Experts say the 170 bones discovered about 17 years ago in South Dakota represent more than half the skeleton of a 40-foot-long, 7.5 ton dinosaur that lived 66 million years ago.
Auctioneer Bonhams & Butterfields is hoping that bids for the T. rex dubbed "Samson" will top $6 million when it is sold Oct. 3 at the Venetian hotel-casino in Las Vegas.
A similar T. rex fossil sold in 1997 for $8.3 million and is now housed at the Field Museum in Chicago. That dinosaur, named "Sue," is 42 feet long and has more than 200 fossilized bones.
Tom Lindgren, a natural history specialist for Bonhams & Butterfields, said "Samson" is the third most complete T. rex skeleton ever discovered, and one of only 42 specimens discovered in the last 100 years with more than 10 percent of the bones.
"This represents the pinnacle of paleontology," Lindgren told The Associated Press on Friday.
"Most of the major museums in the world have casts of T. rexes," as opposed to the real thing, he said. "Bidding on this T. rex is not going to be a gamble, it's going to be the opportunity of a lifetime to whoever gets it."
The female dinosaur's lower jaw was found by the son of a rancher in 1987 and the rest of its bones were excavated in 1992, Lindgren said. It was sold twice to private owners, and is now owned by an American whom Lindgren wouldn't name.
Lindgren said most of the dinosaur's bones have been stored in a warehouse and have never been on exhibit privately or publicly. He would not say how much its current owner invested in it, but said it is more than the $6 million to $8 million he estimates it will sell for.
Lindgren said the estimate is conservative, in part because it is already mounted on a custom steel frame designed for museum display and scientific study.
