During an expedition in Sonora, Mexico, palaeontologist Mark McMenamin unearthed fossils of creatures dated at approximately 600 million years old. These circular fossils, which are known as Ediacarans, seemed to defy explanation. This book documents their discovery. The Ediacarans were a marine life form that existed in Precambrian times, as much as 50 million years before life on earth began to diversify rapidly. Bearing a perhaps superfical resemblance to the jellyfish, the Ediacarans had a quilted body with three curving arms at the centre and a fringe of fine radial lines. McMenamin's curiosity was fuelled by the question of whether the Ediacarans were animals or some other type of organism. How could complex forms of life appear without respect to adaptation, without extensive records of prior evolution? This, it seemed, was exactly what the Ediacarans had done. This book details McMenamin's trip to Namibia, where, with a party including palaeontologist Adolf Seilacher, he investigates a cast made from a colony of fossils in the Nama desert. He chronicles the long, often futile search made by earlier scientists for Ediacara, which began more than a century ago in South Australia, and of the various types of Ediacaran fossils that have been uncovered since. McMenamin concludes that although they were related to animals, Ediacarans were not animals in the strict sense, because they never passed through the embryonic stage that is peculiar to known animal life forms. But they seem to have developed a central nervous system and brains independent from animal evolution. This finding has ramifications for our understanding of evolutionary biology, for it indicates that the path toward intelligent life was embarked upon more than once on this planet.