User:Abyssal/Portal:Devonian

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Introduction

Map of the Earth during the late Devonian, c. 370 Ma.

The Devonian (/dɪˈvoʊni.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 419.2 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 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. (Full article...)

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Selected article on the Devonian world and its legacies

Schinderhannes bartelsi is an anomalocarid known from one specimen from the lower Devonian Hunsrück Slates. Its discovery was astonishing because previously, anomalocaridids were known only from exceptionally well-preserved fossil beds (Lagerstätten) from the Cambrian, 100 million years earlier. Anomalocaridids, such as Anomalocaris, were organisms thought to be distantly related to the arthropods. These creatures looked quite unlike any organism living today—they had segmentedexoskeletons, with lateral lobes used for swimming, five large compound eyes, often set on stalks, and most strikingly, a pair of large, claw-like great appendages that resembled headless shrimp. These appendages are thought to have passed food to the animal's mouth, which resembled a ring of pineapple.(see more...)

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Did you know?

...that fossil Thelodont fish (depiction pictured) surprised scientists by showing that stomachs evolved before jaws?
... that the extinct bivalve subfamily Praenuculinae can be told apart from its sister subfamily by looking at teeth?
... that Arthropleuridea is an extinct class of myriapods which includes, at over 2 meters long, the largest terrestrial arthropods that ever lived?
...that ostracoderms are the earliest known vertebrate animals?

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Selected image

Unconformable base of Middle Devonian lacustrine Lower Stromness Flagstones over gently dipping Lower Devonian aeolian Yesnaby Sandstone, Yesnaby, Mainland, Orkney.
Photo credit: Mikenorton

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Selected article on the Devonian in human science, culture and economics

Marcellus Formation (also classified as the Marcellus Subgroup of the Hamilton Group, Marcellus Member of the Romney Formation, or simply the Marcellus Shale) is a unit of marine sedimentary rock found in eastern North America. Named for a distinctive outcrop near the village of Marcellus, New York, in the United States. The shale contains largely untapped natural gas reserves, and its proximity to the high-demand markets along the East Coast of the United States makes it an attractive target for energy development.

Stratigraphically, the Marcellus is the lowest unit of the Devonian age Hamilton Group, and is divided into several sub-units. Although black shale is the dominant lithology, it also contains lighter shales and interbedded limestone layers due to sea level variation during its deposition almost 400 million years ago. The black shale was deposited in relatively deep water devoid of oxygen, and is only sparsely fossiliferous. Most fossils are contained in the limestone members, and the fossil record in these layers provides important paleontological insights on faunal turnovers. The black shales also contain iron ore that was used in the early economic development of the region, and uranium and pyrite which are environmental hazards. The fissile shales are also easily eroded, presenting additional civil and environmental engineeringchallenges. (see more...)