In early 2008, in just one month of scouring the savanna of central Brazil, scientists discovered 14 new species. One of those new species was a type of legless lizard no one knew existed. A legless lizard? Wouldn't that be called a snake?
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Nope -- they're two entirely different animals from separate evolutionary lines. Legless lizards evolved from the legged lizards with which most of us are familiar; legless snakes evolved from four-legged snakes that most of us have never seen.
But the two do look an awful lot alike. Both have long, slender, cylindrical bodies; forked tongues; scaly exteriors and can often be found slithering through sand. And then, of course, there's the leglessness. It's tough for the casual observer to tell them apart. It's not impossible, though.
In this article, we'll find out what makes a legless lizard a lizard instead of a snake, why it's often called a "glass lizard," and how you might be able to distinguish this lizard from a snake the next time you find yourself looking at a long, slithery, legless reptile. It's not unlikely that you'd come into contact with one since they live all over the world, on every continent except Antarctica, and can thrive in all sorts of climates -- cool, hot, wet and dry. They're pretty widespread throughout the United States, especially in the Southeast and parts of the Midwest, Texas and California.
So let's say you're out hiking and you come across a snake-looking creature, anywhere from 10 inches (25 cm) to 4 feet (122 cm) long. It has the typical reptile coloring, tan or brown, green, bronze or yellowish, and maybe it sports a dark stripe along its back. Is it a snake or a legless lizard?
Legless Lizards vs. Snakes
It's very understandable if you see a legless lizard and assume you're looking at a snake. The two are similar animals, not only in appearance, but also in behavior. Both lay eggs that mature outside the body, both slither along the ground in a roughly S-like fashion, and both eat some of the same things, like mice and bird eggs. Glass lizards also enjoy beetles, grasshoppers, snails and spiders.
They tend to go for the smaller prey. This is because a major physical trait that distinguishes them from snakes: Glass lizards have inflexible jaws. Unlike snakes, they can't "unlock" their jaws to swallow a whole rabbit. A legless lizard has to stick to prey that's smaller than its own head.
There are other differences that are easier to spot. Glass lizards have moveable eyelids; snakes have no eyelids at all. Glass lizards also have ear openings, while snakes don't. And then there's the trait that earned the creature the "glass" moniker.
Legless lizards, like most other lizards, can detach their tail when they need to. When threatened by a predator, one of the legless lizard's main defensive mechanisms is to separate its body from its tail. It leaves the tail behind -- still wriggling -- to distract whatever predator is after it, and then runs away. When the tail breaks off, it often breaks into more than one piece, appearing to shatter like glass. The lizard can only regenerate the tail one time, though, and regeneration can take several months to a year or two [sources: WDNR, LHS].
The tail-drop is a very effective defense mechanism, even if it only has limited use. Most of a legless lizard's length (up to two-thirds) is tail [source: Snakes and Frogs]. A snake has the opposite proportions. If you pick up a legless lizard, you'll notice that it doesn't feel quite like a snake, and that's in part because of this difference in body-to-tail proportion. Since the tail is stiffer than the body, a snake feels more supple than a glass lizard.
A legless lizard's comparatively limited range of motion isn't just about its proportions. Whereas a snake can use its sides and its belly scales to push itself along the ground, a legless lizard can only use its sides. Its motion is only side-to-side, which is a serious drawback in terms of survival. It does just fine when it has objects to push up against, but if it ends up on a totally flat surface, like a paved road, it can't move at all. So whereas a snake can move across a roadway before a car hits it, a legless lizard is just a sitting duck. With more and more development infringing on their habitat, legless lizards increasingly find themselves falling short of their typical 8-to-9 year lifespan [source: WDNR].
Even with all of these differences, glass lizards and snakes appear to come from similar beginnings. In 2007, scientists discovered a 95-million-year-old fossil that's the oldest known proof of the lizard's evolution to a legless state. This new fossil, called Adriosaurus microbrachis, has tiny, nonfunctioning front legs, but still-functioning and normal-sized hind legs. The fossil is the same approximate age as snake fossils that have similar vestigial front legs, leading to the conclusion that snakes and lizards lost their legs around the same time. The new creature is believed to be the closest relative to whatever spawned both snakes and lizards.
For more information on legless lizards and related topics, slide through the links on the next page.
Related HowStuffWorks Articles
More Great Links
- California Legless Lizard Relocation Project. Moss Landing Marine Laboratories. http://www.anniella.org/
- Glass Lizard. Herp Care Collection. http://www.anapsid.org/legless.html
- The Glass Lizards. SnakesAndFrogs. http://www.snakesandfrogs.com/scra/lizards/glasslizards.htm
- Legless Lizard, Other New Species Discovered. National Geographic. May 2, 2008. http://news.nationalgeographic.com/news/2008/05/photogalleries/Brazil-pictures/index.html
- Legless Lizards. LHS Biology Lab. http://www.lawrencehallofscience.org/biolab/wlhleglesslizard.html
- Slender Glass Lizard. University of Georgia Savannah River Ecology Laboratory. http://www.uga.edu/srelherp/lizards/ophatt.htm
- Slender Glass Lizard. (Ophisaurus attenuatus). Wisconsin Department of Natural Resources. http://www.dnr.state.wi.us/ORG/LAND/ER/factsheets/herps/slnliz.htm
- Weird Lizard Fossil Reveals Clues to Snake Evolution, Experts Say. National Geographic News. March 26, 2007. http://news.nationalgeographic.com/news/2007/03/070326-lizard-snakes.html