Image caption The animal combined a lizard-like head with a snake-like body

One of the most primitive snake fossils ever found hints that the slithery reptiles might have originated on land, not in the sea as has been proposed.

The animal, which lived at the same time as the dinosaurs, probably emerged from a line of burrowing reptiles that lost their legs.

Where and how snakes diverged from their legged cousins the lizards has been a mystery.

Details of the find appear in the journal Nature .

The debate over snake origins has been complicated by the scarcity of transitional fossils (those with features in between two groups of creatures).

But new fossils from eastern Wyoming, US, belonging to the ancient snake Coniophis precedens - which lived some 65-70 million years ago - could help clear up the mystery.

According to the analysis by Nicholas Longrich from Yale University and colleagues, Coniophis lived in a floodplain environment and "lacks adaptations for aquatic locomotion".

They describe it as a "transitional snake, combining a snake-like body and a lizard-like head".

"This thing quite probably would have had small legs," Dr Longrich told the AFP news agency.

The ancient reptile's small size, along with physical features of its spine, suggest that it burrowed. And analysis of its jaws show that it fed on relatively large, soft-bodied prey.

But it did not have the flexible jaws that allow modern-day snakes to swallow prey many times their own body size.

"The genesis of the Serpentes (the biological name that defines what we understand as snakes) that began with the evolution of a novel means of locomotion, followed by adaptations facilitating the ingestion of ever larger prey, thereby enabling snakes to exploit a wider range of ecological niches," the researchers write in Nature journal.