Which characteristic defines the Paleozoic era?(1 point) Responses Simple, one-celled life forms were dominant. Simple, one-celled life forms were dominant. Reptiles became dominant after a mass extinction. Reptiles became dominant after a mass extinction. Animals with shells and hard parts were dominant for the first time. Animals with shells and hard parts were dominant for the first time. Mammals and other warm-blooded animals became dominant.

Answer 1

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