Conodont

Live reconstruction

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The conodonts ( Conodonta ( gr ) - " bevel gear " ) are an extinct group of chordates ( Chordata ) with exclusively marine representatives. Its characteristic fossil remains are object of study of micropaleontology and were described in 1856 by Christian Heinrich Pander first time scientifically.

The tooth-like hard parts of the head region of these animals, which together form the so-called conodont apparatus are known as fossils since 1850. But a report on the soft tissue anatomy of the Conodontentiere could be published only since 1983, after the corresponding fossil footprints were discovered in the South African Soom Shale and in Edinburgh. Although so far over 3000 Conodoten species have been described, and they thus represent the most diverse group of fossil chordates at all, the soft body of almost all of these species are still unknown. The oldest conodonts are from frühkambrischen, about 542 million years old sedimentary rocks. The latest can be found in the 200 million year old deposits of the upper Triassic.

Description

The conodonts or Conodontentiere were lancet-shaped open water dwellers. The body was laterally flattened and possessed an asymmetric tail fins to the body end. They were usually only a few centimeters long, the longest animals probably reached body lengths up to 40 millimeters. The body was moved to its entire length by a notochord. The body itself basically consisted of V-shaped muscle elements, the myomeres. The head was at the front end two large side-facing eyes and taking a hand Mundt judge who wore the conodont apparatus. The conodont apparatus was, the conodont elements made ​​of tooth-like structures.

The conodont apparatus of each animal consisted of various structures, which were individually anchored in the tissue. These tooth-like structures were mostly very small, they reached sizes of 0.1 to 2 millimeters and are therefore among the microfossils. They are constructed from fluorapatite with a relatively small proportion of calcium, this material was disposed of cells which stood these structures. The different shapes of the structures indicate different use in food intake.

Although the elements of the conodont apparatus externally and in terms of their chemical composition similarities with the teeth of the jaw animals, so the "higher" vertebrates have, they are these not homologous: the teeth of the jaw animals came out of the highly mineralized tooth-like scales original jawless fish indicate how they still occur in a modified form in sharks, while the Conodontentiere are built much more original and had no scales or similar external hard parts.

Importance

Stratigraphy

The very rapid shape change and thereby enabling high temporal resolution and the amount of discovered tiny conodont elements make them very important index fossils in stratigraphy. Based on the fossils a very delicate subdivision of the Paleozoic as well as parts of the Mesozoic was made because most species only for very short periods occurred in this earth Poche, due to their ( pelagic ) of life were widespread and their fossils occur in various sedimentary rocks ( Faziesunabhängigkeit ).

Commodity Geology

The conodont elements pointing inside an alternation of skeletal phosphate and organic matter. Due to high temperatures during diagenesis (sediment consolidation due to the applied load overlying rock layers ), there is a function of the depth of burial of coalification of organic matter and the original cream-colored elements blackens and are black at about 300 ° C. Even higher temperatures lead on different gray levels back to a lightening. At 700 ° C the elements are completely white and often transparent. On the temperature-dependent discoloration is due a seven- color scale, the so-called Conodont alteration index ( CAI), which is a measure of the thermal overprint and the degree of metamorphism of the rock. At high CAI values ​​were no hydrocarbons in the sediments for a certain period stable, they can not therefore be a reservoir rocks for petroleum. The discoloration of conodonts is therefore an important indicator in prospecting for oil and natural gas.

System

Although the conodont elements are very long known their systematic classification was achieved only through the first finds of soft-tissue fossils by studies of Clarkson in 1982 to 1925 collected in the district of Edinburgh samples of unterkarbonischen " Granton shrimp beds", the results of which he shared with other published in 1983. Up to this time the arrangement was very uncertain, mostly they were placed in the vicinity of the limbs worms ( Annelida ). The soft tissue findings confirm a classification in the early chordates. For a more than a hundred -year-long period of uncertainty was over.

It is discussed whether they (, Craniata vertebrates) are to be classified within the chordates kinship in the skull animals. Histological studies and the lack of gills, however, tend to support the assumption that it is stem lineage representatives of the skull animals.