Snakes can famously disarticulate their jaws, and open their mouths to extreme widths. David Martill from the University of Portsmouth did his best impression of this trick while walking through the Bürgermeister Müller Museum in Solnhofen, Germany. He was pointing out the museum’s fossils to a group of students. “And then my jaw just dropped,” he recalls.

He saw a little specimen with a long sinuous body, packed with ribs and 15 centimetres from nose to tail. It looked like a snake. But it was stuck in unusual rock, with the distinctive characteristics of the Brazilian Crato Formation, a fossil site that dates to the early Cretaceous period. Snake fossils had been found in that period but never that location, and