Conodont

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Conodonts
Temporal range: Cambrian to Late Triassic (Rhaetian)
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ConodontZICA.png
Reconstruction of a conodont
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Two conodont "teeth" and a reconstruction of a conodont
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Conodonta
Eichenberg 1930 [1]
Groups
Synonyms
  • Conodontophorida (otherwise an order according to Sepkoski, 2002 [2] )

Conodonts (Greek kōnos, "cone", + odont, "tooth") 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 (conodont bearers) to avoid ambiguity.

Contents

Conodonts are considered index fossils, fossils used to define and identify geological periods.

Geological history

The conodonts first appeared during the Cambrian Stage 2 (also referred as Tommotian). [3] The still unnamed Cambrian Stage 10 can be defined as the first appearance of Eoconodontus notchpeakensis . The upper boundary is defined as the appearance of Iapetognathus fluctivagus which marks the beginning of the Tremadocian and is radiometrically dated as 485.4 ± 1.9 million years ago.

The Cambrian–Ordovician extinction event occurred approximately 488 million years ago. This early Paleozoic extinction event extirpated many conodonts.

The Lau event, about 420 million years ago, a relatively minor mass extinction during the Silurian period, had a major impact on conodont populations.

The Kačák Event was a period of significant extinctions. The group most affected was the Ammonoidea, although there were also faunal turnovers amongst conodonts and dacryoconarids. [4]

The entire class is postulated to have been wiped out in the Triassic–Jurassic extinction event, which occurred roughly 200 million years ago. [5] Near the end of the Triassic deadly marine biocalcification began to occur, along with oceanic acidification, sea-level fluctuations and the Central Atlantic Magmatic Province (CAMP) releasing carbon dioxide, sulfur dioxide and aerosols. These environmental catastrophes caused the extinction of the conodonts, along with 34% of other marine genera. [6]

The last conodont species to appear, Neohindeodella detrei, existed at the very end of the Rhaetian. The youngest conodont specimen of this species was found in the earliest Hettangian of Hungary, when the final extinction of conodonts occurred.

Discovery and understanding of conodonts

Conodonts, that is, the teeth-like fossils, were first discovered by Heinz Christian Pander, the results published, in Saint Petersburg, Russia, in 1856. [7] The name pander is a common part, in scientific names of conodonts.

It was only in the early 1980s that the first fossil evidence was found of the rest of the animal (see below). In the 1990s exquisite fossils were found in South Africa in which the soft tissue had been converted to clay, preserving even muscle fibres. The presence of muscles for rotating the eyes showed definitively that the animals were primitive vertebrates. [8]

Description

Life restoration of Promissum pulchrum Promissum NT small.jpg
Life restoration of Promissum pulchrum

The 11 known fossil imprints of conodont animals record an eel-like creature with 15 or, more rarely, 19 elements that form a bilaterally symmetrical array in the head.

The organisms range from a centimeter or so[ verification needed ] to 40 cm ( Promissum ) in length. [9] It is now widely agreed[ by whom? ] that conodonts had large eyes, fins with fin rays, chevron-shaped muscles and a notochord.[ citation needed ]

Elements

Conodont elements from the Deer Valley Member of the Mauch Chunk Formation in Pennsylvania, Maryland, and West Virginia, USA

