Turtles are very versatile reptiles, living on both land and in water and in various environments. There are turtles that live in deserts, and there are even turtles that live in cold-weather areas, hibernating to survive the winter. Although there are many kinds of turtles, they all go through the basic reptile life cycle---egg, hatchling and adult.
Turtles are aquatic reptiles while tortoises live on dry land. Sometimes people use the term terrapin to mean either turtle or tortoise, but the terrapin is actually a turtle that lives in brackish water instead of fresh water or the ocean like other turtles. All these creatures have shells, or carapaces, and retractable heads, legs and tails, though the extent to which they can pull their bodies into their shells varies by species. Some turtles can even snap the shell shut to make it harder for predators to attack them.
Though some sea turtles lay their eggs underwater or on beds of moss, most female turtles dig holes in sand or mud and deposit their eggs in clutches made up of one to 100 eggs, then bury them. Unlike the Asian giant tortoise, mother turtles do not remain near their eggs to protect them. The egg shell is pliable but leathery and requires the hatchling to use an "egg tooth" to break through when it has developed enough to emerge, usually in two to three months.
In some species of turtle, temperature determines the gender of hatchlings. In warmer temperatures, females emerge, while in cooler temperatures, males emerge. The hatchlings use an "egg tooth" (a small white protrusion on the nose) to break through the egg shell and then immediately head for the water. Sea turtles live their first years in the ocean, and many are omnivorous during this stage, eating plant and animal matter. Turtles that live primarily on land often dig holes in the dirt with their strong rough feet to keep cool and stay inside their shells to both protect their bodies from drying out and to be safe from predators.
Adult turtles can live on either land or water. They can stay underwater for long periods of time but must emerge for air every so often because they use lungs to breathe instead of gills like fish. When it is time to breed, the male of some species courts the female by rubbing up against her or nodding his head up and down. Others bite the female's legs or bump shells with her. Some female turtles will carry their fertilized eggs with them for a year or more, laying them little by little over time. Neither parent is involved in rearing the hatchlings. Adult turtles can be anywhere from less than 5 inches long, like the endangered Bog Turtle, to over 6 feet, like the leatherback sea turtle, which can weigh up to 1,400 lbs.
Turtles grow at a very slow rate, but time does not take much of a toll on their bodies. The organs of an old turtle are almost identical to that of a young turtle. One of the most ancient creatures on earth, the turtle is also one of the longest-lived. Though the painted turtle lives a relatively short 11 years, some sea turtles live to be well over 100.