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Why do tails of some lizards break so easily?

Why do tails of some lizards break so easily?


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When I was younger once I have tried to catch a ground lizard by its tail but, unfortunately the tail got broken and the lizard ran away.

Why did the lizard's tail get broken so easily while other animals have stronger tails?


It's a self-defense mechanism, the tail falls off during threatening situations, to which the reptile responds by excessively contracting the tail muscles. This process is known as "Autotomy", or "Self-Amputation". Other animals have got "stronger tails" simply because such self-defense mechanism hasn't been developed. https://science.sciencemag.org/content/20/500/149.2 Check this link for more in depth information!


Autotomy

Autotomy means “self-amputation” and is a mechanism to escape from predators. When the animal is attacked the brightly colored tail will break off and wriggle for a few minutes to distract the attacker, allowing the lizard to escape. It occurs in many lizards, such as the iguana, skink, and gecko species, where the tail is not essential for survival ( Figs. 4.13 and 4.14 ). However, species like chameleons and monitors, which rely on their tail for climbing and defense, do not shed their tails. Similarly, the Marine iguana, which relies on its large rudder tail for swimming in the sea, lacks fracture planes.

Autotomy is created by a vertical fracture plane, containing no bone, passing through the body and part of the neural arch of each caudal vertebra (Bellairs 1998h Bellairs & Bryant 1985 Evans 1986 Pough 1998b ). This is a plate of cartilage or connective tissue that develops after ossification. These are not present in the cranial part of the tail so the cloaca and hemipenes are protected. In iguanas the fracture plane is replaced by bone during maturation, resulting in a more stable tail in adults.

After autotomy the stump should never be stitched as the broken tail rapidly forms its own scab that is followed by growth of new epidermis within a week or two. Bleeding is minimal, owing to the action of sphincter muscles in the caudal arteries and valves in the veins. After about 2 weeks regeneration begins and a cylinder of cartilage is formed. This may become calcified, but as it has no individual tail vertebrae it is less flexible than the original model. It is innervated mainly by the last spinal nerves. It is finally covered by scales, which are often smaller and a different color from the original tail (Bellairs 1998h Bellairs & Bryant 1985 Pough 2002 ).

Kinetic jaw for wide gape

Large well-developed adductor (jaw-closing) muscles, so mind your fingers!

Hind foot has first four metatarsal bones lying together while fifth metatarsal lies separated with backward-pointing hook

Tail can self amputate (autotomy)


Scientists Have Figured Out How Lizards Regrow Their Tails, And That's Good News For Humans

When a lizard loses its tail, it grows back. But how?

Scientists have taken a big step closer to answering that question by pinpointing the genes responsible for tail regeneration. And the finding may yield important clues about how to regenerate limbs in humans.

For the study, the researchers took a close look at roughly 23,000 genes found in samples of sliced-up tails of green anole lizards. They found that at least 326 genes in specific spots along each tail were "turned on" during regeneration -- suggesting that lizard DNA has a genetic "recipe" for regeneration.

"We were completely surprised," study co-author Dr. Kenro Kusumi, a professor of life sciences at Arizona State University, told The Huffington Post in an email. "We were expecting all of the regeneration to be focused at the tip of the growing tail. Instead, the cells are dividing in distinct pockets including muscle, cartilage, spinal cord, and skin all throughout the tail."

And from there, the cells would grow into new tissue to form a new tail.

(Story continues below)
The regenerated lizard tails. The green anole lizard (Anolis carolinensis), when caught by a predator, can lose its tail and then grow it back. Researchers have discovered the genetic 'recipe' that explains how this happens.

"Regeneration is not an instant process," study co-author Elizabeth Hutchins, a graduate student at the university, said in a written statement. "It takes lizards more than 60 days to regenerate a functional tail."

What about human limb regeneration? The researchers said their finding may help pave the way for new therapeutic approaches for birth defects and spinal cord injuries -- and possibly arthritis too. Nearly all of the 326 genes pinpointed by the researchers are present in humans as well as lizards, Kusumi said.

"As anyone who suffers from arthritis knows, an important part of the limb are joints, which are cushioned by a specific type of cartilage," Kusumi said in the email. "Lizards grow lots of this cartilage in their regenerated tails, and we hope that this process can be activated to repair arthritis in humans."

The new study was published online in the journal PLOS ONE on August 20, 2014.


Why do lizards lose their tails? -Bailey, Inwood, Iowa

Our planet is home to all kinds of lizards. Maybe you’ve seen one climbing up the wall, scurrying through the grass, or at the pet store. Just the other day I saw a big green iguana when I visited the Washington State University Veterinary Teaching Hospital in search of an answer to your question.

Lizards hatch from eggs, have a backbone, scales, and depend on the environment to keep warm. They have four legs and claws, and a tail, which they sometimes lose and grow back. My friend Marcie Logsdon was taking care of the big iguana and several other exotic animals. She told me all about lizard tails.

Lizards have a series of small bones that run down their back. They are called vertebrae. Along the tail are several weak spots called fracture planes, Logsdon said. They are the places where the tail can detach.

The main reason a lizard loses its tail is to defend itself. When a lizard detaches its tail, the tail whips around and wiggles on the ground.

Nerves from the lizard’s body are still firing and communicating with each other. In fact, sometimes the tail will keep moving for upwards of a half hour. This distracts a predator and gives the lizard plenty of time to escape.

When the lizard’s tail grows back, it’s a bit different than it was before. Instead of a tail made of bone, the new tail is often made out of cartilage, the same stuff that’s in your nose and ears. It can take quite a while for the cartilage to form, too.

The small green anole has a tail that is only about four inches long, but it takes about two months to grow back. Meanwhile, a longer iguana tail might take more than a year to grow back.

Most lizards can only lose their tails so many times before they can’t regrow them anymore. Of course, there are the exceptions. The crested gecko is one lizard that can lose its tail, but it doesn’t grow back.

Like lizards, some squirrels also lose their tails to escape predators. But their tails also don’t grow back. In nature, we see other animals that regrow different parts. Some worms split into pieces can grow into new individual worms. Sea cucumbers can do this as well. Some spiders can even regrow missing legs or parts of legs. Some salamanders can also shed their tails.

You know, tails can come in handy. Some lizards can wrap their tails around vines or branches. Others use their tails as a kind of propeller to help them move through the water. Tails are also useful for balance. And for some lizards, being able to ditch their tail might just save their life.


