Thursophyton

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Thursophyton
Temporal range: Middle Devonian
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Thursophyton milleri Nathorst, part.png
Axes of Thursophyton milleri, detail from Nathorst (1915), Fig. 7
Scientific classification Red Pencil Icon.png
Kingdom: Plantae
Clade: Tracheophytes
Order: incertae sedis
Genus:Thursophyton
Nath. 1915
Type species
Thursophyton milleri
(J.W.Salter) Nath. [1]

Thursophyton ("plant from Thurso") is a form genus of extinct vascular plants known from anatomically preserved specimens originally described from the Givetian (Middle Devonian) of Scotland, and since reported from other parts of northern Europe. [2] The taxonomic position of Thursophyton has been uncertain; most authors have considered it too imperfectly known to place, or have assigned it to the Lycopodiophyta. Unpublished research suggests similarities with spiny genera of the Zosterophyllopsida. [3]

Thurso town in Caithness, Scotland

Thurso is a town and former burgh on the north coast of the Highland council area of Scotland. Situated in the historical area of Caithness, it is the northernmost town on the British mainland.

The Givetian is one of two faunal stages in the Middle Devonian period. It lasted from 387.7 million years ago to 382.7 million years ago. It was preceded by the Eifelian stage and followed by the Frasnian stage. It is named after the town of Givet in France.

Contents

Description

Thursophyton is a genus of terrestrial vascular plants which flourished in the Middle Devonian period. These plants consisted of aerial stems branching dichotomously, trichotomously or pseudomonopodially, at least the main axes clothed in spirally arranged spines up to 7 mm long, which are not leaves as they are not vascularised and leave no scar when removed. [2] The stems contain an elliptical exarch xylem having both annular and spirally thickened tracheids; very little is known about the sporangia. [3]

Vascular plant subkingdom of plants

Vascular plants, also known as tracheophytes, form a large group of plants that are defined as those land plants that have lignified tissues for conducting water and minerals throughout the plant. They also have a specialized non-lignified tissue to conduct products of photosynthesis. Vascular plants include the clubmosses, horsetails, ferns, gymnosperms and angiosperms. Scientific names for the group include Tracheophyta, Tracheobionta and Equisetopsida sensu lato.

The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago (Mya), to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, England, where rocks from this period were first studied.

Species

The type species is Thursophyton milleri. Other species have been suggested (e.g. T. reidii, T. eberfeldense, T. hostimense, T. vahlbergianum) which are usually regarded as synonyms of T. milleri. Because of the poor preservation of much of this plant material from the Devonian period, it is likely that other synonyms exist e.g. Euthursophyton hamperbachense Mustafa from Germany. [3]

Type species term used in zoological nomenclature (also non-officially in botanical nomenclature)

In zoological nomenclature, a type species is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen(s). A similar concept is used for suprageneric groups called a type genus.

See also

Related Research Articles

Lycophyte phylum of plants

The lycophytes, when broadly circumscribed, are a vascular plant (tracheophyte) subgroup of the kingdom Plantae. They are sometimes placed in a division Lycopodiophyta or Lycophyta or a subdivision Lycopodiophytina. They are one of the oldest lineages of extant (living) vascular plants; the group contains extinct plants that have been dated from the Silurian. Lycophytes were some of the dominating plant species of the Carboniferous period, and included tree-like species, although extant (living) lycophytes are relatively small plants.

Lepidodendron – also known as the scale trees – is an extinct genus of primitive, vascular, tree-like plants related to the isoetes (quillworts) and lycopsids. They were part of the coal forest flora. They sometimes reached heights of over 30 metres (100 ft), and the trunks were often over 1 m (3.3 ft) in diameter. They thrived during the Carboniferous Period before going extinct. Sometimes erroneously called "giant club mosses", the genus was actually more closely related to modern quillworts than to modern club mosses.

Equisetidae subclass of plants

Equisetidae is a subclass of vascular plants with a fossil record going back to the Devonian. They are commonly known as horsetails. They typically grow in wet areas, with whorls of needle-like branches radiating at regular intervals from a single vertical stem.

Zosterophyll extinct class of plants

The zosterophylls were a group of extinct land plants that first appeared in the Silurian period. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zosterophyllophyta or Zosterophyta and the class or plesion Zosterophyllopsida or Zosteropsida. They were among the first vascular plants in the fossil record, and had a world-wide distribution. They were probably stem-group lycophytes, forming a sister group to the ancestors of the living lycophytes. By the late Silurian a diverse assemblage of species existed, examples of which have been found fossilised in what is now Bathurst Island in Arctic Canada.

<i>Baragwanathia</i> genus of plants

Baragwanathia is a genus of extinct plants of the division Lycopodiophyta of Late Silurian to Early Devonian age, fossils of which have been found in Australia, Canada, China and Czechia. The name derives from William Baragwanath who discovered the first specimens of the type species, Baragwanathia longifolia at Thomson River.

<i>Drepanophycus</i> genus of plants

Drepanophycus is a genus of extinct plants of the Division Lycopodiophyta of Early to Late Devonian age, found in Eastern Canada and Northeast USA, China, Russia, Egypt and various parts of Northern Europe and Britain.

<i>Asteroxylon</i> genus of extinct plants

Asteroxylon is an extinct genus of vascular plants of the Division Lycopodiophyta known from anatomically preserved specimens described from the famous Early Devonian Rhynie chert and Windyfield chert in Aberdeenshire, Scotland. Asteroxylon is considered the most basal member of the Lycopsida.

