Nematothallus
Encyclopedia
Nematothallus is a form genus
comprising cuticle-like fossil
s.
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. Even so, it was picked up by Jonker (1973), who proposed that Nematothallus represented leaves of Prototaxites, which he interpreted as a red alga.
Further work failed to draw together all aspects of the organism: Edwards (1982) and Edwards and Rose (1984) 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, 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, which are instead referred to as nematoclasts (Graham & Gray 2001).
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. Lang (1945) had it as an epidermal layer, similar to the waxy cuticle of plants today, covering a parenchyma
tous layer. Alternatively, Edwards (1982) proposed that the inner tissue of Nematothallus comprised stringy tubes, with the cellular patterning produced by their ends.
The genus was later formalised by Strother, who discovered better preserved and more complete specimens in Pennsylvania
, America – which appear to show tubes connected to the rims of cuticle. Nematothallus is widespread from the late Silurian, but similar cuticle is reported from the Caradoc
epoch (late Ordovician
). It is, however, difficult to distinguish Nematothallus cuticle from that of arthropod
s.
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.
, Cooksonia
and Steganotheca
in the Ludlow (upper Ludfordian) Whitcliffe formation.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
comprising cuticle-like fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s.
History of research
Nematothallus was first described by Lang in 1937, who envisioned it being an earlyEvolutionary history of plants
The evolution of plants has resulted in increasing levels of complexity, from the earliest algal mats, through bryophytes, lycopods, ferns to the complex gymnosperms and angiosperms of today...
thallose
Thallus (tissue)
Thallus, from Latinized Greek θαλλός , meaning a green shoot or twig, is the undifferentiated vegetative tissue of some organisms in diverse groups such as algae, fungus, some liverworts, lichens, and the Myxogastria. Many of these organisms were previously known as the thallophytes, a polyphyletic...
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. Even so, it was picked up by Jonker (1973), who proposed that Nematothallus represented leaves of Prototaxites, which he interpreted as a red alga.
Further work failed to draw together all aspects of the organism: Edwards (1982) and Edwards and Rose (1984) 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, 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, which are instead referred to as nematoclasts (Graham & Gray 2001).
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. Lang (1945) had it as an epidermal layer, similar to the waxy cuticle of plants today, covering a parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
tous layer. Alternatively, Edwards (1982) proposed that the inner tissue of Nematothallus comprised stringy tubes, with the cellular patterning produced by their ends.
The genus was later formalised by Strother, who discovered better preserved and more complete specimens in Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
, America – which appear to show tubes connected to the rims of cuticle. Nematothallus is widespread from the late Silurian, but similar cuticle is reported from the Caradoc
Caradoc
Caradoc Vreichvras Arm) was a semi-legendary ancestor to the kings of Gwent. He lived during the 5th or 6th century. He is remembered in Arthurian legend as a Knight of the Round Table as Carados Briefbras ....
epoch (late Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
). It is, however, difficult to distinguish Nematothallus cuticle from that of arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s.
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.
Habitat
Nematothallus was originally recovered from the Red Downtonian near the base of the Old Red Sandstone, between the clearly marine Ludlow deposits beneath it, and the unambiguously terrestrial Lower Old Red Sandstone. Further samples came from elsewhere in the Lower Old Red Sandstone (St Maughams Group, lowermost Devonian), where the co-occur with plant spores. Additional, older material occurs with HostinellaHostinella
Hostinella is a form genus, used for bare dichotomously branching stems which have not been found in association with spore-forming organs or sporangia and so cannot be assigned to a more precise genus or species...
, Cooksonia
Cooksonia
Cooksonia is an extinct grouping of primitive land plants. The earliest Cooksonia date from the middle of the Silurian ; the group continues to be an important component of the flora until the Early Devonian, a total time span of...
and Steganotheca
Steganotheca
Steganotheca is a genus of bushy, probably vascular plant with branched axes, known from upper Silurian strata. It has terminal sporangia and reached 5 cm in height....
in the Ludlow (upper Ludfordian) Whitcliffe formation.
Affinity
There is a possibility that the genus represents a lichen, rather than a plant – although this is not yet supported by firm evidence. The biochemistry of the organism is not inconsistent with an algal affinity, but Edwards (1982) considers it unlikely that algae would be preserved as coalified impressions. However, Edwards does note that the surface patterning could have been produced in a similar fashion to surface layers in green algae – that is, by the ends of tightly packed filaments causing indentation on the surface layer. (Just because they were formed in the same way doesn't mean they were formed by green algae, though.)Synonyms
N. taenia and N. lobata were both collapsed into a new form-species Laevitubulus laxus.See also
- CosmochlainaCosmochlainaCosmochlaina is a form genus of nematophyte – an early plant known only from fossil cuticles, often found in association with tubular structures. Where Nematothallus is sometimes used to relate only to tube-like structures, Cosmochlaina refers to the cuticle fragments...
, a closely related sister taxon.
- SpongiophytonSpongiophytonSpongiophyton 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 upper cuticular surface. It is also perforated with pores resembling those of some...
, a similarly enigmatic organism with a similar cuticular patterning. Some material described as Spongiophyton may in fact be Nematothallus.