Prototaxites

Prototaxites is the generic name of an extinct organism from the Devonian of unusually large dimensions. The systematic affiliation is disputed. In the latest work Prototaxites is interpreted as a huge lichen or fungus.

Description

The fossil has been found so far only in fragments. It resembles a tree stump and this similarity is also based his name (Taxus yew = ). In cross section, the fossil shows concentric rings with occasional inclusion of plant residues, which point to a non-continuous growth. The fragments contain the two types of tube-like filaments: a larger type with a diameter of 20-60 microns and a wall thickness of 2-6 microns. Do not bifurcate and are not divided by septa. The smaller filaments have only 5-10 microns in diameter and bifurcate several times.

Way of life

Prototaxites grew on the land between plants such as Psilophyton and Aglaophyton. So far, the fossil of many Devonian fossil sites was found on almost every continent. It was reconstructed with a height of 2-9 m and a " stem diameter " of up to 1 m, the highest and largest organism under the existing land-living organisms. The above findings would be well to the "mushroom " model ( saprophytes ) model fit. However, in this saprophytes model for building such a large biomass a very large area would be necessary so that the saprophyte had received sufficient organic material. This restriction would eliminate the " lichen " model. The lichen would be in direct competition with the then still very small plants. This could explain the size of proto Taxis good. In the latest work will be noted, however, that differ by the isotope ratios of Prototaxites and plants from the same layers clearly. This should not really be the case if Prototaxites photosynthesis as the plants would have operated, would thus have been a lichen.

History

As Dawson ( 1879) first described the fossil, he interpreted it as a fossil genus of gymnosperm from the relationship of the yew. Hence the name Prototaxites. It was later reinterpreted as Codiacee (green algae ). In 1979, the fossil was then interpreted as brown algae. In 2001 an interpretation as a giant mushroom Holobasidiomyceter by Hueber ( 2001). Selosse then pointed to the findings presented by Hueber and came to the conclusion that Prototaxites was more of a lichen. 2007 mounted Boyce et al. new arguments for the interpretation as a mushroom.