More than 4,000 snake species live today, all descended from heavily modified lizard ancestors. Because early snake fossils are rare, researchers have struggled to determine which environments and behaviors shaped their evolution. Together with evidence from marine sediments, the findings reveal several shifts between burrowing, terrestrial and marine lifestyles in early snake evolution. The findings indicate that early snake evolution involved repeated movement between underground, terrestrial and marine environments. This means that early snakes did not follow a single evolutionary pathway," says Researcher Simone Macrì.