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Fossil Reproduction

Strong public interest in dinosaurs and our fossil past has seen a huge boost in requests for fossil displays. Public museums around the country have been asking the Institute of Geological and Nuclear Sciences for the loan of fossil specimens, prompting IGNS to embark on a major fossil reproduction programme.

IGNS holds a unique collection of New Zealand fossils collected over a period of 125 years, covering hundreds of millions of years of geological history. With the large, complete, and more spectacular specimens -- those most interesting for displays -- there is a problem with lending them out.

"Most of these specimens, because of their rarity or exceptional preservation, are designated scientific `type' specimens, meaning that they have been identified as the international standard of reference for the species that they represent," explains IGNS palaeontologist Dr Roger Cooper.

Institutions holding type specimens have an international obligation to ensure the security and protection of the specimens, and their availability for scientists to examine them at any time. Therefore they cannot be loaned out for public display.

To answer public demand, IGNS has started a project to make replicas of these specimens, which will then be available for purchase by museums so they can be mounted in permanent displays. The first fossil replicas should be available soon.

"Initially, we plan to replicate the giant ammonite and reptile specimens," says Cooper.

The giant ammonite, an ancestral relative of the nautilus, lived in New Zealand waters 140 million years ago during the Jurassic Period, making it the oldest of its type. Most ammonite fossils are fairly small, about 100 millimetres in diameter; the giant ammonite discovered by the NZ Geological Survey in 1978 is one of the world's largest, measuring 1.5 metres across. Its age, size and completeness has gained it international recognition.

Because of the large size of some specimens, the replicas will have to be cast in a lightweight material such as fibreglass. The original fossil specimens weigh up to half a tonne.

Institute scientist Ian Keyes has developed techniques for moulding and casting for scientific study over many years. He has had extensive experience in the preparation, extraction, and replication of fossil material. Only the highly trained eye can distinguish the original from his copies. He is working with Wim Spiekeman, a specialist in replicating scientific specimens.

Usually the first step is to make a latex mould of the original. A cast can then be made from the mould in silicone rubber, plaster of Paris, moulding plastic, fibreglass, or other compounds, depending on the requirements. Each material has different properties, and each has disadvantages as well as advantages. The last step is in staining or otherwise colouring the cast to reproduce exactly the surface texture, markings and colour. The final product can be almost impossible to distinguish from the original, especially if lead weights are incorporated in the copy to match the weights.

The casts must be painted to match exactly. Keyes has perfected this art to the extent that visiting experts have more than once been fooled into mistaking a replica for the real thing. In one incident, an internationally renowned German paleontologist, Professor Dolf Seilacher, refused to accept that a specimen in the institute's display was a replica because he had detected, with his hand lens, grains of greensand adhering to its surface.

"These cannot be replicated" he said.

The the sand grains had been plucked from the surface of the original specimen during the making of the latex mould, and then imparted to the plaster cast, giving it an exceptionally realistic appearance.

On another occasion, a student from Otago demanded the return of a dozen specimens in the Institute's reference collection because they were type specimens that belonged in the Otago University Type Collection. They were all replicas.