GEOLOGY

Detailed explanation-1: -Because they evolved rapidly, and moulted like other arthropods, trilobites serve as excellent index fossils, enabling geologists to date the age of the rocks in which they are found.

Detailed explanation-2: -trilobite, any member of a group of extinct fossil arthropods easily recognized by their distinctive three-lobed, three-segmented form. Trilobites, exclusively marine animals, first appeared at the beginning of the Cambrian Period, about 542 million years ago, when they dominated the seas.

Detailed explanation-3: -For instance, Bathyuriscus rotundatus is a trilobite index fossil used to date rocks from the Middle Cambrian (505 million years ago).

Detailed explanation-4: -Some of the most common index fossils are ammonites, trilobites, and graptolites.