Toothless Turtle

An artist's reconstruction of Eorhynchochelys sinensis.

Yu Chen

Fossils from China, Germany, and South Africa have provided clues as to how turtles evolved and how they are related to other reptiles. A recently discovered turtle fossil called Eorhynchochelys sinensis (meaning “dawn beak turtle from China”) had a toothless beak but no shell, filling in another piece of the turtle evolution puzzle.

An international team of paleontologists, led by Chun Li and Xiao-Chun Wu from the Chinese Academy of Sciences, reported the discovery of a nearly complete E. sinensis skeleton in the Guanling District of the Guizhou Province in China. The specimen is estimated to be roughly 220 million years old, slightly older than another turtle specimen, Odontochelys semitestacea, which was found in the same area and had a partial shell but no beak [see “All Boxed Up,” 10/17].

The newly-discovered skeleton of Eorhynchochelys sinensis, a 220 million-year-old turtle that had a beak but no shell.

Wei Gao

The E. sinensis specimen was over six feet long and likely once lived at the edge of a lake, using its stocky limbs and strong claws to dig into the soft soil for food. Instead of curving inward as in other four-legged vertebrates, its wide ribs grew directly outward. This outward growth gave it the disc-shaped body of modern turtles, but E. sinensis’s ribs did not grow to form a shell.

 

Together, E. sinensis and O. semitestacea indicate that turtle characteristics—disc-shaped bodies, hard shells, and toothless beaks—did not evolve in a linear fashion. Instead, closely related species appear to have developed different traits at different times, a process called mosaic evolution. Eventually, all of these characteristics appeared in the same lineage, resulting in modern turtles.

For many years, paleontologists debated whether turtles were part of the diapsid group, which includes crocodiles, birds, and snakes, or whether they were part of an older group known as anapsids. E. sinensis, along with a specimen found in Germany called Pappochelys rosinae, share skull features that confirm turtles’ place among the diapsids. (Nature)