ANIMALS HAVE DIVERSIFIED INTO MILLIONS OF DIFFERENT SPECIES
The evolution of animals, since their first appearance 600 million years ago, has resulted in an extraordinary number and diversity of lifeforms. As a result, animals have evolved many different forms as well as a multitude of ways of moving, obtaining food, and sensing their environment. Throughout the course of animal evolution, the numbers of animal groups and species have increased and, at times, decreased. Today, scientists estimate that there are more than 3 million living species.
Convention on Biological Diversity.