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Conodonts are an extinct group of jawless vertebrates, classified in the class Conodonta. They are primarily known from their hard, mineralised tooth-like structures called "conodont elements" that in life were present in the oral cavity and used to process food. Rare soft tissue remains suggest that they had elongate eel-like bodies with large eyes. Conodonts were a long-lasting group with over 300 million years of existence from the Cambrian to the beginning of the Jurassic. Conodont elements are highly distinctive to particular species and are widely used in biostratigraphy as indicative of particular periods of geological time.
The Early Ordovician is the first epoch of the Ordovician period, corresponding to the Lower Ordovician series of the Ordovician system. It began after the Age 10 of the Furongian epoch of the Cambrian and lasted from 485.4 ± 1.9 to 470 ± 1.4 million years ago, until the Dapingian age of the Middle Ordovician. It includes Tremadocian and Floian ages.
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.
Green Point is located 12 km north of the town of Rocky Harbour in Gros Morne National Park, on the west coast of Newfoundland. It is the home to a small summer fishing community and a drive-in campground. In 2000, Green Point was designated the Global Stratotype Section and Point (GSSP) representing the division between the Cambrian and the Ordovician systems.
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.
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 Collier Shale is a geologic formation in the Ouachita Mountains of Arkansas and Oklahoma. Dating from the Late Cambrian to Early Ordovician periods, the Collier Shale is the oldest stratigraphic unit exposed in Arkansas. First described in 1892, this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas. Purdue assigned the type locality to the headwaters of Collier Creek in Montgomery County, Arkansas, but did not designate a stratotype. As of 2017, a reference section for this unit has yet to be designated.
Iapetognathus is a genus of cordylodan conodonts. It is one of the oldest denticulate euconodont genera known.
Cordylodontidae is a family of conodonts.
Ozarkodina is an extinct genus of conodonts in the family Spathognathodontidae.
Stig M. Bergström is a Swedish-American paleontologist.
Appalachignathus is a genus of multielement conodonts from the Middle Ordovician of North America.
Raymond Lindsay Ethington is an American paleontologist. He works in the Geology department at the University of Missouri in Columbia, Missouri
Variabiloconus 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.
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.
The conodont feeding apparatus is a series of phosphatic-mineralized elements, resembling a set of "teeth", which are found lining the oral surface of the conodont animal.
Protopanderodontida is an order of conodonts which lived from the Furongian to the Wenlock (mid-Silurian). They had a relative simple apparatus with several pairs of coniform elements in the mouth, lacking the more elaborate arrangements found in "complex conodonts" (Prioniodontida).
References
- ↑ Iapetonudus (N. gen.) and Iapetognathus Landing, unusual Earliest Ordovician multielement conodont taxa and their utility for biostratigraphy. Robert S. Nicoll, J.F. Miller, G.S. Nowlan, J.E. Repetski, and Raymond L. Ethington, Brigham Young University Geology Studies, 1999, volume 44, pages 27–101
- ↑ Designation of holotypes for new species of Iapetonudus Nicoll, Miller, Nowlan, Repetski and Ethington and Iapetognathus Landing. Journal of Micropalaeontology, 1999, volume 18, page 124, doi:10.1144/jm.18.2.124
- ↑ Roger A. Cooper; Godfrey S. Nowlan; S. Henry Williams (2001). "Global Stratotype Section and Point for base of the Ordovician System" (PDF). Episodes. 24 (1): 19–28. doi: 10.18814/epiiugs/2001/v24i1/005 .
