Image copyright National Museums Scotland Image caption The nearly complete skeleton reveals a complex early history of turtles

Scientists have found new evidence confirming that turtles once lived without shells.

The almost-complete fossil dates back 228 million years and is bigger than a double bed.

It was discovered in the Guizhou province of south west China

Dr Nicholas Fraser, keeper of natural sciences at the National Museum of Scotland in Edinburgh, said: "It looked like a turtle but then lacked everything of the shell underneath and also the one on top."

"It has the scaffolding in place for the shell to go on to but it doesn't have the shell."

"It has a very characteristic beak at the front end."

The ancient reptile has been named Eorhynchochelys sinensis, which means "Dawn turtle with a beak from China".

Image copyright IVPP Image caption Artist's impression of how the triassic turtle looked

Why is the turtle shell important?

The shell is there to help protect turtles, but it can also help them live underwater for longer.

This is because it stores potassium and magnesium which can help protect it from a build-up of lactic acid.

It is made up of around 50 bones, with ribs, shoulder bones and vertebrae fused together to form a hard external layer.

Dr Fraser says "Turtles are very strange animals. They have a straightjacket of a shell.

"If you can imagine yourself with your shoulders within your rib cage, you'd be pretty restricted."

"They're pretty unusual animals but they have survived over 200 million years."

Image copyright Yu Chen, IVPP Image caption Artist's impression of the earliest known stem turtle

How did the turtle get its shell?

How the turtle shell evolved has puzzled scientists for years.

A number of primitive turtles known from the fossil record already have complete shells.

The oldest known turtle prior to this find, an animal called Odontochelys, had a fully-formed shell over its bottom surface (a part of the shell known as the plastron), but no bony covering on the top of its body (the bit of the shell known as the carapace).

Researchers say the new discovery means we are closer to working out how the turtle's shell evolved.

Dr Fraser explained: "We're seeing it in this animal - with the ribs beginning to expand.

"We are waiting for the next fossil to see what that brings."

The findings were published in the journal Nature.