Spongiophyton
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Spongiophyton was a thallose fossil of the early to mid Devonian, which is notoriously difficult to classify.
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[edit] Affinity
Spongiophyton has been mistakenly interpreted as tree resin[1] and lycopod cuticle,[2] and was later identified as the cuticle of a thalloid plant.[3]
It has most recently been interpreted on morphological[4] and isotopic[5] grounds as a lichen - which would make it the earliest known representative of this group.[6]
However, the significance of the isotopic data has been called into question. Jahren et al. argued that mosses and liverworts had a δ13C signature of under -26‰, and lichens were exclusively > -26‰. But in deducing this they relied solely on their own data, neglecting to include published datasets or bryophytes from a range of habitats. They also failed to take into account any adjustment necessary to overcome post-burial alteration of the δ13C, or to compensate for the different isotopic composition of the early Devonian atmosphere.[7] Repeating Jahren's experiments with these factors taken into account shows that most major groups' δ13C values overlap significantly, and do not provide a statistically significant case for the inclusion of Spongiophyton in any group.[7]
[edit] Morphology
The organism displayed dichotomous branching, and a flattened/eliptical cross section with a really thick (20-80μm) upper cuticlular surface.[8] It is also perforated with pores resembling those of some liverworts .[9]
[edit] Habitat
Spongiophyton probably grew on the banks of rivers.[10]
[edit] Notes and references
- ^ Penhallow (1889) in Fletcher (2004)
- ^ Barbosa (1949) in Fletcher (2004)
- ^ Kräusel (1954) in Fletcher (2004)
- ^ Wilson A. Taylor, Chris Free, Carolyn Boyce, Rick Helgemo, Jaime Ochoada (2004.). "SEM Analysis of Spongiophyton Interpreted as a Fossil Lichen". Int. J Plant Sci. 165(5): 875–881.. doi:. 1058-5893/2004/16505-0018$15.00.
- ^ Jahren, A.H.; Porter, S.; Kuglitsch, J.J. (2003). "Lichen metabolism identified in Early Devonian terrestrial organisms". Geology 31 (2): 99-102. doi:.
- ^ Retallack (1994, "Were the Ediacaran fossils lichens?") suggested that the Ediacaran biota were lichens, but he has since refined this hypothesis (Retallack 2007, "Dickinsonia...").
- ^ a b Fletcher, B.J.; Beerling, D.J.; Chaloner, W.G. (2004). "Stable carbon isotopes and the metabolism of the terrestrial Devonian organism Spongiophyton". Geobiology 2 (2): 107-119. doi:.
- ^ Fletcher (2004)
- ^ Fletcher (2004)
- ^ Gensel et al. 1991; Griffing et al. 2000; in Fletcher (2004)
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