Grandfather Turtle Had No Shell, But Link to Snakes

A newly discovered 240-million-year-old turtle suggests that turtles are more closely related to snakes than anyone ever thought, and it also reveals how turtles first evolved their shells.

"Grandfather turtle," as it has been named, could help to solve longstanding debates about the amazing family tree of all turtles. One theory is that turtles are living dinosaurs, as birds are, but this study, published in Nature, concludes that turtles are more closely related to lizards and snakes.

While it's hard to imagine a slow and hefty turtle slithering on the ground, senior author Hans-Dieter Sues points out, "Snakes are just a large group of legless lizards."

He added that the ancestor that gave rise to turtles would have been "a small, superficially lizard-like reptile with expanded trunk ribs."

Sues and colleague Rainer Schoch analyzed the remains of Grandfather turtle (Pappochelys rosinae), which were found at Schumann quarry in Germany. Based on the anatomy, they do classify turtles as being a "diapsid," a group that includes dinosaurs, birds, pterosaurs, other extinct species, crocodiles, lizards, snakes and the tuatara, which is a lizard-like reptile.

Sues and Schoch, however, believe that turtles are far more related to lizards and snakes than they are to the other major diapsid lineage, which includes dinosaurs and birds.

Eight-inch-long Grandfather turtle did not have a shell, but it certainly had the makings of one, given its broad "T"-shaped ribs and a hard wall of bones along its belly.

"This configuration of the ribs would have immobilized them and led to the development of a novel way of breathing in turtles," Sues said. "Modern developmental studies indicate that the turtle shell formed from bony outgrowths of the vertebrae and ribs."

As for why this happened, the researchers theorize that the turtle shell may have originally developed in water-dwelling reptiles.

"Its main role would have been all-around protection of the vital organs," Sues said, adding that the shell initially might have also "helped with buoyancy control by making the animal heavier."

Snakes and lizards never evolved shells, he said, because they developed other strategies to escape predators. Some extinct lizards did sport heavy body armor, but this was nothing like the heavy shell of today's turtles and tortoises.

Tyler Lyson, curator of vertebrate paleontology at the Denver Museum of Nature & Science, and a leading expert on the evolution of turtles and dinosaurs said the study "is a very important contribution in addressing who turtles are related to, as well as the evolutionary origin of the turtle shell."

Read more at Discovery News