INTRODUCTION

The modern fish fauna is dominated by two very different kinds of fishes, the neoselachians (sharks, skates and rays) and teleosts (e.g. herring, salmon, cod and perches). Both of these major groups originated before the Cretaceous but the age of differentiation (Hennig, 1966) of teleosts is approximately coincident with the temporal limit of this volume – the Late Jurassic/Early Cretaceous – and that of neoselachians is Early Jurassic. The last 145 million years have seen the diversification of neoselachians, resulting in a modern tally of 815 species contained in 164 genera and 42 families. In the same timespan teleosts have shown more impressive diversification to 23 637 species within 4061 genera and 426 families (counts taken from Nelson, 1994). Other, minor groups of fishes inhabiting the modern world include the jawless hagfishes and lampreys (73 species), ratfishes or chimaeriforms (30 species), polypteriforms or bichirs (11 species), lepisosteiforms or garpikes (7 species), amiiforms or bowfins (1 species), the coelacanth and the lungfishes (6 species). Together these make up less than 0.5% of Recent species diversity.

The brief given to contributing authors of this volume includes an invitation to outline the geological history of individual groups with reference to global changes which have taken place. This is rather daunting as it is all too easy to slip into scenario building, assuming cause and effect with little substantive evidence. Such evidence includes an assessment of the nature of the fossil record.