Studies of Fossil Flowers using Synchrotron X-Ray Microtomography

Flowering plants (angiosperms) are the most diverse group of plants living today and dominate almost all terrestrial habitats. Yet viewed in the context of plant evolution and the broader history of terrestrial vegetation the diversity and dominance of flowering plants is a relatively recent development. Unequivocal fossils of angiosperms first appear in the Early Cretaceous about 135 million years before present and the subsequent rise to dominance of the group was rapid. By the end of the Cretaceous, 65 million years before present, flowering plants were widespread, diverse, and abundant. My research has focused on documenting the early evolutionary history of flowering plants through study of fossil flowers and other reproductive structures from Cretaceous age fossil sites in North America, Europe, and Asia. The fossils are small dispersed structures that are isolated from unconsolidated sediments and then studied primarily using scanning electron microscopy (SEM). Details of morphology and anatomy are used to evaluate their systematic relationships and interpret their evolutionary implications. While SEM is very useful for documenting surface morphology, internal structures are difficult to study. Recently we have been using synchrotron x-ray microtomography to visualize internal morphological and anatomical details. X-ray microtomography is providing many important morphological and anatomical details that allow much greater precision in understanding evolutionary relationships. In my presentation I will introduce our research program and then focus on several examples to illustrate how study of the fossil record is illuminating our understanding of the early evolutionary history of flowering plants.