PRASINOPHYTE GREEN ALGAE AND THEIR MICROFOSSIL ANALOGS: GEOBIOLOGICAL IMPLICATIONS

Prasinophyte green algae that produce large reproductive structures called phycoma are often offered as the best modern analog of some of the most ancient eukaryotic fossils, mainly smooth-walled acritarchs that are common in both Proterozoic and Paleozoic strata. However, this relationship is not always based on available knowledge of the biological nature of these algae. In fact, there are more references to pycomate prasinophytes in the geologic literature than in the biological literature. Phycomate prasinophytes are an understudied group of marine phytoplankton, and insights from our knowledge of their biology challenge some of the interpretations of this group in the geologic record. Here, we review what is known about the biology and life cycle of phycomate prasinophytes from the biological literature and present new data comparing the morphology and size distributions of living phycoma and fossils interpreted as prasinophytes. Comparison of the morphology and ecology of modern Prasinophytes and fossil taxa inferred to belong to the Prasinophycea suggests that in many instances, this relationship as analogs is inaccurate or inconclusive; these comparisons demonstrate how knowledge of the biology of modern taxa is required for realistic interpretation of the fossil record of acritarchs. Data we will discuss include the significant size differences between fossil and modern taxa, differences between modern and paleo-environmental distributions, and the preservation potential of modern phycoma. A more comprehensive understanding of the fossil record of Prasinophytes will not only help us to better understand the evolutionary history of the green algae, but also better understand ancient marine ecosystems and the fossil record of single-celled eukaryotes. We want thank Andy Knoll for encouraging and supporting the early development of our work on phycomate prasinophytes and for his endless enthusiasm for this amazing group of phytoplankton.