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5 Slithering Differences Between Snakes and Legless Lizards

Ceci n'est pas un serpent. It's a glass lizard. Image credit: Don Becker via Wikimedia Commons // CC BY-SA 3.0

 
If a limbless reptile like the one above crosses your path, it’s obviously a snake, right? Maybe not. Over the course of evolution, many different lizards have independently lost their legs. Today, we’re looking at the subtle differences that set these creatures apart from their serpentine brethren.

1. WE’VE YET TO FIND A LEGLESS LIZARD WITH A FORKED TONGUE.

All snakes have such tongues—as do a fair number of lizards, including gila monsters, monitor lizards (such as the Komodo dragon), and South American tegus. When it comes to tracking down food, these pronged organs are incredibly useful. Here’s how they work: Wandering animals leave microscopic taste particles floating behind them in the air. Snakes and some lizards gather these up by flicking their forked tongues. After the tongue is drawn back into the mouth, the chemicals are delivered to a sensory apparatus called the vomeronasal organs. These help the reptiles figure out what sort of creature produced the taste particles in question. Although legless lizards are a diverse bunch, none that we know of feature this kind of tongue.

2. SNAKES DON’T HAVE EYELIDS, BUT SOME LEGLESS LIZARDS DO.

Snakes can’t blink (or wink, for that matter). Unlike us, the slithering reptiles don’t possess eyelids. Evolution’s given them a different way to protect their invaluable pupils. In the vast majority of species, a thin, transparent scale covers each eye. These are known as “spectacles” or “brilles” and, like most scales, they’re regularly replaced when the snake sheds its skin.

Numerous lizards—including most geckos—also have brilles instead of eyelids. However, many legless species sport the latter. For example, consider the so-called “glass lizards.” A widespread group, these lithe creatures can be found in Morocco, North America, and parts of Asia. Like snakes, glass lizards are essentially devoid of legs: Their forelimbs are completely gone while their rear legs have evolved into useless nubs that lie buried under the skin. Yet, unlike snakes, glass lizards do possess moveable eyelids.

3. NO KNOWN SNAKE HAS EXTERNAL EAR HOLES.

It’s often said that snakes are deaf. Over the past few decades, research has thoroughly disproved this notion, and we now know that the animals can easily detect certain airborne sounds. So where did the whole myth about snakes not being able to hear come from? Well, the misconception probably has something to do with the fact that snakes don’t have visible ear openings.

Most land vertebrates have both an eardrum and an inner ear. Snakes, on the other hand, lack the former. Their inner ears are connected directly to the jawbones, which usually rest against the ground. Whenever some other animal walks by, its footsteps inevitably produce vibrations. These travel through the earth and cause the snake’s jaw to vibrate in response. The inner ear then signals the brain, which interprets the data and identifies the source of the sound. Low-frequency noises that travel through the air can also be picked up in more or less the same manner.

Look closely at a snake, and you’ll notice that there aren’t any ear holes on the sides of its head. In contrast, most legless lizards have a pair. Then again, some varieties don’t. The Australian Aprasia lizards are adapted for a burrowing lifestyle—one that doesn’t really require external ear cavities. As such, most members of this genus lack these openings altogether.

4. SNAKE JAWS TEND TO BE A LOT MORE FLEXIBLE.

A lora, or parrot snake, eats an evergreen robber frog in Panama. Image credit: Brian Gatwicke via Wikimedia Commons // CC BY 2.0


 
Contrary to popular belief, snakes don’t unhinge or dislocate their jaws while feeding. They simply don’t need to. An average snake can swallow prey that are several times larger than its own head. This feat is made possible by an amazingly flexible set of jaws.

Just like in humans, a snake’s lower jaw consists of two bones called mandibles. Ours meet to form a chin, which is where the separate bones become fused. Snake mandibles aren’t joined together in this manner. Instead, the two lower jawbones can move independently of each other and can even splay apart to a considerable extent.

By comparison, the jaws of most legless lizards are far less maneuverable. As a result, they tend to eat proportionally smaller prey—but there’s an exception to this rule. Burton’s snake lizard (Lialis burtonis) is an unusual predator that specializes in eating other lizards. Bisecting the skull is a special hinge which enables the front of its snout to swing downwards. This gives Burton’s snake lizard enough oral flexibility to swallow fairly big prey whole. Recurved teeth and a muscular tongue help prevent the prey from escaping.

