Try picturing a snake with legs and your brain probably files it under "nightmare fuel" or bad CGI. But dig into the fossil record and you'll find the opposite is true: legs came first. The slither came later. Somewhere between roughly 170 million and 100 million years ago, the ancestors of every cobra, python and garter snake alive today walked around on four limbs, and then, gradually, stopped.
Working out exactly how that happened has taken paleontologists, geneticists and more than a little Argentine desert dust to figure out. Here's where the science actually stands.
