Spongiophyton
| Spongiophyton Temporal range: Early Devonian – Middle Devonian[1] | |
|---|---|
Scientific classification  | |
| Kingdom: | Plantae |
| Phylum: | incertae sedis |
| Family: | †Spongiophytaceae |
| Genus: | †Spongiophyton Kräusel, 1954 |
| Species | |
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Spongiophyton was a thallose fossil of the early to mid Devonian, which is notoriously difficult to classify.
Spongiophyton displayed dichotomous branching, and a flattened/elliptical cross section with a thick (20–80 μm) upper cuticular surface.[2] It is also perforated with pores resembling those of some liverworts.[2] It probably grew on the banks of rivers.[3] Spongiophyton has been mistakenly interpreted as tree resin[4] and lycopod cuticle,[5] and was later identified as the cuticle of a thalloid plant.[6] It has most recently been interpreted on morphological[7] and isotopic[8] grounds as a lichen - which would make it the earliest known representative of this group.[9]
The significance of the isotopic data has, however, 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 wide 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.[2] 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.[2]
Notes
- ↑ Taylor, W. A.; Free, C.; Boyce, C.; Helgemo, R.; Ochoada, J. (2004). "SEM Analysis of Spongiophyton Interpreted as a Fossil Lichen". International Journal of Plant Sciences 165: 875. doi:10.1086/422129.
- ↑ 2.0 2.1 2.2 2.3 Fletcher (2004)
- ↑ Gensel et al.. 1991; Griffing et al. 2000; in Fletcher (2004)
- ↑ Penhallow (1889) in Fletcher (2004)
- ↑ Barbosa (1949) in Fletcher (2004)
- ↑ Kräusel (1954) in Fletcher (2004)
- ↑ Taylor et al. (2004)
- ↑ Jahren et al. (2003)
- ↑ Retallack (1994) suggested that the Ediacaran biota were lichens, but has since refined this hypothesis (Retallack, 2007).
References
- 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:10.1111/j.1472-4677.2004.00026.x.
- Jahren, A. H.; Porter, S.; Kuglitsch, J. J. (2003). "Lichen metabolism identified in Early Devonian terrestrial organisms". Geology 31 (2): 99. Bibcode:2003Geo....31...99J. doi:10.1130/0091-7613(2003)031<0099:LMIIED>2.0.CO;2. ISSN 0091-7613.
- Retallack, G. J. (1994). "Were the Ediacaran fossils lichens?" (PDF). Paleobiology 20 (4): 523–544.
- Retallack, G. J. (2007). "Growth, decay and burial compaction of Dickinsonia, an iconic Ediacaran fossil" (PDF). Alcheringa: an Australasian Journal of Palaeontology 31 (3): 215–240. doi:10.1080/03115510701484705.
- Taylor, Wilson A., Chris Free, Carolyn Boyce, Rick Helgemo, Jaime Ochoada (2004). "SEM analysis of Spongiophyton interpreted as a fossil lichen". International Journal of Plant Sciences 165 (5): 875–881. doi:10.1086/422129.
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