The Six Basic Animal Groups

Invertebrates

• Are animals that neither possess nor develop by a vertebral column (or commonly known as the backbone). Example of this animals are insects, crabs, lobster, snails,and etc.

• Fish

     The first true vertebrates on earth, fish evolved from invertebrate ancestors about 500 million years ago, and have dominated the world’s oceans, lakes, and rivers ever since. There are three main types of fish: bony fish (which includes such familiar species as tuna and salmon); cartilaginous fish (which includes sharks, rays, and skates); and jawless fish (a small family made up entirely of hagfish and lampreys).

  

• Amphibians

  Amphibians are characterized by their semi-aquatic lifestyles (they have to stay near bodies of water, both to maintain the moisture of their skin and to lay their eggs), and today they are among the most endangered animals on earth.

  

• Reptiles
  • Reptiles, like amphibians, make up a fairly small proportion of terrestrial animals—but in the form of dinosaurs, they ruled the earth for over 150 million years. There are four basic types of reptiles: crocodiles and alligators, turtles and tortoises, snakes, and lizards. Reptiles are characterized by their cold-blooded metabolisms—they fuel themselves up by exposure to the sun—their scaly skin, and their leathery eggs, which, unlike amphibians, they can lay some distance away from bodies of water.
  • 
  • Reptiles
    • Reptiles, like amphibians, make up a fairly small proportion of terrestrial animals—but in the form of dinosaurs, they ruled the earth for over 150 million years. There are four basic types of reptiles: crocodiles and alligators, turtles and tortoises, snakes, and lizards. Reptiles are characterized by their cold-blooded metabolisms—they fuel themselves up by exposure to the sun—their scaly skin, and their leathery eggs, which, unlike amphibians, they can lay some distance away from bodies of water.
    • Birds evolved from dinosaurs—not once, but probably multiple times—during the Mesozoic Era, and today they are by far the most prolific flying vertebrates, numbering about 10,000 species spread across 30 separate orders. Birds are characterized by their coats of feathers, their warm-blooded metabolisms, their memorable songs (at least in certain species),
    • 
    •  

      Mammals

       

      • It’s natural for people to consider mammals the pinnacle of evolution–after all, humans are mammals, and so were our ancestors. (In fact, mammals are among the least diverse animal groups—there are only about 5,000 species overall!) Mammals are characterized by their hair or fur (which all species possess during some stage of their life cycles),