Today's turtles' prehistoric predecessor has been found as a fossil in South Africa. At 260 million years old, researchers say that this creature, Eunotosaurus africanus, sheds light on the evolution of modern turtles.
"Eunotosaurus is a critical link connecting modern turtles to their evolutionary past," Dr. Gaberiel Bever, an Honorary Research Associate at the University of the Witwatersrand's (Wits University) Evolutionary Studies Institute (ESI) and scientist at the New York Institute of Technology, said in a news release.
While previous studies on Eunotosaurus have provided answers on how the turtle got its shell, in this study Bever focused on the skull to better understand the history of turtle evolution. He used high-resolution computed tomography to digitally dissect bones and internal structures of multiple fossil skulls.
"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 in a release.
So what did they find? Bever and his colleagues found that the Eunotosaurus skull has a pair of openings set behind the eyes. This is known as a diapsid condition, which allows the jaw muscles to lengthen and flex during chewing, and is also found in lizards, snakes, crocodiles and birds. This is unlike modern turtle skulls, which are anapsid, or without openings. According to the researchers, this means that ancient turtles had a quicker bite.
"We can now draw the well-supported and satisfying conclusion that Eunotosaurus is the diapsid turtle," Bever said in the release. "The skull of Eunotosaurus grows in such a way that its diapsid nature is obvious in juveniles but almost completely obscured in adults. If that same growth trajectory was accelerated in subsequent generations, then the original diapsid skull of the turtle ancestor would eventually be replaced by an anapsid skull, which is what we find in modern turtles."
While this helps scientists better understand the turtle's family tree, further research of the species' origin is still needed.
Their findings were recently published in the journal Nature.
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