Why Does a Lizard Have Watertight Skin?

Maintaining Internal Environment

• Because of the watertight skin that is covered in scales, the lizard can't exchange gases across the skin as can amphibians. Instead, reptiles must depend entirely on their lungs for breathing. The scaly skin on the lizard doesn't get bigger as the animal grows, so this requires that the reptile molt. Molting is the process of shedding skin as the animal gets bigger. The shed skin is then replaced by newer skin that is larger.

  The watertight skin of a lizard is replete with keratin, which is waterproofing protein. This prevents dehydration. Because of the watertight skin, lizards can keep an internal environment that is primarily water even when the external environs are dry.

Integument

• Reptile skin, which is called integument, is made up of the epidermis and the dermis. The epidermis is completely covered by keratin and it is thick on the tail and belly but thin on the dewlap, which is the loose fold of skin that hangs from the neck. Some lizards have hard spikes that are harder bits of integument, as are the keeled ridges that some lizards have. The watertight skin of lizards, turtles, snakes and crocodiles makes it possible for these creatures to live on land because they are not at risk for dehydration. Their eggs are also watertight. The water feeds and protects the growing embryo.

Lizard Facts

• Lizards are in a category of animals called ectotherms, commonly called "cold-blooded," which means their body temperature fluctuates with their surroundings. Most of them live in habitats that are hot. Big lizards, such as the Komodo dragon, can eat large animals, including a young deer, but the smaller lizards survive primarily on insects.

  Iguanas are plant eaters.

Amphibians Versus Reptiles

• Unlike reptiles, amphibians do not have watertight skin and their skin is smooth rather than scaly. Amphibians breathe through their skin, gills and lungs whereas reptiles breathe through their lungs. The legs of amphibians are out to the sides whereas reptile legs are underneath them. Amphibians reproduce via external fertilization while reptiles have internal fertilization.