Turtles have been on earth for over 200 million years, since before the dinosaurs.   Turtles and tortoises are part of the same family, the Testudines.  There are about 335 species (kinds) of them existing today .

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Body

Turtles and tortoises are reptiles, the only ones to have a shell.  Their bodies are protected by a shell on top and underneath.  Their backbone, breastbone and ribs have become part of the shell, so they cannot remove their shells. The shell underneath is called a plastron, and the upper and under shells are joined by a piece called a bridge.  In some turtles the upper shell, or carapace, is not hard and is instead a very thick skin. They are known as soft-shelled turtles. The leatherback turtle is one of these.

The plastron ©Getty Images

The plastron ©Getty Images

 Like all other reptiles, turtles are cold blooded, which means their bodies are the same temperature as the surrounding air or water. They cannot remain active in cold weather. Most hibernate during winter, which means a kind of special sleep.  They are air-breathing animals.

Also like other reptiles, turtles shed their skin, usually in early spring. The shields, or scutes, of the shell lift and peel off, and skin from the head, neck, legs and tail flake off in pieces, to reveal new skin underneath.

Their heads have hard scales and they do not have teeth. Instead they have a beak with sharp edges for cutting food, and they have strong jaws.  Turtles and tortoises do not have ears on the outside. They don't need good hearing, and their senses of sight and smell are excellent.

Turtles pull their legs, tails and heads into the shell for protection.  Some turtles pull their necks into their shells in an 's' shaped curve, and others pull the neck sideways into their shell. The side-necked turtles are only found in the southern hemisphere.

Differences between Turtles and Tortoises

Aldabra giant tortoise ©Getty Images

Aldabra giant tortoise ©Getty Images

Tortoises live almost entirely on land.  They have stumpy legs. Most have a high dome-shaped shell. There are about 40 different kinds of tortoise. Some live in hot desert areas, others live in mountains or forests. When they hibernate, tortoises bury themselves in soil or under rotting plants. Some tortoises are very large. The largest is the Galapagos Tortoise, which grows to about one and a half metres long. It is found on the Galapagos Islands in the Pacific Ocean, and can live for about 200 years. One of the smallest tortoises is the African Speckled Tortoise which grows to about 10 cm long.

An Australian Murray River turtle

An Australian Murray River turtle

Freshwater turtles stay in the water most of the time, and sometimes come onto land. They have long legs and webbed feet with claws. They are found in rivers, streams and lakes.  Freshwater turtles generally hibernate deep in the warm mud in the bottom of a stream, pond or lake.  However, they can hibernate on land in mud or soil. Australia has only turtles, no tortoises. Read about freshwater turtles as pets. 

Sea turtles live in the warmer oceans. Their shells are flatter than those of other turtles and tortoises, which helps them glide through the water. Their legs have developed into flippers. They spend all their lives in the oceans.

Green sea turtle ©Getty Images

Green sea turtle ©Getty Images

There are seven different kinds of sea turtle:

Green sea turtle

One of the largest hard shell sea turtles, it grows to about 1.5 metres in length, weighing over 300kg. Can swim at speed of about 56 kph. There are two kinds: the Atlantic green turtles and the Eastern Pacific green turtles. There about 80 countries where green turtles nest.

Kemp's Ridley sea turtle hatchlings ©Getty Images

Kemp's Ridley sea turtle hatchlings ©Getty Images

Kemp's Ridley

Kemp's Ridley, the smallest and most endangered sea turtle. It has an oval, olive green shell and weighs about 50 kg. The shell is almost circular.  They live in areas where the sea bed is muddy or sandy, where they search for prey. They are found throughout the Gulf of Mexico, and the U.S Atlantic coasts of Florida to New England. Females come ashore in groups to nest and lay eggs.

Hawksbill

Hawksbill, a small beautifully patterned turtle weighing about 50-100 kg. The narrow head allows it to get food from cracks and small gaps in coral reefs, where they are commonly found, as well as rocky areas and estuaries. They are the most tropical of the sea turtles. Their shell is highly prized to make jewellery and hair ornaments, and this is their greatest threat.

Olive Ridley sea turtle ©Getty Images

Olive Ridley sea turtle ©Getty Images

Olive Ridley

Olive Ridley, weighing about 50 kg, with wide, heart-shaped shell that is olive green on top and greenish underneath. The carapace has no ridges and large scutes (scales). They are found in tropical and subtropical seas of Pacific, Indian and Atlantic Oceans, generally in coastal bays and river estuaries. Females come ashore in groups to nest and lay eggs. 

Leatherback sea turtle ©Getty Images

Leatherback sea turtle ©Getty Images

Leatherback

Leatherback, the largest of the sea turtles today. It has no shell, but instead has a leathery skin with raised stripes. It can reach about 300 cm in length and can weigh about 700 kg (the heaviest ever recorded was 916 kg). It is the largest living reptile, and the only one known to remain active in temperatures below 5ºC. They have delicate jaws and eat mostly jellyfish. They are found worldwide, the most wide-ranging of the sea turtles. 

Flatback sea turtle

Flatback, found only in Australian and Papua New Guinea waters. It has a flattish shell, and weighs about 100 kg. They are found in coastal reefs and grassy shallows.

Sea turtle eggs being laid in a sand nest. ©Getty Images

Sea turtle eggs being laid in a sand nest. ©Getty Images

Loggerhead

Loggerhead, weighing about 200 kg, with reddish-brown markings on their heart-shaped carapace. They are found along shallower parts of the Atlantic, Pacific and Indian Oceans. They have powerful jaws with which to crush the shellfish they eat, such as crabs, clams and mussels.

Life Cycle

Female turtles lay eggs after mating with a male.  She digs a hole on land and lays many eggs,  then covers the hole and leaves the eggs. When the eggs hatch, the tiny hatchlings dig to the surface and fend for themselves.  

Sea turtles return to the beach where they hatched to lay their eggs. The  hatchlings run to the sea and swim away. Birds and other predators wait for them to hatch and that run down the sand to the sea is a very dangerous trip for the tiny turtles. Once in the water, turtle hatchlings are still in danger of being eaten, but there are more places to hide.  Only 1% sea turtles reach adulthood.

Diet

Most turtles eat both plants and meat. Some kinds eat mostly plants, but other kinds eat mostly small animals. Sea turtles feed on jellyfish, seaweed, shrimp, crabs, algae and small molluscs. Tortoises are generally herbivores, eating plants.

Conservation Status and Threats

They have survived since before the time of the dinosaurs, but today almost half of the hundreds of species of turtles and tortoises are threatened and are therefore listed as Critically Endangered, Endangered or Vulnerable.

All sea turtles are protected because they are classified as Endangered or Critically Endangered.

Their numbers are reduced because of human activity, such as capturing or killing adults for food and their shells, taking eggs, the destruction and pollution of nesting beaches, ocean pollution and being caught up in fishing nets.

Critically Endangered western swamp tortoise ©Getty Images

Critically Endangered western swamp tortoise ©Getty Images

Other turtles and tortoises are classified individually. Some are not threatened but some are.

For example:

  • The Galapagos giant tortoise is listed as Vulnerable.
  • The western swamp tortoise, found only in a small area of Western Australia, is listed as Critically Endangered.
  • Habitat destruction and loss is one major threat.  Pollution, human activities such as fishing and boating also threaten turtle and tortoise populations.
©Getty Images

©Getty Images