The upper shell of a turtle or tortoise is actually the ribcage. The individual ribs fuse together where they emerge from the spine and extend around the shoulders and pelvis of the animal to form a continuous carapace.
The underside of the shell is a separate piece made from the shoulder girdle and sternum (breastbone). So turtles don’t actually ‘live inside’ their shells, any more than you live inside your own rib cage.
But the shell isn’t made entirely of bone. It’s covered with around 54 plates of horn-like keratin that provide waterproofing and scuff-protection.
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Asked by: Vikram Rathaur, London
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