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