Exploring the animal family tree -- All animals alive on earth today are descended from a tiny, soft-bodied creature that lived in the sea over 600 million years ago. The descendants of this first animal have diversified and multiplied over millions of generations into a countless variety of species.
This simplified animal family tree (below) includes many of the more-recognizable animal groups (phyla), and it highlights several important events in animal evolution. The branch points represent single ancestral species that gave rise to multiple groups of descendants. The descendants share certain characteristics that were present in their common ancestor. Ancient traits that evolved near the base of the tree are shared by more animal phyla than are the traits that evolved closer to the tips of the branches.
Keep in mind that evolution is neither linear nor progressive. Look for traits that were lost in some groups, and traits that evolved more than once. Also note that even after hundreds of millions of years of evolution, many animals are still soft and squishy and live in the ocean.