A 240-million-year-old fossil discovery is being described as an ancestor of modern-day turtles despite not having a shell — although it showed signs of evolving one, paleontologists say.
Named Pappochelys rosinae, Greek for "grandfather turtle," the fossil shows the creature possessed broad ribs in its trunk as well as thick, rib-like structures forming a sort of belly armor, they say.
Some recent studies suggest turtle shells evolved and formed from bony outgrowths of vertebrae and ribs.
The grandfather turtle may have been in the middle of an evolutionary journey in which some soft-backed animals moved toward the hard-shelled turtles of today, the researchers suggest.
It neatly fills in an evolutionary gap between some earlier hypothesized turtle ancestors and more recent recognizable turtle family members, the researchers write in the journal Nature.
"It's a beautiful link between the earliest precursors that we know of turtles, this animal called Eunotosaurus from South Africa that lived about 260 million years ago, and then later turtles that had a fully developed shell," says Hans Sues, a vertebrate paleontologist at the Smithsonian Museum of Natural History in Washington, D.C.
The first fossil of the ancient turtle was found in a lakebed in southeastern Germany and has since been joined by more than a dozen additional specimens, the researchers say.
In additional to filling in an evolutionary gap, P. Rosinae could answer some more questions about the turtle family tree, they say.
Some paleontologists have held that turtles are a form of living dinosaur, as birds are, however, the examination of the grandfather turtle suggests modern turtles are more closely related to snakes and lizards, the researchers say.
While it might be hard to think of creatures with legs being related to modern animals without them, Sues points out that, "Snakes are just a large group of legless lizards."
The hard shell of turtles may have originally begun to evolve in water-dwelling reptiles, he says.
"Its main role would have been all-around protection of the vital organs," Sues said, and may also have "helped with buoyancy control by making the animal heavier."
Unlike turtles, lizards and snakes never evolved shells, instead developing other strategies to protect themselves against predators, the researchers explain.
The "grandfather turtle" would have been around eight inches long, about the size of a modern box turtle, the say.
Before its discovery, the closest thing paleontologists were willing to consider as a true turtle relative was a 220-million-year-old fossil from China that possessed a partly-formed shell and other turtle-like features.