An ancient fossil: Is it a reptile, is it a bird, or is it a hoax?

ARCHAEOPTERYX - whose name means ``ancient feather'' - has long been one of paleontology's most treasured evolutionary links. It combines features of both birds and reptiles. Paleontologists cherish the 150 million-year-old fossil as evidence of an evolutionary transition between reptiles of the dinosaur era and true birds. But is this only the wishful thinking of experts deceived by a hoax?

For the past two years, a famous British astrophysicist, Sir Fred Hoyle, and N. Chandra Wickramasinghe of University College in Cardiff, Wales, have called Archaeopteryx a fake. They insist that a clever forger used limestone paste to add traces of feathers to a reptilian fossil.

Paleontologists generally - including staff at the British Museum of Natural History, which houses the fossil of Archaeopteryx lithographica, to use the full name - reject the claim. A new analysis by museum staff using ultraviolet light to detect organic remains supports their conviction that this is, indeed, the first bird. But the controversy isn't over and the intellectual stakes are high. More than professional reputations is at stake. Were Archaeopteryx proved fraudulent, evolutionists would have to rethink the rise of birds.

Unlike most scientific controversies, this time the public can join in the fun. The museum has prepared an exhibition - ``The Feathers Fly'' - which clearly sets out the pros and cons of the argument in displays and a video presentation. Visitors can examine the fossil itself. They can study the features that paleontologists accept as genuine and ponder features Hoyle and Wickramasinghe consider suspect.

In the ultraviolet analysis, fossil areas showing bones and what appear to be feathers fluoresce, indicating traces of organic remains. Immediate surrounding areas show no fluorescence. This suggests that no organic glue could have been used. And, since inorganic glues were not known when the museum acquired the fossil in the 19th century, curator of paleontology Robin Cooks considers this proof that there was no tampering. Wickramasinghe says inorganic glues could have been devised. He and Hoyle remain skeptical.

When I visited the exhibition last month, the new evidence was not yet represented. Even without it, the case for believing Archaeopteryx to be genuine seemed strong. Other people might reach a different conclusion.

Whether Hoyle and Wickramasinghe are finally proved right or wrong, they have performed a useful service. They have provoked paleontologists to reexamine the evidence and refine their analyses.

What's more, their assault on orthodoxy has sparked a unique exhibition that people living in or visiting London can study to form their own conclusions about this intriguing scientific controversy. That's reason enough to be grateful that these intellectual gadflies brought the issue up.

A Tuesday column. Robert C. Cowen is the Monitor's natural science editor.