Nematothallus
From Wikipedia, the free encyclopedia
| Nematothallus Fossil range: Upper Silurian - lowermost Devonian |
||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Scientific classification | ||||||||||||
|
||||||||||||
| Species | ||||||||||||
|
Nematothallus is a form genus comprising cuticle-like fossils. It was first described by Lang in 1933[2], who envisioned it being an early thallose land plant with tubular features and sporophytes, covered by a cuticle which preserved impressions of the underlying cells. He had found abundant disaggregated remains of all three features, none of which were connected to another, leaving his reconstruction of the phytodebris as parts of a single organism highly conjectural.
Further work failed to draw together all aspects of the organism: Edwards (1982)[3] and Edwards and Rose (1984)[4] both provided thorough descriptions of the cuticular aspects of the plants, while Pratt et al. (1978) and Niklas and Smocovitis (1983) focused on the anatomy of the tubes. Indeed, some workers suggested that the name Nematothallus should only apply to the tubes,[5][6] until Strother (1993) found more complete specimens, with tubes attached to the cuticle. He attempted to unite and formalise the genus, and extended it to include banded tubes,[1] which are instead referred to as nematoclasts (Graham & Gray 2001).[7]
It is possible that Nematothallus consisted of two layers of cuticle, although fossils giving this impression may in fact represent two layers which happened to overlap one another and become stuck. It is not readily established what the cuticle represents.[4] Lang (1945) had it as an epidermal layer, similar to the waxy cuticle of plants today, covering a parenchymatous layer. Alternatively, Edwards (1982) proposed that the inner tissue of Nematothallus comprised stringy tubes, with the cellular patterning produced by their ends.[3]
The genus was later formalised by Strother,[1] who discovered better preserved and more complete specimens in Pennsylvania, America - which appear to show tubes connected to the rims of cuticle.[6] Nematothallus is widespread from the late Silurian, but similar cuticle is reported from the Caradoc epoch (late Ordovician, ).[8] It is, however, difficult to distinguish Nematothallus cuticle from that of arthropods.[6]
Further work by Edwards and Rose has identified oval-shaped growths in places on the cuticles of a limited number of Nematothallus fragments, which develop into holes - whose purpose is unknown. Since they are not found in all Nematothallus individuals, it is unlikely that they were involved in gas exchange - perhaps they were involved in the release of spores? One fossil gives the impression, which may well be an illusion, of spores being trapped between two layers of cuticle.[4]
There is a possibility that the genus represents a lichen, rather than a plant - although this is not yet supported by firm evidence.[9]
[edit] See also
Cosmochlaina, a closely related sister taxon.
[edit] References
- ^ a b c Strother, P.K. (1993). "Clarification of the Genus Nematothallus Lang". Journal of Paleontology 67 (6): 1090–1094.
- ^ a b Lang, W.H. (1937). "On the Plant-Remains from the Downtonian of England and Wales". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 227 (544): 245–291. doi:.
- ^ a b Edwards, D. (1982). "Fragmentary non-vascular plant microfossils from the late Silurian of Wales". Botanical Journal of the Linnean Society 84: 223–256. doi:.
- ^ a b c Edwards, D.; Rose, V. (1984). "Cuticles of Nematothallus: a further enigma". Botanical journal of the Linnean Society 88 (1-2): 35–54. doi:. ISSN 0024-4074.
- ^ Gensel, P.G.; Johnson, N.G.; Strother, P.K. (1990). "Early Land Plant Debris (Hooker's" Waifs and Strays"?)". PALAIOS 5 (6): 520–547. doi:.
- ^ a b c Strother, P.K. (1988). "New Species of Nematothallus from the Silurian Bloomsburg Formation of Pennsylvania". Journal of Paleontology 62 (6): 967–982.
- ^ Graham, L.E.; Gray, J. (2001). "The Origin, Morphology, and Ecophysiology of Early Embryophytes: Neontological and Paleontological Perspectives". Plants Invade the Land: Evolutionary and Environmental Perspectives.
- ^ Edwards, D. (1998). "Stomata in early land plants: an anatomical and ecophysiological approach". Journal of Experimental Botany 49 (90001): 255–278. doi:.
- ^ Retallack, G.J. (2007). "Growth, decay and burial compaction of Dickinsonia, an iconic Ediacaran fossil". Alcheringa: An Australasian Journal of Palaeontology 31 (3): 215–240. doi:.
McGregor and Narbonne (1978): "Upper Silurian trilete spores and other microfossils from the Read Bay Formation, Cornwallis Island, Canadian Arctic"
|
||||||||||||||||||||
