Trilobites are index fossils because they lived over large areas of the world.
Trilobites are index fossils because:
Trilobites are called index fossils and scientists use these fossils to infer the age of rock formations. The trilobite species Paradoxides is used as an example of this reconstruction, and its fossils have been found in eastern Canada, Sweden, Wales, the Czech Republic and Morocco.
Trilobites appeared quickly in the geologic time and then molted just like the other arthropods and thus are used as index fossils by scientist. Thus all the characteristics mentioned in are the reasons why trilobites are used as index fossils.
The correct answer is option B.
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