The Devonian is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at 419.2 million years ago (Ma), to the beginning of the succeeding Carboniferous period at 358.9 Ma. It is named after Devon, South West England, where rocks from this period were first studied.
The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.
Paleobotany, also spelled as palaeobotany, is the branch of botany dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments (paleogeography), and the evolutionary history of plants, with a bearing upon the evolution of life in general. A synonym is paleophytology. It is a component of paleontology and paleobiology. The prefix palaeo- or paleo- means "ancient, old", and is derived from the Greek adjective παλαιός, palaios. Paleobotany includes the study of terrestrial plant fossils, as well as the study of prehistoric marine photoautotrophs, such as photosynthetic algae, seaweeds or kelp. A closely related field is palynology, which is the study of fossilized and extant spores and pollen.
The Rhynie chert is a Lower Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness. It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield chert, is located some 700 m away. The Rhynie chert contains exceptionally preserved plant, fungus, lichen and animal material preserved in place by an overlying volcanic deposit. The bulk of the Devonian fossil bed consists of primitive plants, along with arthropods, lichens, algae and fungi.
Cooksonia is an extinct group of primitive land plants, treated as a genus, although probably not monophyletic. The earliest Cooksonia date from the middle of the Silurian ; the group continued to be an important component of the flora until the end of the Early Devonian, a total time span of 433 to 393 million years ago. While Cooksonia fossils are distributed globally, most type specimens come from Britain, where they were first discovered in 1937. Cooksonia includes the oldest known plant to have a stem with vascular tissue and is thus a transitional form between the primitive non-vascular bryophytes and the vascular 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 a basal member of the Lycopsida.
Prototaxites is an extinct genus of terrestrial fossil fungi dating from the Late Silurian until the Late Devonian periods. Prototaxites formed large trunk-like structures up to 1 metre (3 ft) wide, reaching 8 metres (26 ft) in length, made up of interwoven tubes around 50 micrometres (0.0020 in) in diameter, making it by far the largest land-dwelling organism of its time.
The evolution of plants has resulted in a wide range of complexity, from the earliest algal mats of unicellular archaeplastids evolved through endosymbiosis, through multicellular marine and freshwater green algae, to spore-bearing terrestrial bryophytes, lycopods and ferns, and eventually to the complex seed-bearing gymnosperms and angiosperms of today. While many of the earliest groups continue to thrive, as exemplified by red and green algae in marine environments, more recently derived groups have displaced previously ecologically dominant ones; for example, the ascendance of flowering plants over gymnosperms in terrestrial environments.
Nematothallus is a form genus comprising cuticle-like fossils. Some of its constituents likely represent red algae, whereas others resemble lichens.
Cosmochlaina is a form genus of nematophyte – an early plant known only from fossil cuticles, often found in association with tubular structures. The form genus was put forwards by Dianne Edwards, and is diagnosed by inwards-pointing flanges and randomly oriented pseudo-cellular units. Projections on the outer surface are always present, and sometimes also appear on the inner surface; however, the surface of the cuticle itself is always smooth. The holes in the cuticle are often covered by round flaps, loosely attached along a side.
Ornatifilum is an artificial form genus, which is used to categorise any small, branched filaments with external ornamentation.
Professor Dianne Edwards CBE, FRS, FRSE, FLS, FLSW is a palaeobotanist, who studies the colonisation of land by plants, and early land plant interactions.
Nematoplexus rhyniensis is a fossil known from the Rhynie chert assigned to the nematophytes. It comprises a loose mass of coily aseptate tubes. Tubes which may have originated from a Nematoplexus-like plant are known from earlier Silurian sediments.
Morania is a genus of cyanobacterium preserved as carbonaceous films in the Middle Cambrian Burgess Shale. it is present throughout the shale; 2580 specimens of Morania are known from the Greater Phyllopod bed, where they comprise 4.90% of the community. It is filamentous, forms sheets, and resembles the modern cyanobacterium Nostoc. It would have had a role in binding the sediment, and would have been a food source for such organisms as Odontogriphus and Wiwaxia.
Eldonia is an extinct soft-bodied cambroernid animal of unknown affinity, best known from the Fossil Ridge outcrops of the Burgess Shale, particularly in the 'Great Eldonia layer' in the Walcott Quarry. In addition to the 550 collected by Walcott, 224 specimens of Eldonia are known from the Greater Phyllopod bed, where they comprise 0.43% of the community. Species also occur in the Chengjiang biota, Siberia, and in Upper Ordovician strata of Morocco.
Banded tubes are a type of phytoclast consisting of micrometre-scale tubes with a banded internal ornamentation, and known from terrestrial/freshwater settings from the Early Silurian onwards.
Nematasketum is a nematophyte with internally thickened tubes. It is thought to be terrestrial or freshwater, and seems to be aligned with the fungi.
The Campbellton Formation is a geologic formation in New Brunswick. It preserves fossils dating back to the latest Pragian and Emsian of the Devonian period.
Tortotubus is an early terrestrial fungus. Its growth trajectory can be ascertained from its fossils, which occur across the globe from the Ordovician to the Devonian. These fossils document foraging activities of slender, cell-wide exploratory hyphae; when these hit a source of food, they produced secondary branches that grew back down the original filament, covered themselves with an envelope, and served as pipes to shuttle nutrients to other parts of the organism. Today, mycelium with this growth pattern is observed in the mushroom-forming fungi.
The Silurian-Devonian Terrestrial Revolution, also known as the Devonian Plant Explosion (DePE) and the Devonian explosion, was a period of rapid colonization, diversification and radiation of plants (embryophytes) and fungi on dry lands that occurred 428 to 359 million years ago (Mya) during the Silurian and Devonian periods, with the most critical phase occurring during the Late Silurian and Early Devonian.
