What Animals Were In The Ordovician Period

Online exhibits : Geologic time scale : Paleozoic Era

The Ordovician Period

The Ordovician Period lasted almost 45 1000000 years, beginning 488.three million years ago and ending 443.seven million years ago.* During this menstruation, the surface area north of the tropics was almost entirely bounding main, and well-nigh of the world's country was collected into the southern supercontinent Gondwana. Throughout the Ordovician, Gondwana shifted towards the South Pole and much of it was submerged underwater.

The Ordovician is best known for its diverse marine invertebrates, including graptolites, trilobites, brachiopods, and the conodonts (early vertebrates). A typical marine community consisted of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods. More than recently, tetrahedral spores that are similar to those of primitive land plants take been establish, suggesting that plants invaded the land at this time.

From the Lower to Middle Ordovician, the Earth experienced a milder climate — the conditions was warm and the atmosphere independent a lot of moisture. Even so, when Gondwana finally settled on the Southward Pole during the Upper Ordovician, massive glaciers formed, causing shallow seas to drain and bounding main levels to driblet. This probable acquired the mass extinctions that characterize the terminate of the Ordovician in which sixty% of all marine invertebrate genera and 25% of all families went extinct.

Life

Ordovician strata are characterized by numerous and diverse trilobites and conodonts (phosphatic fossils with a tooth-like advent) found in sequences of shale, limestone, dolostone, and sandstone. In improver, blastoids, bryozoans, corals, crinoids, also every bit many kinds of brachiopods, snails, clams, and cephalopods appeared for the offset time in the geologic record in tropical Ordovician environments. Remains of ostracoderms (jawless, armored fish) from Ordovician rocks comprise some of the oldest vertebrate fossils.

Despite the appearance of coral fossils during this time, reef ecosystems connected to exist dominated by algae and sponges, and in some cases by bryozoans. Yet, there apparently were too periods of consummate reef plummet due to global disturbances.

Ordovician sea

The major global patterns of life underwent tremendous change during the Ordovician. Shallow seas covering much of Gondwana became convenance grounds for new forms of trilobites. Many species of graptolites went extinct past the close of the menstruum, but the beginning planktonic graptolites appeared.

In the late Lower Ordovician, the diversity of conodonts decreased in the North Atlantic Realm, but new lineages appeared in other regions. Seven major conodont lineages went extinct, but were replaced by nine new lineages that resulted from a major evolutionary radiation. These lineages included many new and morphologically different taxa. Sea level transgression persisted causing the drowning of almost the entire Gondwana craton. By this fourth dimension, conodonts had reached their height development.

Although fragments of vertebrate bone and fifty-fifty some soft-bodied vertebrate relatives are at present known from the Cambrian, the Ordovician is marked by the advent of the oldest complete vertebrate fossils. These were jawless, armored fish informally called ostracoderms, but more correctly placed in the taxon Pteraspidomorphi. Typical Ordovician fish had large bony shields on the head, small, rod-shaped or platelike scales covering the tail, and a slitlike oral fissure at the anterior cease of the animal. Such fossils come up from nearshore marine strata of Ordovician historic period in Australia, Due south America, and western North America.

Maybe the most "groundbreaking" occurrence of the Ordovician was the colonization of the land. Remains of early terrestrial arthropods are known from this time, every bit are microfossils of the cells, cuticle, and spores of early state plants.

Stratigraphy

The Ordovician was named by the British geologist Charles Lapworth in 1879. He took the name from an ancient Celtic tribe, the Ordovices, renowned for its resistance to Roman domination. For decades, the epochs and series of the Ordovician each had a type location in Britain, where their feature faunas could be establish, but in recent years, the stratigraphy of the Ordovician has been completely reworked. Graptolites, extinct planktonic organisms, have been and still are used to correlate Ordovician strata.

Peculiarly good examples of Ordovician sequences are found in Mainland china (Yangtze Gorge area, Hubei Province), Western Australia (Emanuel Germination, Canning Basin), Argentina (La Chilca Germination, San Juan Province), the United States (Deport River Range, Utah), and Canada (Survey Peak Formation, Alberta). Ordovician rocks over much of these areas are typified by a considerable thickness of lime and other carbonate rocks that accumulated in shallow subtidal and intertidal environments. Quartzites are also present. Rocks formed from sediments deposited on the margins of Ordovician shelves are usually dark, organic-rich mudstones which bear the remains of graptolites and may have thin seams of iron sulfide.

Tectonics and paleoclimate

During the Ordovician, most of the globe's state — southern Europe, Africa, South America, Antarctica, and Australia — was nerveless together in the super-continent Gondwana. Throughout the Ordovician, Gondwana moved towards the South Pole where it finally came to residuum by the end of the period. In the Lower Ordovician, Northward America roughly straddled the equator and almost all of that continent lay underwater. By the Middle Ordovician North America had shed its seas and a tectonic highland, roughly corresponding to the later Appalachian Mountains, formed along the eastern margin of the continent. Also at this time, western and central Europe were separated and located in the southern tropics; Europe shifted towards Northward America from higher to lower latitudes.

During the Middle Ordovician, uplifts took place in most of the areas that had been under shallow shelf seas. These uplifts are seen as the precursor to glaciation. Also during the Middle Ordovician, latitudinal plate motions appear to have taken identify, including the due north drift of the Baltoscandian Plate (northern Europe). Increased sea floor spreading accompanied by volcanic activity occurred in the early Middle Ordovician. Body of water currents changed as a consequence of lateral continental plate motions causing the opening of the Atlantic Ocean. Ocean levels underwent regression and transgression globally. Because of bounding main level transgression, flooding of the Gondwana craton occurred as well as regional drowning which caused carbonate sedimentation to finish.

During the Upper Ordovician, a major glaciation centered in Africa occurred resulting in a severe drop in sea level which tuckered nearly all craton platforms. This glaciation contributed to ecological disruption and mass extinctions. About all conodonts disappeared in the Due north Atlantic Realm while only certain lineages became extinct in the Midcontinental Realm. Some trilobites, echinoderms, brachiopods, bryozoans, graptolites, and chitinozoans too became extinct. The Atlantic Bounding main airtight as Europe moved towards North America. Climatic fluctuations were farthermost as glaciation continued and became more than extensive. Cold climates with floating marine ice developed as the maximum glaciation was reached.

Localities

Canning Bowl, Commonwealth of australia: A dandy multifariousness of fossil gastropods has been uncovered in the Canning Basin.
Lake Winnipeg, Manitoba, Canada: The limestones of this region accept preserved many spectactular fossils of Ordovician macroalgae.

Resource

Detect out more about the Ordovician paleontology and geology of North America at the Paleontology Portal.
Run into the Wikipedia page on the Ordovician.

Source: https://ucmp.berkeley.edu/ordovician/ordovician.php

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