Grandfather of all turtles found in a German quarry
The 20-centimetre long animal has been named Pappochelys, or "grandfather turtle".
“The mystery of how the turtle got its shell has been a long-standing question in evolutionary biology,” said Hans-Dieter Sues, curator of vertebrate paleontology in the Department of Paleobiology at the Smithsonian’s National Museum of Natural History.
“In the case of Pappochelys, we see that its belly was protected by an array of rod-like bones, some of which are already fused to each other," he told Smithsonian Science News.
"Such a stage in the evolution of the turtle shell had long been predicted by embryological research on present-day turtles but had never been observed in fossils—until now.”
Sues and palaeontologist Rainer Schoch of Germany's State Museum of Natural History Stuttgart have been studying more 18 fossils of the creature. Their findings are published in Nature.
The new fossil is 20 million years older than the previous earliest-known turtle, Odontochelys from China, which carried a rudimentary shell on its back.
Eunotosaurus, considered the oldest precursor of turtles, dates back to 260 million years ago and lived in present-day South Africa. It features many characteristics only found in turtles, including broad ribs and a lack of intercostal muscles, which attach between the rib bones. Eunotosaurus also has a long slender tail. By comparison, Odontochelys lived in present-day China 220 million years ago and has a fully developed plastron, a long tail and jaws with small teeth. Pappochelys fits neatly between these two turtle precursors at 240 million years, sharing some characteristics with Eunotosaurus but having only a partially fused plastron.