Rhyniophytina

Rhyniophytina is a subdivision of extinct early vascular plants that are considered to be similar to the genus Rhynia, found in the Early Devonian. Sources vary in the name and rank used for this group, some treating it as the class Rhyniopsida, others as the division Rhyniophyta. The informal term rhyniophytes is also used. The first definition of the Rhyniophytina was by Banks, since when there have been many redefinitions, including by Banks himself. "As a result, the Rhyniophytina have slowly dissolved into a heterogeneous collection of plants ... the group contains only one species on which all authors agree: the type species Rhynia gwynne-vaughanii". When defined very broadly, the group consists of plants with dichotomously branched, naked aerial axes ("stems") with terminal spore-bearing structures (sporangia).

<i>Psilophyton</i> Genus of fossil plants

Psilophyton is a genus of extinct vascular plants. Described in 1859, it was one of the first fossil plants to be found which was of Devonian age. Specimens have been found in northern Maine, USA; Gaspé Bay, Quebec and New Brunswick, Canada; the Czech Republic; and Yunnan, China. Plants lacked leaves or true roots; spore-forming organs or sporangia were borne on the ends of branched clusters. It is significantly more complex than some other plants of comparable age and is thought to be part of the group from within which the modern ferns and seed plants evolved.

Polysporangiophyte

Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation (sporophyte) has branching stems (axes) that terminate in sporangia. The name literally means many sporangia plant. The clade includes all land plants (embryophytes) except for the bryophytes whose sporophytes are normally unbranched, even if a few exceptional cases occur. While the definition is independent of the presence of vascular tissue, all living polysporangiophytes also have vascular tissue, i.e., are vascular plants or tracheophytes. Fossil polysporangiophytes are known that have no vascular tissue, and so are not tracheophytes.

<i>Horneophyton</i>

Horneophyton, a member of the Horneophytopsida, is an extinct early plant which may form a "missing link" between the hornworts and the Rhyniopsida. It is among the most abundant organisms found in the Rhynie chert, a Devonian Lagerstätte in Scotland. A single species, Horneophyton lignieri, is known. Its probable female gametophyte is the form taxon Langiophyton mackiei.

<i>Pertica</i> genus of plants (fossil)

Pertica is a genus of extinct vascular plants of the Early to Middle Devonian. It has been placed in the "trimerophytes", a strongly paraphyletic group of early members of the lineage leading to modern ferns and seed plants.

Hicklingia is a genus of extinct plants of the Middle Devonian. Compressed specimens were first described in 1923 from the Old Red Sandstone of Scotland. Initially the genus was placed in the "rhyniophytes", but this group is defined as having terminal sporangia, and later work showed that the sporangia of Hicklingia were lateral rather than strictly terminal, so that it is now regarded as having affinities with the zosterophylls.

Huia is a genus of extinct vascular plants of the Early Devonian. The genus was first described in 1985 based on fossil specimens from the Posongchong Formation, Wenshan district, Yunnan, China.

Adoketophyton is a genus of extinct vascular plants of the Early Devonian. The plant was first described in 1977 based on fossil specimens from the Posongchong Formation, Wenshan district, Yunnan, China. These were originally named Zosterophyllum subverticillatum; later the species was transferred to a new genus as Adoketophyton subverticillatum. One cladistic analysis suggested that it is a lycophyte, related to the zosterophylls. Other researchers regard its placement within the vascular plants as uncertain.

Distichophytum is a genus of extinct vascular plants of the Late Silurian (Ludfordian) to Early Devonian (Emsian), around 426 to 393 million years ago. The genus has a tangled taxonomic history, also being known as Bucheria and Rebuchia.

<i>Nothia</i>

Nothia was a genus of Early Devonian vascular plants whose fossils were found in the Rhynie chert in Scotland. It had branching horizontal underground stems (rhizomes) and leafless aerial stems (axes) bearing lateral and terminal spore-forming organs (sporangia). Its aerial stems were covered with small 'bumps' (emergences), each bearing a stoma. It is one of the best described early land plants. Its classification remains uncertain, although it has been treated as a zosterophyll. There is one species, N. aphylla.

Tetraxylopteris is a genus of extinct vascular plants of the Middle to Upper Devonian. Fossils were first found in New York State, USA. A second species was later found in Venezuela.

Yarravia is a genus of extinct vascular plants mainly known from fossils found in Victoria, Australia. Originally the rocks in which they were found were considered to be late Silurian in age; more recently they have been found to be Early Devonian. Specimens consist only of incomplete leafless stems, some of which bore groups of spore-forming organs or sporangia which were fused, at least at the base.

<i>Taeniocrada</i>

Taeniocrada is a genus of extinct plants of Devonian age. It is used as a form genus for fossil plants with leafless flattened stems which divided dichotomously and had prominent midribs regarded as containing vascular tissues. It has been suggested that some species assigned to this genus were aquatic.

References

  1. Nathorst, A.G. (1915). "Zur Devonflora des westlichen Norwegens". Bergens Museums aarbok. 3 (9): 1–34.
  2. 1 2 Arber, E.A. Newell (1921). Devonian Floras: a study of the origin of Cormophyta. Cambridge: Cambridge University Press.
  3. 1 2 3 Perry, Ian (1989). The fossil flora of Shetland and surrounding areas (PDF) (PhD). University of Bristol.