There are four main groups of reptiles: turtles and tortoises; lizards and snakes; crocodiles and alligators; and the tuatara, the only species left from an ancient group of reptiles that goes back to the dinosaurs. Some reptiles spend most of their time in water, and many spend their time on land. Reptile species can be found in all types of habitats except polar ice and tundra.
Most reptiles make nests or dig holes to lay their eggs in. Some, like crocodiles and alligators and some species of snakes, then stay to guard the nest and even help the hatchlings get started in life. But most mother reptiles leave the nest once the eggs are laid. The hatchlings are independent from the start and must find their own food and shelter.