Jonathan Amos at BBC News:
Found in Lebanon, the specimen is one of only three examples of an ancient snake with preserved leg bones.
One rear leg is clearly visible but researchers had to use a novel X-ray technique to examine another leg hidden inside the fossil rock.
Writing in the Journal of Vertebrate Paleontology, the team says the snake records an early stage in limb loss.
The scientists' high-resolution 3D images suggest the legs in this particular species, Eupodophis descouensi, grew more slowly, or for a shorter period of time.
It is a conclusion made possible only after seeing all the bones obscured inside the limestone, and determining that although the creature possessed ankle bones, it actually had neither foot nor toe bones.