Money for old bones: Dinosaur fossils become big business

Sotheby's is to auction some of the world's rarest prehistoric relics

She possesses a set of fearsome jaws, is in spectacular condition for her age and would make a striking addition to any drawing room – provided you have one big enough to contain her 33ft-long set of fossilised bones.

Anyone with a seriously large wallet could soon be able to buy this rare, partially complete fossilised skeleton of an Allosaurus, a large carnivorous dinosaur that lived about 150 million years ago and is sometimes referred to as the T. rex of the Jurassic Period – T. rex itself lived much later during a period known as the Cretaceous Period.

The female Allosaurus, discovered in a fossil graveyard in the US state of Wyoming, is one of the prime exhibits going on sale later this year at the French headquarters of Sotheby's in Paris. She is expected to attract huge interest from the growing number of wealthy fossil collectors keen to snap up one of the rarest of dinosaur finds.

Another item on sale is a flying carnivorous reptile with a 35-inch wingspan called Dorygnathus banthesis, displayed in the original black matrix rock it was found in when it was unearthed in 1932 from a site in Holzmaden, Germany. Sotheby's estimates that the oval-skulled pterosaur will fetch €160,000-€250,000 (£145,000-£247,000).

If neither of these beasts takes your fancy, then how about a complete skeleton of a fish-eating Plesiosaurus, a type of primitive marine lizard that lived about 190 million years ago?

It was dug out from a limestone outcrop in Blockley, Gloucestershire, in the early 1990s. Sotheby's says that the 6ft 7in by 9ft 10in skeleton is the best-preserved specimen of a Plesiosaurus to date, meaning it could easily go for more than £300,000. For those who do not like the idea of taking a fearsome carnivore home with them, there is the alternative of bagging a pair of petrified crabs buried suddenly near Vicenza in Italy 45 million years ago.

Alternatively, there is a fossilised palm leaf and accompanying fishes dating from the Eocene Period some 50 million years ago, about 15 million years after the dinosaurs went extinct but before mammals had fully risen to take their place as the dominant, large terrestrial lifeforms.

"Whether you look at them as artistic masterpieces or wonders of nature, dinosaur skeletons, fossils and minerals retrace the saga of evolution, especially that of mighty terrestrial and marine mammals that are now extinct," said Professor Eric Mickeler, a palaeontologist and the expert consultant on the Sotheby's sale.

Whatever the motives of those wanting to own such magnificent specimens, it is clear that collecting and dealing in fossil relics of a prehistoric age is big business, according to Lorraine Cornish, a senior conservator at the Natural History Museum in London, who is involved in the museum's purchases of fossils.

"We try not to buy on the commercial market. For a start we have limited funds, but we also don't particularly want to encourage the sale of fossils that may be dug up without the details of the find being recorded, which would mean the loss of important scientific information," Mrs Cornish said.

"But we have to accept that dealing in fossils is a reality. Some very wealthy people are passionate about the fossils they collect and they want the best, just like some people want the best works of art," she added.

One of the prime fossil exhibits in the Natural History Museum in London is a heavy-clawed dinosaur called Baryonyx walkeri which was unearthed in a clay pit near Dorking in Surrey.

One of its distinctive claws was found sticking out of the ground by William Walker, a local amateur collector, in 1983.

Mr Walker took the claw to the museum, whose experts organised a proper excavation. In return, Mr Walker received replica claws and had the species named after him.

"We try to develop really close relationships with amateur fossil collectors. In that way, if they find something they are likely to bring it and show it to us first," Mrs Cornish said.

In Britain it is perfectly legal to collect and deal in fossils of dinosaurs or other prehistoric animals provided that certain guidelines are met, such as securing the approval of the landowner and getting particular permission from official authorities if the collecting area falls within a designated Site of Special Scientific Interest, which are often established to protect the best fossil deposits.

Although there is no legislation specifically designed with fossils in mind, guidelines dictate that detailed records of the find should be kept and the excavation should be done with sufficient care.

One important site for amphibian fossils near North Berwick, for instance, was entirely removed illegally in a matter of hours by a collector using a mechanical digger.

Some of the most important finds have been made by amateur and professional fossil collectors. One such collector, Stan Wood, unearthed the earliest known fossil reptile near Bathgate in West Lothian.

The eight-inch-long fossil, known as "Lizzie", was later sold to the National Museums of Scotland for £180,000 – considerably less than Mr Wood could have received if he had sold it to foreign collectors, according to Matt Dale, an Edinburgh fossil dealer who now runs Mr Wood's fossil business.