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The Cambrian Period was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 55.6 million years from the end of the preceding Ediacaran Period 541 million years ago (mya) to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, and its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name of Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, our understanding of the Cambrian biology surpasses that of some later periods.
The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 million years ago (Mya) to the start of the Silurian Period 443.8 Mya.
Conodonts are extinct agnathan chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils found in isolation and now called conodont elements. Knowledge about soft tissues remains limited. The animals are also called Conodontophora to avoid ambiguity.
The Ordovician–Silurian extinction events, when combined, are the second-largest of the five major extinction events in Earth's history in terms of percentage of genera that became extinct. This event greatly affected marine communities, which caused the disappearance of one third of all brachiopod and bryozoan families, furthermore numerous groups of conodonts, trilobites, and graptolites. The Ordovician–Silurian extinction occurred during the Hirnantian stage of the Ordovician Period and the subsequent Rhuddanian stage of the Silurian Period. The last event is dated in the interval of 455 to 430 million years ago, lasting from the Middle Ordovician to Early Silurian, thus including the extinction period. This event was the first of the big five Phanerozoic events and was the first to significantly affect animal-based communities.
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.
The Dapingian is the third stage of the Ordovician and the first stage of the Middle Ordovician. It is preceded by the Floian and succeeded by the Darriwilian. The top of the Floian is defined as the first appearance of the conodont species Baltoniodus triangularis which happened about 470 million years ago. The Dapingian lasted for about 2.7 million years until about 467.3 million years ago.
The Whiterockian, often referred to simply as the Whiterock, is an earliest or lowermost stage of the Middle Ordovician. Although the Whiterockian or Whiterock Stage refers mainly to the early Middle Ordovician in North America, it is often used in the older literature in a global sense.
Nealeodus is a genus of conodonts which existed in what is now Canada during the middle Ordovician. It was described as a new genus for the species Lenodus martinpointensis by Svend Stouge in 2012.
Spinodus is a genus of conodonts. A new species, S. wardi, was described from the middle Ordovician of Canada by Svend Stouge in 2012.
Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2013.
Iapetognathus fluctivagus is a species of denticulate cordylodan conodonts belonging to the genus Iapetognathus. It existed during the Tremadocian Age of the Ordovician. It is an important index fossil in biostratigraphy.
Westergaardodina is a species-rich genus of spine, U or W-shaped paraconodont known from Middle Cambrian to Lower Ordovician strata.
The Beekmantown Group is a late Cambrian to lower–middle Ordovician geologic group that occurs in the northeastern United States, datable from its conodont fauna. It contains dolomitic sandstones and carbonates from just off land from the palaeocoastline.
Iapetognathus is a genus of cordylodan conodonts. It is one of the oldest denticulate euconodont genera known.
Erraticodon is an extinct genus of conodonts in the family Chirognathidae.
Furnishina is an extinct genus of conodonts in the family Furnishinidae from the Cambrian.
Variabiloconus is an extinct genus of conodonts.
Microzarkodina is an extinct genus of conodonts mainly from the Middle Ordovician of Baltoscandia. The Microzarkodina apparatus probably consisted of 15 or 17 elements: four P, two or four M and nine S elements. The S elements include different Sa, Sb1, Sb2, and Sc element types.
Histiodella is an extinct genus of conodonts.
References
- ↑ Dubinina, S. V., and A. V. Ryazantsev (2008), Conodont stratigraphy and correlation of the Ordovician volcanogenic and volcanogenic sedimentary sequences in the South Urals, Russ. J. Earth Sci., 10, ES5001, doi:10.2205/2008ES000302.
- ↑ The Base of the Middle Ordovician Series Using Graphic Correlation Method Svend Stouge, Wang Xiofeng, Li Zhihong, Chen Xiaohong, and Wang Chuanshang.
- ↑ Svend Stouge (2012). "Middle Ordovician (late Dapingian–Darriwilian) conodonts from the Cow Head Group and Lower Head Formation, western Newfoundland, Canada". Canadian Journal of Earth Sciences. 49 (1): 59–90. doi:10.1139/e11-057.
