Turtle ancestor disproves bone-shed theory

220 million year old fossil gives first indication of the evolution of the tank

Odontochelys semitestacea © Marlene Hill Donnelly / Field Museum
Read out

How did turtles get to their tank? An answer to this question is now provided by a newly discovered fossil in China: the 220-million-year-old prehistoric turtle has an incomplete protective shell and thus gives an insight into the evolution of the tank. The study now published in "Nature" also refutes the theory that the shell has developed from bone scales of the skin.

Since the age of dinosaurs, the turtles have barely changed, even then they had a stable bone armor that protected their entire hull. The skin of some reptiles living today, such as the crocodiles, is studded with bony scales, probably similar to the dinosaurs. So far, some researchers have assumed that the tanks of turtles from such so-called Osteoderms could have developed.

Broadened ribs instead of dander

With the discovery of a first turtle fossil from the Triassic with incomplete tank, this theory could now be checked and refuted at the same time. The relic was discovered in the Chinese province of Guizhou near the city of Guiyang and is 220 million years old. Olivier Rieppel, head of the geological department of the Chicago Field Museum, has now studied the fossil in collaboration with Chinese and Canadian colleagues.

The Odontochelys semitestacea - half-shell toad with teeth - baptized species apparently had no bone scales and from the shell only the lower half. The carapace is incomplete and seems to be an extension of its spine and ribs.

Reinvention of nature

This fits in with investigations into the embryonic development of today's turtles, which show that the spine and ribs gradually widen and then fuse together. "This is the first turtle with an incomplete shell, " explains Rieppel. "The tank is an evolutionary innovation. In any case, our animal tells people that they can forget the idea of ​​tortoise tracks with osteoderms. "Ad

According to the researcher Odontochelys probably lived predominantly in the water. The half-tank then protected the sensitive belly from swimming from near the surface when swimming near the surface. "Rural-life reptiles had their bellies close to the ground, less exposed to danger, " said Rieppel.

(Field Museum, 01.12.2008 - NPO)