Lizard tails exhibit modifications that facilitate tail loss and minimize tissue damage

As a general rule, all lizard species capable of tail regeneration exhibit the ability to shed or readily lose their tails as a method of escape from potential predators. This ability of “self-amputation”, known as autotomy, is facilitated by several modifications to lizard tail tissues that work to minimize tissue damage during tail loss. For example, lizard tail vertebrae contain structures known as fracture planes, pre-formed breaks in the bone along which tails readily separate (1) ( Fig. 2 ). Each fracture plane is continuous with autotomy septa that pass through fat, muscle, and connective tissue. Furthermore, fracture planes and autotomy septa are positioned just distal to sphincters and valves in caudal arteries and veins, respectively. Autotomy planes/septa do not bisect the tail spinal cord, however, which is severed during tail loss. Thus, following tail loss by autotomy, tail tissues separate along fracture planes and autotomy septa, minimizing bone and muscle tissue damage, and blood vessel sphincters/valves remaining in tail stumps contract to limit blood loss. The resultant tail stump ends at the vertebrae fracture plane and includes a severed spinal cord ( Fig. 3A ).

Autotomous lizard tail vertebrae contain fracture planes. Original tails of (A) Anolis carolinensis, (B) Hemidactylus frenatus, (C) Heteronotia binoei, and (D) Hoplodactylus duvaucelii analyzed by micro computed tomography and highlighting the diversity of fracture plane position and structure. Open arrowheads denote intravertebral fracture plane. White-filled arrowheads mark intervertebral pads (ip). Black-filled arrowheads identify Z-joints (z). Bar = 100 μm.

Representative lizard tails (A) 0, (B) 3, (C) 6, (D) 9, (E) 12, (F) 15, (G) and 28 days following tail loss highlighting the important structures involved with tail regrowth. ac, apical cap bl, blastema ct, cartilage tube dst, degenerated stump tissue m, muscle rm, regenerated muscle rsc, regenerated spinal cord sc, spinal cord we, wound epithelium ve, vertebra.

While fracture planes and autotomy septa greatly reduce tissue damage following autotomy, they are apparently not required for regeneration. For example, amputation of gecko tails by scalpel blades outside of fracture planes does not appear to affect tail regeneration (2), with both autotomized and amputated tails regenerating similarly. However, other studies involving Anolis lizards have indicated that amputated tails significantly regenerate shorter compared to autotomized tails (3). Perhaps the most telling evidence supporting the hypothesis that tail regeneration does not require autotomy planes is the fact that amputations made to regenerated tail regions are able to re-regenerate ( Fig. 4 ). As previously mentioned, regenerated lizard tail skeletons consist of unsegmented cartilage tubes ( Fig. 4A,B ). While lizard cartilage tubes partially calcify, they do not develop fracture planes ( Fig. 4B ). Interestingly, amputations to either proximal or distal regenerated regions resulted in re-regenerated tails of similar lengths to those regrown from original tail amputation sites ( Fig. 4C ) (Lozito, unpublished data). Regeneration efficiency was influenced by both position and lizard species. For example, in Anolis lizards, proximal regenerated tail regions re-regenerated in response to 98% of amputations, while more distal regions re-regenerated in response to only 9.57% of amputations (Lozito, unpublished data). In geckos, however, distal regenerated tails regions re-regenerated in response to 100% of amputations (Lozito, unpublished data). In this light, it appears that fracture planes and regeneration are separate, and the inability of other reptilian tails to regenerate (snakes, turtles, rarely in crocodilians) is probably not due to a lack of fracture planes. Instead, it is probable that regenerative lizards possess some cell-type and/or signal that is not found in non-regenerative reptiles and that is responsible for initiating regeneration.

Regenerated lizard tails are able to re-regenerate following amputation. (A,B) Mature lizard tail regenerates with CTs were amputated in (1) the original tail vertebra (Orig), (2) the proximal regenerated tail (Prox), or (3) the distal regenerated tail (Dist). (A) Morphological and (B) microCT analyses of an intact mature lizard regenerate showing relative position of amputation sites. (B) The skeletons of original, but not regenerated, tail regions. Fracture planes (fp) are present in (C𠄾) Following 4 weeks of regeneration, tails amputated in the (C) original tail, (D) proximal regenerate, or (E) distal regenerates were analyzed for overall regenerate elongation. fp, fracture plane. Bar = 0.5 cm.


Why salamanders can regrow perfect tails, but lizards can’t

You are free to share this article under the Attribution 4.0 International license.

New research explains why tail regeneration is perfect in salamanders and imperfect in lizards—and may help clarify why mice can’t regenerate their tails at all.

Stem cells in the spinal cord are the ultimate limiting factor, scientists report in the Proceedings of the National Academy of Sciences.

“The traditional animal model for regeneration is the salamander,” says senior author Thomas P. Lozito, assistant professor in the orthopaedic surgery department, the Center for Cellular and Molecular Engineering, and the McGowan Institute for Regenerative Medicine at the University of Pittsburgh.

“Salamanders can regenerate a wide variety of tissues—brain, heart, parts of their eyes, limbs, tails—but they have whole classes of molecule types and tissues that just aren’t found in mammals, so we really haven’t been able to apply very much of what we found in the salamander to humans.”

“You can easily tell a lizard with a regenerated tail. It doesn’t get anything right.”

If the goal is to translate regeneration research to non-regenerating species like humans, the lizard is a much better model than the salamander, according to Lozito. Lizards are the closest relative to mammals that can regenerate an appendage, and they have a similar genome and biochemistry.

But lizards cannot regenerate lost limbs at all, and their regenerated tails are much simpler than the originals.

Salamanders tails regenerate perfectly, whereas lizard tails grow back imperfectly, and mouse tails don’t grow back at all. (Credit: Thomas P. Lozito)

“You can easily tell a lizard with a regenerated tail,” Lozito says. “It doesn’t get anything right. The scales are different the color pattern is different, and then when you look inside the tail, all the tissues are different. There’s no bone the skeleton is completely cartilaginous, just tubes within tubes.”

Understanding what separates perfect regeneration in the salamander from imperfect regeneration in the lizard lays the groundwork for bridging the gap to non-regenerating species, he says.

Lozito’s lizard of choice is the mourning gecko, which has several interesting properties, including a high tolerance for transplantation.

