told ABC News she recalls getting a call from Cooper about the finding.

"Oh my goodness we have got something incredible on our hands," Hatton said about the discovery at the time.

Sotheby's will auction the specimen on July 17 with an estimated value of $4 million to $6 million in New York. Sotheby's sold a 200-pound Tyrannosaurus rex head in 1997 for $8.3 million.

As for how Apex earned its name, Sotheby's says its considered the largest and most complete stegosaurus ever discovered.

For nearly a decade, a stegosaurus specimen named Sophie, located in the National History Museum in London, held the title of the largest and most complete stegosaurus ever discovered. Apex is 30% larger than Sophie, based on the femur length of 45 inches, according to Sotheby's.

"Through the careful process of excavation, preparation, and installation, 'Apex' sets a new standard for all future discoveries of this magnitude, and further reinforces the enduring appeal of Stegosaurus and its vaunted status in popular culture," said Hatton in a press release.

But the Sotheby's sale next month could also stir up a longstanding debate about whether or not dinosaur fossils should be sold to private collectors.

Paul David Polly, a professor of earth and atmospheric sciences at Indiana University, said auctions often put the focus on finding complete dinosaurs versus studying the surrounding environment, giving an incomplete picture of the specimen.

"[An auction] fetishizes the complete skeletons of dinosaurs over a good careful scientific study," said David Polly

Additionally, at the hands of private collectors, fossils may not be available to the public which prevents scientists from studying them.

"Because [the fossils] are in a private collection, they can't contribute to the diversity of things we know about the world," said Canadian paleontologist Greg Funston.

Regardless, it is legal to sell fossils that were found on private property in the U.S. Other countries like Canada, Brazil and South Africa restrict the sale and export of fossils found in those countries.

David Polly said private landowners will grant access to the person who can pay the most, which often is not the scientists. "People come to perceive fossils as having monetary worth and scientists who work for nonprofits don't have money to buy fossils," he said.

Hatton says there are other issues to consider amid the debate over the private sale of fossils. "I think the debate is more whether dinosaurs should be considered property and that's a much larger conversation," said Hatton.

Spencer G. Lucas, an American paleontologist with the New Mexico Museum of Natural History and Science, said commercial paleontology can preserve fossils for science and education.

"My hope would be that [the fossils] would be available for scientific research," he said.

Prior to its sale on July 17, Apex will be on exhibition at Sotheby’s galleries in New York, the auction house says. The exhibition will be free and open to the public.