- CLASS: Reptilia (Reptiles)
- ORDER: Chelonia
- FAMILIES: 13, including Cheloniidae (sea turtles), Emydidae (pond and river turtles), and Testudinidae (tortoises)
- GENERA: 75
- SPECIES: 328 recognized modern species
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.
HABITAT AND DIET
Most turtles and tortoises are omnivores, eating plants and food of various kinds, like fish, snails, worms, and insects. Many are strictly herbivores and only eat grasses, leafy plants, flowers, fruits, and even cactus. Some are specialists: the leatherback turtle and the hawksbill turtle 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 types, like map turtles and the river terrapin, 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, aquatic turtles eat a variety of foods, including earthworms, minnows, goldfish, chopped mice, fruit, yams, and leafy greens. The land tortoises enjoy a variety of vegetables and leafy greens, along with occasional items 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!
All turtles and tortoises lay eggs, which they bury in soil, sand, or vegetation. Some lay only a few oblong-shaped eggs, while others lay dozens to 100 or more round eggs. Once the eggs are laid, any babies that hatch are on their own; the mother does not incubate or care for her eggs or for the hatchlings when they emerge (the one exception is the brown tortoise, which guards her nest from predators.) Hatchlings have an egg tooth they use to break out of the shell. After that, they have to find food on their own. For many turtles and tortoises, the temperature in the nest determines the sex of the hatchlings: warmer nests result in more females, cooler ones result in more males.
Once you see these amazing reptiles in action, we think you’ll agree that conservation efforts to save them are important so they will be around for many, many more years to come.
People and 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, of course, 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.” Chinese people eat enormous quantities of turtles; more than 10 million turtles are exported to China and 180 million Chinese softshell turtles are farm-raised each year for consumption in China.
All over the world, habitats are being destroyed or polluted. In the U.S., for example, the loss of streamside habitats everywhere is hurting turtle populations. Off-road vehicles in the desert are destroying desert tortoise habitats, and urban rain run-off is carrying trash and poison into lakes, streams, and creeks.
So what’s being done? Many governments as well as zoos and wildlife organizations are coming together to try to save the world’s turtles. Governments are also starting to work together to enforce turtle export laws and to police the markets in Asia where turtles are sold and traded.
The Roti Island snake-necked turtle has been heavily exploited by the pet trade and is now virtually extinct. 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.
The majority of the most critically endangered turtles in the world are found in Madagascar and Southeast Asia. San Diego Zoo Wildlife Alliance, the Turtle Survival Alliance, and the Wildlife Conservation Society have created a global conservation program for freshwater turtles and tortoises. We have conservation scientists currently guiding conservation programs for giant river turtles in Myanmar, Cambodia, and Malaysia, and doing conservation work for critically endangered turtles in Indonesia, Laos, and Vietnam. Significant progress toward saving of many of the 300 freshwater turtles and tortoises is on the horizon.
In our own backyard, we are working to save local southwestern pond turtles, San Diego’s only native freshwater turtle. Normally found in pools within natural streams and sloughs, pond turtles are becoming rare within coastal Southern California. Among the nonnative wildlife that compete with pond turtles for food, or might eat them, are green sunfish, American bullfrogs, African clawed frogs, red-eared sliders, and crayfish.
San Diego Zoo Wildlife Alliance, U.S. Geological Survey, San Diego Association of Governments, and the California Department of Fish and Game kicked off a joint project in 2009 to help this reptile. As a part of this study, scientists brought female turtles from the Sycuan Peak Ecological Reserve to the Zoo in 2009 and 2010. The females laid their eggs at the Zoo and then were returned to the reserve. Ten of the eggs hatched. After nonnative predators were removed, five of the juveniles were reintroduced into the Reserve in July 2013. We also have 12 pond turtles living in our Elephant Odyssey habitat at the Zoo that are not part of this study but are serving as educational ambassadors for this project and for turtles.
We hope that learning about turtles inspires you to help conserve wildlife in your own backyard by not releasing unwanted pet turtles, like red-eared sliders, and helping to keep local watersheds clean. We encourage you to join local volunteer organizations that help restore local watersheds by removing exotic plants and trash.