There are many different types of turtles on Earth, ranging from small turtles that make ideal pets, to larger turtles unsuited for captivity. There are also tortoises, which are types of turtles adapted specially to live on land, rather than in the water. Turtles are one of the oldest groups of reptiles on the planet, with ancestors who lived more than 215 million years ago, making them even older than snakes or lizards. With over 300 species crossing fourteen surviving families, there are turtles on every continent on Earth except Antarctica, and they have been a part of human myth and culture for millennia.
There are three suborders of turtles, of which only two have living representatives. One of these, Cryptodira, contains most of the types of turtles known to people, including all tortoises and marine turtles. The other order, Pleurodira, contains the types of turtles known as side-necked turtles, a group of freshwater turtles that bring their heads into their shells in a distinctive manner. Although tortoises and terrapins are both also turtles, many people use the word turtle to refer only to marine turtles, terrapins to refer to freshwater turtles, and tortoise to refer to land-dwelling turtles.
Different types of turtles are regulated as pets in the United States, mostly because of concerns over their ability to contract and transmit salmonella. As a result, the sale of turtles under four inches (10cm) in length is illegal in all states, except for educational purposes. Some species of turtles, such as the Red-eared Slider, are also regulated in some states, as they may be seen as invasives.
There are many types of turtles on Earth, but only a handful are commonly seen as pets in the Western world. A number of these are tortoises, as the fact that they dwell on land makes them easier to care for in many ways. Generally, the types of turtles favored as pets are relatively small, can survive in a variety of temperature and humidity ranges, and have flexible diets. Some species of turtles are very fragile, and these do not tend to make good pets.
The Spotted Turtle, Clemmys guattata, is one popular pet turtle. They are originally from the United States, and can live either outdoors where the temperature is warm enough, or in an aquarium. They need a temperature range of between 72 and 81 degrees Fahrenheit (22-27 degrees Celsius), and are carnivorous. The North American Wood Turtle, Clemmys insculpta, is another popular pet turtle, able to live in a temperature range of 65 to 80 degrees Fahrenheit (18-26 degrees Celsius). They will burrow into the loam of an aquarium if provided for them, and also love to climb trees, making a closed top crucial.
The Red-Footed Tortoise, Geochelone carbonaia, is one of the more popular of the land tortoises for pets. A tropical tortoise from South America, they need a terrarium kept at over 70% humidity and between 75 and 85 degrees Fahrenheit (24-29 degrees Celsius). The Russian Tortoise, Testudo horsfieldii, is another popular pet tortoise, in part because of its small size. In fact, a Russian Tortoise was one of the first animals in deep space, sent by the Russians from 14 Septembe to 21 September, 1968.