Conodont

From Wikipedia, the free encyclopedia

iConodonts
Fossil range: Late Cambrian to Late Triassic
A Conodont
A Conodont
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Conodonta
Groups

Protoconodonta
Paraconodonta
Euconodonta

The word conodont can mean:-

  • A type of extinct worm-like animal with distinctive conical or multi-denticulate teeth made of apatite (calcium phosphate).
  • The teeth of these animals, which are almost always the only parts preserved as fossils.

The second defininition is the most common one, but sometimes when it is necessary to speak of the animal itself, they are called conodontophora ("bearers of conodonts"), 'Conodonta', the "conodont animal", or simply conodonts.

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 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.

Prior to the discovery of complete specimens, it wasn't entirely clear that these fossils were in fact teeth. For this reason, in the literature they are commonly referred to as conodont "elements", leaving the function unspecified. While it is still not certain whether these organs functioned as teeth for chewing or filter feeding apparatus, the localization of the elements in the head of the animal has led to the widespread use of the term "teeth".

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 analysis by Donoghue et. al (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 darkens when heated. They are therefore used as a proxy for thermal alteration in the host rock. This feature has made them a useful tool for petroleum exploration. The Conodont Alteration Index (CAI) is a scale which correlates conodont color to maximum rock temperature at depth.

Teeth are of three forms: coniform (cones), ramiform (bars), and pectiniform (platforms).

[edit] External links

[edit] 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., 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.
  • Sweet, Walter. The Conodonta.
Retrieved from "http://en.wikipedia.org../../../c/o/n/Conodont.html"