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Ancient Shell-Less Turtle With Toothless Beak Sheds Light On Evolution Secrets

Aug 23, 2018 11:36 PM EDT
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A turtle's shell is the most recognizable feature of the creature, but that wasn't the case in a turtle fossil from 228 million years ago.

At that stage in turtle evolution, it hasn't grown a shell yet. The newly discovered species is also the very first known stem turtle with a toothless beak.

Scientists Find New Turtle Species

A study published in the journal Nature introduced the modern turtle's ancestor as Eorhynchochelys sinensis. Found in the Guizhou province of China, it was reportedly a gigantic animal that's more than 6 feet long with a Frisbee-shaped body and a long tail.

Olivier Rieppel, one of the study authors and a paleontologist at Chicago's Field Museum, says that the Eorhynchochelys likely lived in shallow waters, digging for food in the mud.

Of course, the most striking characteristics of the animal fossil are the absence of the shell and the presence of the distinct toothless beak, both of which help piece together the complex lineage that resulted in the modern turtle.

Turtles And Mosaic Evolution

Until now, turtle evolution has been a huge question mark in palaeontology. Fortunately, the Eorhynchochelys is able to clear up a few of the lingering questions about the evolution of these creatures.

"This impressively large fossil is a very exciting discovery giving us another piece in the puzzle of turtle evolution," Nick Fraser, another study author from the National Museums Scotland, explains. "It shows that early turtle evolution was not a straightforward, step-by-step accumulation of unique traits but was a much more complex series of events that we are only just beginning to unravel."

Scientists have previously found evidence of an early turtle with a partial shell, but no beak. On the other hand, the Eorhynchochelys had a distinctly formed beak but no shell.

The contradiction suggests that mosaic evolution took place, which means traits evolve independently at varying rates with the different ancestral species potentially getting different combination of traits. While modern turtles have both shells and beaks, its ancestors may have just gotten one or the other until the various genetic mutations occurred in the same animal.

Skull Secrets Solved

Finally, the Eorhynchochelys was also able to settle one debate: whether early turtles were diapsids with two holes on the side of the skull or anapsids with none. It turns out, the species was a diapsid, belonging in the same reptile group as modern lizards and snakes.

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