A "turtle" that lived more than 200 million years ago had a Frisbee-shaped body but no shell, scientists have discovered.
The global team behind the study believes the new form was probably an inhabitant of coastal waters foraging on land as well as in the water. The skull of Eorhynchochelys helped solve the decades old debate as to whether turtle ancestors were part of the same reptile group as modern lizards and snakes - diapsids, which are known to have had two holes on the sides of their skulls early in their evolution - or if they were anapsids, which did not have these holes.
There are a couple of key features that make a turtle a turtle: its shell, for one, but also its toothless beak. Recently, however, a fossil turtle was found that had no shell at all, but that did have a beak. The name itself is pretty straightforward - Eorhynchochelys means "dawn beak turtle", or the first turtle that has a beak, and sinensis means "from China", since the lead author Li Chun of China's Institute of Vertebrate Paleontology and Paleoanthropology discovered it in China. It's given scientists a new understanding of the animals' evolution.
Although it lacks the carapace and plastron (shell) that is so characteristic of a modern turtle, the "scaffolding" for the building of the shell is clearly in place. Mosaic evolution is the idea which suggests that different traits can evolve independently from each other, and at different rates. Eventually, the genetic mutations occurred in the same animal.
Eorhynchochelys was collected from sediments in Guizhou in south western China about 25 feet (7.5 metres) below where Odontochelys was found - indicating its older age.
British co-author Dr Nick Fraser, from National Museums Scotland, said: 'This impressively large fossil is a very exciting discovery giving us another piece in the puzzle of turtle evolution. A new fossil research is providing some clues.
The skull of Eorhynchochelys sinensis shows signs that the species was a diapsid.
Eorhynchochelys has even more to offer in the clarification of turtle ancestry. "They really went off the normal path in terms of their anatomy and did a number of things that are really unusual", said Dr. Robert Reisz from the University of Toronto. "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".
"Until I saw this fossil, I didn't buy some of its relatives as turtles".