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Can a turtle tuck its head all the way inside its shell?

Turtle shells evolved over the course of 300 million years, but self-defense wasn't the initial driver, researchers think.
The Atlantic

Why Turtles Evolved Shells: It Wasn't for Protection

Travel back in time to 260 million years ago, just before the dawn of the dinosaur era. Journey to what is now South Africa, and make your way to a river bank. Then, wait. If you’re lucky, you might ...