Buzz
When a limbless reptile similar to the one pictured here crosses your path, you might assume it's a snake. However, that's not always the case. Throughout evolutionary history, numerous lizard species have independently lost their limbs. Today, we’ll explore the subtle yet significant differences that distinguish these creatures from snakes.
1. No legless lizard discovered so far possesses a forked tongue.
Snakes are known for their forked tongues, a trait shared by several lizard species, such as gila monsters, monitor lizards (including the Komodo dragon), and South American tegus. These specialized tongues play a crucial role in locating prey. Here's how they function: As animals move, they leave behind microscopic chemical particles in the air. Snakes and certain lizards collect these particles by flicking their forked tongues. Once the tongue retracts, the chemicals are transferred to the vomeronasal organs, which analyze the particles to identify the source. Despite the diversity among legless lizards, none are known to have this type of tongue.
2. SNAKES LACK EYELIDS, WHILE SOME LEGLESS LIZARDS RETAIN THEM.
Snakes are incapable of blinking or winking, as they lack eyelids entirely. Instead, evolution has equipped them with a unique adaptation to safeguard their eyes. Most snake species feature a thin, transparent scale over each eye, referred to as “spectacles” or “brilles.” These scales are shed and replaced periodically, just like the rest of their skin.
Many lizards, such as geckos, also have brilles instead of eyelids. However, several legless lizard species, like the glass lizards, retain movable eyelids. Found in regions like Morocco, North America, and parts of Asia, glass lizards are nearly limbless, with their forelimbs entirely absent and their hind limbs reduced to small, non-functional remnants beneath the skin. Despite their snake-like appearance, their eyelids set them apart.
3. SNAKES LACK EXTERNAL EAR OPENINGS.
A common misconception is that snakes are deaf. However, scientific research over the years has debunked this myth, proving that snakes can detect certain airborne sounds. The confusion likely stems from the absence of visible ear holes in snakes, which has led to the false belief that they cannot hear.
Unlike most land vertebrates, which possess both an eardrum and an inner ear, snakes lack the former. Their inner ears are directly linked to their jawbones, which typically rest on the ground. When another animal moves nearby, its footsteps create vibrations that travel through the ground, causing the snake’s jaw to vibrate. These vibrations are detected by the inner ear, which sends signals to the brain for interpretation, allowing the snake to identify the sound’s source. Additionally, low-frequency airborne sounds can be detected in a similar manner.
If you examine a snake closely, you’ll observe that it lacks ear holes on the sides of its head. In contrast, most legless lizards have visible ear openings. However, exceptions exist, such as the Australian Aprasia lizards, which are adapted for burrowing and typically lack external ear cavities, as their lifestyle doesn’t necessitate them.
4. SNAKES HAVE HIGHLY FLEXIBLE JAWS.
A lora, or parrot snake, consumes an evergreen robber frog in Panama. Image credit: Brian Gatwicke via Wikimedia Commons // CC BY 2.0
Contrary to a common myth, snakes do not unhinge or dislocate their jaws when feeding. Instead, their jaws are incredibly flexible, enabling them to swallow prey much larger than their own heads without the need for such extreme adaptations.
Similar to humans, a snake’s lower jaw is made up of two bones known as mandibles. In humans, these bones fuse to form the chin, but in snakes, they remain separate. This allows the two lower jawbones to move independently and even stretch apart significantly, providing remarkable flexibility.
In contrast, the jaws of most legless lizards are far less flexible, limiting them to smaller prey. However, Burton’s snake lizard (Lialis burtonis) is an exception. This unique predator feeds primarily on other lizards. Its skull features a specialized hinge that allows the front of its snout to swing downward, granting it the ability to swallow relatively large prey. Recurved teeth and a strong tongue further ensure the prey cannot escape.
5. MANY LEGLESS LIZARDS CAN DETACH AND REGROW THEIR TAILS WHEN THREATENED.
Unlike snakes, crocodilians, turtles, or tortoises, which cannot regenerate lost tails, many lizard species possess this remarkable ability. When threatened, these lizards can shed a portion of their tail, which later regrows, albeit not as perfectly as the original. This survival mechanism allows them to escape predators, as the detached tail continues to twitch, distracting the attacker. For a vivid example, see these graphic images of a tailless glass lizard.
The length of a legless lizard’s tail often correlates with its habitat. Burrowing species or those that live in sandy environments tend to have shorter tails, as longer tails would hinder their movement. Conversely, surface-dwelling lizards typically have longer tails, which help protect more critical body parts from predators by increasing the chances of a tail grab rather than a fatal injury.
