Plant evolution viewed through a functional and paleoclimatic prism

Abstract

The fossil record of plants offers a spectacular window on the trajectories of biotic replacement, failed and triumphant evolutionary experiments, and the responses of life to envi-ronmental catastrophes. Consequently, plant fossils have long inspired hypotheses about the inner workings of evolution and the possible genetic and environmental catalysts provoking bursts of evolutionary change. Although necessarily a biased lens (Behrensmeyer, Kidwell, and Gastaldo, 2000), fossils do offer a unique perspective on the temporal and spatial scales of evolution, while framing these in the context of a dynamic Earth. However, study of the ''dead'' is only one line of in-quiry, because no matter how well-preserved a particular fossil is, the past plant it marks cannot be greened and coaxed to grow from the rocks. To fully understand the mechanisms driv-ing evolution, life's genealogy, development, as well as ecol-ogy must be infused into the geological pattern. The field of paleobotanical research has recently accelerated on several fronts, fueled by advances in rock dating methods (Knoll and Carroll, 1999), mega-analyses to study patterns of biotic replacement (Lupia, Lidgard, and Crane, 1999), micro-scale and macro-scale biochemical analyses of fossils (Arens, Jahren, and Amundson, 2000; Briggs, Evershed, and Lock-heart, 2000; Boyce, Hazen, and Knoll, 2001), plus new ap-proaches to taphonomy (Behrensmeyer, Kidwell, and Gastal-do, 2000) and clarification of phylogenetic patterns as well as developmental rules and functional biology of extant groups (Mathews and Donoghue, 1999; Chaw et al., 2000; Cronk, 2001; Pryer et al., 2001; Boyce and Knoll, 2002). And all the while, the fossil record of plants grows richer and richer by the year, exposing new interfaces for the application of tech-niques and opportunities for addressing questions. Taken by this spirit, and a belief in the importance of combining studies of the dead plants with living ones, K. J. Willis and J. C. McElwain, two players in the paleobotanical renaissance, have fashioned a new, undergraduate-targeted text on the evolution of plants. The content of the text, The Evolution of Plants, is colored by both Willis' and McElwain's interests in paleoclimatology and the functional biology of extinct plants. Willis' research, based out of the School of Geography and Environment at Oxford University, has largely focused on the long-term re-lationships between vegetation dynamics (largely Holocene processes) and environmental changes, as well as possible co-evolution between early angiosperms and dinosaurs. At the Field Museum, McElwain's work centers on using structure– function relations of fossil plants to reconstruct geologic-time 1 The evolution of plants. K. J. Willis and J. C. McElwain. Oxford Univer-sity Press. 2002.