The end of the paleozoic era was signaled by

The correct answer for the question that is being presented above is this one: "B. mass extinction of land and sea animals." The end of the paleozoic era was signaled by mass extinction of land and sea animals.

Here are the following choices:

A. the development of humans

B. mass extinction of land and sea animals

C. the development of organisms with hard parts

D. both a and b