detail
Figures 1, 2. Conodonts from the Deer Valley Member of the Mauch Chunk Formation, Keystone quarry, Pa. This collection (93RS-79c) is from the lower 10 cm of the Deer Valley Member. Note the nonabraded, although slightly broken, conodont elements of the high-energy oolitic marine facies of the Deer Valley Member.
1. Kladognathus sp., Sa element, posterior view, X140 2. Cavusgnathus unicornis, gamma morphotype, Pa element, lateral view, X140
3-9. Conodonts from the uppermost Loyalhanna Limestone Member of the Mauch Chunk Formation, Keystone quarry, Pa. This collection (93RS-79b) is from the upper 10 cm of the Loyalhanna Member. Note the highly abraded and reworked aeolian forms.
3, 4. Kladognathus sp., Sa element, lateral views, X140
5. Cavusgnathus unicornis, alpha morphotype, Pa element, lateral view, X140
6, 7. Cavusgnathus sp., Pa element, lateral view, X140
8. Polygnathus sp., Pa element, upper view, reworked Late Devonian to Early Mississippian morphotype, X140
9. Gnathodus texanus?, Pa element, upper view, X140
10-14. Conodonts from the basal 20 cm of the Loyalhanna Limestone Member of the Mauch Chunk Formation, Keystone quarry, Pa. (93RS-79a), and Westernport, Md. (93RS-67), note the highly abraded and reworked aeolian forms
10. Polygnathus sp., Pa element, upper view, reworked Late Devonian to Early Mississippian morphotype, 93RS-79a, X140
11. Polygnathus sp., Pa element, upper view, reworked Late Devonian to Early Mississippian morphotype, 93RS-67, X140
12. Gnathodus sp., Pa element, upper view, reworked Late Devonian(?) through Mississippian morphotype, 93RS-67, X140
13. Kladognathus sp., M element, lateral views, 93RS-67, X140
14. Cavusgnathus sp., Pa element, lateral view, 93RS-67, X140 Conodonts.jpg
Conodont elements from the Deer Valley Member of the Mauch Chunk Formation in Pennsylvania, Maryland, and West Virginia, USA
detail
Figures 1, 2. Conodonts from the Deer Valley Member of the Mauch Chunk Formation, Keystone quarry, Pa. This collection (93RS–79c) is from the lower 10 cm of the Deer Valley Member. Note the nonabraded, although slightly broken, conodont elements of the high-energy oolitic marine facies of the Deer Valley Member.
1. Kladognathus sp., Sa element, posterior view, X140 2. Cavusgnathus unicornis, gamma morphotype, Pa element, lateral view, X140
3–9. Conodonts from the uppermost Loyalhanna Limestone Member of the Mauch Chunk Formation, Keystone quarry, Pa. This collection (93RS–79b) is from the upper 10 cm of the Loyalhanna Member. Note the highly abraded and reworked aeolian forms.
3, 4. Kladognathus sp., Sa element, lateral views, X140
5. Cavusgnathus unicornis, alpha morphotype, Pa element, lateral view, X140
6, 7. Cavusgnathus sp., Pa element, lateral view, X140
8. Polygnathus sp., Pa element, upper view, reworked Late Devonian to Early Mississippian morphotype, X140
9. Gnathodus texanus?, Pa element, upper view, X140
10–14. Conodonts from the basal 20 cm of the Loyalhanna Limestone Member of the Mauch Chunk Formation, Keystone quarry, Pa. (93RS–79a), and Westernport, Md. (93RS–67), note the highly abraded and reworked aeolian forms
10. Polygnathus sp., Pa element, upper view, reworked Late Devonian to Early Mississippian morphotype, 93RS–79a, X140
11. Polygnathus sp., Pa element, upper view, reworked Late Devonian to Early Mississippian morphotype, 93RS–67, X140
12. Gnathodus sp., Pa element, upper view, reworked Late Devonian(?) through Mississippian morphotype, 93RS–67, X140
13. Kladognathus sp., M element, lateral views, 93RS–67, X140
14. Cavusgnathus sp., Pa element, lateral view, 93RS–67, X140

Conodont teeth are the earliest found in the fossil record. [10] The evolution of mineralized tissues has been puzzling for more than a century. It has been hypothesized that the first mechanism of chordate tissue mineralization began either in the oral skeleton of conodont or the dermal skeleton of early agnathans.

The element array constituted a feeding apparatus that is radically different from the jaws of modern animals. They are now termed "conodont elements" to avoid confusion. The three forms of teeth, i.e., coniform cones, ramiform bars, and pectiniform platforms, probably performed different functions.

