Lizards

  There are about 3,000 species of living lizards. Common lizards include iguanas, chameleons, and geckos. Lizards live on every continent except Antarctica. Most lizards prey on insects or on other small animals. A few of the larger species, such as the chuckwalla and desert iguana of the southwestern United States, feed on plants. The Komodo dragon feeds on prey as large as goats and deer. Only two species of lizards are venomous. They are the Gila monster of the south western United States and northern Mexico and the related beaded lizard of south Mexico.

   Most lizards rely on agility, speed, and camouflage to elude predators. if threatened by a predator, some lizards have the ability to detach their tail. This ability is called autonomy. The tail continues to twitch and squirm after it detaches, drawing the predator's attention while the lizard escapes. The lizard grows a new tail in several weeks to several months, depending on the species.

   Most lizards are small, measuring less than 30 cm ( 12 in. ) in length. The largest lizards belong to the monitor family (Varanidae ). Like snakes, monitors have deeply forked tongues that pick up airborne particles and transfer them to the Jacobson's organ in the roof of the mouth.

   Snakes

  There are about 2,500 species of snakes, and like lizards, they are distributed worldwide. The most obvious characteristics of snakes is the lack of legs, which affects all other aspects of their biology. What was the selective pressure that caused snakes to evolve leglessness? One possibility is that the ancestors of snakes were terrestrial but lives in thick vegetation, where legs were a hindrance to rapid movement.

   The graceful movements of snakes are made possible by their unique anatomy. A snake has a backbone of 100 to 400 vertebrae , and a pair of ribs are attached to each vertebrae. These bones provide the framework for thousands of muscles. The muscles manipulate not only the skeleton but also the snakes's skin, causing the overlapping scales to extend and contract.

    A snake may just seize and swallow its prey. However, many snakes employ one of two methods for killing: constriction or injection of venom. Snakes that are constrictors wrap their bodies around prey. A constrictor suffocates its prey by gradually increasing the tension in its coils, squeezing a little tighter each time the prey breathes out. This technique is used both by large snakes, such as boas, pythons, and anacondas, and by smaller snakes, such as gopher snakes and king snakes.

    Some snakes inject their prey with a toxic venom in one of three different ways. The snakes with fangs in the back of the mouth, such as the boomslang and twig snakes of Africa, bite the prey and use grooved teeth in the back of the mouth to guide the venom into the puncture. Cobras, kraits, and coral snakes are elapids. Elapid snakes inject poisons though two small, fixed fangs in the front of the mouth. Vipers inject venom through large, mobile fangs in the front of the mouth. Rattlesnakes, Copperheads, and water moccasins are examples of vipers. When a viper strikes, these hinged fangs swing forward from the roof of the mouth and inject venom more deeply than can the fangs of elapids.

    Once killed, the prey must be swallowed whole because a snake's curved, needlelike teeth are not suited for cutting or chewing. Several feature of a snake's skull enable it to swallow an animal larger in diameter than its head. The upper and lower jaws are loosely hinged and move independently, and can open to an angle of 130 degrees. In addition, a snake's lower jaw, palate, and parts of its skull are joined by a flexible, elastic ligament that allows the snake's head to stretch around its prey.

For any questions email Mr. Reilly at biosnake@aol.com