The first snakes likely resembled lizards, with four legs and a long tail. As they evolved, some snake species eventually lost their limbs while their backbones began to lengthen and their body muscles and scales adapted to allow slithering movement. Fossils of early snakes from around 167 million years ago show these transitional lizard-like forms with rudimentary or reduced hind limbs. Over millions of years, natural selection favored individuals with enhanced gliding and burrowing abilities until limbless snakes as we know them today became the norm within their diverse lineage.