Some major groups left the ocean and evolved further on land. Some members of those groups later returned to the ocean, such as mammals, reptiles, birds, and flowering plants. What could be the significance of this process?

The significance of this process is that those group that returned to the ocean, that is, mammals, reptiles, birds and flowering plants developed the adaptations to live on both land and in water. They can survive on both types of habitat because they have developed the adaptations to live on both. These animals were the first group of animals that survived both on land and in water during evolution.