Spongiophyton Temporal range:
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Scientific classification | |
Kingdom: | Plantae |
Division: | incertae sedis |
Family: | † Spongiophytaceae |
Genus: | †
Spongiophyton Kräusel (1954) |
Type species | |
†Spongiophyton lenticulare
[2]
[3] (Barbosa) Kräusel (1954)
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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. [4] It is also perforated with pores resembling those of some liverworts. [4] It probably grew on the banks of rivers. [5] Spongiophyton has been mistakenly interpreted as tree resin [6] and lycopod cuticle, [7] and was later identified as the cuticle of a thalloid plant. [8] It has most recently been interpreted on morphological [9] and isotopic [10] grounds as a lichen—which would place it with Winfrenatia among the earliest known representatives of this group. [11]
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. [4] 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. [4]