INTRODUCTION

The great majority of bryozoans secrete calcareous skeletons and the phylum consequently enjoys a rich fossil record extending back to the Early Ordovician. Modern bryozoans are colony-forming, typically sessile, suspension feeders which can be key components of epibenthic environments (for summaries of bryozoan biology, see Ryland, 1970; McKinney & Jackson, 1989). Although marine bryozoans are distributed throughout the world from intertidal to abyssal depths, they peak in relative abundance on non-tropical continental shelves. Here, they may be the dominant carbonate producers, and fossil bryozoans are important components of many Cenozoic temperate limestones (Nelson et al., 1988). Two essential factors controlling local bryozoan distribution are the existence of suitable hard (e.g. rocks and shells) or firm (e.g. algae) substrata for attachment, and an adequate supply of phytoplankton for food. Conversely, high levels of sedimentation and/or disturbance, and stagnant conditions on the sea-bed are disfavourable factors.

The first aim of this chapter is to undertake a short survey of the Cretaceous and Cenozoic fossil record of bryozoans in order to trace the origin of the modern bryozoan fauna. Temporal rather than the biogeographical or phylogenetic origin will be investigated, and evidence will be sought for possible effects of global change on broad-scale evolutionary patterns.