在海里生活的不全是鱼类，还有不少哺乳动物，如鲸、海象、海狮、海豚等。那么，海里为什么会有哺乳动物呢？原来，在很久以前，这些哺乳动物的祖先是生活在陆地上的，后来随着生存环境的变化，它们从陆地上迁入了水中。当时的身体结构和模样都和现在有很大的不同，为了适应水 Lack of life in the sea is a fish, there are many mammals, such as whales, walrus, sea lions, dolphins and so on. So, why the sea mammals do? It turned out that a long time ago, the ancestors of these mammals lived on land, and later with the changing environment, they moved from the land into the water. At that time the body structure and appearance are now and very different, in order to adapt to the water