Fossil turtle didn't have a shell yet, but had the first toothless turtle beak

August 22, 2018, Field Museum
An illustrated scene depicting Eorhynchochelys in life. Credit: IVPP

There are a couple of key features that make a turtle a turtle: its shell, for one, but also its toothless beak. A newly-discovered fossil turtle that lived 228 million years ago is shedding light on how modern turtles developed these traits. It had a beak, but while its body was Frisbee-shaped, its wide ribs hadn't grown to form a shell like we see in turtles today.

"This creature was over six feet long, it had a strange disc-like body and a long tail, and the anterior part of its jaws developed into this strange beak," says Olivier Rieppel, a paleontologist at Chicago's Field Museum and one of the authors of a new paper in Nature. "It probably lived in shallow water and dug in the mud for food."

The new species has been christened Eorhynchochelys sinensis—a mouthful, but with a straightforward meaning. Eorhynchochelys ("Ay-oh-rink-oh-keel-is") means "dawn beak turtle"—essentially, first turtle with a beak—while sinensis, meaning "from China," refers to the place where it was found by the study's lead author, Li Chun of China's Institute of Vertebrate Paleontology and Paleoanthropology.

Eorhynchochelys isn't the only kind of early turtle that scientists have discovered—there is another early turtle with a partial but no beak. Until now, it's been unclear how they all fit into the reptile family tree. "The origin of turtles has been an unsolved problem in paleontology for many decades," says Rieppel. "Now with Eorhynchochelys, how turtles evolved has become a lot clearer."

Illustration showing what Eorhynchochelys would have looked like in life. Credit: Adrienne Stroup, Field Museum

The fact that Eorhynchochelys developed a beak before other early turtles but didn't have a shell is evidence of mosaic —the idea that traits can evolve independently from each other and at a different rate, and that not every ancestral species has the same combination of these traits. Modern turtles have both shells and beaks, but the path evolution took to get there wasn't a straight line. Instead, some turtle relatives got partial shells while others got beaks, and eventually, the genetic mutations that create these traits occurred in the same animal.

"This impressively large fossil is a very exciting discovery giving us another piece in the puzzle of turtle evolution," says Nick Fraser, an author of the study from National Museums Scotland. "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."

Fine details in the skull of Eorhynchochelys solved another turtle evolution mystery. For years, scientists weren't sure if turtle ancestors were part of the same reptile group as modern lizards and snakes—diapsids, which early in their evolution had two holes on the sides of their skulls—or if they were anapsids that lack these openings. Eorhynchochelys's skull shows signs that it was a diapsid. "With Eorhynchochelys's diapsid skull, we know that turtles are not related to the early anapsid reptiles, but are instead related to evolutionarily more advanced diapsid reptiles. This is cemented, the debate is over," says Rieppel.

Photograph of the fossil turtle Eorhynchochelys. Credit: Nick Fraser, National Museums Scotland

The study's authors say that their findings, both about how and when turtles developed shells and their status as diapsids, will change how scientists think about this branch of animals. "I was surprised myself," says Rieppel. "Eorhynchochelys makes the turtle family tree make sense. Until I saw this fossil, I didn't buy some of its relatives as . Now, I do."

Explore further: Scientists discover key clues in turtle evolution

More information: A Triassic stem turtle with an edentulous beak, Nature, DOI: 10.1038/s41586-018-0419-1 , https://www.nature.com/articles/s41586-018-0419-1

Related Stories

Scientists discover key clues in turtle evolution

September 2, 2015

A research team led by NYIT scientist Gaberiel Bever has determined that a 260-million year-old fossil species found in South Africa's Karoo Basin provides a long awaited glimpse into the murky origins of turtles.

Study of oldest turtle fossil

November 26, 2008

With hard bony shells to shelter and protect them, turtles are unique and have long posed a mystery to scientists who wonder how such an elegant body structure came to be.

Key link in turtle evolution discovered

June 25, 2015

An international team of researchers from the United States and Germany have discovered a key missing link in the evolutionary history of turtles. The new extinct species of reptile, Pappochelys, was unearthed in an area ...

Evolutionary origin of the turtle shell

May 30, 2013

Through careful study of an ancient ancestor of modern turtles, researchers now have a clearer picture of how the turtles' most unusual shell came to be. The findings, reported on May 30 in Current Biology, help to fill a ...

Recommended for you

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

blazh femur
4 / 5 (1) Aug 23, 2018
I'm sorry, your policy is 228 million years old. It doesn't cover shell damage.
TorbjornLarsson
1 / 5 (2) Aug 23, 2018
The title seems misleading, the reconstruction shows a transitional toothed beak as far as I can see. Even better if so, and akin to the transitional toothed beaked bird fossil they found the other year.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.