"Big John", 66 million years old and the largest triceratops skeleton ever unearthed at eight metres long, was sold at auction to a US collector on Thursday for a gargantuan 6.6 million euros.
The final price reached at the Drouot auction house in Paris -- 5.5 million euros before fees -- was well above the expected 1.5 million euros.
Big John's skeleton is 60 percent complete, and was unearthed in South Dakota, United States in 2014 and put together by specialists in Italy.
He will return to the US and the private collection of the unnamed buyer, who the auction house said had fallen "in love" with Big John after coming to view him.
The buyer beat 10 other bidders, with three in particular driving up the price in the final minutes.
"I wasn't expecting this," said paleontologist Iacopo Briano who was overseeing the sale.
Big John lived during the Upper Cretaceous period, the final era of dinosaurs, and died in a floodplain, buried in mud that kept him very well preserved.
A horn injury near his cranium suggests he got into at least one nasty fight.
The sale was still far off the record of $31.8 million paid last year for a 67-million-year-old Tyrannosaurus rex skeleton in New York.
But the price all but guaranteed that museums would be excluded from the purchase.
"We can't compete," said Francis Duranthon, director of the Toulouse Museum of Natural History, ahead of the auction.
He said even the initial expected price represented 20 to 25 years of his acquisitions budget.
So Big John is headed for a private collection, but the auction house said there is still a chance the buyer may lend the skeleton to a museum or gallery for public viewings.
Scientists were able to analyse the bones before the auction.
The triceratops is among the most distinctive of dinosaurs due to the three horns on its head -- one at the nose and two on the forehead -- that give the dinosaur its Latin name.
Dinosaur sales can be unpredictable, however: in 2020, several specimens offered in Paris did not find takers after minimum prices were not reached.