The two theories about snakes are that they developed from land lizards or are descended from creatures that lived in the oceans.

To investigate, experts have been using a technique known as synchrotron-radiation computed laminography on an ancient fossil.

The 95-million-year-old fossil is one of three in the world that show a snake with preserved leg bones. One leg can be seen outside the fossil, but scientists had only guessed that the other was hidden inside.

Computed laminography involves taking thousands of 2D X-rays and stitching them together into a 3D image. By studying this, the researchers could see that the snake’s second leg only has ankle bones, but no foot or toe bones. Experts now think that this species of snake lost its legs because they grew slowly or for a short time, but that it may be another ten years before the question of how snakes lost their legs is fully answered.

Check out the video below to see the researchers' cool 3D scan of the ancient fossil.