Oldest Turtle Found; May Crack Shell-Evolution Mystery

Fossils of the oldest-known turtles, unearthed in southwestern China, may help answer an evolutionary enigma--how did the turtle get its shell?

The 220-million-year-old animals did not have full shells, or carapaces, on their backs, researchers found.

But the newfound creatures did sport fully developed plastrons--the flat part of a turtle shell that covers and protects the belly.

The discovery supports the theory that turtle shells formed from the underside--plastron first--and grew bony extensions of ribs and backbones that eventually joined to form the classic shell that exists today.