By Scott A. Rowan
A scute is a plate of hardened keratin found on many animals, most notably the carapace of turtles, tortoises or terrapins, and the “armored” bony surface of crocodiles, alligators and caimans.
For reptiles, the number of scutes can vary. However, the carapace for turtles, tortoises and terrapins is composed of an interlocking bony structure that is covered by 13 main scutes (central and costal scutes) ringed by several smaller ones (nuchal, marginal, and supracaudal scutes).
Much like the black and white patches on a soccer ball, scutes interlock to cover and protect the domed bony carapace of any species in the Order Testudines (turtles, tortoises, terrapins). Covering a curved surface, whether it is a soccer ball wrapped in leather or a round piece of artwork covered in mosaic tiles, requires many small pieces that fit together like jigsaw pieces to create a curved, protective surface.
When the once-flexible scutes of a turtles carapace harden, they interlock to form a rock-hard surface that protects the animal from predators and the environment.
Keratin is the same material found in human fingernails and most animal horns, structures that combine flexibility with protection.
The Vertebrate Integument Volume 1, Theagarten Lingham-Soliar, (Springer, Verlag Berlin Heidelberg).