10 Facts About Turtles and Tortoises

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How Much Do You Know About Turtles and Tortoises?

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One of the four main families of reptiles—along with crocodiles, lizards and snakes, and tuataras—turtles and tortoises have been objects of human fascination for thousands of years. But how much do you really know about these poky, vaguely comical reptiles? Here are 10 essential facts about turtles and tortoises, ranging from how these vertebrates evolved to why it's unwise to keep them as pets.

02
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The Meaning of "Turtle" and "Tortoise" Depends on Where You Live

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Few things in the animal kingdom are more confusing than the difference between turtles and tortoises, for linguistic rather than anatomical reasons. Terrestrial (non-swimming) species should technically be referred to as tortoises, but residents of North America are just as likely to use the word "turtle" across the board; further complicating matters, in Great Britain, "turtle" refers exclusively to marine species, and never to tortoises. To avoid misunderstandings, most scientists and conservationists refer to turtles, tortoises and terrapins under the blanket name "chelonians" or "testudines" (and naturalists and biologists specializing in the study of these reptiles are known as "testudinologists.")

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Turtles Are Divided Into Two Major Families

A side-necked turtle. Getty Images

The vast majority of the 350 or so species of turtles and tortoises are "cryptodires," meaning these reptiles retract their heads straight back into their shells when threatened; the rest are "pleurodires," or side-necked turtles, which fold their necks to one side when retracting their heads. (There are other, more subtle anatomical differences between these two testudine suborders; for example, the shells of cryptodires are composed of 12 bony plates, while pleurodires have 13, and also have narrower vertebrae in their necks) Pleurodire turtles are restricted to the southern hemisphere, including Africa, South America and Australia, while cryptodires have a worldwide distribution and account for most familiar turtle and tortoise species.

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The Shells of Turtles Are Securely Attached to Their Bodies

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You can forget all those cartoons you saw as a kid in which a turtle jumps naked out of its shell, then dives back in when threatened. The fact is that the shell, or carapace, of a turtle is securely attached to its body; its inner layer is connected to the rest of the turtle's skeleton by various ribs and vertebrae. The shells of most turtles and tortoises are composed of "scutes," or hard layers of keratin (the same protein as in human fingernails); the exceptions are soft-shelled turtles and leatherbacks, the carapaces of which are covered with thick skin. Why did turtles and tortoises evolve shells in the first place? Clearly as a means of defense against predators; even a starving shark would think twice about breaking its teeth on the carapace of a Galapagos tortoise!

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Turtles Have Bird-Like Beaks--and No Teeth

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You might think turtles and birds are as different as any two animals can be, but in fact these two vertebrate families share an important trait in common: they're equipped with beaks, and they completely lack teeth. The beaks of meat-eating turtles are sharp and ridged, and can do serious damage to the hand of an unwary human, while the beaks of herbivorous turtles and tortoises have serrated edges ideal for cutting fibrous plants. Compared to other reptiles, the bites of turtles and tortoises are relatively weak; still, the alligator snapping turtle can chomp down on its prey with a force of over 300 pounds per square inch, about the same as an adult human male (let's keep things in perspective, though; the bite force of a saltwater crocodile measures over 4,000 pounds per square inch!)

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Some Turtles Can Live for Over 100 Years

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As a rule, slow-moving reptiles with cold-blooded metabolisms have longer life spans than comparably sized mammals or birds: even a relatively small box turtle can live for 30 or 40 years, and a Galapagos tortoise can easily hit the 200-year mark. If it manages to survive into adulthood (and most turtle babies never get the chance, since they're gobbled up by predators immediately after hatching), a turtle will be invulnerable to most predators thanks to its shell, and there are hints that the DNA of these reptiles undergoes more frequent repair and that their stem cells are more easily regenerated. It should come as no surprise that turtles and tortoises are avidly studied by gerontologists, who hope to isolate "miracle proteins" that can help extend the human life span.

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Most Turtles Don't Have Very Good Hearing

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Because their shells provide such a high degree of protection, turtles and tortoises haven't evolved the advanced auditory capabilities of, say, herd animals like wildebeest and antelopes. Most testudines, while on land, can only hear sounds above 60 decibels (for perspective, a human whisper registers at 20 decibels), although this figure is much better in the water, where sound conducts differently. The vision of turtles isn't much to brag about,either, but it gets the job done, allowing carnivorous testudines to track prey--and, also, some turtles are especially well adapted to seeing at night. Overall, the general intelligence level of testudines is low, though some species can be taught to navigate simple mazes and others have been shown to possess long-term memories.

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Turtles and Tortoises Lay Their Eggs in the Sand

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Depending on species, turtles and tortoises lay anywhere from 20 to 200 eggs at a time (one outlier is the eastern box tortoise, which lays only three to eight eggs). The female digs a hole in a patch of sand and soil, deposits her clutch of soft, leathery eggs, and then promptly ambles away. What happens next is the kind of thing producers tend to leave out of TV nature documentaries: nearby carnivores raid the turtle nests and devour most of the eggs before they've had a chance to hatch (for example, crows and raccoons eat about 90 percent of the eggs laid by snapping turtles). Once the eggs have hatched, the odds aren't much better, as immature turtles unprotected by hard shells are gobbled up like scaly hors d'oeuvres. Basically, all it takes is one or two hatchlings per clutch to survive in order to propagate the species--the others just wind up being part of the food chain!

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The Ultimate Ancestor of Turtles and Tortoises Lived During the Permian Period

Protostega, a giant turtle of the Cretaceous period. Wikimedia Commons

Turtles have a deep evolutionary history that extends to a few million years before the Mesozoic Era (better known as the Age of Dinosaurs). The earliest identified testudine ancestor is a foot-long lizard called Eunotosaurus, which lived in the swamps of Africa 260 million years ago and had wide, elongated ribs curving along its back, an adumbration of the shells of later turtles and tortoises. Other important "missing links" in testudine evolution include the late Triassic Pappochelys and the early Jurassic Odontochelys, a soft-shelled marine turtle that sported a full set of teeth. Over the ensuing tens of millions of years, the earth was home to a series of truly monstrous prehistoric turtles, including Archelon and Protostega, each of which weighed almost two tons!

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Turtles Don't Make Ideal Pets

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Turtles and tortoises may seem like the ideal "training pets" for kids (or for adults who don't have a lot of energy), but there are some very strong arguments against their adoption. First, given their unusually long life spans, testudines can be a long-term commitment; second, turtles need very specialized (and sometimes very expensive) care, especially as regards their cages and food and water supplies; and third, turtles are carriers of salmonella, serious cases of which can land you in the hospital and even endanger your life. (You don't necessarily have to handle a turtle to contract salmonella, as these bacteria can thrive on the surfaces of your home.) The general view of conservation organizations is that turtles and tortoises belong in the wild, not in your kid's bedroom!

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The Soviet Union Once Shot Two Tortoises Into Space

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It sounds like a series on the SyFy Channel, but Zond 5 was actually a spacecraft launched by the Soviet Union in 1968, carrying a payload of flies, worms, plants, and two presumably very disoriented tortoises. Zond 5 circled the moon once and returned to Earth, where it was discovered that the tortoises had lost 10 percent of their body weight but were otherwise healthy and active. What happened to the tortoises after their triumphant return isn't known—there are no records of a ticker-tape parade through the streets of Moscow—and given the long life spans of their breed, it's possible that they're still alive today. One likes to imagine them mutated by gamma rays, blown up to monster sizes, and spending their dotage in a post-Soviet research facility on the fringes of Vladivostok.