“The spinal cord is the master regulator of tail regeneration…”

This feature allowed Lozito and colleagues to take neural stem cells—the nascent precursors of neurons and glia, the non-neuronal cells that surround them—from the salamander and insert them into the lizard’s regenerating tail stump. They wanted to see what holds back tail regeneration in the lizard: the biochemical environment or the lizard’s native stem cells.

The transplanted salamander stem cells retained their ability to differentiate into multiple cell types, including neurons. By contrast, lizard neural stem cells could become only glial cells, which don’t process the messages that direct movement and feeling.

The regenerated lizard spinal cord (top right) contains fewer nerves than the original (top left) and they are encased in a tube of cartilage. In contrast, regenerated salamander spinal cord (bottom right) has all of the structure and form of the original (bottom left). (Credit: Thomas P. Lozito)

“It was a nice surprise,” says lead author Aaron Sun, a physician-scientist trainee who completed part of his research in Lozito’s lab. “And it goes to show that maybe the regenerative processes are still somewhat conserved.”

Fish retinas heal themselves. Could ours, too?

But perhaps the most surprising observation, Sun says, is that the traditionally described “neural stem cells” driving regeneration in the lizard are not “true” neural stem cells at all. Although they check many of the classic boxes, they fall short of a defining characteristic—the ability to spring forth a diversity of cell types.

That explains why there isn’t perfect tail regeneration in the lizard, Lozito says. The neural stem cells can’t produce the different cell types that would be needed to recreate the asymmetries of the original spinal cord, which in turn stymies the development of bony vertebrae.

“The spinal cord is the master regulator of tail regeneration, and these differences that we’re seeing between lizard and salamander tails are due to differences in stem cell quality,” Lozito says. “It’s all because of the neural stem cells.”


Internal Fertilization

The information below is adapted from OpenStax Biology 43.2

Internal fertilization occurs most often in land-based animals, although some aquatic animals also use this method. There are three ways that offspring are produced following internal fertilization:

  • Fertilized eggs are laid outside the female’s body and develop there, and the embryo receives nourishment from the yolk that is a part of the egg. This occurs in most bony fish, many reptiles, some cartilaginous fish, most amphibians, two mammals, and all birds.
  • Fertilized eggs are retained inside the female’s body, but the embryo receives nourishment from the egg’s yolk and the young are fully developed when they are hatched. This occurs in some bony fish, some sharks, some lizards, some snakes, some vipers, and some invertebrate animals.
  • Fertilized eggs are retained inside the female, and the embryo receives nourishment from the mother’s blood through a placenta. The offspring develops in the female and is born alive. This occurs in most mammals, some cartilaginous fish, and a few reptiles.

Internal fertilization has the advantage of protecting the fertilized egg from dehydration on land. In many instances, the embryo is isolated within the female, which limits predation on the young. Internal fertilization also increases the likelihood of fertilization by a specific male. Fewer offspring are produced through this method, but their survival rate is higher than that for external fertilization.


Leaping Lizards: Quirky Facts About Those Resident Reptiles

Tree lizards show off their colorful bellies while doing pushups to defend their territories. (Photo: Bob Demers/UANews)

You hear them scurrying in the underbrush. You see them running up trees. Maybe you've even spotted one in your shower, or stuck to your kitchen window.

If you live in Tucson, you're accustomed to seeing lizards. But how much do you really know about them?

The Old Pueblo is home to roughly a dozen different species of lizards, says John Wiens, a University of Arizona professor of ecology and evolutionary biology who studies reptiles and amphibians.

On the UA campus, Wiens says, there are three main native species. The most common, active year-round, are tree lizards, which are small, brown or gray in color — and can be tough to spot because of the way they blend into rocks and tree bark. Sonoran spotted whiptails, with their long tails and dark and light stripes, are fast moving and always on the go. The desert spiny lizard has a thicker body and is longer than the other two, reaching up to 12 inches — and, true to its name, is covered in imposing spines. The whiptail and desert spiny lizards are active mostly in the warmer months, from March to October.

Though not native to Arizona, Mediterranean geckos also are common in warmer months, Wiens says. Attracted to insects around lights at night, they are the ones you may have spotted in silhouette on your windows, thanks to their sticky feet.

Lizards are without a doubt part of everyday life in the desert. They're also fascinating creatures, with some unique quirks that set them apart from other desert dwellers.

Wiens shared some insights into how lizards behave:

1. Lizards like it hot … but not too hot.

Lizards enjoy sunny days and are most active in Tucson during the warmer months.

However, when temperatures climb into the 90s and 100s, lizards try to avoid direct sunlight. They might seek a shady spot or retreat into a rock crevice or abandoned rodent burrow, Wiens says.

"In some ways, what's comfortable for us is a pretty good indication of what's comfortable for them," Wiens says. "They pretty much like the same temperatures that we do."

To beat the summer heat, lizards generally are most active in the early morning and around sunset — like many Tucsonans.

2. They do pushups for the ladies.

You might have seen a lizard doing pushups in your yard, on a wall or on the side of a tree. Tree lizards, desert spiny lizards and other members of the "iguanian" group of lizards engage in this behavior as a way to defend their territory against rival males and perhaps show off to potential mates, Wiens says.

As they do pushups, they show off bright blue patches on their bellies, and throat patches that can be blue, green, red, yellow or orange.

Both male and female lizards set up territories of just a few feet.

"An optimal territory for a male overlaps the territory of a bunch of females, and that's what they're going to be fighting other males over," Wiens says.

3. They can ditch their tails when trouble's afoot and regrow new ones.

Many lizards, including the native species on the UA campus, are born with tails that are pre-broken, so if they find themselves in a tough spot — maybe a cat or bird has them by the tail — they can easily detach their tails and run.

The tail will continue to wriggle for a few moments after removal, and if the lizard is lucky, the predator will go after the abandoned appendage instead.

The lizard's blood vessels close on their own to keep the critter from bleeding to death, and the tail will grow back after several months, Wiens says.

The tactic isn't totally without consequences, however. Wiens says research has shown that lizards without tails tend to lose social status with their peers and may have a harder time defending territories or getting mates.

4. Males aren't always needed for reproduction.

Some species of lizards, including the Sonoran spotted whiptail and about half a dozen other whiptail species in Arizona, have evolved to be asexual. Even in the absence of males, they continue to reproduce, with the mother laying eggs that result in her exact clones, Wiens says.

