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Conodonts

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Conodonts

Conodonts
Temporal range: 495–199.6Ma
Late Cambrian to Late Triassic
Reconstruction of a conodont
Two conodont "teeth" and a reconstruction of a conodont
Groups
  • Protoconodonta
  • Conodonta
    • Paraconodonta
    • Euconodonta
Synonyms
  • Conodontophorida

Conodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse. The animals are also called Conodontophora (conodont bearers) to avoid ambiguity.

Description

The eleven known fossil imprints of conodont animals depict an eel-like creature with 15 or, more rarely, 19 elements forming a bilaterally symmetrical array in the head. This array constituted a feeding apparatus radically different from the jaws of modern animals. There are three forms of teeth, coniform cones, ramiform bars, and pectiniform platforms, which may have performed different roles.

The organisms range from a centimeter or so[verification needed] to the giant Promissum, 40 cm in length.[1] It is now widely agreed that conodonts had large eyes, fins with fin rays, chevron-shaped muscles and a notochord.

The entire class of conodonts are postulated to have been wiped out in the Triassic–Jurassic extinction event, which occurred roughly 200 million years ago.[2]

Ecology

The "teeth" of some conodonts have been interpreted as filter-feeding apparatuses, filtering out plankton from the water and passing it down the throat. Others have been interpreted as a "grasping and crushing array".[1]

The lateral position of the eyes makes a predatory role unlikely.

The preserved musculature hints that some conodonts (Promissum at least) were efficient cruisers but incapable of bursts of speed.[1]

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.[3]

Milsom and Rigby envision them as vertebrates similar in appearance to modern hagfish and lampreys,[4] and phylogenetic analysis suggests that they are more derived than either of these groups.[5] This analysis, however, comes with one caveat: early forms of conodonts, the protoconodonts, appear to form a distinct clade from the later paraconodonts and euconodonts. It appears likely that the protoconodonts represent a stem group to the phylum containing chaetognath worms, indicating that they are not close relatives of true conodonts.[6] Moreover, some analyses do not regard conodonts as either vertebrates or craniates, because they lack the main characteristics of these groups.[7]

 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





Elements

For many years, conodonts were known only from enigmatic tooth-like microfossils, which occur commonly but not always in isolation, and were not associated with any other fossil. These phosphatic microfossils are now termed "conodont elements" to avoid confusion.

They are widely used in biostratigraphy.

Conodont elements are also used as paleothermometers, a proxy for thermal alteration in the host rock. This is 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.

It was not until early 1980s that the conodont teeth were found in association with fossils of the host organism, in a konservat lagerstätte.[10] This is because most of the conodont animal was soft-bodied, thus everything but the teeth were not suited for preservation under normal circumstances.

The conodont apparatus may comprise a number of discrete elements, including the spathognathiform, ozarkodiniform, trichonodelliform, neoprioniodiform, and other forms.[11]

See also

  • Lau event - mass extinction event with major impact on conodonts

Notes

References

Paleontology portal

Further reading

  • Gould, Stephen Jay (1985). "Reducing Riddles". In The Flamingo's Smile, 245-260. New York, W.W. Norton and Company. ISBN 0-393-30375-6.
  • Knell, Simon J. The Great Fossil Enigma: The Search for the Conodont Animal (Indiana University Press; 2012) 440 pages
  • Sweet, Walter. The Conodonta.

External links

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