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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.
In the geologic timescale, the Aeronian is the age of the Llandovery epoch of the Silurian period of the Paleozoic era of the Phanerozoic eon that began 440.8 ± 1.2 Ma and ended 438.5 ± 1.1 Ma. The Aeronian age succeeds the Rhuddanian age and precedes the Telychian age, all in the same epoch.
Dob's Linn is a small steep valley in Dumfries and Galloway, just north of the A708 road between Moffat and Selkirk, in Scotland. It is part of the Grey Mare's Tail Nature Reserve which is owned by the National Trust for Scotland. According to tradition, Dob's Linn is named for a covenanter, Halbert Dobson, who took refuge there from Government troops during The Killing Time in the late 17th century.
The Cefn-cerig road, a road near Cefn-cerig Farm, Llandovery, Wales, is the location of the Global Boundary Stratotype Section and Point (GSSP) which marks the boundary between the Aeronian and Telychian stages of the Silurian period on the geologic time scale. The GSSP was ratified in 1984.
In the geologic timescale, the Telychian is the age of the Llandovery epoch of the Silurian period of the Paleozoic era of the Phanerozoic eon that is comprehended between 438.5 ± 1.2 Ma and 433.4 ± 0.8 Ma, approximately. The Telychian age succeeds the Aeronian age and precedes the Sheinwoodian age.
In the geological timescale, the Llandovery epoch occurred at the beginning of the Silurian period. The Llandoverian epoch follows the massive Ordovician-Silurian extinction events, which led to a large decrease in biodiversity and an opening up of ecosystems.
Wills Creek Formation is a mapped Silurian bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia.
The Ireviken event was the first of three relatively minor extinction events during the Silurian period. It occurred at the Llandovery/Wenlock boundary. The event is best recorded at Ireviken, Gotland, where over 50% of trilobite species became extinct; 80% of the global conodont species also become extinct in this interval.
Richard John Aldridge was a British palaeontologist and academic, who was Bennett Professor of Geology at the University of Leicester.
Nerepisacanthus is an extinct genus of acanthodian, probably acritolepid, from Middle Silurian deposits of New Brunswick, Canada. Nerepisacanthus is known from many incomplete but articulated specimens. It was collected from the Cunningham Creek Formation, near Nerepis, southern New Brunswick. It was first named by Carole J. Burrow in 2011 and the type species is Nerepisacanthus denisoni.
A bioevent or bio-event is an event recognised in a sequence of sedimentary rocks, where there is a significant change in the biota as recorded by assemblages of fossils over a relatively short period of time. It has been defined as "short-term locally, regionally, or interregionally pervasive changes in the ecological, biogeographical, and/or evolutionary character of biotas that are isochronous or nearly so throughout their range". Bioevents either relate to diversification of a particular fossil group or a reduction, these may equate to speciation events or extinction events, or may only represent migration. Records of the appearance and disappearance of particular taxa at a single locality are insufficient to define a bioevent.
The Beaverfoot Formation is a stratigraphic unit of Late Ordovician to Early Silurian (Llandovery) age. It is present on the western edge of the Western Canada Sedimentary Basin in the Rocky Mountains of British Columbia and Alberta, and the Purcell Mountains of British Columbia. It consists of carbonate rocks, and was named for the Beaverfoot Range at Pedley Pass southeast of Golden, British Columbia by L.D. Burling in 1922.
Wurmiella is an extinct conodont genus.
Spathognathodontidae is an extinct conodont family ranging from the Silurian to the Devonian.
Ozarkodina is an extinct genus of conodonts in the family Spathognathodontidae.
Balognathidae is an extinct conodont family.
Anticostiodus is an extinct genus of multielement conodonts. Specimens have been described from the Lower Silurian of Gun River Formation of Anticosti Island, Quebec. Two species are included under the genus, Anticostiodus fahraeusi and Anticostiodus boltoni. Both species occur near the base of the Distomodus staurognathoides zone and in an open subtidal environment.
Distomodus is an extinct genus of conodonts.
Conodonts are an extinct class of animals whose feeding apparatuses called teeth or elements are common microfossils found in strata dating from the Stage 10 of the Furongian, the fourth and final series of the Cambrian, to the Rhaetian stage of the Late Triassic. These elements can be used alternatively to or in correlation with other types of fossils in the subfield of the stratigraphy named biostratigraphy.
The Waukesha Biota refers to the biotic assemblage of the Konservat-Lagerstätte of Early Silurian age within the Brandon Bridge Formation in Waukesha County and Franklin, Milwaukee County, Wisconsin. It is known for the exceptional preservation of its diverse, soft-bodied and lightly skeletonized taxa, including many major taxa found nowhere else in strata of similar age.
References
- ↑ Conodonten des Silurs. Otto H. Walliser, Hessisches Landesamt für Bodenforschung, 1964 - 106 pages
- ↑ An updated Telychian (Late Llandovery, Silurian) conodont zonation based on Baltic faunas. Peep Männik, Lethaia, Volume 40, Issue 1, pages 45–60, March 2007, doi : 10.1111/j.1502-3931.2006.00005.x
