Question

Which characteristic defines the Paleozoic era?(1 point)
Responses

Reptiles became dominant after a mass extinction.
Reptiles became dominant after a mass extinction.

Simple, one-celled life forms were dominant.
Simple, one-celled life forms were dominant.

Mammals and other warm-blooded animals became dominant.
Mammals and other warm-blooded animals became dominant.

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

Answer 1

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

(The Paleozoic begins with the Cambrian Explosion, when many animals developed shells and other hard parts.)