Sorry, sea serpents. Snakes, it seems, slithered off their lizard legs on land. A new analysis of a primitive snake fossil suggests that these animals emerged from a line of burrowing reptiles.

Snakes are in the same reptilian order that includes lizards, but just how and where they split off to live their legless lives has been a bit of a mystery. Transitional fossils showing the move from four-legged lizard to belly-crawling snake have remained scarce. However, that the jawbones of a Cretaceous snake from North America suggest that it might be the earliest snake on record. And this serpent was terrestrial, clearing up decades of debate about whether snakes evolved for swimming or slithering, researchers reported online July 25 in Nature (Scientific American is part of Nature Publishing Group).

The first known example of the snake in question, Coniophis precedens, was collected in eastern Wyoming and described from a single vertebra in 1892. In the 120 years since, additional vertebrae and jaw bones from the species " have been collected but never described," wrote the researchers, led by Nicholas Longrich, of Yale University's geology and geophysics department. Their analysis shows that the 70 million-year-old specimen is probably the most primitive known snake—and a sister line to the nearly 3,000 snake species that exist today.

The early snake had slightly hooked teeth and a relatively flexible jaw joint, but much of the overall shape was still similar to a lizard. Its long slender body measured about 70 centimeters from snout to the base of its tail. In sum, it combined "a snake-like body with a lizard-like head," the researchers noted, which could have provided advantages for burrowing—and eating. (There are some legless lizards, but they have a slightly different skeletal structure and other distinctive lizard features.) Earlier research suggested that the first snakes might have been best adapted to feed on insects and other invertebrates. But the teeth and jaws of C. precedens suggests that it was "suited to piercing and holding soft-bodied prey," specifically small vertebrates.

This proto-snake likely lived in a floodplain area and "lacks adaptations for aquatic locomotion," the researchers noted. Instead, its vertebrae and the shape of its jaw suggest a life accustomed to burrowing, with time spent aboveground hunting for prey. Even ancient sea-faring snakes such as Simoliophiidae likely evolved from lines similar to this early landlubber.