CHEMICAL ANALYSIS OF PRESERVED OIL-BODY CELLS IN DEVONIAN LIVERWORTS

Plant-herbivore interactions are among the most complex and diverse ecological interactions in terrestrial ecosystems. Some of the earliest fossil evidence for plant-herbivore interactions is found in liverwort fossils from the Middle Devonian Catskill Delta deposits of New York. Liverworts (Marchantiophyta) are a morphologically diverse clade of non-vascular plants thought to have diverged from all other land plants shortly after they colonized the land. The remarkably well-preserved Metzgeriothallus sharonae is the oldest known liverwort taxon. These fossils exhibit evidence of both insect attacks – in the form of feeding traces representing nine different damage types – and plant defenses – in the form of dark, scattered cells that are thought to be homologous to the oil body cells of extant liverworts. Liverwort oil bodies are membrane-bound organelles that contain a vast array of terpenoids and other compounds. In most liverworts they are found in all plant cells; however, in some taxa single large oil bodies are sequestered in specialized cells that are distributed through the plant thalli in a pattern very similar to that of the dark cells found in Paleozoic liverworts such as M. sharonae. The precise function of these unique organelles is unknown, although most evidence supports an anti-herbivory function. Here we present preliminary results from chemical analysis of these liverwort fossils to determine if they contain remnant traces of defensive chemicals or diagenetically altered defensive chemicals. We focus primarily on solid-phase microextraction gas chromatography-mass spectrometry, a highly sensitive technique for recovering volatiles and semi-volatiles from solid samples. If this does not yield any compounds indicative of chemical defenses (either original compounds or diagenetically altered compounds) we will use other methods, such as pyrolysis gas chromatography-mass spectrometry, that can analyze heavier compounds. The primary goal is to recover evidence of the original chemical defenses, or failing that, evidence that these dark cells in the fossils did once contain defensive chemicals such as terpenoids. This is the first attempt to reconstruct fossil plant chemical defenses, which is critical for understanding the evolution of plant-herbivore interactions through time.