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Vertebrate, animal with a backbone, or spinal column, made of interlocking units called vertebrae. This strong but flexible structure supports the body and anchors the limbs, and it also protects the nerves of the spinal cord. Vertebrates include fish, amphibians, and reptiles, as well as birds and mammals. In all vertebrates, the spinal column forms part of a complete internal skeleton. Unlike the hard external skeleton covering an insect, which is periodically shed as the insect grows, a vertebrate’s internal skeleton can grow gradually along with the rest of the body.

Vertebrates make up only about 2 percent of the animal species, and they belong to just 1 of more than 30 phyla, or overall groups, in the animal kingdom. Despite this, vertebrates occupy a dominant position in almost all habitats and are by far the most familiar animals. When asked to name an animal at random, most people identify a type of vertebrate.

There are several reasons why vertebrates are so successful and so noticeable. One has to do with their size. Invertebrates—that is, animals without backbones, such as worms, shellfish, and insects—tend to be small and slow moving. This is because they lack effective ways to support a large body and the muscles needed to power it. Vertebrates, on the other hand, have evolved a much more versatile support system. Their skeletons can be adapted for use in many different ways and work just as well in an animal weighing 4 tons as in one weighing 113 g (4 oz). As a result, vertebrates have been able to develop bigger, faster bodies than invertebrates.

Vertebrates also have highly developed nervous systems. With the help of specialized nerve fibers, they can react very quickly to changes in their surroundings, giving them a competitive edge.

See Types of Vertebrates