Found... in a museum!
Fossil-hunters have found several extinct snakes with stunted hind legs, and modern boas and pythons still have a pair of little spurs. “But no snake has ever been found with four legs. This is a once-in-a-lifetime discovery.”This finding has substantial implications regarding the evolution of snakes. More details at Ed Yong's incomparable Not Exactly Rocket Science blog at National Geographic.
Martill called the creature Tetrapodophis: four-legged snake. “This little animal is the Archaeopteryx of the squamate world,” he says. (Squamates are the snakes and lizards.)