Turtle Fossil Yields Clues To Its Evolution

Scientists in China have found the oldest fossil yet of a turtle. Previously, scientists thought turtles evolved on land, but this new discovery suggests they may have first inhabited the water and then moved on land.

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MICHELE NORRIS, Host:

There is stunning news today from the world of turtle paleontology. Scientists are reporting they found a turtle on the half-shell, literally. It's a 220-million-year-old fossil, found in China, of a turtle that had a shell underneath its belly but no shell on its back.

As NPR's Joe Palca reports, this new discovery should help scientists answer a question that's puzzled both them and kids. Just how did the turtle get its shell?

JOE PALCA: It's hard to overstate just how exciting the Chinese find is.

EUGENE GAFFNEY: It is probably the most important discovery concerning turtles for the past 40 or 50 years.

PALCA: Paleontologist Eugene Gaffney has spent his 40-year research career studying turtles. He's recently retired from the American Museum of Natural History in New York. Until the Chinese fossil came along, he had introduced the world to the oldest turtle, a fossil found in Germany. That turtle looked like a turtle, with a hard shell covering its back.

GAFFNEY: But this specimen has sort of a halfway, intermediate-formed turtle shell.

PALCA: In fact, the new find is known as Odontochelys semitestacea.

OLIVIER RIEPPEL: Semitestacea means half shells.

PALCA: Olivier Rieppel is with the Field Museum in Chicago. He's a co-author on the paper in the journal Nature describing the Chinese finding. He says the new fossil represents a kind of primitive turtle, one that hasn't quite figured out how to make the hard shell on top and bottom that modern turtles have. By studying this kind of intermediate step, scientists should learn more about how the turtle shell evolved. Now, Rieppel says a hard shell is critical for a turtle planning to make a living on dry land.

RIEPPEL: An animal like a turtle living on land will not be attacked from below. It will be attacked from above.

PALCA: But Rieppel says a turtle living in the water can get by without a shell on top, because swimming animals will typically be attacked from below. That's why Rieppel and his colleagues in China believe this turtle has a marine origin.

Rieppel says another factor arguing in favor of a watery lifestyle is that the part of southwestern China where the fossil was found was a marine basin 230 million years ago. In addition to the half shell, the Chinese turtle has another remarkable feature.

RIEPPEL: This turtle has teeth, which modern turtles don't have, so that's a very primitive character of this fossil turtle.

PALCA: Modern turtles have a hard beak made of keratin instead of teeth. Now, it may seem odd that an animal that had managed to evolve something as clever as teeth would then un-evolve them, but paleontologist Robert Reisz says it isn't. Reisz is at the University of Toronto Mississauga.

ROBERT REISZ: Remember, birds do that, too. Their ancestors had teeth, and birds eliminated their dentition and developed a similar structure to that of turtles, and they have that beak that they use very efficiently.

PALCA: And that's the great thing about paleontology: specialization. Someone has actually taken the time to compare the beaks of birds with the beaks of turtles. American Museum of Natural History's Gene Gaffney says you can get even more specialized than that.

GAFFNEY: There have been a number of people that have devoted their careers to studying turtle ears and their physiology and functions and so forth.

PALCA: The career opportunities abound. Joe Palca, NPR News, Washington.

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