What’s the difference between a legless lizard and a snake?
When I posted a story, a few days ago, about 4 species of legless lizard discovered recently in California, a few people asked me, “Why is this called a legless lizard? Why don’t they just call these snakes?” I thought this was a good time to talk about the difference between “snakes” and “legless lizards”.
First off, some herpetologists consider snakes to be just another group of extremely varied and distinct legless lizards. Some would put snakes on an even footing with lizards as one of a few groups within a larger reptilian group called the saurians. Some would stick with the current taxonomy of the Squamata. Regardless of this, lets for the sake of this post consider snakes a distinct and different group from the rest of the “lizards”.
There are actually a few different groups of legless lizards, this is a physical trait that has popped up more than once in the evolutionary history of lizards. Also, it is generally accepted that snakes evolved from monitor lizards, or from a common ancestor with monitor lizards.
1. Snakes have no ears, internal, nor external. Most groups of legless lizards have ears, and you can often see the ear opening on the outside of the side of the head, no such hole exists on snakes.
2. Snakes have a forked tongue and a jacobson’s organ for chemoreception (smell), while most groups of legless lizards do not have forked tongues. Some may not possess a jacobson’s organ.
3. Snakes have a single row of wide belly scales, to aid in movement along surfaces. Most groups of legless lizards do not have such highly specialized belly scales.
4. Snakes do not posses eye lids, but a clear hard window like structure over the eye called a brille or spectacle. The brille is often referred to as a clear scale over the eye, but the structure is believed to be a fused structure composed of the upper and lower eyelids, which evolved over the millenia. Most legless lizards possess typical eyelids.
There are definitely more external and internal anatomical differences between snakes and the different groups of legless lizards, but these are 4 that I thought would be the most noticeable.
(photos of legless lizards, Anniella spp., by Alex Krohn)