NEW YORK − One of the most pristine stegosaurus skeletons ever discovered is set to be sold to the highest bidder and could become one of the most expensive fossils ever sold at auction.

On July 17, the stegosaurus, named Apex, will be auctioned at Sotheby's in New York City, the auction house said Wednesday. The skeleton is one of the largest and most well-preserved ever discovered, measuring approximately 27 feet long and 11.5 feet tall, Sotheby's said.

"It carries an estimate of $4-6 million, making it one of the most valuable dinosaur fossils ever offered," Sotheby's said in a release.

Apex was discovered by a paleontologist on land he owns in Colorado, the auction house said.

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How expensive is Apex the stegosaurus?

Sotheby's estimates Apex's value, depending on how much it's auctioned for, could rise to be among the ranks of the most expensive dinosaur fossils ever.

The record for the most expensive fossil was set in October 2020, when a Tyrannosaurus rex named Stan sold for $31.8 million, according to Sotheby's spokesman Derek Parsons.

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Why is Apex so valuable?

Apex the stegosaurus is one of the best fossils of its kind ever unearthed, according to Cassandra Hatton, who leads Sotheby’s Science & Popular Culture Department.

Besides the quality of preservation, another reason Apex is expected to fetch a high price is because stegosauruses are among the most recognizable and popular dinosaurs, Hatton said.

The stegosaurus' "unmistakable silhouette has been a source of fascination and wonder for generations," Hatton said in a Wednesday statement.

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Where was Apex discovered in Colorado?

The fossil was discovered in May 2022 and the excavation process was completed in October 2023, Sotheby's said.

A "well-known and respected commercial paleontologist" discovered Apex on "his own private land" in Moffat County, Colorado. The area is part of the famed Morrison Formation, a geologic formation deposited about 150 million years ago − which is about the time Apex would have died, officials have said.

Experts said they determined the stegosaurus "lived to an advanced age" because the skeleton shows signs of arthritis.