How Turtle Shells Grow

A turtle's shell is predominantly keratin, the same fibrous protein found in bones, nails, teeth and horns. Baby turtles hatch with a perfectly formed shell that hardens and continues to grow, regenerate or shed throughout its life. A healthy turtle has a shiny shell.

  1. Regeneration

    • If a turtle is not fed properly its shell will develop poorly.

      The top of the shell is called the carapace, and it is formed from 38 flat squares of keratin called scutes. In hard-shelled turtles these are fused together and grow individually as the turtle's body gets bigger. The total number of scutes never increases, and in some species you can see "growth rings" on the shell where extra keratin layers are laid down.

    Replacement

    • A turtle cannot crawl out of its shell.

      Some hard-shelled turtles replace scutes with new ones. Instead of growing keratin over the old layers, the scutes are purged and new portions of carapace grow in their place.

    Shedding

    • Soft-shelled turtles need sand to help with shedding.

      The carapace of a soft-shelled turtle looks like thick leathery skin, and during times of growth, it sheds in fine layers that peel from the shell. The turtle digs in sand to rub away the old skin and polish the new carapace layer.