Why do turtles and tortoises have shells?
Quick Answer
Turtle shells are protective body structures made from ribs and spine that evolved for defense. They also help support the body and, in some species, reduce injury from predators.
The Full Story
A turtle shell is not a separate exoskeleton; it is part of the animal’s skeleton. The top shell, the carapace, and the bottom shell, the plastron, are fused with ribs and vertebrae. Fossils such as Odontochelys from about 220 million years ago show that shell evolution was gradual in early turtles. Shells likely evolved for protection first, with other functions like support developing later. Because the shell is living bone, it grows with the animal and is richly supplied with blood vessels and nerves.
Key Facts
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