Cretaceous and Tertiary climate change and the past distribution of megathermal rainforests

The history of megathermal (currently ‘‘tropical’’) rainforests over the last 30 kyr is now becoming relatively well-understood, as demonstrated by the many contributions in this volume. However, our perception of their longer-term history remains highly fragmentary. There is a real need for a better understanding of rainforest history on an evolutionary time scale, not only to have a better idea of the biological, geological, and climatic factors which have led to the development of the most diverse ecosystem ever to have developed on planet Earth, but also since the implications of rainforest history on an evolutionary time scale are inextricably linked to a plethora of other issues currently receiving wide attention. Determining the place and time of origin and/or radiation of angiosperms (which overwhelmingly dominate present day megathermal rainforests), establishing patterns of global climate change, clarifying the nature of global temperature gradients through time, understanding the successive switching from greenhouse to icehouse climates, global warming, patterns of dispersal of megathermal plants and animals, higher rank (ordinal) taxonomy and the nature of controls on global diversity gradients are but some issues which are being clarified with the better understanding of the long-term history of megathermal rainforests.