Minute toothlike fossil composed of the mineral apatite (calcium phosphate); conodonts are among the most frequently encountered fossils in marine sedimentary rocks of Paleozoic age. They are the remains of animals that lived 543–248 million years ago that are believed to have been small marine invertebrates living in the open oceans and coastal waters throughout the tropical and temperate zones.
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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. The animal is also called conodontophora (conodont bearers) to avoid ambiguity.
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.
They are considered by Milsom and Rigby to be vertebrates similar in appearance to modern hagfish and lampreys,Milsom, C. & Rigby, S (2004). Fossils at a Glance. Victoria, Australia: Blackwell Publishing, 155 pp. and phylogenetic analysis suggests that they are more derived than either of these groups.Donoghue, P.C.J.; Forey, P.L.; Aldridge, R.J. (2000). "Conodont affinity and chordate phylogeny". Biological Reviews 75 (02): 191–251. Retrieved on 2008-04-07. 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.
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. This is because most of the conodont animal was soft-bodied, thus everything but the teeth were not suited for preservation under normal circumstances.