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How the Turtle's Shell Evolved

from the BBC News Online

A newly discovered fossil from China has shed light on how the turtle's shell evolved. The 220 million-year-old find, described in Nature journal, shows that the turtle's breast plate developed earlier than the rest of its shell.

The breast plate of this fossil was an extension of its ribs, but only hardened skin covered its back. Researchers say the breast plate may have protected it while swimming.

The turtle fossil, found near Guangling in south-west China, is thought to be the ancestor of all modern turtles, although it differs markedly; it has teeth rather than a bony plate, the shell only covers its underside and it has a long tail.