442 FOSSIL PLANTS/Fungi and Lichens Winfrenatia (Figures 1G and 1H) consists of a mycelial mat, constructed of interwoven aseptate hyphae Along the upper surface of the mat are numerous shallow relatively uniform depressions (Figure 1G) Within many of these depressions are coccoid unicells that are morphologically similar to certain extant cyanobacteria; also present are clusters of the same cells within mucilaginous investments that are interpreted to be stages in the life history of the cyanobacterium Hyphae of the fungus extend into the depressions and become intertwined with the cyanobacteria (Figure 1H) The range of features observed in Winfrenatia, including the size of the thallus and the number of depressions on the surface, have allowed speculations as to the life-history strategy, which included the production of new cells of the photobiont to maintain the symbiosis and support the fungus and, at the same time, an increase in the size of the fungal mycelial mat It has been suggested that Winfrenatia is not a true lichen but rather an unstable association in which a fungus parasitized a cyanobacterial colony While the physiological stability of a symbiotic association in the fossil record may never be fully deciphered, the definition of a lichen as a controlled parasitism is perhaps more accurate, as it underscores the varying degrees of lichenization that appear in modern ecosystems In that context, Winfrenatia may quite accurately be regarded as an Early Devonian lichen The systematic position of the fungal partner of Winfrenatia has not been conclusively identified The presence of aseptate hyphae and certain thick-walled sculptured spores associated with the mycelial mats suggest that the affinities of the fungus may lie close to the Zygomycetes This is especially noteworthy since there is only one extant lichen with a zygomycetous mycobiont and a cyanobacterial photobiont, Geosiphon pyriforme In this unique endosymbiotic association, cyanobacteria of the genus Nostoc become encapsulated in pear-shaped bladders formed by the fungus A few fossil lichens have been reported from the Cenozoic, most of which are preserved in Tertiary amber That these fossils represent lichens is relatively easy to demonstrate, since their morphology closely resembles that of extant lichens; some forms can even be assigned to modern families and genera In addition to these lichens, there are a few reports of adpressed lichen thalli, including a fossil Lobaria from Miocene rocks at Redding Creek (California) and the foliicolous (leaf-colonizing) lichen Pelicothallos, which was discovered on an angiosperm leaf from the Eocene of Tennessee It remains puzzling why lichens are so rare in the fossil record, or have been so infrequently described One reason may be that ancient lichens were quite different in appearance from those seen today, and, as a result, it is difficult to recognize these organisms in the fossil record Moreover, some workers have pointed out that many lichen-dominated habitats, such as tundra and mountains, have a relatively low potential for yielding fossils However, lichens today also thrive in many environments that could lead to preservation, including swamp forests Still, even in the extensive Carboniferous coal swamp forests, which have been studied extensively for more than 150 years, not a single compelling lichen fossil has ever been recorded Concluding Remarks As is the case in many areas of palaeontology, the discovery and recognition of ‘unique’ fossils requires an intersection between the vagaries of preservation and the necessary expertise to interpret the fossil Historically, relatively little attention has been directed at fossil bacteria, algae, fungi, and other miscellaneous organisms in which taxonomic placement has been difficult As palaeontologists strive to understand the complexities of the biological and physical world of the past, it is becoming increasingly clear that organisms such as fungi and lichens were not only present but played pivotal roles in shaping the ecosystems of the past Glossary Clamp-connections Outgrowths of fungal hyphae that, at cell division, make a connection between the resulting two cells by fusion with the lower Coal balls Preservation type in which mineral matter has filled the cell lumens and intercellular spaces but has not replaced the cell walls Coprolites Fossilized faecal material Hypha (plural hyphae) Tubular filament that is the structural component of the majority of fungi and may be coenocytic or septate Mycelium (plural mycelia) The total mass of hyphae that constitutes the vegetative portion or thallus of a fungus Mycoparasite A fungus that is parasitic on another fungus Mycorrhiza Mutualistic association of a fungus with (the roots of) a higher plant Necrosis Localized death of living cells due to infection or injury Parasite An organism that obtains nourishment from another living organism Pathogen Any organism capable of causing a disease Saprophyte An organism that obtains nutrients from dead organic material