the earliest fossils possessing features typical of fungi date to the paleoproterozoic era, some (ma); these multicellular benthic organisms had filamentous structures capable of anastomosis, in which hyphal branches recombine. other recent studies (2009) estimate the arrival of fungal organisms at about 760–1060 ma on the basis of comparisons of the rate of evolution in closely related groups. for much of the paleozoic era (542–251 ma), the fungi appear to have been aquatic and consisted of organisms similar to the extant chytrids in having flagellum-bearing spores. phylogenetic analyses suggest that the flagellum was lost early in the evolutionary history of the fungi, and consequently, the majority of fungal species lack a flagellum. the evolutionary adaptation from an aquatic to a terrestrial lifestyle necessitated a diversification of ecological strategies for obtaining nutrients, including parasitism, saprobism, and the development of mutualistic relationships such as mycorrhiza and lichenization. recent (2009) studies suggest that the ancestral ecological state of the ascomycota was saprobism, and that independent lichenization events have occurred multiple times.