This video says about itself:
Lizards, Snakes and Legs (Evolution)
27 September 2008
David Attenborough explaining how lizards lost their legs.
From daily The Independent in Britain:
Ancient snake skull found in Argentina could reveal why the reptiles have no legs
The research challenges the theory that snakes originally became limbless as they began to live in the sea
John von Radowitz
27 November 2015
A fossilised snake skull found in Argentina may have solved the mystery of how the animals lost their legs.
Rather than shed them to become better swimmers as they began to inhabit aquatic environments, the skull, from 90 million years ago, suggests legs became an evolutionary disadvantage as the ancestors of modern snakes wriggled into increasingly narrow burrows in pursuit of prey.
The research challenges the theory that snakes originally became limbless as they began to live in the sea. The secret of the lost limbs was revealed by an examination of the inner ear of Dinilysia patagonica, a two-metre long relative of the modern snake.
Using Computed Tomography (CT), scientists found a distinctive structure in its bony canals and cavities that was also turned out to be present in modern burrowing snakes and lizards.
But the structure, which may assist with the detection of prey and predators, was missing from snakes that live in water or above ground. Lead scientist Dr Hongyu Yi, from the University of Edinburgh’s School of GeoSciences, said: “How snakes lost their legs has been a mystery to scientists but it seems this happened when their ancestors became adept at burrowing.
“The inner ears of fossils can reveal a remarkable amount of information and are very useful when the exterior of fossils are too damaged or too fragile to examine.”
The findings, published in the journal Science Advances, confirm Dinilysia patagonica as the largest burrowing snake ever known.
Co-author Dr Mark Norell, from the American Museum of Natural History, said: “This discovery would not have been possible a decade ago. CT scanning has revolutionised how we can study ancient animals.
“We hope similar studies can shed light on the evolution of more species, including lizards, crocodiles and turtles.”
A CT scan is an advanced form of X-ray that generates detailed 3D images of organs and skeletal structures.
See also here.
Four fossils previously identified as lizards now known to be dinosaur-age primitive snakes. A study led by Michael Caldwell, from the university of Alberta in Canada, has shed new light on the evolution of snakes from their legged ancestors. Four fossils found in England, Portugal and the United States that were previously thought to be lizards have been reevaluated and shown to actually be early serpents. The new fossils were dated to 143-167 million years ago, pushing back the date of the earliest known snake by more than fifty million years. The fossils also contradict a theory which suggested that the characteristic long and thin facial structure of snakes evolved only after the loss of the legs: here.
Dear Kitty. Some blog 
Pingback: Dinosaur extinction, new theory | Dear Kitty. Some blog
Pingback: Fossil snake discovery in Tennessee, USA | Dear Kitty. Some blog
Pingback: Biggest dinosaur ever discovered | Dear Kitty. Some blog
Pingback: Caecilian amphibians’ snake-like venom, new discovery | Dear Kitty. Some blog