What's especially fascinating, Wiens says, is that when two asexual female whiptails are kept together, they actually produce a greater number of fertile eggs than they would on their own. They even engage in pseudo copulation, with each taking turns acting as the male and experiencing hormone cycles that more closely mimic that of a male.

"This sort of 'fake mating' actually appears to be really important for increasing their fertility," Wiens says. "They've lost normal sex, but they've retained these behavioral components."

5. They aren't dangerous.

This fact might not be so quirky, but it's important to understand, Wiens says.

Lizards can look intimidating. Some even engage in intimidating behavior for example, the regal horned lizard — known colloquially as the horned toad — may squirt blood out of its eyes when it gets upset.


Lizards

Canyon spotted whiptail

Canyon Spotted Whiptail
(
Aspidoscelis burti)
This large, spotted whiptail inhabits mountain canyons and arroyos, sometimes entering lowland desert along streams. It prefers dense, shrubby vegetation into which it can dash and hide when a predator comes near.
Body length: 3½ - 5½ in (9 - 14 cm)
Diet: Insects and spiders

Clark's spiny lizard

Photo courtesy of Mike Wall

Clark’s Spiny Lizard (Sceloporus clarkii)
These large lizards are commonly found in trees, but they are extremely alert and will usually go to the opposite side of the tree when approached. It prefers somewhat humid environments at a higher elevation.
Body length: 3 – 6 in (7.3 - 14.2 cm)
Diet: Insects, spiders, some plant material

Photo courtesy of Dave Prival

Desert Spiny Lizard (Sceloporus magister) The desert spiny lizard is very similar to Clark’s spiny lizard but is found at lower elevations. It is more comfortable on the ground and rocks than on trees. They often take shelter under rocks or in rodent burrows.
Body length: 3¼ - 6 in (8.2 - 14.2 cm)
Diet: Insects, spiders, centipedes, lizards, and occasional plant material

Eastern collard lizard

Photo courtesy of Dave prival

Eastern Collared Lizard (Crotaphytus collaris) The eastern collared lizard is one of the most colorful lizards in the Sonoran Desert. They are predatory lizards with strong jaw muscles used to grasp insects and other lizards. They can run on their hind legs, giveing them an enormous stride and fast pace. The extra height allows them to see distant prey, too. Their tails do not break away easily, probably due to the fact that they are helpful in maintaining balance.
Body length: 3 - 4.6 in ( 7.6 - 11.6 cm)
Total length: 10 in (25 cm)
Diet: Insects (mainly grasshoppers) and lizards

Photo courtesy of Dave Prival

Greater Earless Lizard
(Cophosaurus texanus) Similar in size, shape, and habits to the zebra-tailed lizard, the greater earless lizard is found at a slightly higher elevation. As its name implies, it has no ear openings.
Body length: 1⅞ -3½ in (4.7 - 8.9 cm)
Diet: Insects and spiders

Greater short-horned lizard

Photo courtesy of dave prival

Greater Short-horned Lizard
(
Phrynosoma hernandesi)
The short, stubby horns and small size of the greater short-horned lizard distinguish it from the regal horned lizard. They are more cold tolerant than regal horned lizards and found at higher elevations. Young are born live in clutches of up to 48!
Body length: 1¾ - 4⅞ in (4.4 - 12.4 cm)
Diet: Ants and other insects, spiders, snails

Lesser earless lizard

Photo courtesy of Dave Prival

Common Lesser Earless Lizard (Holbrookia maculata ) This lizard is similar to the zebra-tailed and greater earless lizard. However, it is smaller and drabber in coloration, lacking black bands on the underside of its tail. It’s also not as fast as a zebra-tailed or greater earless lizard. Body length: 1½ - 2½ in (4.1 - 6.3 cm) Diet: Insects, spiders and other lizards

Long-nosed leopard lizard

Photo courtesy of Roy C Murray

Long-nosed Leopard Lizard
(
Gambelia wislizenii) Though the long-nosed leopard lizard is different in appearance from the collared lizard, both have similar habits. Long-nosed leopard lizards are capable of running on their hind legs while searching for prey and prefer open areas with scattered plants and lots of room to run.
Body length: 3¼ -5¾ in (8.2 - 14.6 cm)
Diet: Insects and other invertebrates, lizards, snakes, small rodents

Madrean alligator lizard

Photo courtesy of Dave Prival

Madrean Alligator Lizard (Elgaria kingii) Madrean alligator lizards have short limbs, a slim body, and an extremely long tail. Because their dorsal and ventral scales are reinforced with bone, they have a fold of skin along each side of its body to expand for breathing or to make room for food and eggs. They prefer to live in dense vegetation and leaf litter in moist areas along permanent or temporary streams.
Body length: 3 - 5½ in (8.9 - 14.2 cm)
Diet: Insects and scorpions

Ornate tree lizard

Photo courtesy of Dave Prival

Ornate Tree Lizard (Urosaurus ornatus) The ornate tree lizard is commonly found in cottonwood or mesquite trees along riparian areas. Its markings blend well with the bark to help it avoid predators. Recent research has found that female tree lizards do not necessarily pick a male based on physical traits. Instead, she selects a territory and then selects a male whose range overlaps hers.
Body length: 1½ - 2¼ in (3.8 - 5.7) cm
Diet: Insects and spiders

Regal horned lizard

Photo courtesy of Dave Prival

Regal Horned Lizard (Phrynosoma solare ) The regal horned lizard is the largest horned lizard in the U.S. It is easily recognized by 4 large horns at the rear of its head. They are often found in the uplands of the Sonoran Desert where saguaros are dominant. These stout lizards eat mostly ants and are sometimes spotted around ant mounds. When attacked by a predator, they squirt blood from a pore in the eyelid region. The blood is apparantly distasteful to canid predators.
Body length: 3 - 4.6 in (7.6 - 11.7 cm)
Diet: Ants

Side-blotched lizard

Photo courtesy of Dave Prival

Side-blotched Lizard (Uta stansburiana) The common side-blotched lizard is distinguished by a bluish-black blotch on each side of the chest, directly behind the front legs. This is one of the most common lizards in arid regions of the western U.S. and can be found in various habitat types.
Body Length: ½ -2½ in (3.8 - 6.3 cm)
Diet: Insects, spiders, and scorpions

Sonoran spotted whiptail

Sonoran Spotted Whiptail (Aspidoscelis sonorae) The Sonoran spotted whiptail has six stripes along its body and an orange-brown tail. Most whiptails reproduce through parthenogenesis (asexual reproduction), meaning that all Sonoran spotted whiptails are genetically identical females! They lay unfertilized eggs that hatch into a population of clones.
Body length: 2½ - 3½ in (6.3 - 8.9 cm)
Diet: Insects and spiders

Sonoran tiger whiptail

Sonoran Tiger Whiptail (Aspidoscelis tigris) This active lizard is found in desert and semi-arid habitats, avoiding densely vegetated areas. It prefers areas where plants are sparse, and it has plenty of room to run. It eats insects (larvae, termites, grasshoppers, beetles), spiders, scorpions, and other lizards.
Body length: 2.4 – 5 in (6 - 12.7 cm)
Diet: Insects, spiders, scorpions, and other lizards.

