When it stalked the plains of modern-day Mongolia, the Tarbosaurus bataar was one of the most fearsome predators of the dinosaur age. Measuring up to 12m long and carrying 64 flesh-ripping teeth, this bus-sized killer's Latin name roughly translates to Terror Lizard.
Some 70 million years later, a Tarbosaurus is once more on the loose, spreading confusion and concern at its whereabouts. And this time the ferocious killer – or at least one of its prized fossilised skeletons worth some £700,000 – is somewhere in Britain.
The American authorities have incited a hunt for an intact Tarbosaurus fossil in the UK after a Florida-based fossil dealer last week pleaded guilty to running a lucrative international dinosaur smuggling operation out of Mongolia, with Britain at its hub.
Eric Prokopi, who now faces up to 17 years in prison, admitted to illegally importing "multiple containers of dinosaurs" from the vast central Asian country via the UK, including a "nearly complete" Tarbosaurus skeleton which, according to court papers, remains at an unspecified location in Britain.
The fossil Tarbosaurus, a close relative of Tyrannosaurus Rex found only in a portion of Mongolia's Gobi Desert, is one of six sets of dinosaur fossils that Mr Prokopi has agreed to forfeit so they can be returned to Mongolia.
But unlike the five others which were in Mr Prokopi's possession and have been seized by American officials, the British Terror Lizard remains at large. A copy of Mr Prokopi's plea agreement obtained by The Independent describes each of the dinosaurs, including: "One nearly complete Tyrannosaurus bataar skeleton purchased from a Mongolian individual and located in Great Britain."
A source with knowledge of the case said: "This particular fossil is not currently in the custody of British law enforcement. Its exact whereabouts is being established but we would like to see it in safe custody soon. At present, someone's dinosaur is indeed missing."
The hunt for the fossil, which it is understood is the subject of a request from the Mongolian government to London seeking help to secure its return, follows a lengthy investigation into a global trade in dinosaur bones ranging from a New York auction to a prominent British fossil dealer on Dorset's world-renowned Jurassic Coast.
Legal documents seen by The Independent show that Chris Moore, who plies his trade from a fossil shop in the quiet seaside town of Charmouth, sent a consignment of fossils to Mr Prokopi in 2010 along with paperwork passed to detectives investigating the illegal sale of another Tarbosaurus which went spectacularly wrong.
The near-intact skeleton was offered for sale by Mr Prokopi last May at an auction in Manhattan, where it fetched nearly $1.1m (£680,000). But the deal was dramatically halted following an intervention on behalf of the Mongolian President, Tsakhiagiin Elbegdorj, insisting that the fossil was his country's property. Under Mongolian law, all fossils remain state property and their sale abroad is forbidden without a permit which was not obtained by Mr Prokopi.
Within hours an American judge granted an order staying the sale by Dallas-based Heritage Auctions and prompted a criminal investigation by the Department for Homeland Security which last week resulted in Mr Prokopi, 38, a self-declared "commercial palaeontologist", admitting three charges, including the falsification of customs forms and complicity in fraud.
In a statement to a New York court last week, Mr Prokopi said he had asked for the labels on the relics he bought to be deliberately "vague and misleading so that they didn't bring attention to the shipment".
Mr Moore, who runs a company called Forge Fossils, has denied any involvement in the case against Mr Prokopi. The British dealer's American lawyer, John Cahill, said yesterday he had no comment to make on Mr Prokopi's guilty pleas. Earlier this year, Mr Cahill said: "Mr Moore is not involved in the case and has no interest in becoming involved in it."
In the formal legal complaint brought against Mr Prokopi, investigators said they had been given paperwork by Heritage Auctions relating to the sale of the 7.3m-long Tarbosaurus skeleton which included a "commercial invoice" from Mr Moore and a customs declaration stating that the dinosaur fossil had been imported from Britain.
The complaint, filed last October, said: "The commercial invoice lists the contents as containing '2 large rough (unprepared) fossil reptile heads'; '6 boxes of broken fossil bones'; '3 rough (unprepared) fossil reptiles'; '1 fossil lizard'; '3 rough (unprepared) fossil reptiles'; and '1 fossil reptile skull'."
Mr Moore, who is not accused of any wrongdoing, did not respond to a list of emailed questions from The Independent, including an enquiry about the whereabouts of a Tarbosaurus skull he offered for sale in June 2010 at a London antiques fair with a price tag of £125,000.
Mr Moore said he had acquired the skull from an unspecified central Asian country. There is consensus among p palaeontologists that Tarbosaurus bataar was native to modernday Mongolia and that known intact specimens originate from a specific location in the Gobi Desert, known as the Nemegt Basin.
Speaking at the time of the antiques fair, Mr Moore said: "We bought a large slab of sandstone with bones sticking out of it and brought it back to our workshop in Charmouth. Gradually, over four or five months, we dug away to reveal what was in there. You can never tell what you're going to find. This is incredible though. There's probably six to eight other ones which are known about and museums have got those."
For the moment at least, however, the location of the British Tarbosaurus skeleton in the Prokopi case remains a mystery.
Scotland Yard yesterday confirmed that its art and antiques unit had been contacted by the US Department of Justice but insisted it was not currently investigating the case.
A spokeswoman said: "At this time no request for assistance has been made and there is no Metropolitan Police Service investigation."
All of which could yet prove a source of frustration for the Mongolian authorities, who are now seeking one of the largest ever repatriations of fossils. President Elbegdorj last week announced plans for a museum to host the dinosaurs, including three Tarbosauruses, once they return.
Prosecutors said the case has helped to lift the lid on a widescale transcontinental black market in dinosaur fossils originating from Mongolia.
Sources in the central Asian country, whose mining-driven economic growth has prompted a new interest in its cultural heritage, said its own investigators believed a ring of middlemen had been responsible for a steady flow of remains, worth up to £1m at a time, to the United States via Japan and Britain since at least 2003.
Preet Bharara, the US Attorney who brought the case, said: "Fossils and ancient skeletal remains are part of the fabric of a country's natural history and cultural heritage, and black marketeers like Prokopi who illegally export and sell these wonders, steal a slice of that history. We are pleased that we can now begin the process of returning these prehistoric fossils."
A lawyer representing Mr Prokopi, who had travelled to Mongolia and spent a year cleaning and mounting the Tarbosaurus skeleton he eventually offered for sale, said his client was co-operating with American investigators as part of his plea deal and expected to receive a "fair and reasonable" sentence as a result.
Following the halt of the auction last May, the American dealer issued statement saying he had acted in good faith and was "just a guy in Gainesville, Florida, trying to support my family, not some international bone smuggler".
In the light of his admissions, it turns out that is just what Mr Prokopi is. All that remains to be answered is just who helped him - and where in Britain the mortal remains of a rapacious killer of enduring fascination to monied collectors has been stashed.