Question

which is a difference between the paleozoic and mesozoic era?
animals lived in the water during the mesozoic and on land in the paleozoic.
the first birds emerged in the paleozoic era while mammals first emerged in the mesozoic.
many different species of dinosaurs lived in the mesozoic, but they all died off in the paleozoic.
animal complexity increased during the paleozoic while the first flowering plants appeared in the mesozoic era.

Explanation:

During the Paleozoic era, there was an increase in animal complexity with the Cambrian - explosion and other evolutionary events. The first flowering plants (angiosperms) appeared during the Mesozoic era. Animals lived in water and on land in both eras. Birds first appeared in the Mesozoic, and mammals also had early forms in the Mesozoic. Dinosaurs lived in the Mesozoic and did not exist in the Paleozoic.

Answer:

Animal complexity increased during the Paleozoic while the first flowering plants appeared in the Mesozoic era.