Reptile is the common name for one of the main groups of land vertebrates. It is not used so much by biologists, who use more accurate terms.
The name “reptile” comes from Latin and means “one who creeps”. All living reptile species are cold blooded, have scaly skin, and lay eggs. Reptiles also share an arrangement of the heart and major blood vessels which is different from that of mammals.
Many important groups of reptiles are now extinct. The great majority of present-day reptiles are snakes and lizards.
The study of living reptiles is called herpetology.
Most reptiles have a three-chambered heart.
There are some interesting exceptions to the general physiology. For instance, crocodilians have an anatomically four-chambered heart. Also, some snake and lizard species (e.g., pythons and monitor lizards) have three-chambered hearts that become functionally four-chambered hearts during contraction.
All reptiles breathe using lungs. Aquatic turtles have developed more permeable skin. Even with these adaptations, breathing is never fully accomplished without lungs. Crocodilians actually have a muscular diaphragm like that of mammals, freeing space for the lungs to expand.
Reptilian skin is covered in a horny epidermis, making it watertight and enabling reptiles to live on dry land, in contrast to amphibians. Compared to mammalian skin, that of reptiles is rather thin and lacks the thick dermal layer that produces leather in mammals. Exposed parts of reptiles are protected by scales or scutes, sometimes with a bony base, forming armor. In lepidosaurians such as lizards and snakes, the whole skin is covered in overlapping epidermal scales.
Many small reptiles such as snakes and lizards which live on the ground or in the water are vulnerable to being preyed on by all kinds of carnivorous animals. Thus avoidance is the most common form of defense in reptiles. At the first sign of danger, most snakes and lizards crawl away into the undergrowth, and turtles and crocodiles will plunge into water and sink out of sight.
Reptiles may also avoid confrontation through camouflage. Using a variety of grays, greens, and browns, these animals can blend remarkably well into the background of their natural environment.
If the danger arises so suddenly that flight may be harmful, then crocodiles, turtles, some lizards, and some snakes hiss loudly when confronted by an enemy. Rattlesnakes rapidly vibrate the tip of the tail, which is composed of a series of nested, hollow beads.
If all this does not deter an enemy, different species will adopt different defensive tactics.
Snakes use a complicated set of behaviors when attacked. Some will first elevate their head and spread out the skin of their neck in an effort to look bigger and more threatening. Failure of this may lead to other measures practiced particularly by cobras, vipers, and closely related species, who use venom to attack. The venom is modified saliva, delivered through fangs.
When a crocodile is concerned about its safety, it will gape to expose the teeth and yellow tongue. If this doesn’t work, the crocodile gets a little more agitated and typically begins to make hissing sounds. After this, the crocodile starts to get serious, changing its posture dramatically to make itself look more intimidating. The body is inflated to increase apparent size. If absolutely necessary it may decide to attack an enemy.
Some species try and bite, some will use their heads as sledgehammers and literally smash an opponent, some will rush or swim toward the threat from a distance, even chasing them onto land or galloping after them.
Geckos, skinks, and other lizards that are captured by the tail will shed part of the tail structure through a process called autotomy and thus be able to flee. The detached tail will continue to wiggle, creating a deceptive sense of continued struggle and distracting the predator’s attention from the fleeing prey animal. The animal can partially regenerate its tail over a period of weeks. The new section will contain cartilage rather than bone, and the skin may be distinctly discolored compared to the rest of the body.