The main characteristic that sets turtles and tortoises apart from other reptiles is their shell. It is made of bone fused to the skeleton, and covers both the back and belly. For extra protection, the shell is covered with thick, horny scales. If threatened, most turtles and tortoises are able to draw their heads and necks backwards into their shells.
Turtles and tortoises do not have teeth. Instead they have a sharp, horny, beak-like mouth. They are mostly plant-eaters, but some kinds also feed on insects, fish, snails and even small mammals and birds.
Tortoises are found on land. They have stumpy, scaly legs with short toes. Tortoises move slowly, relying on their high-domed, heavy shells to protect them from predator. Turtles live in the water, some in the oceans and others in freshwater rivers and ponds. Most have webbed feet, but some ocean turtles spend so much time in the water that they have developed paddle-like flippers that allow them to swim at speed.
All turtles and tortoises breed and lay eggs on land. Some large sea turtles can lay over 100 eggs at once, returning to the same beaches every year. They dig holes in the sand, lay their eggs and then cover them over. Then they return to the water. After hatching, the young must dig their way to the surface. Many newly-hatched turtles are killed by predators as they make their way from the beach to the sea.
Crocodilians are meat-eating reptiles that spend much of their time in water. They include crocodiles and alligators, and also the gharial, which has a long, narrow snout. Crocodilians use their long tails to swim, but can also run at speed on land. Most species live in freshwater rivers and lakes, especially tropical swamps. A few, such as the saltwater crocodile, live in sea estuaries.
Crocodilians feed on a wide range of prey, including fish, turtles, birds, and mammals. The largest crocodiles, which can grow to more than seven metres long, will even kill deer and cattle. They lie in the water, waiting for their prey to come down to the water to drink. Then they lunge out with their powerful jaws, dragging their prey into the water to drown.
Crocodilians can lie with their bodies almost completely hidden underwater, because their eyes and nostrils are on top of their heads. They also have a transparent “third eyelid” which closes to protect their eyes when they submerge. They can close off part of their throat to avoid swallowing water while feeding.
Like all reptiles, crocodiles and alligators lay their eggs on land. Some kinds, such as the Nile crocodile, dig holes into which they lay their eggs, covering them over with soil to keep them warm. Others build nests of plant material. They will guard their eggs and defend their young.
The tuatara is the only member of an ancient group of reptiles that lived on Earth even before the dinosaurs. Lizard-like in shape, the tuatara lives in burrows on small islands off New Zealand. It basks in the sun during the day, and feeds at night, hunting insects, worms and small lizards.
Like turtles and tortoises, the tuatara is very long-lived. It becomes an adult at 20 years old, and may live for over 120 years.
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