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Question

Fossil 'X' is older than fossil 'Y'. Identify the accurate answer for this from the options given below.

A
Fossil 'X' has got some of the vestigial organs which are functional in 'Y'
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B
Fossil 'Y' has got homologous and analogous organs of fossil 'X'
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C
Fossil 'X' is found in deeper sediments than 'Y'
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D
Fossil 'X' was found in better state than that of 'Y'
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Solution

The correct option is C Fossil 'X' is found in deeper sediments than 'Y'
Fossils are remains or traces of hard parts of ancient life-forms found in rocks preserved in the Earth’s crust. These include the whole body of the extinct organism, inorganic remains of plants and animals, remains of bones or even moulds, casts and footprints embedded in stratified rocks.

After its death, the body of the organism starts decomposing and decaying. Its starts to get covered with sediments which later form Rock layers. Fossils are usually found in sedimentary rocks.

Older fossils are found in deeper sediments whereas fossils which are comparatively new are present closer to the surface. The deeper the sedimentary layer or strata is, the older the fossil would be. This is because the inner or lower sedimentary layer was formed prior to the upper ones, perhaps many years ago. According to the question, fossil 'X' is older than fossil 'Y'. So fossil 'X' is found in a lower stratum of undisturbed sedimentary rocks than fossil 'Y'. Hence option c is correct.

Figure : Arrangement of fossils in the sedimentary rocks

The fossils which are newer should be actually in a better condition to be preserved than the ones which are older. This is because more degradation happens in fossils as they grow older. In this case fossil ‘X’ is older than fossil ‘Y’, so fossil 'Y' should be in a better state of preservation than fossil 'X'. Hence option d is incorrect.

Vestigial, homologous or analogous organs are studied in living organisms, it is difficult to study them in fossils. Hence option a and b are incorrect.

Analogous structures include those organs in different organisms that have different structures but apparently appear similar as they perform similar functions. Examples include fins of fishes and flippers of whales.

Figure : Fins of fishes and flippers of whales

Homologous organs are those organs which have the same fundamental structure and origin but look different and perform different functions. For example, forelimbs of whales, bats, cheetah and humans. Their forelimbs consist of humerus, radius, ulna, carpals, metacarpals and phalanges.

Figure : Homologous organs

Organs which are present in reduced form and do not perform any function in the body but correspond to fully developed functional organs of related animals are called vestigial organs.
For example, vermiform appendix in humans.

Figure : Vermiform appendix





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