Scientists Solve The Mystery behind Evolution of Turtle Shell

First Posted: May 31, 2013 08:15 AM EDT

If you've ever wondered how the turtle got its shell, you aren't the only one. Scientists who have long been mystified by this question have finally resolved the mystery. Careful study of model of an ancient ancestor of modern turtles helped them gain a clear insight into how turtles got their shells.

For the study, published in the journal Current Biology, scientists at Yale University and the Smithsonian Institution studied an extinct fossil of a reptile known as Eunotosaurus. The fossil was found in South Africa.

On analyzing the fossil, scientists suggest that the origin of the turtle shell dates back to some 40 million years prior to what was assumed. 

"It was very contentious," Tyler Lyson, a paleontologist who recently received his doctoral degree at Yale and is now a fellow at the Smithsonian, said in a press statement.  "For the past 200 years, there's been a lot of ink spilled on the question."

In 2008, a 220-million-year-old turtle fossil was found in China. The specimen, known as Odontochelys semitestacae, helped scientists learn that it had a complete developed shell on its belly called plastron, but the shell on the back was not formed. Rather, they noticed that the partial shell outside was made of broadened ribs and vertebrae.

After a few years, a specimen called Eunotosaurus Africanus was discovered, which was 40 million years older than the previous specimen found in China. On carefully analyzing the specimen, researchers learnt that the new species had nine broadened ribs that are present only in turtles. It didn't have any intercostal muscles between its ribs, paired belly ribs and had a specialized mode of rib development, which clearly showed that Eunotosaurus was the first species that formed the evolutionary branch of turtles.

"Eunotosaurus neatly fills an approximately 30-55-million year gap in the turtle fossil record. There are several anatomical and developmental features that indicate Eunotosaurus is an early representative of the turtle lineage; however, its morphology is intermediate between the specialised shell found in modern turtles and primitive features found in other vertebrates," Lyson explains.

Further, the scientists plan to investigate other aspects of the turtle's respiratory systems.

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