For many years, conodonts were known only from enigmatic tooth-like microfossils (200 micrometers to 5 millimeters in length [11] ), which occur commonly, but not always in isolation, and were not associated with any other fossil. Until the early 1980s, conodont teeth had not been found in association with fossils of the host organism, in a konservat lagerstätte. [12] This is because the conodont animal was soft-bodied, thus everything but the teeth was unsuited for preservation under normal circumstances.

These microfossils are made of hydroxylapatite (a phosphatic mineral). [13] The conodont elements can be extracted from rock using adequate solvents. [14] [15] [16]

They are widely used in biostratigraphy. Conodont elements are also used as paleothermometers, a proxy for thermal alteration in the host rock, because under higher temperatures, the phosphate undergoes predictable and permanent color changes, measured with the conodont alteration index. This has made them useful for petroleum exploration where they are known, in rocks dating from the Cambrian to the Late Triassic.

Multielement conodonts

Model of elements of Manticolepis subrecta - a conodont from the Upper Frasnian of Poland - photography taken in the Geological Museum of the Polish Geological Institute in Warsaw Manticolepis subrecta.jpg
Model of elements of Manticolepis subrecta - a conodont from the Upper Frasnian of Poland - photography taken in the Geological Museum of the Polish Geological Institute in Warsaw

The conodont apparatus may comprise a number of discrete elements, including the spathognathiform, ozarkodiniform, trichonodelliform, neoprioniodiform, and other forms. [17]

In the 1930s, the concept of conodont assemblages was described by Hermann Schmidt [18] and by Harold W. Scott in 1934. [19] [20] [21] [22]

Elements of ozarkodinids

The feeding apparatus of ozarkodinids is composed at the front of an axial Sa element, flanked by two groups of four close-set elongate Sb and Sc elements which were inclined obliquely inwards and forwards. Above these elements lay a pair of arched and inward pointing (makellate) M elements. Behind the S-M array lay transversely oriented and bilaterally opposed (pectiniform, i.e. comb-shaped) Pb and Pa elements. [23]

Ecology

The "teeth" of some conodonts have been interpreted as filter-feeding apparatuses, filtering plankton from the water and passing it down the throat.[ citation needed ] Others have been interpreted as a "grasping and crushing array". [9] The lateral position of the eyes makes it unlikely that conodonts were active predators.[ citation needed ] The preserved musculature suggests that some conodonts (Promissum at least) were efficient cruisers, but incapable of bursts of speed. [9]

A study on the population dynamics of Alternognathus has been published. Among other things, it demonstrates that at least this taxon had short lifespans lasting around a month. [24]

Classification and phylogeny

As of 2012, scientists classify the conodonts in the phylum Chordata on the basis of their fins with fin rays, chevron-shaped muscles and notochord. [25]

Milsom and Rigby envision them as vertebrates similar in appearance to modern hagfish and lampreys, [26] and phylogenetic analysis suggests they are more derived than either of these groups. [27] However, this analysis comes with one caveat: early forms of conodonts, the protoconodonts, appear to form a distinct clade from the later paraconodonts and euconodonts. Protoconodonts likely represent a stem group to the phylum that includes chaetognath worms; this conclusion suggests that chaetognaths are not close relatives of true conodonts. [28] Moreover, some analyses do not regard conodonts as either vertebrates or craniates, because they lack the main characteristics of these groups. [29]

  Craniata  

Hagfish [Note 1]

  Vertebrata  
  Hyperoartia  

Lampreys

Conodonta

Paraconodontida

Proconodontida [Note 2]

  Euconodonta [Note 3]  

Protopanderodontida

Panderontida

  Prioniodontida  

Paracordylodus

Balognathidae

Prioniodinida

Ozarkodinida

Heterostracans, osteostracans and gnathostomes

Taxonomy

Conodonta taxonomy based on Sweet & Donoghue [30] [32] , Mikko's Phylogeny Archive [33] and Fish classification 2017. [34]

