Microbial mats are common in many benthic marine and aquatic settings. Some microbial mats bind sediments to form fossilizable structures, often called stromatolites or microbialites. We are working with other researchers (J. Bernhard, WHOI, R. Summons, MIT, and P. Visscher, UConn) to learn more about the role of heterotrophic eukaryotes. The evolution of cetain protist groups may have influenced the types of fossilizable structures found in the fossil record. We are studying the eukaryotic communities and their biomarker signatures associated with modern stromatolites and thrombolites from the Bahamas and Australia to better understand the formation of these structures.