About a year ago several prominent British scientists, led by astronomer Sir Fred Hoyle, claimed that a fossil long thought to be the earliest known bird, Archeopteryx, was a hoax in which the image of feathers had been fraudulently added to a fossil skeleton of a small dinosaur.

Since its discovery in Germany in the 1860s, the fossil has been offered as one of the most dramatic examples of organic evolution because it appears to represent a transitional species of dinosaurian reptile evolving into a bird. The hoax allegations, trumpeted widely in the British press, threatened to rival the Piltdown Man hoax as a scandal in the house of Darwinism.

Now, however, a team from the British Museum (Natural History) has refuted the allegations, publishing what the team calls "proof of authenticity" showing that Archeopteryx, feathers and all, is real.

The fossil consists of imprints on the surface of a limestone slab, outlining the animal's bones and, flaring away from the bones, feathers. It appears as if, when the animal died around 140 million years ago, its carcass landed on a mud flat and was then buried and flattened by more sediments.

When discovered, the mud had turned to limestone that split easily along the original bedding plane, revealing a flattened fossil with the bone structure of a crow-sized dinosaur (except for collarbones joined to form a birdlike wishbone) and the feather imprints.

Hoyle and the other challengers had asserted that the feather imprints were faked shortly after the discovery by coating the slab with a thin limestone-based cement and imprinting it with modern feathers.

The British Museum team, which is publishing its findings in next week's issue of Science, used microscopes to examine the surface of the fossil and cross sections through the imprints. They found no sign of an added layer. Moreover, they compared the surface with the corresponding face of the slab that split away and found that for every microscopic bump there was a mirror indentation on the opposite face.

The clincher, however, was the finding of nearly invisible hairline cracks filled with ancient mineral deposits running vertically through the horizontal imprints. The cracks on the fossil slab correspond perfectly with those on the opposite face. The museum group concluded that it would have been impossible for forgers to duplicate the complementary crack patterns on both faces.