The mystery of the turtle shell evolution may be revealed with the discovery of the world's oldest turtle fossil, a 220 Million year old creature with only a partial shell. The turtle fossil, found near Guangling in south-west China, is thought to be the ancestor of all modern turtles, although it differs markedly; it has teeth rather than a bony plate, the shell only covers its underside and it has a long tail. The fossil find helps to answer the key questions about the evolution of turtles.

The existing theories propose that the shell developed from plates on the skin, and was similar to the body armour found on ankylosaurs and some other dinosaurs. While another said that the shell was an extension of the backbone and ribs. The bone theory was supported by embryonic evidence; as turtles mature in the egg, their backbone expands outward and ribs broaden to meet and form a shell.

However, the latest research of the newly discovered fossil clinches in favour of the bone theory. Dr Olivier Rieppel, a researcher at the Field Museum in Chicago said that the animal's ribs are broad, but have not fused. A partial shell extends from its backbone. The bottom part of the shell is complete, but the top part isn't. Supporting the view, Dr. Wu and his colleagues, including Chinese researchers Chun Li, Li-Ting Wang and Li-Jun Zhao said this makes sense because it lived in the water, and predators would have probably attacked it from below. Hence, the discovery suggests that turtles may have first evolved in the water, rather than on land.

Dr Robert Reisz, a paleontologist at the University of Toronto said the fossil is a "really great discovery," and an important chapter in turtle history. The Paper on the find showing convincing evidence of how the protective covering evolved was published in the British journal, Nature.