TURTLESHELL
Turtle shell
The turtle shell is a highly complicated shield for the ventral and dorsal parts of turtles, tortoises and terrapins, completely enclosing all the vital organs of the turtle and in some cases even the head. It is constructed of modified bony elements such as the ribs, parts of the pelvis and other bones found in most reptiles. Therefore turtles have no backs. The bone of the shell consists of both skeletal and dermal bone, showing that the complete enclosure of the shell probably evolved by including dermal armor into the rib cage.The above text is a snippet from Wikipedia: Turtle shell
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