How did the turtle's shell come?

Once upon a time, there was only one turtle on the earth, and it had no shells.

One day, it met a tiger. The tiger wanted to eat the turtle. The turtle turned around and ran, but it was already late. The tiger just caught up and grabbed it. The turtle hurriedly hid in a shell. The tiger grabbed the shell and bite it. The tiger could only go down in a dejected manner. However, the tortoise could not come out if it came out. After a long time, the turtle's shell was deformed. Later, the children born to it also looked like this.

Since then, the tortoise has a protective shell.