Portal:Devonian

The Devonian Portal

A map of Earth as it appeared 390 million years ago during the Middle Devonian Epoch

The Devonian (/dəˈvoʊni.ən, dɛ-/ də-VOH-nee-ən, deh-) 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 419.62 million years ago (Ma), to the beginning of the succeeding Carboniferous period at 358.86 Ma. It is the fourth period of both the Paleozoic and the Phanerozoic. It is named after Devon, South West England, where rocks from this period were first studied.

The first significant evolutionary radiation of life on land occurred during the Devonian, as free-sporing land plants (pteridophytes) began to spread across dry land, forming extensive coal forests which covered the continents. By the middle of the Devonian, several groups of vascular plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants (pteridospermatophytes) appeared. This rapid evolution and colonization process, which had begun during the Silurian, is known as the Silurian-Devonian Terrestrial Revolution. The earliest land animals, predominantly arthropods such as myriapods, arachnids and hexapods, also became well-established early in this period, after beginning their colonization of land at least from the Ordovician Period.

Fishes, especially jawed fish, reached substantial diversity during this time, leading the Devonian to be called the Age of Fishes. The armored placoderms began dominating almost every known aquatic environment. In the oceans, cartilaginous fishes such as primitive sharks became more numerous than in the Silurian and Late Ordovician. Tetrapodomorphs, which include the ancestors of all four-limbed vertebrates (i.e. tetrapods), began diverging from freshwater lobe-finned fish as their more robust and muscled pectoral and pelvic fins gradually evolved into forelimbs and hindlimbs, though they were not fully established for life on land until the Late Carboniferous. (Full article...)

Refresh with new selections below (purge)

Selected Devonian Article

Montage of trilobite genera: Top row: Walliserops, Phacops and Cambropallas; bottom row: Isotelus, Kolihapeltis and Ceratarges

Trilobites (/ˈtraɪləˌbaɪts, ˈtrɪlə-/; meaning "three-lobed entities") are extinct marine arthropods that form the class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 22,000 species having been described. Because trilobites had wide diversity and an easily fossilized mineralised exoskeleton made of calcite, they left an extensive fossil record. The study of their fossils has facilitated important contributions to biostratigraphy, paleontology, evolutionary biology, and plate tectonics. Trilobites are placed within the clade Artiopoda, which includes many organisms that are morphologically similar to trilobites, but are largely unmineralised. The relationship of Artiopoda to other arthropods is uncertain.

Trilobites evolved into many ecological niches; some moved over the seabed as predators, scavengers, or filter feeders, and some swam, feeding on plankton. Some even crawled onto land. Most lifestyles expected of modern marine arthropods are seen in trilobites, with the possible exception of parasitism (where scientific debate continues). Some trilobites (particularly the family Olenidae) are even thought to have evolved a symbiotic relationship with sulfur-eating bacteria from which they derived food. The largest trilobites were more than 70 centimetres (28 in) long and may have weighed as much as 4.5 kilograms (9.9 lb).

The first appearance of trilobites in the fossil record defines the base of the Atdabanian/Cambrian Stage 3 time period of the Early Cambrian around 521 million years ago. Trilobites were already diverse and globally dispersed shortly after their origination, with trilobites reaching an apex of diversity during the late Cambrian–Ordovician, and remained diverse during the following Silurian and early Devonian. During the mid-late Devonian, their diversity strongly declined, being impacted by successive extinction events, including the Taghanic event, the Late Devonian mass extinction/Kellwasser event and the Hangenberg/end-Devonian mass extinction, wiping out most trilobite diversity and leaving Proetida as the only surviving order. Their diversity moderately recovered during the Early Carboniferous, before dropping to persistently low levels during the late Carboniferous and Permian periods, though they remained widespread until the end of their existence. The last trilobites disappeared in the end-Permian mass extinction event about 251.9 million years ago, by which time only a handful of species remained. (Full article...)

List of selected Devonian articles

Selected Devonian land plant article

Archaeopteris fossil leaves

The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the trimerophytes, and eventually gave rise to the spermatophytes, ancestral to both gymnosperms and angiosperms (flowering plants). They have been treated formally at the rank of division Progymnospermophyta or class Progymnospermopsida (as opposite). The stratigraphically oldest known examples belong to the Middle Devonian order the Aneurophytales, with forms such as Protopteridium, in which the vegetative organs consisted of relatively loose clusters of axes. Tetraxylopteris is another example of a genus lacking leaves. In more advanced aneurophytaleans such as Aneurophyton these vegetative organs started to look rather more like fronds, and eventually during Late Devonian times the aneurophytaleans are presumed to have given rise to the pteridosperm order, the Lyginopteridales. In Late Devonian times, another group of progymnosperms gave rise to the first really large trees known as Archaeopteris. The latest surviving group of progymnosperms is the Noeggerathiales, which persisted until the end of the Permian.

