My research takes advantage of the unique opportunities of plants, including cellular preservation in fossils and the repeated evolution of similar morphological structures, to study the evolution of development and physiology in geologic time. Previous investigations of morphologically similar leaves in distantly related plant lineages have demonstrated that the evolution of convergent morphological patterns involves the evolution of convergent developmental processes and that morphological diversity through time has been shaped by developmental constraints. Work in the last year has demonstrated that these multiple independent evolutionary experiments have also involved detailed convergence of leaf functional attributes. Additional physiological studies have provided an understanding of how environmental stresses such as water deficits impose morphological changes during leaf growth. This may allow the use of fossil plants to assess important ecological parameters that are typically not available from the fossil record, such as plant architecture and placement within the forest canopy.

Collaborative work with the Carnegie Astrobiology team involves the application of emerging techniques of fine-scale chemical analysis to the study of the biology of fossil and extant organisms. In the last year this research has allowed us to identify several evolutionary shifts in the wall chemistry of vascular cells that have been involved in the diversification of complex land plants and correlated with the convergent evolution of leaves described above. Also, comparative analyses of the chemistry preserved in fossils have provided a preliminary determination of the biological affinities of a bizarre Paleozoic fossil, Prototaxites, which produced enormous tree-like trunks composed of intertwined, 50 micron-diameter tubes. Different specimens cluster into two discrete populations of carbon isotopic values. Pending further organic analyses to rule out the possibility of diagenetic artifacts, this isotopic disparity may well reflect heterotrophy upon isotopically distinct sources, suggesting Prototaxites was a twenty foot tall fungus.

I am involved in an extensive, ongoing collaboration with members of the Carnegie Astrobiology team, George Cody, Marilyn Fogel, and Bob Hazen. Our work involves the application of emerging techniques of fine-scale chemical analysis to the study of the physiology and biochemistry of fossil and extant organisms. In the last year this research has allowed us to identify several evolutionary shifts in the wall chemistry of vascular cells that have been involved in the diversification of complex land plants and to make a preliminary determination of the biological affinities of enigmatic Paleozoic fossil, which appears likely to have been a twenty foot tall fungus.