Snakes are the most streamlined of all the vertebrate animals. A snake has no limbs, wings, flippers nor other appendages to help it move, eat and defend itself. In spite of their seemingly simplistic anatomy, snakes can do nearly everything other vertebrates do, moving on all types of terrain, even tunneling underground and swimming. Snakes can climb and move silently among the branches of trees. With their hinged jaws, snakes can kill and eat relatively large prey.
Snakes are the most modern of all species of reptiles, first appearing in the Cretaceous period fossil record about 130 million years ago, during the time of the dinosaurs. It is likely that they evolved from burrowing, ground dwelling lizards. Some limbless lizards look very much like snakes. Such lizards can only be distinguished from snakes by the lizards movable eyelids and external ears. Snakes have neither. Snakes are found in a much wider range of habitats than lizards, suggesting that snakes are better able to adapt to environments. Snakes gave up external ears to adapt to burrowing under ground and developed clear scales to shield their eyes from dust and damage. They evolved elongated internal organs, specialized muscles and resilient, scaled skins of varied pattern and color that provide camouflage and some limited protection from predators and the elements. Snakes have also evolved a host of instinctive behaviors that enable them to find and catch prey, hide from predators, reproduce and survive in a great variety of climates.
The senses of taste and smell are important in snakes. The snake’s flickering forked tongue, still thought by some to cause the snake’s “sting,” is, in fact, use for picking up the slightest traces of airborne scents and transferring these to sensory pits inside the mouth to create taste. In the roof of the snake’s mouth is a special structure, called Jacobson’s organ, which is linked to the snake’s brain by a branch of the olfactory nerve. The constant flicking in and out of its tongue is the snake’s efficient way of sampling the air for important scents. When the snake’s tongue is withdrawn into its mouth, it rests inside Jacobson’s organ and the chemicals that it has retrieved from the air are detected by its nerve endings and transmitted to its brain. Some snakes have even evolved infrared heat sensors for finding their prey in the dark or underground, and some snakes have developed poisonous venoms and the apparatus to deliver them. Snakes move by wiggling their bodies into a series of curves, while pushing backwards with their rib muscles against the ground. They can also move forward by arching their backs in a series of humps and pushing forward, an approach that they use for climbing trees and navigating on narrow surfaces. Snakes swim by whipping their bodies from side to side like eels. Snakes have become integral components of varied ecosystems throughout the world and are incredibly unique and remarkable animals.
Among reptiles, snakes are easily the most unpopular with people. Many people have an irrational, senseless fear of snakes. For centuries, snakes have figured prominently in the religions, customs and folklore of peoples throughout the world. To early humans, snakes must have seemed to possess almost supernatural characteristics, moving without legs, capturing prey without the aid of appendages, shedding an old scarred skin to reveal a bright new youthful skin and, with some species, causing sickness or death with a single bite.