Turtle, tortoise, and terrapin: what’s the difference?

Turtle, tortoise, and terrapin: what’s the difference?

Turtle, tortoise, and terrapin: what’s the difference? All turtles, tortoises, and terrapins are reptiles. Scientists often refer to them as chelonians, because they are in the taxonomic order called Chelonia (from the Greek word for tortoise). They all have scales, lay eggs, and are ectothermic; they vary in size from fitting in your hand to about 1,800 pounds (817 kilograms). Chelonians live everywhere from deserts to oceans to backyard creeks. So, why are there different names? Those common names usually refer to differences in where the reptiles live and how they use their habitat. Here are some generally accepted differences between the types of chelonians:

Turtle: Spends most of its life in the water. Turtles tend to have webbed feet for swimming. Sea turtles (Cheloniidae family) are especially adapted for an acquatic life, with long feet that form flippers and a streamlined body shape. They rarely leave the ocean, except when the females come ashore to lay their eggs, although some, such as the green sea turtle, do come out on reefs and beaches to bask. Other turtles live in fresh water, like ponds and lakes. They swim, but they also climb out onto banks, logs, or rocks to bask in the sun. In cold weather, they may burrow into the mud, where they go into torpor until spring brings warm weather again.

Tortoise: A land-dweller that eats low-growing shrubs, grasses, and even cactus. Tortoises do not have webbed feet; their feet are round and stumpy for walking on land. Tortoises that live in hot, dry habitats use their strong forelimbs to dig burrows. Then, when it’s too hot in the sun, they slip underground.

Terrapin: Spends its time both on land and in water, but it always lives near water, along rivers, ponds, and lakes. Terrapins are often found in brackish, swampy areas. The word “terrapin” comes from an Algonquian word for turtle.

Turtles and tortoises are a very old group of reptiles, going back about 220 million years. Of all wildlife with backbones, turtles are the only ones that also have a shell, made up of 59 to 61 bones covered by plates called scutes, which are made of keratin like our fingernails. The turtle cannot crawl out of it because the shell is permanently attached to the spine and the rib cage. The shell’s top is called the carapace, and the bottom is the plastron. Turtles can feel pressure and pain through their shells, just as you can feel pressure through your fingernails.

Some turtles can pull their heads, legs, and feet inside their shells; they are known as “hidden-necked turtles.” In order to make room inside the shell, they sometimes have to exhale air out of their lungs, which makes a hissing sound. Other turtles can’t pull their legs or heads into their shells. Some of these have long necks and protect their heads by tucking them sideways into the shell. They are known as “side-necked turtles.” Tortoise shells aren’t as heavy as you might think. The shell contains many tiny air chambers, which makes it a little lighter.

Leatherback sea turtles and softshell turtles have a rounded, flattened carapace, and the entire shell is covered with tough, leathery skin supported by tiny bones. The shell’s bone elements are reduced, making the shell flexible for swimming and diving. Leatherback turtles dive up to 3,000 feet (900 meters) below the ocean surface; at this depth, the incredible water pressure would crush a turtle with a heavy shell and less flexible body.

Turtles and tortoises do not have ears like ours, but they can feel vibrations and changes in water pressure that tell them where food, or a predator, might be. They do have a good sense of smell, which helps them find food. The skin of a turtle or tortoise, especially the land tortoises, may look leathery and tough, but it is actually very sensitive. In fact, wildlife care specialists at the San Diego Zoo have found that the Galápagos tortoises seem to enjoy having their necks rubbed.

Some turtles seem to have senses or instincts that we do not fully understand. Tracking equipment shows that some sea turtles migrate thousands of miles (kilometers) through the sea on regular routes, returning every two or three years to the same beaches to lay their eggs.

Aquatic turtles have some unique abilities that allow them to stay underwater. Some can pump water in and out of their mouth and throat, where the rich lining of blood vessels takes oxygen directly from the water. Some turtles can stay submerged for days at a time by moving water in and out of their cloaca to gain oxygen; they are know in Australia as “bum breathers.” Large, webbed, paddle-like feet allow aquatic turtles to push through the water with ease. The Fly River turtle is the only freshwater turtle with true flippers like those of ocean-dwelling turtles.