There are over 2 million kinds of living organisms on Earth, and more are being discovered all the time. Scientists divide these things into groups. This book looks at the group of animals classified as vertebrates: fish, amphibians, reptiles, birds and mammals. Find out about the characteristics, life cycles, and habitats of each group of animals. Discover the ways in which vertebrates have adapted to survive. Learn how some animals are threatened with extinction and why we need to make sure that a diversity of animals are protected for the future. This title was previously published by Hodder Wayland as Classification: The Animal Kingdom. This edition has been simplified and updated.