The ribs of a 240 million-year-old fossil hold clues to how the first turtle shell evolved. And its skull shape seems closer to that of lizards and snakes than to an ancestor of dinosaurs and birds.

The shell itself is made from broadened and flattened ribs, fused to parts of the turtle’s backbone (so that unlike in cartoons, you couldn’t pull a turtle out of its shell).

As turtle embryos develop, their shells grow directly from the animals' ribs, and adult turtles' ribs are fused to the shell carapace. Some scientists conclude this must have been how the shells ...

In 2008, the discovery in China of a nearly 220 million years old fossil of an undisputed turtle precursor, represented a major advance in our understanding of the evolution of the turtle shell.