As I recently discussed, snakes are genetically nested within lizards. One of the major evolutionary implications of this fact is that snakes used to have legs. Just this week, researchers  heralded the discovery of a major fossil, helping to bridge the putative transition from legged-lizard ancestors to modern legless snakes.
Tetrapodophis 125-113 million years ago
A casual glance at Tetrapodophis reveals that it has a very snake-like body, possessing a typical snake-like count of over 150 vertebrae before the tail. To a trained morphologist, there are also a number of other features that are notably serpentine including recurved teeth and an intramandibular joint to allow for the widening of the gape, among others.
The most noteworthy feature, however, is the retention of all four limbs.
Above is a forelimb
and here are the hindlimbs.
Eupodophis 101-94 million years ago
After the appearance of Tetrapodophis, there are at least four known species of snakes that show evidence of a major modification compared to their predecessor: they have completely lost their forelimbs, but still retain hindlimbs. In Eupodophis, the example species I highlight here, the hindlimbs are further reduced, eliminating the foot bones altogether.
By contrast, modern snakes of course do not have legs. Some species, such as pythons and boas, have pelvic spurs, apparent remnants of the pelvis and femur, but the transition from legged to legless lizards appears to be mostly complete.
Questions for Creationists
Is it possible that God created snakes with legs? Where did they go? Is it a coincidence that the species with four legs appears in rocks that are older than the species with two legs, and before any snake species that have no legs? Is it also a coincidence that snakes are genetically nested within legged lizards?