In this topic you will learn why having a backbone has certain advantages.

Although vertebrates have very different characteristics, they all have a backbone which is part of the endoskeleton. An endoskeleton has two important jobs. It supports the body and protects the soft inner organs.

Vertebrates are divided into seven classes based on several characteristics. Vertebrates are also classified by how they control body temperature. Fish, amphibians, and reptiles are cold-blooded. A cold-blooded animal gets heat from outside its body and cannot control its body temperature. Its body temperature changes with the temperature of its surroundings. Birds and mammals are warm blooded. Their body temperature is constant. Their body temperature does not change much, because they use the energy from the food they eat to keep a constant body temperature.

All fish share several characteristics. They are cold-blooded vertebrates that live in fresh or salt water. They have streamlined bodies and gills for breathing.

Amphibians, such as frogs and toads, are cold blooded. They are vertebrates that spend part of their life in the water and part on land. Amphibians usually start out their life in the water.

Reptiles are cold-blooded animals with a backbone and an endoskeleton. Reptiles have skin with scales or plates. Turtles, lizards, snakes, alligators, and crocodiles are examples of reptiles.

Birds have several distinct characteristics. Birds have feathers. They have beaks without teeth and two legs with clawed feet. They are warm-blooded animals that lay eggs with strong shells.

A mammal is a warm-blooded vertebrate with fur or body hair. Mammals feed milk to their young, and all but a few mammals are complete when born, rather than hatching from an egg. Mammals live in almost every kind of habitat and move in almost every kind of way.

The backbone gives a vertebrate support and allows it to grow to a very large size. This explains why vertebrates are the largest animals on Earth.