Which characteristic defines the Paleozoic era?

Question

A. Reptiles became dominant after a mass extinction.
B. Animals with shells and hard parts were dominant for the first time.
C. Simple, one-celled life forms were dominant.
D. Mammals and other warm-blooded animals became dominant.

Answer 1

The characteristic that defines the Paleozoic era is:

B. Animals with shells and hard parts were dominant for the first time.

The Paleozoic era, which lasted from about 541 to 251 million years ago, saw significant developments in the evolution of life, including the appearance of the first hard-shelled organisms in the Cambrian period.