Lizards are a diversified bunch; among them are walking terrestrial, burrowing terrestrial, aquatic, arboreal (tree-dwelling), and even aerial (gliding) types.
Diversity and Distribution of Lizards
Numbering approximately 4,500 species, the lizards are the largest group of reptiles. Lizards are found nearly from pole to pole in the major zoogeographical zones of every continent except Antarctica. They are also scattered over the islands of the Atlantic, Pacific, and Indian oceans as well as the island continent of Australia.
Living lizards are aligned into 40 families. Some of the more familiar are: Geckos (Gekkonidae) are among the more common and familiar and have characteristics that include a nocturnal nature, a relatively small size, agility, large eyes, and toe pads that allow them to defy gravity underneath and along vertical surfaces. Unlike most lizards, geckos are capable of making chirping or clicking vocalizations.
Iguanas (Iguanidae), including the most familiar New World lizards, the marine iguana of the Galapagos Islands, and the flying dragons (Draco) of Southeast Asia. Expanding its ribs like an umbrella to form a gliding surface, this lizard launches itself from trees to glide 30 m (100 feet) or more.
Skinks (Scincidae), with elongated bodies and reduced limbs in many species and chameleons (Chamaeloeonidae), a group of arboreal lizards, mostly of Africa and Madagascar are noted for their prehensile tail, ability to snag prey from afar with an extensible tongue, and the talent to change their body color at will.
The Body Plan of a Lizard
A lizard’s body is long and cylindrical (flattened horizontally) or compressed (flattened vertically), depending on the species. Lizards typically possess a blunt head with movable eyelids and external ear opening, four powerful legs with five clawed toes on each leg, and a long tail.
Lizards range in size from the Caribbean gecko (Sphaerodactylus ariasae) that at 16 mm (0.63 inch) long can curl up on a dime to the giant monitor lizards (Varanus komodensis), often called Komodo dragons after the place in Indonesia where they were first discovered.
Most lizards are colored in varying shades of greens, browns, and blacks, although some sport dazzling reds, yellows, oranges, blues, and white. Many are also adorned with ornamental crests, frills, and throat fans. Due to their smooth shiny appearance, some lizards can appear slimy or slippery; their skin is actually very dry due to the absence of excretory glands.
All lizards possess a well-developed tongue that can be extended to varying degrees. However, none do so as dramatically or from such long range as the Old World chameleons. Using high speed video and x-ray film, zoologists have calculated that the chameleon’ tongue shoots out of its mouth at more than 26 body lengths per second – 21.6 kilometers per hour (13.4 miles per hour), and can snag prey 1/6 their own size located two body lengths away. That’s the equivalent of a six-foot person snagging a full-grown turkey from 12 feet away using only their tongue.
Most lizards are carnivores that feed mainly on insects, worms, birds, mammals, and other reptiles. About 2 percent of all known species are herbivorous, especially the iguanas which consume a wide variety of plant material. The marine iguana of the Galapagos islands (Amblyrhynchus cristatus), the world’s only marine lizard, dives up to 15 m (50 feet) under water to nibble algae off rocks. The diets of lizards may shift with maturity and seasonal changes.
Dangerous and Potentially Deadly Lizards
The giant Komodo dragons will regularly kill prey as large as pigs and small deer and have been known to bring down water buffalo. They will also attack and kill humans.
“Monitor saliva is chock full of deadly species of bacteria, and most bitten prey that escape die
from a fast-moving bacterial super-infection. Like sharks following a few molecules of blood to a bleeding fish, the monitor just waits until it senses a light smell of new death and follows the scent to the source.”
(Jane Stevens)
The Gila monster (Heloderma suspectum) of the southwestern United States desert regions and the related Mexican beaded lizard (H. horridum) of Mexico and Guatemala are the only known venomous lizards on the planet. Gila monsters lack fangs and thus introduce their venom with a chewing bite. While painful, this bite is seldom fatal to humans.
As the only member of order Squamata with legs, lizards are found nearly everywhere worldwide making them one of the most familiar and common reptiles.
Related Articles
The Characteristics of Alligators and Crocodiles
The Characteristics of Turtles
 |
 |
 |