Zebra-tailed lizard

Photo courtesy of Dave Prival

Zebra-tailed Lizard
(
Callisaurus draconoides )
This speedy lizard has a long, flat tail and long, slender legs. It prefers hard soils with few plants. When at rest, it often wags its banded black and white tail that give the zebra-tailed lizard its name. This behavior is likely used to draw attention away from the vulnerable head to the break-away tail.
Body length: 2¼ - 4 in (6.3 - 10.1 cm)
Diet: Insects and other invertebrates, some lizards and plant material

Desert iguana

Desert Iguana (Dipsosaurus dorsalis ) The desert iguana is primarily herbivorous. It is found in sandy areas where creosote bush is the dominant plant. It is often seen climbing the bush to feed on its flowers and buds. They are extremely tolerant of high temperatures, remaining active mid-day on hot summer days when most other lizards are seeking shelter.
Body length: 4 - 5¾ in (10.1 - 14.6 cm)
Diet: Plant leaves, buds and flowers, as well as some insects

Gila monster

Photo courtesy of Dave Prival

Gila Monster (Heloderma suspectum) Gila Monsters are one of only 2 venomous lizards in the world! They produce venom in glands of the lower jaw and channel it along grooves in the teeth for secretion. Gila monsters are most active during daylight from spring through fall, but they spend up to 98 % of their time in their burrows.
Body length: 9 - 14 in
Diet: small mammals, nestling birds and eggs, reptile eggs, and carrion

Great plains skink

Photo courtesy of Dave Prival

Great Plains Skink (Eumeces obsoletus) This is a large, slim-bodied lizard with extremely shiny scales and short limbs. It prefers habitats near sources of moisture, such as canyon bottoms with grass and low shrubs. Young skinks have black bodies with bright blue tails. Body size: 3½ - 5½ in (8.9 - 14.2 cm) Diet: Insects, spiders, snails, other lizards

Western banded gecko

Photo courtesy of Dave Prival

Western Banded Gecko (Coleonyx variegates ) This nocturnal, desert lizard has moveable eyelids and large eyes with vertical pupils. If disturbed, it will wave its tail back and forth, drawing attention away from its head and body. Like most lizards, the tail of the western banded gecko easily breaks off to give the lizard a chance to escape. However, the tail of the gecko stores fat for hard times and periods of dormancy, so the loss of its tail could lead to the eventual death of the lizard.
Body length: 4.5 – 6 in (11.4 – 15cm)
Diet: insects and other invertebrates


Contents

Largest and smallest

The adult length of species within the suborder ranges from a few centimeters for chameleons such as Brookesia micra and geckos such as Sphaerodactylus ariasae [2] to nearly 3 m (10 ft) in the case of the largest living varanid lizard, the Komodo dragon. [3] Most lizards are fairly small animals.

Distinguishing features

Lizards typically have rounded torsos, elevated heads on short necks, four limbs and long tails, although some are legless. [4] Lizards and snakes share a movable quadrate bone, distinguishing them from the rhynchocephalians, which have more rigid diapsid skulls. [5] Some lizards such as chameleons have prehensile tails, assisting them in climbing among vegetation. [6]

As in other reptiles, the skin of lizards is covered in overlapping scales made of keratin. This provides protection from the environment and reduces water loss through evaporation. This adaptation enables lizards to thrive in some of the driest deserts on earth. The skin is tough and leathery, and is shed (sloughed) as the animal grows. Unlike snakes which shed the skin in a single piece, lizards slough their skin in several pieces. The scales may be modified into spines for display or protection, and some species have bone osteoderms underneath the scales. [6] [7]

The dentitions of lizards reflect their wide range of diets, including carnivorous, insectivorous, omnivorous, herbivorous, nectivorous, and molluscivorous. Species typically have uniform teeth suited to their diet, but several species have variable teeth, such as cutting teeth in the front of the jaws and crushing teeth in the rear. Most species are pleurodont, though agamids and chameleons are acrodont. [8] [6]

The tongue can be extended outside the mouth, and is often long. In the beaded lizards, whiptails and monitor lizards, the tongue is forked and used mainly or exclusively to sense the environment, continually flicking out to sample the environment, and back to transfer molecules to the vomeronasal organ responsible for chemosensation, analogous to but different from smell or taste. In geckos, the tongue is used to lick the eyes clean: they have no eyelids. Chameleons have very long sticky tongues which can be extended rapidly to catch their insect prey. [6]

Three lineages, the geckos, anoles, and chameleons, have modified the scales under their toes to form adhesive pads, highly prominent in the first two groups. The pads are composed of millions of tiny setae (hair-like structures) which fit closely to the substrate to adhere using van der Waals forces no liquid adhesive is needed. [9] In addition, the toes of chameleons are divided into two opposed groups on each foot (zygodactyly), enabling them to perch on branches as birds do. [a] [6]

Locomotion

Aside from legless lizards, most lizards are quadrupedal and move using gaits with alternating movement of the right and left limbs with substantial body bending. This body bending prevents significant respiration during movement, limiting their endurance, in a mechanism called Carrier's constraint. Several species can run bipedally, [10] and a few can prop themselves up on their hindlimbs and tail while stationary. Several small species such as those in the genus Draco can glide: some can attain a distance of 60 metres (200 feet), losing 10 metres (33 feet) in height. [11] Some species, like geckos and chameleons, adhere to vertical surfaces including glass and ceilings. [9] Some species, like the common basilisk, can run across water. [12]