Other characteristics:

Vascular cambium with unlimited growth potential is present as well as xylem and phloem.
Ancestors of the earliest seed plants as well as the first true trees.

Strong monopodial growth is exhibited. (Full article...)

List of selected Devonian articles

Selected Devonian formation

Cut Bakken core samples

The Bakken Formation (/ˈbɑːkən/ BAH-kən) is a rock unit from the Late Devonian to Early Mississippian age occupying about 200,000 square miles (520,000 km²) of the subsurface of the Williston Basin, underlying parts of Montana, North Dakota, Saskatchewan and Manitoba. The formation was initially described by geologist J. W. Nordquist in 1953. The formation is entirely in the subsurface, and has no surface outcrop. It is named after Henry O. Bakken (1901–1982), a farmer in Tioga, North Dakota, who owned the land where the formation was initially discovered during oil drilling.

Besides the Bakken Formation being a widespread prolific source rock for oil when thermally mature, significant producible oil reserves exist within the rock unit itself. Oil was first discovered within the Bakken in 1951, but past efforts to produce it have faced technical difficulties.

In April 2008, a USGS report estimated the amount of recoverable oil using technology readily available at the end of 2007 within the Bakken Formation at 3.0 to 4.3 billion barrels (680,000,000 m³), with a mean of 3.65 billion. Simultaneously the state of North Dakota released a report with a lower estimate of 2.1 billion barrels (330,000,000 m³) of technically recoverable oil in the Bakken. Various other estimates place the total reserves, recoverable and non-recoverable with today's technology, at up to 24 billion barrels. A recent estimate places the figure at 18 billion barrels. In April 2013, the U.S. Geological Survey released a new figure for expected ultimate recovery of 7.4 billion barrels of oil. (Full article...)

List of selected Devonian formation articles

Selected Devonian fish article

Teeth of Platycephalichthys, in CosmoCaixa Barcelona

Tristichopterids (Tristichopteridae) were a diverse and successful group of fish-like tetrapodomorphs living throughout the Middle and Late Devonian. They first appeared in the Eifelian stage of the Middle Devonian. Within the group sizes ranged from a few tens of centimeters (Tristichopterus) to several meters (Hyneria and Eusthenodon).

Some tristichopterids share some of the features of the elpistostegalians, a diverse clade of tetrapodomorphs close to the origin of (and including) tetrapods.^{[better source needed]} This mainly concerns the shape of the skull and a reduction in size of the posterior fins.

An old and persistent notion is that Eusthenopteron was able to crawl onto land using its fins. However, there is no evidence actually supporting this idea. All tristichopterids had become extinct by the end of the Late Devonian. (Full article...)

List of selected Devonian fish articles

Selected Devonian invertebrate

Fossil specimen of Eurypterus remipes housed at the State Museum of Natural History Karlsruhe in Karlsruhe, Germany

Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 million years ago. The group is likely to have appeared first either during the Early Ordovician or Late Cambrian period. With approximately 250 species, the Eurypterida is the most diverse Paleozoic chelicerate order. Following their appearance during the Ordovician, eurypterids became major components of marine faunas during the Silurian, from which the majority of eurypterid species have been described. The Silurian genus Eurypterus accounts for more than 90% of all known eurypterid specimens. Though the group continued to diversify during the subsequent Devonian period, the eurypterids were heavily affected by the Late Devonian extinction event. They declined in numbers and diversity until becoming extinct during the Permian–Triassic extinction event (or sometime shortly before) 251.9 million years ago.

Although popularly called "sea scorpions", only the earliest eurypterids were marine; many later forms lived in brackish or fresh water, and they were not true scorpions. Some studies suggest that a dual respiratory system was present, which would have allowed for short periods of time in terrestrial environments. The name Eurypterida comes from Ancient Greek εὐρύς (eurús), meaning "wide, broad", and πτερόν (pterón), meaning "wing", referring to the pair of wide swimming appendages present in many members of the group.

The eurypterid order includes the largest known arthropods ever to have lived. The largest, Jaekelopterus, reached 2.5 meters (8.2 ft) in length. Eurypterids were not uniformly large and most species were less than 20 centimeters (8 in) long; the smallest eurypterid, Alkenopterus, was only 2.03 centimeters (0.80 in) long. Eurypterid fossils have been recovered from every continent. A majority of fossils are from fossil sites in North America and Europe because the group lived primarily in the waters around and within the ancient supercontinent of Euramerica. Only a handful of eurypterid groups spread beyond the confines of Euramerica and a few genera, such as Adelophthalmus and Pterygotus, achieved a cosmopolitan distribution with fossils being found worldwide. (Full article...)