Fool’s gold holds fossil treasure

They float like tiny jewels encased in stone: most are only a few millimetres or centimetres long but full of incredible detail - boasting tiny tentacles, eyes, legs, and forceps-like pincers. 'Many of them are entirely soft-bodied, they have no right to be preserved over 525 million years. They should really have quickly decomposed on the sea bottom, or have been eaten, or destroyed over millions years of earth history' explains Derek Siveter of Oxford University's Museum of Natural History and the Department of Earth Sciences. These are the Chengjiang fossils from Yunnan, China, on display at the Oxford University Museum of Natural History, in the first major exhibition of these fossils outside China. The Chengjiang fossils, first unearthed in 1984, are particularly important because they open up a window onto one of the most important events in the history of life: the so-called Cambrian 'explosion' when most of the major animal groups we know today first appeared in the fossil record. The big question has always been: where did this dazzling variety of animals come from? Did they suddenly develop or were earlier examples of complex animals simply never preserved? These particular fossils have survived because of an amazing stroke of luck: 'The preservation of all the soft tissues is a result of the organic materials of these animal bodies being replaced by 'fool's gold' - iron pyrites . It means their forms have been captured for posterity,' Derek tells me.