Senses

Lizards make use of their senses of sight, touch, olfaction and hearing like other vertebrates. The balance of these varies with the habitat of different species for instance, skinks that live largely covered by loose soil rely heavily on olfaction and touch, while geckos depend largely on acute vision for their ability to hunt and to evaluate the distance to their prey before striking. Monitor lizards have acute vision, hearing, and olfactory senses. Some lizards make unusual use of their sense organs: chameleons can steer their eyes in different directions, sometimes providing non-overlapping fields of view, such as forwards and backwards at once. Lizards lack external ears, having instead a circular opening in which the tympanic membrane (eardrum) can be seen. Many species rely on hearing for early warning of predators, and flee at the slightest sound. [13]

As in snakes and many mammals, all lizards have a specialised olfactory system, the vomeronasal organ, used to detect pheromones. Monitor lizards transfer scent from the tip of their tongue to the organ the tongue is used only for this information-gathering purpose, and is not involved in manipulating food. [14] [13]

Some lizards, particularly iguanas, have retained a photosensory organ on the top of their heads called the parietal eye, a basal ("primitive") feature also present in the tuatara. This "eye" has only a rudimentary retina and lens and cannot form images, but is sensitive to changes in light and dark and can detect movement. This helps them detect predators stalking it from above. [15]

Venom

Until 2006 it was thought that the Gila monster and the Mexican beaded lizard were the only venomous lizards. However, several species of monitor lizards, including the Komodo dragon, produce powerful venom in their oral glands. Lace monitor venom, for instance, causes swift loss of consciousness and extensive bleeding through its pharmacological effects, both lowering blood pressure and preventing blood clotting. Nine classes of toxin known from snakes are produced by lizards. The range of actions provides the potential for new medicinal drugs based on lizard venom proteins. [16] [17]

Genes associated with venom toxins have been found in the salivary glands on a wide range of lizards, including species traditionally thought of as non-venomous, such as iguanas and bearded dragons. This suggests that these genes evolved in the common ancestor of lizards and snakes, some 200 million years ago (forming a single clade, the Toxicofera). [16] However, most of these putative venom genes were "housekeeping genes" found in all cells and tissues, including skin and cloacal scent glands. The genes in question may thus be evolutionary precursors of venom genes. [18]

Respiration

Recent studies (2013 and 2014) on the lung anatomy of the savannah monitor and green iguana found them to have a unidirectional airflow system, which involves the air moving in a loop through the lungs when breathing. This was previously thought to only exist in the archosaurs (crocodilians and birds). This may be evidence that unidirectional airflow is an ancestral trait in diapsids. [19] [20]

Reproduction and lifecycle

As with all amniotes, lizards rely on internal fertilisation and copulation involves the male inserting one of his hemipenes into the female's cloaca. [21] The majority of species are oviparous (egg laying). The female deposits the eggs in a protective structure like a nest or crevice or simply on the ground. [22] Depending on the species, clutch size can vary from 4–5 percent of the females body weight to 40–50 percent and clutches range from one or a few large eggs to dozens of small ones. [23]

In most lizards, the eggs have leathery shells to allow for the exchange of water, although more arid-living species have calcified shells to retain water. Inside the eggs, the embryos use nutrients from the yolk. Parental care is uncommon and the female usually abandons the eggs after laying them. Brooding and protection of eggs does occur in some species. The female prairie skink uses respiratory water loss to maintain the humidity of the eggs which facilitates embryonic development. In lace monitors, the young hatch close to 300 days, and the female returns to help them escape the termite mound where the eggs were laid. [22]

Around 20 percent of lizard species reproduce via viviparity (live birth). This is particularly common in Anguimorphs. Viviparous species give birth to relatively developed young which look like miniature adults. Embryos are nourished via a placenta-like structure. [24] A minority of lizards have parthenogenesis (reproduction from unfertilised eggs). These species consist of all females who reproduce asexually with no need for males. This is known in occur in various species of whiptail lizards. [25] Parthenogenesis was also recorded in species that normally reproduce sexually. A captive female Komodo dragon produced a clutch of eggs, despite being separated from males for over two years. [26]

Sex determination in lizards can be temperature-dependent. The temperature of the eggs' micro-environment can determine the sex of the hatched young: low temperature incubation produces more females while higher temperatures produce more males. However, some lizards have sex chromosomes and both male heterogamety (XY and XXY) and female heterogamety (ZW) occur. [25]

Diurnality and thermoregulation

The majority of lizard species are active during the day, [27] though some are active at night, notably geckos. As ectotherms, lizards have a limited ability to regulate their body temperature, and must seek out and bask in sunlight to gain enough heat to become fully active. [28]

Territoriality

Most social interactions among lizards are between breeding individuals. [27] Territoriality is common and is correlated with species that use sit-and-wait hunting strategies. Males establish and maintain territories that contain resources which attract females and which they defend from other males. Important resources include basking, feeding, and nesting sites as well as refuges from predators. The habitat of a species affects the structure of territories, for example, rock lizards have territories atop rocky outcrops. [29] Some species may aggregate in groups, enhancing vigilance and lessening the risk of predation for individuals, particularly for juveniles. [30] Agonistic behaviour typically occurs between sexually mature males over territory or mates and may involve displays, posturing, chasing, grappling and biting. [29]

Communication

Lizards signal both to attract mates and to intimidate rivals. Visual displays include body postures and inflation, push-ups, bright colours, mouth gapings and tail waggings. Male anoles and iguanas have dewlaps or skin flaps which come in various sizes, colours and patterns and the expansion of the dewlap as well as head-bobs and body movements add to the visual signals. [31] [6] Some species have deep blue dewlaps and communicate with ultraviolet signals. [27] Blue-tongued skinks will flash their tongues as a threat display. [32] Chameleons are known to change their complex colour patterns when communicating, particularly during agonistic encounters. They tend to show brighter colours when displaying aggression [33] and darker colours when they submit or "give up". [34]

Several gecko species are brightly coloured some species tilt their bodies to display their coloration. In certain species, brightly coloured males turn dull when not in the presence of rivals or females. While it is usually males that display, in some species females also use such communication. In the bronze anole, head-bobs are a common form of communication among females, the speed and frequency varying with age and territorial status. Chemical cues or pheromones are also important in communication. Males typically direct signals at rivals, while females direct them at potential mates. Lizards may be able to recognise individuals of the same species by their scent. [31]

