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South African team uncovers answers to the origin of turtles

4 September 2015

Professor Gaberial Bever and the research team at Wits University's internationally respected Evolutionary Studies Institute (ESI), believe their detailed analysis of the skulls of Eunotosaurus africanus confirms a definite link between pre-dinosaur reptiles and the modern turtle.

Eunotosaurus is a lizard-like prehistoric reptile, first discovered in South Africa in the 19th century and long believed to be an ancestor of the turtle. It lived during the Permian Period, 30 million years before the first dinosaurs and 20 million years before Pappochelys, the creature uncovered in Germany in June 2015 that is believed to be the earliest-known turtle.

At just 30cm long, Eunotosaurus had a wide and rounded ribcage and skull with similar characteristics to the modern turtle – one scientist famously described it as "a strange, gluttonous lizard that swallowed a small Frisbee". These similarities have been the subject of much debate since its discovery.

Bever told Reuters news agency this week: "Where turtles came from, evolutionarily speaking, and how they are related to the other major groups of living reptiles – lizards, snakes, crocodiles and birds – has been a topic of vigorous debate for as long as we've had a theory of evolution."

Using advanced scanning technology, the team digitally dissected the cranial bones of the skulls of the four fossil specimens available, to confirm Eunotosaurus as the oldest-known member of the turtle group. "Using imaging technology gave us the opportunity to take the first look inside the skull of Eunotosaurus. What we found not only illuminates the close relationship of Eunotosaurus to turtles, but also how turtles are related to other modern reptiles," Bever said.

With this new insight, along with information from previous research, including Pappochelys and another fossil found in China in 2008, the Odontochelys (a little younger than Eunotosaurus, at only 220 million years old), Bever's team "now have a remarkable series of transitional forms that take us from an almost lizard- like creature to the modern turtle body plan that is so interesting and bizarre".

What has the skull revealed?

ESI found that the Eunotosaurus' skull is diapsid, with a pair of openings just behind the eyes that allowed its jaw muscles to flex during chewing. This is unique and distinctive in modern lizards, snakes and some birds, yet not found in modern turtles, which have the anapsid skull formation - fused directly to the jaw bone, giving the turtle its characteristic slow biting and chewing movements.

The argument Bever and the research makes is that "if turtles are closely related to the other living reptiles, then we would expect the fossil record to produce early turtle relatives with diapsid skulls".

In terms of previous theories on the evolution, the anapsid-diapsid distinction was used to argue that modern turtles were from an ancient lineage, and not closely related to modern lizards, crocodiles and birds who have a diapsid ability. They are not.

"The new data from Eunotosaurus rejects this hypothesis… and we can now draw the well-supported and satisfying conclusion that Eunotosaurus is the diapsid turtle. This is the fossil that science has been searching for, for more than 150 years," Bever explained.

"Imaging technology gave us the opportunity to take the first look inside the skull of Eunotosaurus, and what we found not only illuminates the close relationship of Eunotosaurus to turtles, but also how turtles are related to other modern reptiles," Bever said.

The next step for the Wits team is to use the same techniques to find links between other diapsid reptiles and the modern turtle, and build up a detailed family tree of the species' journey to now.

"The beauty of scientific discoveries is that they tend to reveal more questions than they answer, and there is still much we don't know about the origin of turtles," the professor concluded.

The ESI is the largest palaeontological and palaeoanthropological research entity in Africa and one of the largest of its kind in the world. An amalgamation of the Bernard Price Institute for Palaeontological Research and the Institute for Human Evolution, the institute publishes over 80 research publications annually based on global research collaborations, extensive fieldwork and some of the world's most cutting-edge palaeontology technology.

It is one of the world's foremost brains trust for evolutionary study and research, and continues the work of and builds on the reputation of one of the university's most beloved and globally celebrated palaeoanthropologists, the late Professor Emeritus Phillip Tobias.

Bever's full report and detailed video analysis has been published in the international science journal, Nature.

SAinfo reporter