Oldest Turtle Found; May Crack Shell-Evolution Mystery

Fossils of Odontochelys semitestacea, a 220-million-year-old primitive turtle (above, an artists rendering), were found recently in China.

The fossils, which do not have fully formed shells, may be the missing link that shows how modern-day turtles evolved their distinctive hard backs, experts said in November 2008.

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.

http://news.nationalgeographic.com/news/2008/11/081126-oldest-turtle.html

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