Acoustic communication is less common in lizards. Hissing, a typical reptilian sound, is mostly produced by larger species as part of a threat display, accompanying gaping jaws. Some groups, particularly geckos, snake-lizards, and some iguanids, can produce more complex sounds and vocal apparatuses have independently evolved in different groups. These sounds are used for courtship, territorial defense and in distress, and include clicks, squeaks, barks and growls. The mating call of the male tokay gecko is heard as "tokay-tokay!". [32] [31] [35] Tactile communication involves individuals rubbing against each other, either in courtship or in aggression. [31] Some chameleon species communicate with one another by vibrating the substrate that they are standing on, such as a tree branch or leaf. [36]

Distribution and habitat

Lizards are found worldwide, excluding the far north and Antarctica, and some islands. They can be found in elevations from sea level to 5,000 m (16,000 ft). They prefer warmer, tropical climates but are adaptable and can live in all but the most extreme environments. Lizards also exploit a number of habitats most primarily live on the ground, but others may live in rocks, on trees, underground and even in water. The marine iguana is adapted for life in the sea. [6]

The majority of lizard species are predatory and the most common prey items are small, terrestrial invertebrates, particularly insects. [6] [37] Many species are sit-and-wait predators though others may be more active foragers. [38] Chameleons prey on numerous insect species, such as beetles, grasshoppers and winged termites as well as spiders. They rely on persistence and ambush to capture these prey. An individual perches on a branch and stays perfectly still, with only its eyes moving. When an insect lands, the chameleon focuses its eyes on the target and slowly moves towards it before projecting its long sticky tongue which, when hauled back, brings the attach prey with it. Geckos feed on crickets, beetles, termites and moths. [6] [37]

Termites are an important part of the diets of some species of Autarchoglossa, since, as social insects, they can be found in large numbers in one spot. Ants may form a prominent part of the diet of some lizards, particularly among the lacertas. [6] [37] Horned lizards are also well known for specializing on ants. Due to their small size and indigestible chitin, ants must be consumed in large amounts, and ant-eating lizards have larger stomachs than even herbivorous ones. [39] Species of skink and alligator lizards eat snails and their power jaws and molar-like teeth are adapted for breaking the shells. [6] [37]

Larger species, such as monitor lizards, can feed on larger prey including fish, frogs, birds, mammals and other reptiles. Prey may be swallowed whole and torn into smaller pieces. Both bird and reptile eggs may also be consumed as well. Gila monsters and beaded lizards climb trees to reach both the eggs and young of birds. Despite being venomous, these species rely on their strong jaws to kill prey. Mammalian prey typically consists of rodents and leporids the Komodo dragon can kill prey as large as water buffalo. Dragons are prolific scavengers, and a single decaying carcass can attract several from 2 km (1.2 mi) away. A 50 kg (110 lb) dragon is capable of consuming a 31 kg (68 lb) carcass in 17 minutes. [37]

Around 2 percent of lizard species, including many iguanids, are herbivores. Adults of these species eat plant parts like flowers, leaves, stems and fruit, while juveniles eat more insects. Plant parts can be hard to digest, and, as they get closer to adulthood, juvenile iguanas eat faeces from adults to acquire the microflora necessary for their transition to a plant-based diet. Perhaps the most herbivorous species is the marine iguana which dives 15 m (49 ft) to forage for algae, kelp and other marine plants. Some non-herbivorous species supplement their insect diet with fruit, which is easily digested. [6] [37]

Antipredator adaptations

Lizards have a variety of antipredator adaptations, including running and climbing, venom, camouflage, tail autotomy, and reflex bleeding.

Camouflage

Lizards exploit a variety of different camouflage methods. Many lizards are disruptively patterned. In some species, such as Aegean wall lizards, individuals vary in colour, and select rocks which best match their own colour to minimise the risk of being detected by predators. [40] The Moorish gecko is able to change colour for camouflage: when a light-coloured gecko is placed on a dark surface, it darkens within an hour to match the environment. [41] The chameleons in general use their ability to change their coloration for signalling rather than camouflage, but some species such as Smith's dwarf chameleon do use active colour change for camouflage purposes. [42]

The flat-tail horned lizard's body is coloured like its desert background, and is flattened and fringed with white scales to minimise its shadow. [43]

Autotomy

Many lizards, including geckos and skinks, are capable of shedding their tails (autotomy). The detached tail, sometimes brilliantly coloured, continues to writhe after detaching, distracting the predator's attention from the fleeing prey. Lizards partially regenerate their tails over a period of weeks. Some 326 genes are involved in regenerating lizard tails. [44] The fish-scale gecko Geckolepis megalepis sheds patches of skin and scales if grabbed. [45]

Escape, playing dead, reflex bleeding

Many lizards attempt to escape from danger by running to a place of safety [46] [b] for example, wall lizards can run up walls and hide in holes or cracks. [9] Horned lizards adopt differing defences for specific predators. They may play dead to deceive a predator that has caught them attempt to outrun the rattlesnake, which does not pursue prey but stay still, relying on their cryptic coloration, for Masticophis whip snakes which can catch even swift prey. If caught, some species such as the greater short-horned lizard puff themselves up, making their bodies hard for a narrow-mouthed predator like a whip snake to swallow. Finally, horned lizards can squirt blood at cat and dog predators from a pouch beneath its eyes, to a distance of about two metres (6.6 feet) the blood tastes foul to these attackers. [48]

Fossil history

The earliest known fossil remains of a lizard belong to the iguanian species Tikiguania estesi, found in the Tiki Formation of India, which dates to the Carnian stage of the Triassic period, about 220 million years ago. [49] However, doubt has been raised over the age of Tikiguania because it is almost indistinguishable from modern agamid lizards. The Tikiguania remains may instead be late Tertiary or Quaternary in age, having been washed into much older Triassic sediments. [50] Lizards are most closely related to the Rhynchocephalia, which appeared in the Late Triassic, so the earliest lizards probably appeared at that time. [50] Mitochondrial phylogenetics suggest that the first lizards evolved in the late Permian. It had been thought on the basis of morphological data that iguanid lizards diverged from other squamates very early on, but molecular evidence contradicts this. [51]

Mosasaurs probably evolved from an extinct group of aquatic lizards [52] known as aigialosaurs in the Early Cretaceous. Dolichosauridae is a family of Late Cretaceous aquatic varanoid lizards closely related to the mosasaurs. [53] [54]

Phylogeny

External

The position of the lizards and other Squamata among the reptiles was studied using fossil evidence by Rainer Schoch and Hans-Dieter Sues in 2015. Lizards form about 60% of the extant non-avian reptiles. [55]

Internal

Both the snakes and the Amphisbaenia (worm lizards) are clades deep within the Squamata (the smallest clade that contains all the lizards), so "lizard" is paraphyletic. [56] The cladogram is based on genomic analysis by Wiens and colleagues in 2012 and 2016. [57] [58] Excluded taxa are shown in upper case on the cladogram.

