''Spongiophyton'' was a thallose

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

of the early to mid-

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

, which is notoriously difficult to classify. ''Spongiophyton'' displayed

dichotomous branching This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...

, and a flattened/elliptical cross section with a thick (20–80 μm) upper cuticular surface.Fletcher (2004) It is also perforated with pores resembling those of some liverworts. It probably grew on the banks of rivers. ''Spongiophyton'' has been mistakenly interpreted as

tree resin In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

and

lycopod Lycopodiopsida is a class of vascular plants known as lycopods, lycophytes or other terms including the component lyco-. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching s ...

cuticle, and was later identified as the cuticle of a thalloid plant. It has most recently been interpreted on morphological and isotopicJahren ''et al.'' (2003) grounds as a

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.Winfrenatia ''Winfrenatia'' is a genus that contains the oldest-known terrestrial lichen, occurring in fossils preserved in the lower Devonian Rhynie chert. The genus contains the single species ''Winfrenatia reticulata'', named for the texture of its sur ...

among the earliest known representatives of this group.Retallack (1994) suggested that the

Ediacaran biota The Ediacaran (; formerly Vendian) biota is a Taxonomy (biology), taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (). These were composed of enigmatic tubular and frond-sh ...

were lichens, but has since refined this hypothesis (Retallack, 2007). The significance of the isotopic data has, however, been called into question. Jahren ''et al.'' argued that

moss Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...

es and liverworts had a signature of under ‰, and lichens were exclusively > ‰. But in deducing this they relied solely on their own data, neglecting to include published datasets or

bryophyte The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited in ...

s from a wide range of habitats. They also failed to take into account any adjustment necessary to overcome post-burial alteration of the , or to compensate for the different isotopic composition of the early Devonian atmosphere. Repeating Jahren's experiments with these factors taken into account shows that most major groups' values overlap significantly, and do not provide a statistically significant case for the inclusion of ''Spongiophyton'' in any group.

Notes

References

* * * * * Lichens Devonian life Paleozoic life of Ontario Paleozoic life of New Brunswick {{devonian-plant-stub