ScienceShot: How a Lizard Lost Its Legs

by Brian Switek 

Credit: (Left to Right) Robert Reisz; Gary Nafis

"Worm lizards," a group of mostly legless reptiles, have long puzzled zoologists. Are these animals (right)—also known as amphisbaenians—lizards that lost their legs over time, or are they closer relatives of snakes? Thanks to an approximately 45-million-year-old worm lizard fossil found in Messel, Germany's exquisite fossil deposits, the mystery has now been solved: Amphisbaenians are truly lizards, after all. As reported online today in Nature, the nearly complete skeleton of the small fossil lizard Cryptolacerta hassiaca (left) had a thick skull characteristic of modern worm lizards, yet the reptile retained arms and legs. Although this animal was about 20 million years too late to be a direct ancestor of other worm lizards, the researchers propose that it retained the form of worm lizard ancestors and is therefore useful in tracking the group's origins. Not only does the find indicate that these peculiar lizards independently paralleled snakes by losing their limbs, but that a sturdy skull adapted to burrowing and rooting through the leaf litter preceded the loss of limbs in these lizards. Once the lizards began burrowing, their arms and legs gradually became reduced in size and they eventually took on a superficially snakelike appearance.