5. WHEN THREATENED, MANY LEGLESS LIZARDS CAN DISCARD AND RE-GROW THEIR TAILS.

If a snake, crocodilian, turtle, or tortoise loses its tail, the animal won’t be able to replace it with a new one. In the world of reptiles, that talent is reserved for lizards. Many—but not all—lizard species can famously lose a segment of their tail and then regenerate it (although the replacement is not as good as the original). This is no parlor trick: Out in the wild, it’s a potentially life-saving maneuver. Should a predator seize a lizard by the tail, the whole appendage can break off. Afterward, this discarded appendage might flail and spasm, distracting the attacker long enough for our lizard to escape. Check out some graphic images of a glass lizard sans tail.

There’s a correlation between a legless lizard’s habitat and the length of its tail. Species that burrow through dirt or spend most of their time submerged in sand have relatively short tails. In contrast, those that live at the surface have rather long ones. Why is this? To lizards with subterranean habits, lengthy tails can be a nuisance because they create excessive drag during digs. Up above the soil, however, a really long tail reduces the odds of some predator snagging a more vital part of the body.

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Slow Motion Is the Only Way to Appreciate a Chameleon’s Lightning-Fast Tongue
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From the unusual way they walk, to their ability to change color, the evolutionary adaptations of chameleons are pretty bizarre, and some of them remain mysterious even to scientists. Their super-powered tongues, for instance, can dart out so quickly that the movement can barely be seen with the naked eye. But modern high-speed cameras have enabled researchers at the University of South Dakota to observe this appendage at work like never before. The video below, shared over at The Kid Should See This, includes some of that groundbreaking footage, and it's pretty amazing to watch.

Shooting at 3000 frames per second, the camera was able to capture every split-second aspect of the chameleon's tongue strike. Slowed down, the video allows you to see how every component of the process works in harmony: First, muscles in the lizard’s tongue contract like the string of a bow. Then, when that tension is released, the bony base of the tongue shoots forward, pushing the sticky, elastic part toward the chameleon’s prey.

According to Christopher Anderson, one of the scientists who conducted the high-speed camera research, larger chameleons can catapult their tongues forward at distances of one to two times their body length. For smaller chameleons, this distance can reach up to two and a half times their body length. “Small chameleons need to be able to eat more food for their body size than large chameleons,” he tells bioGraphic in the video, “and so by being able to project their tongues proportionately further than these large species, they basically are opening up additional feeding opportunities to themselves that they wouldn’t have if they had a shorter tongue.”

To see one of nature’s greatest hunting tools in action, check out the full video below.

[h/t The Kid Should See This]

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There May Be an Ancient Reason Why Your Dog Eats Poop
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Dogs aren't known for their picky taste in food, but some pups go beyond the normal trash hunting and start rooting around in poop, whether it be their own or a friend's. Just why dogs exhibit this behavior is a scientific mystery. Only some dogs do it, and researchers aren't quite sure where the impulse comes from. But if your dog is a poop eater, it's nearly impossible to steer them away from their favorite feces.

A new study in the journal Veterinary Medicine and Science, spotted by The Washington Post, presents a new theory for what scientists call "canine conspecific coprophagy," or dogs eating dog poop.

In online surveys about domestic dogs' poop-eating habits completed by thousands of pet owners, the researchers found no link between eating poop and a dog's sex, house training, compulsive behavior, or the style of mothering they received as puppies. However, they did find one common link between the poop eaters. Most tended to eat only poop that was less than two days old. According to their data, 85 percent of poop-eaters only go for the fresh stuff.

That timeline is important because it tracks with the lifespan of parasites. And this led the researchers to the following hypothesis: that eating poop is a holdover behavior from domestic dogs' ancestors, who may have had a decent reason to tuck into their friends' poop.

Since their poop has a high chance of containing intestinal parasites, wolves poop far from their dens. But if a sick wolf doesn't quite make it out of the den in time, they might do their business too close to home. A healthier wolf might eat this poop, but the parasite eggs wouldn't have hatched within the first day or two of the feces being dropped. Thus, the healthy wolf would carry the risk of infection away from the den, depositing the eggs they had consumed away in their own, subsequent bowel movements at an appropriate distance before the eggs had the chance to hatch into larvae and transmit the parasite to the pack.

Domestic dogs may just be enacting this behavior instinctively—only for them, there isn't as much danger of them picking up a parasite at home. However, the theory isn't foolproof. The surveys also found that so-called "greedy eaters" were more likely to eat feces than dogs who aren't quite so intense about food. So yes, it could still be about a poop-loving palate.

But really, it's much more pleasant to think about the behavior as a parasite-protection measure than our best pals foraging for a delicious fecal snack. 

[h/t The Washington Post]

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