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Conodonts are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements found in isolation and now called conodont elements. Knowledge about soft tissues remains limited. They existed in the world's oceans for over 300 million years, from the Cambrian to the beginning of the Jurassic. Conodont elements are widely used as index fossils, fossils used to define and identify geological periods. The animals are also called Conodontophora to avoid ambiguity.
The Tremadocian is the lowest stage of Ordovician. Together with the later Floian Stage it forms the Lower Ordovician Epoch. The Tremadocian lasted from 485.4 to 477.7 million years ago. The base of the Tremadocian is defined as the first appearance of the conodont species Iapetognathus fluctivagus at the Global Boundary Stratotype Section and Point (GSSP) section on Newfoundland.
The Furongian is the fourth and final epoch and series of the Cambrian. It lasted from 497 to 485.4 million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three stages: the Paibian, Jiangshanian and the unnamed 10th stage of the Cambrian.
Stage 10 of the Cambrian is the still unnamed third and final stage of the Furongian series. It follows the Jiangshanian and precedes the Ordovician Tremadocian Stage. The proposed lower boundary is the first appearance of the trilobite Lotagnostus americanus around 489.5 million years ago, but other fossils are also being discussed. The upper boundary is defined as the appearance of the conodont Iapetognathus fluctivagus which marks the beginning of the Tremadocian and is radiometrically dated as 485.4 million years ago.
Westergaardodina is a species-rich genus of spine, U or W-shaped paraconodont known from Middle Cambrian to Lower Ordovician strata.
Iapetognathus is a genus of cordylodan conodonts. It is one of the oldest denticulate euconodont genera known.
Cordylodontidae is a family of conodonts.
Palmatolepis is an extinct conodont genus in the family Palmatolepidae. It was the most abundant genus of conodonts of the Late Devonian, disappearing during the Devonian/Carboniferous crisis.
Furnishinidae is an extinct family of conodonts in the order Paraconodontida.
Proconodontus is an extinct genus of conodonts in the family Proconodontidae. The specimens are found in Cambrian formations.
Gapparodus is an extinct genus of conodonts in the family Furnishinidae. Gapparodus gapparites is a species of the Early Cambrian of Shuijingtuo Formation in China.
William Madison Furnish was an American paleontologist. He taught at the University of Iowa.
Acanthodus is an extinct genus of conodonts.
Kallidontus is an extinct genus of conodonts.
Utahconus is an extinct genus of conodonts.
Variabiloconus is an extinct genus of conodonts.
Eoconodontus is an extinct genus of conodonts of the Late Cambrian. It is a two-elements genus from the Proconodontus lineage.
Protoconodonts are an extinct taxonomic group of conodonts or, possibly, Chaetognaths.
Protohertzina is a genus of conodonts or, possibly, Chaetognaths, found at the beginning of the Cambrian explosion.
The Minaret Formation is a Late Cambrian limestone formation of the Heritage Group of Antarctica. The age of the formation is established to be Guzhangian to Cambrian Stage 10, dated at ranging from 500 to 488 Ma.
References
- ↑ Kambrische Conodonten. Klaus J. Müller, Zeitschrift der Deutschen Geologischen Gesellschaft Band 111 (1959), pages 434-485
- ↑ Upper Furongian (Cambrian) conodonts from the Degerhamn quarry road section, southern Öland, Sweden. Bagnoli, G.; Stouge, S. 2014: GFF, doi:10.1080/11035897.2013.858768
- ↑ Middle Cambrian (Upper Series 3) protoconodonts and paraconodonts from the Machari Formation at Eodungol Section, Yeongwol, Korea. Byung-Su Lee (2013), Journal of Earth Science 24 (2), pages 157–169, doi:10.1007/s12583-013-0318-1
