It's similar to how the ancient Chinese thought that the turtle had supernatural powers of prophecy. As a result, they made divination blocks out of turtle shells, and carved half of the ancient oracle bone scriptures on them as well.
就像中國古人認為神龜通靈，知事吉凶，所以卜卦用龜甲，甲骨文字也刻在龜甲上一般。