Although most lizards walk on all fours, some use only their hind limbs when running. Some snakes and legless lizards move by attaching their belly scales to rough surfaces and pulling themselves forward. To help movement through the water, aquatic turtles have flippers or webbed feet and sea snakes are equipped with flattened tails. No modern reptile can fly, but certain tropical snakes and lizards have developed a means of flattening their bodies and gliding from tall trees. There were once about 16 orders in this class.
Turtles exist throughout the world except in the coldest climates.
The greatest abundance and variety of turtles are found in temperate regions. The more primitive pleurodirans are known as the side-necked turtles because they bend their neck sideways in order to bring it into the shell. Most turtles live in freshwater habitats, but many spend time on land, either traveling between bodies of water or hibernating. The females come ashore during warm months to lay eggs. The tortoises are strictly land dwelling, and many inhabit deserts or other arid environments.