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Conodonts were animals of the chordate that disappeared in...

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Conodonts were animals of the chordate that disappeared in...  [#permalink]

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27 May 2017, 05:19
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based on 22 sessions

82% (03:12) correct 18% (01:02) wrong

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Conodonts were animals of the chordate that disappeared in the Triassic-Jurassic extinction event. The conodont animal, an eel-like creature that inhabited ancient seas and lakes, used to host from 15 to 19 conodont elements, phosphatic microfossils.

Conodont elements vary in shape, ranging in shape from cones, ramiform bars, pectiniform platforms, being although in size between less than one millimeter to a few millimeters. Their use is unclear, as they have been interpreted as a plankton filter-feeding apparatuses, or elements to crush and grasp, even if the lateral position of the condo's eyes make it unlikely that the animal was a predator.

Conodont elements are extremely important microfossils for their use as time markers, as their species evolved quite rapidly at certain times allowing to determine with good accuracy the relative age of sedimentary rock by virtue of their presence. They are widely used in biostratigraphy with applications ranging applied scientific research to petroleum exploration.

Conodont elements are also used as paleo thermometers, as they can be used to record the temperature of the hosting rock, with the conodont alteration index. A pale brown colour indicates that the conodonts have not been exposed to temperatures above 80° Celsius, while progressively darker colours are associated with higher temperatures; black conodonts are found in rock exposed to temperatures above 300°C, as the organic matter present in the conodont elements carbonises, while conodonts exposed to even higher temperatures lose all of the color and present themselves as light grey. The conodont alteration index is frequently used to estimate the maximum temperatures reached by sedimentary rocks throughout the palaeozoic, due to its ease of measurement and the abundance of conodont elements in marine carbonates.

Scientists were for a long time puzzled about the appearance of the conodont animal until a well preserved fossil was found in a Lagerstätte. Lagerstätte are sedimentary deposits that exhibit exceptionally well preserved fossils, especially fossil with soft tissues that are not decomposed, thanks to an anoxic environment with minimal presence of bacteria. This environment allowed for the preservation of a conodont animal of a size of a few dozen centimetres."

1. The author of the passage is primarily concerned to

A) provide a brief overview of the use of conodonts in biostratigraphy

B) explain what are a conodonts, their main characteristics and some of their applications in scientific research and industry

C) illustrate the causes of the disappearance of conodonts in the Triassic-Jurassic extinction event

D) provide a proof of the uncertain existence of the sedimentary deposits know as Lagerstätte

E) clarify the relationship between conodont colour and the paleo temperature or the rocks that bear them

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Re: Conodonts were animals of the chordate that disappeared in...  [#permalink]

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02 Oct 2018, 18:03

+1 kudos to the posts containing answer explanations of all questions

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Re: Conodonts were animals of the chordate that disappeared in...   [#permalink] 02 Oct 2018, 18:03
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