FOR decades they have been known only as the ''lost dinosaurs of Egypt'', but a team of palaeontologists have finally tracked them down and, with them, evidence of one of the biggest animals ever to walk the earth.

Searching in a corner of the Sahara desert all but ignored since the second world war, the scientists were looking for fossil beds at the Bahariya oasis, about 180 miles south-west of Cairo, originally discovered in German expeditions a century ago.

Between 1910 and 1914, Baron Ernst Stromer von Reichenbach, the geologist, unearthed a wealth of fossils, including bones from four new smaller species of dinosaurs and other ancient creatures. Stromer wrote papers on his discoveries at Bahariya between 1915 and 1936.

However, his trove of prehistoric finds was lost when the Munich museum in which it was housed was destroyed during an allied bombing raid in 1944.

The Egyptian site remained then largely forgotten by palaeontologists until a team from Pennsylvania University began exploring the area in 1999.

They eventually rediscovered Stromer's original fossil bed and went one better by unearthing the partial skeleton of a new genus of colossal dinosaur, Paralititan stromeri, dating from the Cretaceous period (about 146 to 65 million years ago), and signs of ancient mangrove swamps in the middle of what is now one of the driest places on earth.

Paralititan, which means ''tidal giant'', is the first dinosaur discovery reported from the site since 1935.

Reporting their finds in today's edition of the journal Science, the American team said a 5.5ft humerus, or upper arm bone, suggests that the new creature is very close to the size of Argentinosaurus, currently the largest dinosaur known to man.

Joshua Smith, the discoverer of Paralititan, estimates that the giant four-legged beast may have measured 80 to 100ft long and weighed 60 to 70 tons.

As a huge dinosaur that was apparently traipsing through an ancient mangrove forest, Paralititan breaks significant new ground for palaeontologists. Mr Smith said: ''While now arid, the Bahariya oasis, where we found the dinosaur, was apparently more like the Florida Everglades during the late Cretaceous period.''

Based upon the types of rock in which the bones were found - largely sandstone and organic-rich mudstone showing clear evidence of weak wave action - Mr Smith's team deduced that the herbivore was standing on the edge of a tidal channel in very shallow water when it perished 94 million years ago.

His team hopes that further discoveries at Bahariya will help answer some questions about a relatively mysterious time and place in vertebrate history.

Scientists have found groups of vertebrates that were common to South America and Madagascar during the late Cretaceous period, but these same groups appear to be missing from Africa. Some palaeontologists think this pattern exists because the South American and Malagasy land masses were somehow connected at the time, to the exclusion of Africa.

The Science researchers suggest, however, that this puzzling absence may be simply a matter of fewer researchers working at African sites, making fewer discoveries to fill in the gap.

An analysis of Paralititan's skeletal features convinced the researchers that the fossil was a new species of titanosaurid, a group of long-necked, long-tailed, plant-eating dinosaurs that includes some of the largest land animals ever.Along with Paralititan, the researchers uncovered other fossils they believe may belong to some of Stromer's lost dinosaur species.