NEW HAVEN, Conn. (AP) – A young paleontologist from the Yale Peabody Museum of Natural History in New Haven thinks he has solved one of the oldest mysteries in paleontology – how did the turtle get its shell?

The founder of modern paleontology, Georges Cuvier, asked this question in the early 1800s. He believed that, over time, the turtle’s ribs had flattened, spread and fused together to become that trademark shell. It would explain why the shell was fused with the vertebrae and why the shell grows from the ribs of turtle embryos.

But most present-day paleontologists believe the turtle is more like an armadillo, with skin that hardened into plates of armor that fused over many generations, and attached to the turtle’s internal skeleton. With no fossils to prove it, however, the theory would remain just that, a theory.

Until Walter Joyce, the 35-year-old manager of the Peabody’s vertebrate collection, got his hands on a 210-million-year-old turtle unearthed in New Mexico. The fossil shows the shell and the ribs are distinct, not fused. That means the shell evolved from the skin, not the ribs, Joyce said.

“Most of us thought it was true, but nobody had the proof, and we scientists always want proof,” Joyce said. “As far as turtles go, this was the biggest question out there. Turtles are such an ancient group of reptiles. To find a fossil old enough and in good enough shape to settle the issue was almost impossible.”

The earliest turtles, which date back 199 to 251 million years ago to the Triassic period, were terrestrials, which were unlikely to be preserved as fossils. They had very thin shells that would be easily turned to powder by the elements. Such turtles had only been found in Argentina, Germany, Greenland and Thailand.

That is where Joyce’s partner, Spencer Lucas, makes his entrance in this detective story. The curator of the New Mexico Museum of Natural History and Science in Albuquerque discovered fragments of what Joyce later identified as a new species of Triassic turtle in northeast New Mexico more than a decade ago.

But those fragments were too small to tell scientists very much. Lucas returned in 2006, however, and found erosion had revealed more bones, including what could be called a fossilized smoking gun a piece of shell that clearly shows the turtle’s ribs growing underneath the shell, not fused to it.

Lucas didn’t yet know what he had found. He thought it was part of the same turtle he had found earlier, but wanted Joyce, one of only 20 paleontologists worldwide to specialize in turtles, to study his find. But that first required the fossil to be painstakingly cleaned and illustrated, a monthslong process.

The result was the fossil evidence needed to settle the skin-versus-rib debate and establish this new species of turtle, the Chinlechelys tenertesta. This turtle lived on the land, with a 14-inch-long shell that was between one and two millimeters thick, Joyce said. It most likely ate plants and insects.

Joyce and Lucas published their team’s conclusions online last week in Proceedings B, one of the scientific journals of The Royal Society, Great Britain’s national academy of science. The findings will be published in its printed publication by the end of the year, Joyce said.

AP-ES-10-25-08 0004EDT

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