Graptolites lived in the earth's oceans from 540 million years ago to 320 million years ago, when they became extinct. For most of that time they dominated the upper layers of the ocean in tropical regions as the earth's first large zooplankton. They varied from a few millimetres in length to more than a metre; they lived by the countless billion, and their skeletons are preserved today in vast numbers in varied strata in every continent except Antarctica. Because of their diversity, they are a powerful correlative tool: units of time of much less than a million years are identifiable, and within individual rock sequences evolutionary changes can be studied, which makes them of prime importance to economic geologists. Graptolites are, however, still the subject of lively debate -- little is established about their lives, and although skeletons abound, the soft parts of only one graptolite have been found -- in deposits 500 million years old in Tasmania. As well as providing a full summary of the current state of knowledge relating to graptolites, the team of specialists who contribute to this book also address the biological questions raised by these fossils, and provide pointers for further research. Contents: Part I. The Organism: Definition and appearance; Preservation; Construction; Distribution; Biology; Evolution; Relationship to other organisms; Sex life. Part II. The Fossil: Collection and preparation; Identification; Correlative uses. Appendices: Glossary of technical terms; Where to find them in Britain and other countries; Classification and evolution; Further reading.BARRIE RICKARDS is Reader in Palaeobiology, University of Cambridge, and curator of the Sedgwick Museum of Geology. DOUGLAS PALMER is a freelance geologist and writer.