Its name in Arabic is Wadi Hitan but it is known as the Valley of the Whales.

For years palaeontologists have been unearthing a remarkable collection of whale fossils, all the more surprising because the area is now inland desert in upper Egypt.

It is believed that about 40 million years ago the area was submerged in water, part of the Tethys Sea. As the sea retreated north to the Mediterranean it left a series of unique rock formations and also a cornucopia of fossils.

One of the most exceptional finds was a 37 million-year-old whale from the species Basilosaurus isis, unearthed by a team led by Prof Philip Gingerich of the University of Michigan in the United States.

But now it has become the subject of a bizarre customs wrangle at Cairo airport.

Prof Gingerich explained that this was the only complete specimen from this species of whale.

It provides evidence of how whales evolved from being land-based creatures to go back into the sea -a reverse of the usual evolutionary process.

Basilosaurus isis retained tiny feet, a useless reminder of its evolution from land animal to sea-dweller.

The limbs are human sized, even though the creature is 15m-16m long.

For the past two years Prof Gingerich and his team have been painstakingly reassembling the skeleton back in Michigan. It is now being returned to Egypt for a new museum, planned for the Valley of the Whales.

But according to the Egyptian media the whale skeleton is stuck at Cairo airport.

Customs agents are demanding a $40,000 fee.

It is not clear how they came to that figure as prehistoric fossils have no agreed market value.

In any case the Egyptian authorities who are importing the fossil are refusing to pay.

A senior official from the ministry of tourism has warned that the issue needs to be resolved speedily, otherwise it could cause a "big scandal" for Egypt, he said.

Prof Gingerich joked that it had taken two-and-a-half years to be allowed to export the fossil to the United States, and it could take another two-and-a-half years to get it back.