ConodontaPander 1856 non Eichenberg 1930 sensu Sweet & Donoghue 2001 [Conodontia; Conodontophorida Eichenberg 1930; Conodontochordata]

See also

Notes

  1. Here, the hagfish are treated as a separate clade, as in Sweet and Donoghue's 2001 tree produced without cladistic analysis. [30] However, it has been recognised by some [31] that the hagfish and lampreys may be closer to one another in their own clade, the Cyclostomata.
  2. The clade Proconodontida is also known as Cavidonti.
  3. Euconodonta is referred to as "Conodonti" by Sweet and Donoghue, [30] although this is not widely used[ original research? ].

Related Research Articles

Chordate phylum of animals

A chordate is an animal of the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail: these five anatomical features define this phylum. Chordates are also bilaterally symmetric, and have a coelom, metameric segmentation, and circulatory system.

Agnatha Superclass of fishes

Agnatha is a superclass of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct species. The group is sister to all vertebrates with jaws, known as gnathostomes.

Ostracoderm class of fishes

Ostracoderms are the armored jawless fish of the Paleozoic. The term does not often appear in classifications today because it is paraphyletic or polyphyletic, and has no phylogenetic meaning. However, the term is still used as an informal way of loosely grouping together the armored jawless fishes.

<i>Promissum</i> Genus of Conodont

Promissum is an extinct genus of conodonts, primitive chordates, that lived during the Upper Ordovician period.

Philip Donoghue British paleontologist

Philip Conrad James Donoghue FRS is a British palaeontologist and Professor of Palaeobiology at the University of Bristol.

Richard John Aldridge was a British palaeontologist and academic, who was Bennett Professor of Geology at the University of Leicester.

Professor Mark Andrew Purnell is a British palaeontologist, Professor of Palaeobiology at the University of Leicester.

The Pander Society is an informal organisation founded in 1967 for the promotion of the study of conodont palaeontology. It publishes an annual newsletter. Although there are regular meetings of the Pander Society, at the Annual Meeting of the Geological Society of America, at European Conodont Symposia, and elsewhere, any meeting of three or more "Panderers" is considered an official meeting of the "Pander Society". The society is headed by the Chief Panderer, currently Maria Cristina Perri of the Università di Bologna. The society confers two awards, the Pander Medal for a lifetime of achievement in conodont palaeontology, and the Hinde Medal for an outstanding contribution to conodont palaeontology by a young Panderer.

Prioniodontida, also known as the "complex conodonts", is a large clade of conodonts that includes two major evolutionary grades; the Prioniodinina and the Ozarkodinina. It includes many of the more famous conodonts, such as the giant ordovician Promissum (Prioniodinina) from the Soom Shale and the Carboniferous specimens from the Granton Shrimp bed (Ozarkodinina). They are euconodonts, in that their elements are composed of two layers; the crown and the basal body, and are assumed to be a clade.

Maurits Lindström was a Swedish geologist and paleontologist. Lindströms initial work was divided among two topics conodont paleontology and the structural geology of the Scandinavian Caledonides in Lappland.

Proconodontida is an order of conodonts.

Ozarkodinida is an extinct conodont order. It is part of the clade Prioniodontida, also known as the "complex conodonts". There are two suborders of Ozarkodinida : Prioniodinina and Ozarkodinina.

Jerzy Dzik is a Polish paleontologist.

Proconodontus is an extinct genus of conodonts in the family Proconodontidae. The specimens are found in Cambrian formations.

Klaus Jürgen Müller was a German paleontologist.

Walter C. Sweet was an American paleontologist.

Stig M. Bergström is a Swedish-American paleontologist.

Gilbert Klapper is a paleontologist.

Protoconodonts are an extinct taxonomic group of conodonts or, possibly, 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.

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Further reading