Most habitats that lichens dominate, such as tundra, mountains, and deserts, have a very low chance of yielding fossils. Thus, the fossil record of lichens is scanty. Some Early Proterozoic filamentous microfossils from the Witwatersrand of South Africa, dated between 2.2 and 2.7 billion years old, have been interpreted as lichen-like associations between two different microbes (Hallbauer and van Warmelo 1974). However, the fossil filaments are only about 1 to 2 microns in diameter, which makes them smaller than most fungi, but about the size of various kinds of filament-forming bacteria. Also, similar microstructures can be produced in the laboratory by chemical reactions. Some paleontologists doubt that these are real fossils (Cloud and Pierce 1977). If they are real, they may not be lichens in the usual sense of the word -- although lichen-like symbioses between algae and filamentous bacteria have been found living.
The oldest certain fossil lichen is Early Devonian (about 400 million years old) from the Rhynie Chert, near Aberdeen, Scotland (Taylor et al. 1995). At about this time, there were several unusual plant-like organisms living on land, including the mat-like nematophytes, crust-like spongiophytes, m and the huge, log-like Prototaxites (which was originally described as a fossil conifer trunk). Under the microscope, these can be seen to be made up of intertwining filaments, and some paleontologists have proposed that these fossils are unusual lichens. Spongiophytes may plausibly be lichens (Stein et al. 1993), but the microscopic filaments that make up nematophytes and Prototaxites lack the typical branching patterns of fungal hyphae. They probably represent isolated offshoots of an algal lineage, "unsuccessful experiments" in colonizing the land, which left no descendants.
A few lichen fossils are known from Mesozoic and Cenozoic rocks. They include at least two genera from Oligocene Baltic amber (Larson 1978; Garty et al. 1982). They also include the fossil Lobaria shown below at right, from Miocene rocks at Redding Creek, California (MacGinite, 1937). Compare this fossil with a living specimen of Lobaria pulmonaria below at left. The living lichen was found growing on an alder tree in Washington State, USA.
The late Precambrian "Ediacara fossils" are usually considered to be early animals. Retallack (1994), however, has theorized that these Vendian organisms were lichens, or something like lichens. This theory is largely based on the fact that some of these seem to have been fairly resistant to being compressed after burial. There are a number of problems with this theory (Waggoner 1995) and it has not been widely accepted. Why not take a look at some of these fossils and see what you think?
Cloud, P. and Pierce, D. 1977. Experimental production of pseudomicrofossils. GSA Abstracts with Programs 9: 102.
Garty, J., Giele, C., and Krumbein, W. E. 1982. On the occurrence of pyrite in a lichen-like inclusion in Eocene amber (Baltic). Palaeogeography, Palaeoclimatology, Palaeoecology 39: 139-147.
Hallbauer, D. K. and van Warmelo, K. T. 1974. Fossilized plants in thucholite from Precambrian rocks of the Witwatersrand, South Africa. Precambrian Research 1: 199-212.
Larson, S. G. 1978. Baltic Amber -- A Palaeobiological Study. Entomonograph 1. Scandinavian Science Press, Klampenborg, Denmark.
MacGinitie, H. D. 1937. The flora of the Weaverville beds of Trinity County, California, with descriptions of the plant-bearing beds. Carnegie Institution of Washington Publications 465 (3): 131.
Retallack, G. J. 1994. Were the Ediacaran fossils lichens? Paleobiology 20: 523-544.
Stein, W. E., Harmon, G. D., and Hueber, F. M. 1993. Spongiophyton from the Lower Devonian of North America reinterpreted as a lichen. American Journal of Botany 80 (6): 93.
Taylor, T. N., Hass, H., Remy, W., and Kerp, H. 1995. The oldest fossil lichen. Nature 378: 244.
Waggoner, B. M. 1995. Ediacaran lichens: a critique. Paleobiology 21: 393-397.