Hirst shark that sold for about $8m is fourth 2017 work dated to 1990s

A Damien Hirst shark preserved in formaldehyde that was purchased by American billionaires was dated to the 1990s even though it was not made until 2017, the Guardian can reveal.

- Maeve McClenaghan

The 4-metre tiger shark, dissected into three parts, is the centrepiece of a luxury bar in the Palms casino resort in Las Vegas. It first appeared there six years ago, with the title: The Unknown (Explored, Explained, Exploded), 1999.

However, an investigation has established that it was made in 2017, almost two decades after the date publicly ascribed to the work. The sculpture was bought by the billionaire brothers Lorenzo Fertitta and Frank Fertitta III, and there are suggestions it cost about $8m (£6.4m).

The huge shark is the fourth formaldehyde sculpture by Hirst now known to have been made in 2017, despite having been dated to the 1990s. The other three, made with a dove, a small shark and two calves, have in recent years been exhibited with 1990s dates in galleries in Hong Kong, New York, Oxford and London.

The revelation that some of Hirst's formaldehyde works were given dates that do not accord with the dates they were physically made has rocked the art world this week.

"Cases like this don't help assuage doubts about the lack of transparency in the art world," said Jo Baring, a former director of Christie's auction house in the UK. "Hirst is an artist who wields so much power, he is much in demand by museums, who want to boost their ticket sales, and also collectors who want to own a touch of the stardust. But that power means that people are afraid to challenge or ask questions." Hirst did not directly respond to questions when asked about The Unknown. Sources familiar with the creation of the sculpture said it was made in 2017 in preparation for its installation in the hotel.

When it was unveiled to much fanfare in 2018, the previously unseen tiger shark was described by the casino as a piece from the 1990s.

The "1999" date was contained in the work's title, which is typically provided by the artist, and included in promotional material.