Vertebrates refer to animals which possess a backbone. Blooded refers to animals whose body temperatures are the same as the outside temperature. Most fish have scales and are cold-blooded. Most fish propel themselves through water with weaving movements and control direction with fins. Although some fish, such as sharks, bear live young, most fish eggs are fertilized and hatch in water.
Most amphibians deposit their eggs in water or a moist, protected place.
Reptiles are found in a variety of habitats in warm and temperate zones and range in size from 2-in. Nearly all lay porous, shelled eggs or bear their young on land. Reptiles evolved from amphibians and were the dominant fauna in the Mesozoic era, often called the Age of Reptiles.