Reptiles: Turtle & Tortoise

Range: found in temperate and tropical regions of all oceans and all continents except Antarctica Habitat: aquatic species—oceans, swamps, freshwater lakes, ponds, and streams; terrestrial species—deserts, forests, and grasslands

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. So why the different names? Those common names usually refer to differences in where the species live and how they use their habitat. But the names are also used differently in other parts of the world. For instance, in Australia only sea turtles are called turtles–everything else is called a tortoise! But 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 aquatic 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. 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 legs 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 Indian word meaning "a little turtle.”

Turtle shell trivia

Turtles and tortoises have hard, protective shells that are made up of 59 to 61 bones covered by plates called scutes. Like your bones, a turtle’s shell is part of its skeleton. 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 up against the shell. They are known as "side-necked turtles.”

The leatherback turtle’s Dermochelys coriacea shell is a little different. It does not provide the bony, heavy protection of other turtle shells. Instead, as you might guess from its name, the leatherback turtle’s back is covered with a leathery skin supported by tiny bones. This adaptation allows the turtle to 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.

Turtle sense

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, keepers at the San Diego Zoo have found that the Galápagos tortoises Geochelone nigra really enjoy having their necks rubbed. They close their eyes in contentment, and will follow the keepers around wanting more!

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. No one knows how sea turtles find their way over that great distance, year after year, to the same beaches.

Nesting habits

All turtles and tortoises lay eggs, which they bury in soil, sand, or vegetation. Some species lay only a few oblong-shaped eggs, while others lay dozens to 100 or more round eggs. Once the eggs are laid, they are on their own. The mother does not incubate or care for her eggs or for the hatchlings when they emerge. Hatchlings have an egg tooth they use to break out of the shell, and some species have a yolk sac attached to their underside where they can absorb nutrients for the first few days. After that, they have to find food on their own. For many species, the temperature in the nest determines the sex of the hatchlings: warmer areas result in females, cooler areas result in males.

Dinnertime for turtles

Most turtles and tortoises are omnivores, so they will eat both plants and animal food of various kinds, like fish, snails, worms, or insects. Many are strictly herbivores, though, and only eat grasses, leafy plants, flowers, fruits, and even cactus. Some are specialists: the leatherback turtle and the hawksbill turtle Eretmochelys imbricata dine on jellyfish, even poisonous ones. Some turtles have broad, expanded jaws for crushing the shells of mollusks.

Turtles and tortoises don’t have teeth. Instead, their mouths have a hard, sharpened edge that they use to bite with, kind of like a bird’s beak. Some species, like map turtles Graptemys sp. and the river terrapin Batagur baska, also have a hard shelf, or secondary palate, in the upper jaw that helps them crush foods like snails or plant stems and fruits.

At the San Diego Zoo, our aquatic turtles are fed a variety of foods, including earthworms, minnows, goldfish, chopped mice, fruit, yams, and leafy greens. They are also given a special treat the keepers call Jell-O wigglers: a gelatin ball that contains pellets with vitamins and minerals. Our land tortoises are fed a variety of vegetables and leafy greens, along with occasional treats like hibiscus flowers, melons, cactus pads, and tomatoes. The Galápagos tortoises in particular seem to be attracted to anything red, and they love their tomatoes! If a tortoise needs medicine, the keepers often put it in a tomato because they are sure the tortoise will eat it.

What’s the future for turtles?

Sometimes people build roads, homes, and hotels at the edges of lakes, rivers, and seas where turtles come to lay their eggs. This can really confuse turtles and they may not lay eggs as a result. That means fewer baby turtles. Trash in the oceans, like fishing nets and lines and plastic bags, can entangle and kill sea turtles. Slow-moving tortoises are easily caught for food or "pets.” The Roti Island snake-necked turtle Chelodina mccordi has been heavily exploited by the pet trade and is now virtually extinct in the wild. The San Diego Zoo established a breeding group of these endangered turtles and partners with the Turtle Survival Alliance in Europe. In 2005, we hatched the first of several clutches of eggs at our reptile facility, producing 15 offspring.