Prototaxites
Prototaxites is the generic name of an extinct Devonian organismof unusually large dimensions. The systematic affiliation is, however, controversial. In the most recent work, Prototaxites is interpreted as a giant lichen or a fungus.
description
The fossil has so far only been found in fragments. It resembles a tree stump and its name ( Taxus = yew ) is based on this similarity . In cross-section, the fossil shows concentric rings with the occasional inclusion of plant remains, which indicate discontinuous growth. The fragments contain two types of tubular filaments: a larger type with a diameter of 20 to 60 μm and a wall of 2 to 6 μm thick. They do not fork and are not divided by septa. The smaller filaments are only 5–10 μm in diameter and fork several times.
Way of life
Prototaxites grew in the country between plants such as Psilophyton and Aglaophyton . So far, the fossil has been found in many Lower Devonian fossil sites on almost every continent. With a reconstructed height of 2 to 9 m and a "trunk diameter" of up to 1 m, it was the tallest and largest organism among the organisms living on land at that time. The above findings would fit well with the “fungus model” (saprophyte model). However, in this saprophyte model, a very large area would be required to build up such a large biomass so that the saprophyte would have found sufficient organic material. This restriction would no longer apply to the “lichen model”. The lichen would be in direct competition with the very small plants of that time. That might well explain the size of Prototaxis . In the latest work, however, it is pointed out that the isotope ratios of Prototaxites and of plants from the same layers differ significantly. This finding does not fit the assumption that Prototaxites photosynthesized like plants.
history
When Dawson (1859) first described the fossil, he interpreted it as a fossil genus of the naked species from the family of the yew tree. Hence the name Prototaxites . It was later reinterpreted as Codiacee (green algae). In 1979 the fossil was interpreted as brown algae. In 2001 it was interpreted as a giant holobasidiomyceter fungus by Hueber (2001). Selosse then reinterpreted the findings presented by Hueber and came to the conclusion that Prototaxites was more of a lichen. In 2007 Boyce et al. new arguments for interpretation as a mushroom.
literature
- Francis M Hueber: Rotted wood – alga – fungus: the history and life of Prototaxites Dawson 1859 . In: Review of Palaeobotany and Palynology . tape 116 , no. 1-2 , August 2001, pp. 123-158 , doi : 10.1016 / S0034-6667 (01) 00058-6 .
- Marc-André Selosse: Prototaxites: A 400 MYR Old Giant Fossil, A Saprophytic Holobasidiomycete, or A Lichen? In: Mycological Research . tape 106 , no. 6 , June 2002, p. 642-644 , doi : 10.1017 / S0953756202226313 .
- C. Kevin Boyce, Carol L. Hotton, Marilyn L. Fogel, George D. Cody, Robert M. Hazen, Andrew H. Knoll, Francis M. Hueber: Devonian landscape heterogeneity recorded by a giant fungus . In: Geology . tape 35 , no. 5 , 2007, doi : 10.1130 / G23384A.1 ( PDF ).
