Bird fossil defended against hoax charge.

Bird fossil defended against hoax charge

There was a disturbing sense of deja vu last year when the British Museum's Archaeopteryx fossil, long thought to be the earliest known bird, was branded as a hoax by several prominent scientists. Could this be another Piltdown Man? researchers asked. Also house in the British Museum, the Piltdown Man was exposed as a fake in 1953. But a careful analysis of the Archaeopteryx fossil confirms that it is authentic, reports a team of paleontologists in the May 2 SCIENCE.

Alan J. Charig and his colleagues at the British Museum in London say that ultraviolet and microscopic photographs show that, contrary to allegations, the animal's flaring feathers could not have been pressed by a forger.

The 150-million-year-old Archaeopteryx specimen was discovered in 1861 in a Bavarian limestone quarry that has yielded five other fossil birds generally considered to be of the same species. The fossil is thought to be a prime example of evolution in action because it appears to represent a species in transition between reptiles and birds. Imprints on two pieces of a stone slab that formed a mold around the fossil outline a creature that had the teeth and many skeletal features of a reptile, most likely a small dinosaur, along with birdlike characteristics such as feathers and fused collarbones.

But in 1985, British astrophysicist Fred Hoyle and other critics based at University College in Cardiff, Wales, claimed that a limestone paste was probably used to create the image of feathers around a genuine reptilian skeleton. Photographs of the fossil, said Hoyle, reveal a fine-grained substance under the feathers and distinctive blobs that could be remnants of a forger's cement. He and his colleagues also contended that elevated and depressed regions on one slab are not perfectly mirrored on the other.

The British Museum scientists used microscopes to examine the surface of the fossil and cross sections of the imprints. They found no evidence of an added cement layer or artificial feather impressions. The blobs cited by critics, maintain the investigators, are natural irregularities created when the limestone was split to reveal the ancient bird. These and other irregularities, they add, often become slightly exaggerated after years of cleaning and examination.

Critics also have noted areas where the same feather appears to make two slightly displaced impressions, but the British Museum scientists say these "double strikes' are the likely result of two overlapping layers of feathers.

The most conclusive evidence that Archaeopteryx is genuine, however, is provided by hairline cracks running in various directions across the feathers and other parts of the impression. The cracks show up under ultraviolet photography, and those on the main slab correspond perfectly with those on the opposite face. It would be impossible, contend the researchers, to forge exactly matching crack patterns.

Photo: The controversial Archaeopteryx fossil.