This book has developed from a joint research programme on Global Change and the Biosphere developed by the Palaeontology Department at The Natural History Museum, London, and the Department of Geological Sciences at University College London in 1994. Research on global change has attracted a huge number of scientists around the world over the last 20 years, primarily because of many governments' concerns about human impact on our environment. Most of this effort has concentrated on the last few thousand years of Earth history, when there have been major and rapid changes in climate and sea level that are continuing today and will undoubtedly affect our immediate future. But the world has been changing continually throughout its history, and our Global Change project was designed therefore to bring this much longer-term, geological perspective to the issues that concern us all today.

This volume provides a comprehensive review of the response of many different animal and plant groups to global change over the last 145 million years, since the beginning of the Cretaceous Period. It brings together contributions from members of the NHM/UCL team and other invited authors, to form a volume aimed at the advanced student and the many researchers who may need a long-term view of global change and its influence on Earth's biota.

The editors are very grateful to all the contributors for meeting our deadlines so closely.

INTRODUCTION

The Cephalopoda are an exclusively marine class of the Phylum Mollusca with a history extending back to Cambrian times. Their fossil record is remarkable for both its abundance and the diversity of shell form displayed. Thus the cephalopods can be divided into three informal groups, the nautiloids, ammonoids and coleoids. These were formerly regarded as three orders or subclasses, but the nautiloids include a very diverse array of forms that nowadays are divided into several orders. The nautiloid cephalopods reached their peak of diversity during Early Palaeozoic times and by the beginning of the Mesozoic most groups had long become extinct (Flower, 1988, fig. 1). Conversely, the Ammonoidea were a Late Palaeozoic to Mesozoic group while the Coleoidea are predominantly a Mesozoic to Recent subclass.

This chapter firstly reviews briefly the main changes in cephalopod distribution over the last 145 million years, in particular showing their varying response to the K/T boundary event. It goes on to concentrate on the Cretaceous interval (145–65 Ma), when two cephalopod groups, the ammonites and the belemnites, were among the most common marine macrofossils. Both groups appear to have been very sensitive to several parameters of global change. Thus, interpreting their ecology and determining the changing patterns in their distribution through space and time provides fundamental clues to the nature of Cretaceous palaeogeography, climate and oceanography. The influence of sea-level change and ocean currents is highlighted.

The simple desire to understand the world we live in has driven scientists for more than two centuries to study the history of life through time. It soon became evident to the early workers that this history is most certainly not a continuous one. Indeed, the recognition of sudden and fundamental changes in faunas and floras through time led to the designation of the segments of Earth history that we know as geological periods. The two greatest discontinuities in life's history, since organisms evolved fossilizable hard parts, are the mass extinctions that define the boundaries of three great segments of Earth history, the Palaeozoic, the Mesozoic and the Cenozoic eras.

What caused these and many other changes in the Earth's biota? For a long time palaeontologists have realized that faunal and floral changes are the result of either evolutionary innovations or of environmental changes at many different scales. This volume addresses biotic changes through time for a wide variety of organisms from tiny single-celled calcareous nannoplankton to the largest whale. We concentrate on the past 145 million years of Earth history because this is a large enough segment of time to allow us to evaluate both geologically instantaneous global environmental changes and environmental trends that take millions of years to unfold.

INTRODUCTION

What comes over so clearly in the contributions to this volume is that the nature and rates of biotic response to global change have been very variable. While many biotic groups show a marked response to the physical variables of global change considered in Chapters 2 and 3, in others the main changes over the last 145 Ma have been driven primarily by intrinsic or extrinsic biological factors. Furthermore, any organisms that contributed substantially to carbon burial (e.g. trees, corals, nannofossils) helped to drive global change. In this chapter we bring together some of the common strands that have emerged from the preceding chapters.

ENVIRONMENTAL CONSIDERATIONS AND BIOTIC RESPONSE

Climate change, itself a product of other components of global change, is a key forcing mechanism for global biotic change. The time interval embraced by this volume witnessed a major change in Earth's climatic history, from a very warm ‘greenhouse’ state in the Cretaceous through a long, but far from monotonic, decline through much of the Cenozoic to the present-day icehouse world. During the ‘green-house’ phase, climate varied but apparently changed only slowly over many thousand to several million years. But as global climate cooled a clearly marked cyclicity developed, driven by Milankovitch and sub-Milankovitch scale cycles.