Turtles are the only reptiles that do not have teeth. Instead they have strong horny beaks. They are also the only reptiles with hard shells. The top shell is called the carapace and the bottom shell is called the plastron. A turtle's backbone is attached to its top shell.
Turtles are the longest-lived vertebrates.
Some turtles live to be over 100 years old. The gender of most turtles is determined by environmental cues, not genetically as occurs in mammals. The temperature at which eggs incubate determines whether the hatchlings will be male or female. The giant leatherback turtle is the largest sea turtle.