AMPHISBAENIA (worm lizards, not usually considered "true lizards")

SERPENTES (snakes, not considered to be lizards)

Taxonomy

In the 13th century, lizards were recognized in Europe as part of a broad category of reptiles that consisted of a miscellany of egg-laying creatures, including "snakes, various fantastic monsters, […], assorted amphibians, and worms", as recorded by Vincent of Beauvais in his Mirror of Nature. [59] The seventeenth century saw changes in this loose description. The name Sauria was coined by James Macartney (1802) [60] it was the Latinisation of the French name Sauriens, coined by Alexandre Brongniart (1800) for an order of reptiles in the classification proposed by the author, containing lizards and crocodilians, [61] later discovered not to be each other's closest relatives. Later authors used the term "Sauria" in a more restricted sense, i.e. as a synonym of Lacertilia, a suborder of Squamata that includes all lizards but excludes snakes. This classification is rarely used today because Sauria so-defined is a paraphyletic group. It was defined as a clade by Jacques Gauthier, Arnold G. Kluge and Timothy Rowe (1988) as the group containing the most recent common ancestor of archosaurs and lepidosaurs (the groups containing crocodiles and lizards, as per Mcartney's original definition) and all its descendants. [62] A different definition was formulated by Michael deBraga and Olivier Rieppel (1997), who defined Sauria as the clade containing the most recent common ancestor of Choristodera, Archosauromorpha, Lepidosauromorpha and all their descendants. [63] However, these uses have not gained wide acceptance among specialists.

Suborder Lacertilia (Sauria) – (lizards)

  • Family †Bavarisauridae
  • Family †Eichstaettisauridae
  • Infraorder Iguania
    • Family †Arretosauridae
    • Family †Euposauridae
    • Family Corytophanidae (casquehead lizards)
    • Family Iguanidae (iguanas and spinytail iguanas)
    • Family Phrynosomatidae (earless, spiny, tree, side-blotched and horned lizards)
    • Family Polychrotidae (anoles)
      • Family Leiosauridae (see Polychrotinae)
      • Family Liolaemidae (see Tropidurinae)
      • Family Leiocephalidae (see Tropidurinae)
      • Family Gekkonidae (geckos)
      • Family Pygopodidae (legless geckos)
      • Family Dibamidae (blind lizards)
      • Infraorder Scincomorpha
        • Family †Paramacellodidae
        • Family †Slavoiidae
        • Family Scincidae (skinks)
        • Family Cordylidae (spinytail lizards)
        • Family Gerrhosauridae (plated lizards)
        • Family Xantusiidae (night lizards)
        • Family Lacertidae (wall lizards or true lizards)
        • Family †Mongolochamopidae
        • Family †Adamisauridae
        • Family Teiidae (tegus and whiptails)
        • Family Gymnophthalmidae (spectacled lizards)
        • Family Anguidae (slowworms, glass lizards)
        • Family Anniellidae (American legless lizards)
        • Family Xenosauridae (knob-scaled lizards)
        • Family Varanidae (monitor lizards)
        • Family Lanthanotidae (earless monitor lizards)
        • Family Helodermatidae (Gila monsters and beaded lizards)
        • Family †Mosasauridae (marine lizards)

        Convergence

        Lizards have frequently evolved convergently, with multiple groups independently developing similar morphology and ecological niches. Anolis ecomorphs have become a model system in evolutionary biology for studying convergence. [65] Limbs have been lost or reduced independently over two dozen times across lizard evolution, including in the Anniellidae, Anguidae, Cordylidae, Dibamidae, Gymnophthalmidae, Pygopodidae, and Scincidae snakes are just the most famous and species-rich group of Squamata to have followed this path. [64]

        Most lizard species are harmless to humans. Only the largest lizard species, the Komodo dragon, which reaches 3.3 m (11 ft) in length and weighs up to 166 kg (366 lb), has been known to stalk, attack, and, on occasion, kill humans. An eight-year-old Indonesian boy died from blood loss after an attack in 2007. [66]

        Numerous species of lizard are kept as pets, including bearded dragons, [67] iguanas, anoles, [68] and geckos (such as the popular leopard gecko). [67]

        Lizards appear in myths and folktales around the world. In Australian Aboriginal mythology, Tarrotarro, the lizard god, split the human race into male and female, and gave people the ability to express themselves in art. A lizard king named Mo'o features in Hawaii and other cultures in Polynesia. In the Amazon, the lizard is the king of beasts, while among the Bantu of Africa, the god Unkulunkulu sent a chameleon to tell humans they would live forever, but the chameleon was held up, and another lizard brought a different message, that the time of humanity was limited. [69] A popular legend in Maharashtra tells the tale of how a common Indian monitor, with ropes attached, was used to scale the walls of the fort in the Battle of Sinhagad. [70] In the Bhojpuri speaking region of India and Nepal, there is a belief among children that, on touching Skunk's tail three (or five) time with the shortest finger gives money.

        Green iguanas are eaten in Central America, where they are sometimes referred to as "chicken of the tree" after their habit of resting in trees and their supposedly chicken-like taste, [71] while spiny-tailed lizards are eaten in Africa. In North Africa, Uromastyx species are considered dhaab or 'fish of the desert' and eaten by nomadic tribes. [72]

        Lizards such as the Gila monster produce toxins with medical applications. Gila toxin reduces plasma glucose the substance is now synthesised for use in the anti-diabetes drug exenatide (Byetta). [17] Another toxin from Gila monster saliva has been studied for use as an anti-Alzheimer's drug. [73]

        Lizards in many cultures share the symbolism of snakes, especially as an emblem of resurrection. This may have derived from their regular moulting. The motif of lizards on Christian candle holders probably alludes to the same symbolism. According to Jack Tresidder, in Egypt and the Classical world they were beneficial emblems, linked with wisdom. In African, Aboriginal and Melanesian folklore they are linked to cultural heroes or ancestral figures. [74]


        1. We've yet to find a legless lizard with a forked tongue.

        Snakes have forked 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.

        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.


        Watch the video: Gomera Eidechsen (February 2023).