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In response to the post by Richard "Rik" Hill on 7/21/1995, I would like to throw out my own two centimes worth. Most living lichens are terrestrial. There are, however, a few marine lichens. Most of these marine lichens are, as Ben Waggoner pointed out, found in the rocky intertidal environment. There are a very few species which are strictly rocky subtidal. As far as I know, a rocky intertidal or subtidal environment has not been proposed for any of the Ediacaran localities. If Ediacaran organisms have not been transported from elsewhere, then they must have lived on soft substrates. As far as I know, there are no marine lichens on soft substrates. Kappen (1973, p. 363) noted that lichens colonize seashores as long as the seashore doesn't consist of loose or soft substrates. Clearly, living marine lichens encrust hard substrates. There are, however, terrestrial lichens living on soft substrates. Another big problem with relating Ediacaran organisms to living marine lichens is that it appears that marine lichens have only recently invaded the oceans, probably long after the Precambrian. Kappen (1973, p. 364) noted that "The very pronounced zonation of lichens in and around aquatic environments and the specialization of only a few taxa show that aquatic habitats represent extreme environments" for lichens. Though Retallack's (1994) lichen hypothesis may at first glance seem plausible, the closer you look at the available information on lichens today, the less plausible his hypothesis becomes. There are just too many inconsistencies that must be overlooked in order to accept Ediacaran organisms as lichens (as we know them today). On the flip-side, I think that we should reexamine Ediacaran localities to see if any of them could be non-marine. If a marine environmental interpretation is upheld for these localities, then based on what we know of marine lichens today, I think that we can safely reject the hypothesis that the Ediacaran organisms were lichens. I would not rule out, however, the possibility that some (though not all) Ediacaran organisms may represent some other kind of autotroph or plant-like organisms which went extinct right before the Cambrian explosion and therefore left no living descendents for us to examine today. As far as Nematophytales (_Nematothallus_, _Prototaxites_, etc.), their affinities are also very controversial. They were enigmatic nonvascular plants that lived in the Silurian and Devonian. _Prototaxites_ were trunk-like objects that got up to 1 m in diameter and up to 2 m in length (Stewart and Rothwell, 1993). Impressive for an Early Devonian plant. Nematophytales are characterized by having an internal anatomy unlike any plant living today. They consisted of two sizes of tubules: small, intertwining tubes and large, vertical tubes. Nematophytales have been related to brown algae, red algae, and to fungi. What makes them so exciting is that they probably represent a separate evolution of land plants unrelated to the other one by vascular plants (Stewart and Rothwell, 1993). Nematophytales went extinct at the end of the Devonian(?) leaving behind no descendents. Needless to say, even if Nematophytalians were some kind of giant lichen, I think there are very few if any similarities between them and Ediacaran fossils in the way of their morphology, taphonomy, or environment. Kappen, L., 1973, Response to extreme environments, in Ahmadjian, V., and Hale, M.E., eds., The lichens: New York, Academic Press, p. 311-380. Retallack, G.J., 1994, Were the Ediacaran fossils lichens? Paleobiology, v. 20, p. 523-544. Stewart, W.N., and Rothwell, G.W., 1993, Paleobotany and the evolution of plants: Cambridge University Press. Cheers, ------------------------------------------------------------------------- Michael Kirby Department of Geology University of California, Davis Davis, California 95616 USA
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