GENERAL GEOLOGY

Detailed explanation-1: -The Cambrian Period saw the explosion of new kinds of invertebrate animals in the oceans, including trilobites (Figure 2), primitive kinds of shellfish, including brachiopods and molluscs, and other groups of invertebrates that failed to survive the end of this period.

Detailed explanation-2: -The Phanerozoic is divided into three eras: the Paleozoic (550 to 250 million years ago), the Mesozoic (250 to 65 million years ago), and the Cenozoic (65 million years ago to the present). The Paleozoic has been called the Age of Invertebrates because of the rapid development of invertebrate animals during that time.

Detailed explanation-3: -They were particularly abundant during Palaeozoic times (248–545 million years ago) and are often the most common fossils in rocks of that age.

Detailed explanation-4: -During the Paleozoic Era (541 to 251.9 million years ago), fish diversified and marine organisms were very abundant. In North America, the Paleozoic is characterized by multiple advances and retreats of shallow seas and repeated continental collisions that formed the Appalachian Mountains.

Detailed explanation-5: -Trilobites served to neatly bookend the Paleozoic, arising in the Lower Cambrian, some 521 million years ago, and lasting until the end of the Permian. But these amazing arthropods were far from the only creatures living in those ancient seas.