Fossil of a four-legged snake

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.”
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.)

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.