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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, which are usually found in isolation and are 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.
Agnatha is an infraphylum of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both living (cyclostomes) and extinct species. Among recent animals, cyclostomes are sister to all vertebrates with jaws, known as gnathostomes.
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.
The Conococheague Formation is a mapped Appalachian bedrock unit of Cambrian age, consisting primarily of limestone and dolomite. It occurs in central Maryland, southern and central Pennsylvania, the Valley and Ridge of Virginia and easternmost West Virginia.
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.
Proconodontida is an order of conodonts which originated in the late Cambrian (Furongian) and persisted partly through the Ordovician. The ancestral proconodont, Proconodontus, was one of the earliest euconodonts to appear. Proconodonts are often equated with the broader group Cavidonti, which occupies one side of a basal division in the evolution of early euconodonts in the Cambrian. All other euconodonts occupy Conodonti, the other side of the Cambrian split.
Paraconodonts (Paraconodontida) are an extinct order of probable chordates, closely related or ancestral to euconodonts. The order contains the superfamily Furnishinacea, itself containing the families Westergaardodinidae and Furnishinidae.
Furnishinidae is an extinct family of paraconodonts.
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.
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 group of Cambrian animals known from fossilized phosphatic tooth-like structures. They were originally described as an informal group of early conodonts, though more recent studies consider them to be more closely related to chaetognaths.
Protohertzina is a genus of conodonts or, possibly, Chaetognaths, found at the beginning of the Cambrian explosion.
References
- ↑ A suprageneric taxonomy of the conodonts. Maurits Lindström, Lethaia, October 1970, Volume 3, Issue 4, pages 427–445, doi : 10.1111/j.1502-3931.1970.tb00834.x
- ↑ Zona de Proconodontus tenuiserratus (Conodonta), Cambrico superior, Formación La Cruz, Mendoza, Argentina. S Heredia, Ameghiniana, 2013
- ↑ The early Cambrian Proconodontus Fossils in Akesu-Wushen area, Xinjiang, and their geologic significance. Y Sao, G Linzhi, Institute of Geology Chinese Academy of Geological Sciences, 1992
- ↑ Late Cambrian euconodonts from Sweden. Hubert Szaniawski and Stefan Bengtson, 1998, Proceedings of the Sixth European Conodont Symposium (ECOS VI), Palaeontologia Polonica 58, 7-29 (pdf, retrieved 2 June 2016)
