Conodont

The word conodont can mean:-

A type of extinct worm-like animal with distinctive conical or multi-denticulate teeth made of apatite (calcium phosphate).
Their teeth, which nearly always are the only part preserved.

The animals are sometimes called conodontophora ("bearers of conodonts"), taking the word "conodont" to refer to the teeth, but the strictly correct name for the animal group is 'Conodonta'.

These tiny teeth are quite common in Paleozoic rocks and sands (250 to 500 million years old), but body fossils were not found until the early 1980s. A well-preserved and unusually large genus, Promissum, was found in 1994. The teeth (or more formally "elements") show complex specialized structures, and survived through the ages and the fossilization process due to their resilient phosphatic chemical composition; the teeth were probably used to filter out plankton and pass it down the throat.

Conodonts and their presumed relatives are known from the Cambrian to the Late Triassic. The earliest forms are identified as protoconodonts, followed by paraconodonts, followed by euconodonts (or "true conodonts").

Following the discovery of eleven body fossils in Scotland and South Africa, most paleontologists think conodonts (which turn out to have fins with fin rays, chevron-shaped muscles, a notochord, and eyes) are in the phylum Chordata. Conodonts are today generally thought to be chordates/vertebrates but debate exists. Milsom and Rigby (2004) consider them to be vertebrates similar in appearance to modern hagfish and lampreys. Most paleontologists (following Szaniawski) place the protoconodonts in a phylum along with the chaetognath worms, indicating that they are not close relatives of the true conodonts. Complete fossils of conodont animals are rare, but the eleven imprints that have been found show an eel-like creature with 15 or, more rarely, 19 elements forming a bilaterally symmetrical array in the head, comprising a feeding apparatus radically different from the jaws of modern animals.

Cladistic analyses by Donoghue et. al (1998, 2000) suggest that conodonts are vertebrates. The paraconodonts (known only from teeth) are thought to be related, but the relationship is unclear. According to Donoghue, protoconodonts are not related to the rest.

Conodont teeth are phosphatic and their colour changes with the temperature at burial (and are therefore used as a proxy for thermal alteration in the host rock). This feature has made them a useful tool for petroleum exploration. Teeth are of three forms: coniform (cones), ramiform (bars), and pectiniform (platforms).

External links

http://animaldiversity.ummz.umich.edu/site/accounts/information/Vertebrata.html
http://tolweb.org/tree?group=Euconodonta&contgroup=Vertebrate
http://www.palaeos.com/Vertebrates/Units/030Conodonta/030.000.html
http://geology.csusb.edu/faculty/wbl/cdont_art.htm
http://www.le.ac.uk/geology/map2/map2stuff/model.html
http://www.geocities.com/CapeCanaveral/Hall/1383/2TopCone.htm

References

Aldridge, R. J., Briggs, D. E. G., Smith, M. P., Clarkson, E. N. K. & Clark, N. D. L. (1993), The anatomy of conodonts. "Philosophical Transactions of the Royal Society of London, Series B", 340, 405-421.
Aldridge, R. J. & Purnell, M. A. (1996). The conodont controversies. "Trends in Ecology and Evolution", 11, 463-468.
Donoghue, P. C. J., Purnell, M. A., & Aldridge, R. J. (1998), Conodont anatomy, chordate phylogeny and vertebrate classification. Lethaia, 31, 211-219.
Donoghue, P. C. J., Forey, P. L. & Aldridge, R. J. (2000), Conodont affinity and chordate phylogeny. "Biological Reviews". 75, 191-251.
Milsom, C. & Rigby, S (2004). Fossils at a Glance. Victoria, Australia: Blackwell Publishing, 155 pp.

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