Abigail Lane

Our picture of the history of the earth's biodiversity is based on data on the ranges of fossil taxa through time. The most widely accepted model for how life today became so diverse is that of Sepkoski, Raup, and others, which shows a rapid rise in diversity during the Cambrian and Ordovician, followed by a long plateau through most of the Palaeozoic. This plateau, which is thought to represent an equilibrium, 'terminates' with the end-Permian mass extinction when diversity falls dramatically only to rise thereafter. Recently, Benton (1995) has argued that the plateau does not represent an equilibrium, which reflects the carrying capacity of the globe at that time, but is an artefact of the record. This model views the history of biodiversity as one of exponential expansion, punctuated by numerous setbacks caused by mass extinctions. It is clear that the underlying model of biodiversification is fundamental to our understanding not only of the history of past life, but also of the impact of human activities on the global biota today.

The Palaeozoic plateau is one of the most compelling lines of evidence for a global equilibrium. Benton (1997) has shown, however, that while the plateau is particularly evident in plots at ordinal or familial level, it decays at generic level, and might resolve into an exponential curve on the basis of species data.

I am exploring the nature of this plateau on the basis of existing and new databases, and testing the assertion that it is an artefact. This involves understanding the nature of different kinds of diversity data and preservational settings, including concentrated shell beds (coquinas) and exceptionally preserved faunas (Konservat-Lagerstatten) such as the Burgess Shale. I am also investigating the interplay between diversity at different scales (local, regional, and global: i.e. alpha, beta, and gamma). This project has the potential to revolutionize our understanding of the diversification of life on earth, and addresses a number of fundamental palaeobiological research areas that are currently of great interest. A Burgess Shale fossil of the arthropod Sanctacaris

References
Benton, M. J. 1995. Diversification and extinction in the history of life. Science, 268, 52- 58.
Benton, M. J. 1997. Models for the diversification of life. Trends in Ecology and Evolution, 12, 490-495.