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[Greek kōnos, cone + –ODONT.]
A group of extinct marine animals that are often abundant in strata of Late Cambrian to Late Triassic age, a time span of about 300 million years. Only the mineralized elements, which are usually 0.2 to 2 mm (0.008 to 0.08 in.) in dimension (the largest known reach 14 mm or 0.6 in.), are normally preserved. They are routinely extracted as isolated discrete specimens by chemical degradation of the rock in which they occur. In the earliest euconodonts (“true” conodonts, as opposed to the more primitive, and possibly unrelated, protoconodonts and paraconodonts), the elements comprise an upper crown and a basal body. The basal body occupies a cavity in the base of the crown, but is not present in the majority of post-Devonian species. In advanced conodonts the crown incorporates regular patches of opaque, finely crystalline, white matter.
For many years, conodont taxonomists treated individual element types as separate species. There are three major shape categories, coniform, ramiform, and pectiniform (see illustration). Coniform elements were dominant in the Cambrian to Early Ordovician and common until the Devonian. Ramiform (comblike) elements extend into elongate processes with various arrangements of denticles. Pentiniform elements include straight and arched blades, and may be expanded laterally to form a platform.
assemblage.">
Conodont elements: (a, b) coniform elements, (c, d) ramiform elements, (e, f) pectiniform blade elements, (g, h) pectiniform platform elements, (i) bedding-plane assemblage.
In the absence of preserved soft parts, the nature of the affinities of conodonts was the subject of considerable speculation and debate. Since the first discovery of isolated elements in 1856, conodonts have been variously aligned with algae, higher plants, several wormlike phyla, mollusks, arthropods, lophophorates, chaetognaths, and chordates, or have been assigned to a separate phylum, Conodonta. It was not until 1983 that evidence of the soft parts was described by D. E. G. Briggs, E. N. K. Clarkson, and R. J. Aldridge, on the basis of the first of several specimens discovered in lower Carboniferous rocks near Edinburgh, Scotland. The evidence of the soft-part morphology indicates that the conodonts belong within the chordates; it is no longer possible to justify their separation as a phylum, Conodonta. See also Chordata.
Although the biological affinities of conodonts and the function of the elements were essentially unknown until recently, they have nonetheless been extensively studied because of their important geological applications. Most significant of these is the use of conodont elements in biostratigraphy. See also Stratigraphy.
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The noun has 2 meanings:
Meaning #1:
tiny fossil cone-shaped tooth of the most primitive vertebrate: the conodont
Meaning #2:
small (2 in) extinct eellike fish with a finned tail and a notochord and having cone-shaped teeth containing cellular bone; late Cambrian to late Triassic; possible predecessor of the cyclostomes
| Conodonts Fossil range: Late Cambrian to Late Triassic |
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 Reconstruction of a Conodont
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Conodonts are extinct chordates that form the class Conodonta. For many years, conodonts were known only from enigmatic tooth-like microfossils, which despite their common occurrence were always found in isolation, and were not associated with any other fossil. These phosphatic microfossils, now termed conodont elements to avoid confusion (e.g. Zhuravlev 2007), are widely used in biostratigraphy; they are also used as paleothermometers, because phosphate undergoes a predictable series of color changes as it experiences higher temperatures. It was not until early 1980s that the conodont teeth were found in association with fossils of the host organism, in a konservat-lagerstätten.[1] This is because most of the conodont animal was soft-bodied, thus everything but the teeth were not suited for preservation under normal circumstances. A few exceptionally preserved fossils have revealed the full conodont animal; new discoveries have expanded the known body fossil record, and a more consistent impression of the animals has emerged.
Once thought to only exist on the millimetre scale, a well-preserved and unusually large genus, Promissum, was found in 1994.[2] It's now widely agreed that conodonts bore large eyes, fins with fin rays, chevron-shaped muscles and a notochord. The latter three are characteristic features of the phylum Chordata (ie., the vertebrates), leading to their current classification.[3] However, such a classification is far from secure: whilst Milsom and Rigby (2004) consider them to be vertebrates similar in appearance to modern hagfish and lampreys, an opinion supported by cladistic analysis carried out by Donoghue et al. (2000). This analysis, however, comes with one caveat: early forms of conodonts, the protoconodonts, appear to form a distinct clade from the later paracononts and euconodonts: most paleontologists[verification needed] (following Szaniawski)[citation needed] deem the protoconodonts to represent a stem group to the phylum containing chaetognath worms, indicating that they are not in fact close relatives of the true conodonts.
The eleven known fossil imprints of conodont animals, sometimes referred to as conodontophora, depict 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. The conodont animal is considered to have been a herbivore: despite their ferocious appearance, the "teeth" were probably used to filter out plankton and pass it down the throat.[citation needed] However, it's not impossible that some were used at biting teeth; the three forms (in the jargon, coniform cones, ramiform bars, and pectiniform platforms) of teeth may have performed different roles. The lateral position of the eyes makes a carnivorous role unlikely.
Because conodonts are phosphatic, they undergo a series of permanent and predictable color-changes when heated to different temperatures. 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 where they are known, in rocks dating from the Cambrian to the Late Triassic. The Conodont Alteration Index (CAI) is a scale which correlates conodont color to the maximum rock temperature attained at depth.
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more |
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| WordNet. WordNet 1.7.1 Copyright © 2001 by Princeton University. All rights reserved. Read more |
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| Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Conodont". Read more |
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