The fossilised skull of a mosasaurus will highlight an auction at Antiquities Saleroom on December 6 in Erie, Colorado.
The 65-70m year old lot is valued at $25,000-35,000 and weighs around 136 kilos.
Mosasaurus resembled crocodiles and lived in the waters of the area we now know as North America and western Europe during the Maastrichtian age of the Cretaceous period.
They are thought to have hunted in the shallows, feeding on fish, turtles and ammonites and are named for the Meuse River in central Europe where the first specimen was discovered.
The fossil is a complete specimen and features a small, centralised depression indicating it was bitten, possibly by another mosasaurus.
In 2008, a mosasaurus skull realised $24,000 at Bonhams' Natural History Sale in New York.
Last week a diplodocus skeleton sold for $650,000 at Summers Place Auctions in West Sussex, UK.
A rare first issue, first edition copy of the Adventures of Huckleberry Finn by Mark Twain, featuring its original green pictorial cloth, is valued at $15,000-20,000 in the same sale.
The controversial book, a satire on southern US attitudes to racism, was first published in England in 1884 and the US in 1885, and was immediately the subject of intense literary criticism.
In 2005, Mark Twain's personal copy of Huckleberry Finn realised $108,000 at Christie's New York.
It failed to beat the Huckleberry Finn record, which was set in 2004 by a publisher's first binding copy featuring a lithographed frontispiece and a unique dedication by the author.
It sold for an impressive $265,100.
PFC Auctions is currently offering this Hudson River Steamboat pamphlet signed by Mark Twain.
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