By the end of the period all major animal lineages were present in the seas due to a great adaptive radiation of animals

The correct answer to this open question is the following.

Although there are no options attached we can say the following.

The correct answer is the Cambrian period.

By the end of the Cambrian period, all major animal lineages were present in the seas due to the great adaptive radiation of animals.

We are talking about 500 to 540 million years ago on planet Earth.

Scientists consider that during the Cambrian period, major groups of animals diversified. Marine animals such as trilobites were among the first fossils discovered by scientists. Oxford curator Edward Luhyd started to study these fossils in 1668.