If you know when a turtle is born you can tell a turtle’s age by its Shell. By looking at its shell, you can tell the age of a young turtle, but not of an old turtle. The bony shells of turtles are covered with thin plates called shields. “Growth rings” accumulate on most turtle’s shields as they grow.
Each ring stands for a year’s growth. These rings can indicate the age of a turtle up to about fifteen years. After that, you can no longer tell a turtle’s age by counting the rings. They have either become too crowded together or have begun to wear off.
Soft shelled turtles, or those with smooth, hard shells, don’t have growth rings. The average lifespan of many turtles is well under 20 years. The really old turtles are generally tortoises and almost always live in protected places. So now you can tell a friend about your pet turtle’s age by counting its Shell.
How do turtles live so much longer than other animals? One theory has to do with the fact that turtles are cold-blooded and have what scientists call a slow metabolism. They don’t have to eat as much food to survive, since they use energy they get from food very, very slowly. Since they are cold-blooded, they also don’t need to use a lot of energy to keep themselves warm.
A second idea about why turtles live so long is also related to that low metabolism. Turtles often hibernate. They sink down into the mud at the bottom of a lake or pond, going dormant for the season (kind of like hibernation), and use even less energy.
A third idea about why turtles seem to outlive so many other animals. They have evolved special defenses against predators.
It seems that using energy slowly and having good defenses may be two key things that help turtles live slow and die old. But there are still many exciting questions left when it comes to aging and lifespan.
Content for this question contributed by Matt Chapman, resident of Concord, Contra Costa County, California, USA