Despite the worldwide diversity of fungi and their importance in ecological interactions, little is known about their diversity through the fossil record and almost nothing about their interactions through evolutionary time. A unique window into fungal evolution and interaction is provided, however, by the famous Rhynie Chert in Scotland, with its exceptional preservation of plant and animal remains including cellular details of associated microbial and fungal organisms. The sandstone deposits are dated to Devonian times, ca. 400 million years ago, and record some of the earliest known land plants and animals. Dr. Thomas Taylor at the University of Kansas and his colleagues have been expanding our knowledge of the freshwater environment preserved in these deposits, with a program of meticulous analysis and description of the broad range of fungi found in association with many of these plants and animals. Because fungi are heterotrophs, they require a nutritional interaction with other organisms to obtain a source of carbon. The fungi that existed in the Rhynie Chert ecosystem were involved in a variety of saprophytic, parasitic, and mutualistic associations with several groups of organisms (cyanobacteria, eubacteria, algae, macroplants) as well as other fungi. For example, some of the associations involve plant roots in the form of endomycorrhizae; and some of these plants possessed free-living gametophytes that also appear to harbor mutualistically associated fungi. Also present in this Lower Devonian ecosystem was at least one lichen that consisted of colonies of cyanobacteria with the fungus. To date, the major fungal groups present in the Rhynie Chert appear to be chytrids and zygomycetes. Documenting the occurrence of various fungal taxa and their interactions provides a unique opportunity to place these associations in an evolutionary context and to test hypotheses about the first appearance of such interactions, and to compare these associations with those known to exist today.
