The family lived from the Lower Ordovician to the Devonian and have shells in which the apertural margins tend to flare.
These zones are identical with those found in the rocks of the same age in North Wales, the Bala series, and the terms Bala or Caradoc series are used indifferently by geologists when referring to the uppermost substage of the Ordovician System.
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It is the fifth of the six subdivisions (in ascending order) of the Ordovician System, comprising all those rocks deposited worldwide during the Caradocian Age (458 to 448 million years ago).
Remaining to do postgraduate research, he began work on the Ordovician of the Bala area and then the Silurian of Ludlow.
It was active as a normal fault during deposition of Late Ordovician to mid-Silurian sedimentary rocks, downthrowing to the northwest.
Fferam-uchaf shows small but stratigraphically important outcrops, but is an important site for an understanding of Lower Ordovician palaeogeography.
Arenig-Llanvirn (Ordovician) rocks exposed in inland outcrops, coastal cliffs
Just to the south of La Châtre, some twelve kilometres south of Vic, the Variscan-faulted rocks of the Massif Central begin with Cambrian/Ordovician migmatite.
This site is designated due to its geological quality: Robeston Wathen Quarries SSSI has one special feature: Caradoc - Ashgill (late Ordovician) sedimentary rocks in disused quarries
Frisco clover is known as a "narrow endemic" because it grows on a particular substrate: gravelly and bouldery volcanic soils, Ordovician limestone, and dolomite.
The Welsh Basin was a northeast-southwest aligned back-arc depositional basin during the Cambrian, Ordovician and Silurian periods during which a considerable thickness of marine sediments was laid down in the area.
However it turned out (Flower 1976) based on a reassessment of Lower Ordovician and Whiterockian formations in northeastern China that Polydesmia is predated by Wutinoceras, its assumed primitive nature rather a derived condition.
Allocotoceras is an endocerid from the Lower Ordovician (upper Canadian) of Australia (Tasmania), included in the Endoceratidae, based on small, straight or gently curved siphuncles.
This line is found in the Middle Ordovician Asery Level deposits of the Volkhov River region near Saint Petersburg, Russia.
The fossils of this species are found only in the middle Ordovician deposits of the Volkhov River region near Saint Petersburg, Russia.
Asteriacites are found in European and American rocks, from the Ordovician period onwards, and are especially numerous in the Jurassic system.
Bourgueticrinids first appeared in the fossil record during the Triassic period, although other crinoid groups, now extinct, originated in the Ordovician.
It was featured in the Ordovician section of the BBC series Sea Monsters (a spin-off to the successful Walking with Dinosaurs) as a nearly blind, feeble-eyed apex predator, and also had a brief cameo in Walking with Monsters, bobbing in the water.
Similar genus of trilobites occur in the Ordovician outcrops of the Volkhov River, near St. Petersburg, Russia.
In North America Clarkoceras is found in early Lower Ordovician, Gasconadian age shallow marine sediments near Smith Basin, State of New York, the Llano Uplift of Central Texas, and the El Paso Group of the eastern Rocky Mountains of Trans-Pecos Texas and Southern New Mexico.
It is known from the Lower Ordovician of Russia (Oeland series, Pavlovsk).
Discoceras has been found in Middle and Upper Ordovician sediments in Northern Europe, Baffin Island in Canada, Yunnan and Hubei provinces in China, and in Punjab, India.
described Geisonocerina among a suite of 12 nautiloid genera from the Ordovician of the Black Hills, South Dacota.
In the Ordovician, the Appalachian Mountains began to form and by the end of the Paleozoic were tall peaks.
Intejocerida is the name given to a group of generally straight shelled nautiloid cephalopods originally found in Lower and Middle Ordovician sediments in the Angara River basin in Russia; defined in the Treatise as an order, and combined there with the Endocerida in the Endoceratoidea.
Litoceras is a trocholitid (Tarphycerida) genus that has been found in the Lower and Middle Ordovician of Newfoundland.
The Ordovician meteor event is a proposed shower of L chondrite meteors that occurred during the Middle Ordovician period, roughly 470 million years ago.
Fossil traces in Ordovician limestone and 300-year-old giant trees, vestiges of the great eastern deciduous forest that once covered Tennessee, are important collections on the site, as are pioneer trees and seasonal wildflowers.
They discovered that the “Spirorbis” fossils found in sedimentary strata, including the Joggins and other Carboniferous coal measures, deposited from the Ordovician to Triassic periods are the remains of an extinct order of lophophorates (now called microconchids) unrelated to modern marine tube worms (Annelids) to which the genus Spirorbis belongs.
All the rocks of Red Screes are part of the Borrowdale Volcanic Group, formed on the margin of an ancient continent during a period of cataclysmic volcanic activity during the Caradoc Epoch of the Ordovician Era, roughly 450 million years ago.
They are highly regarded for their scenery, and also for the exposures of geological strata, which include Ordovician Tumblagooda sandstone, Triassic Wittecarra sandstone and Kockatea shale.
The type species for the genus, Similodonta similis, has been found in Late Ordovician, Ashgill epoch, sediments of the upper Richmond Group exposed near Spring Valley, Minnesota.
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Similodonta spjeldnaesi is a late Ordovician species found in and described from the Upper Chasmops Shale, Ringerike, Norway.
It is of geological interest because it provides outstanding exposures of five Cretaceous formations unconformably overlying the Ordovician Tumblagooda sandstone.
The Tremadocian, the first internationally-recognized stage of the Ordovician Period of the Paleozoic Era.