The world’s oldest fossil of a turtle discovered off the coast of China last year turns out to be… a sea turtle! The fossil, thought to be 220 million years old, gives scientists new insights into how turtles got their shells. It provides evidence that turtle shells formed from their bellies as extensions of the backbone and ribs, not as bony plates evolved from skin. The lower shell is thought to have protected the swimming proto-turtles from predators lurking below.
The fossil also suggests that turtles evolved in the sea and only later spread onto land. In other words, the earliest turtles may have actually been sea turtles!