We fear from them as they have the potential to kill us by their venom. They are snakes. Snakes belong to the suborder Serpents and are legless, crawling and elongating reptiles. They are different from lizards as they lack eyelid and external ears. They are ectothermic, amniotes covered by overlapping scales like all other squamates. The skull bones of snakes are demarcated by presence of a large number of joints that enable them to feed on a prey which is much larger than them. Jaws are highly movable. They have a single functional lung. Some species bear a pair of vestigial claws on either side of the cloaca. They are present in all continents except Antarctica. Fifteen families have been recognized comprising of 456 genera and 2,900 species. They range in size from 10 cm like that of thread snake to the larger pythons and anacondas which are about 7.6 meters long. The recently discovered fossil of snake Titanoboa was about 15 meters long.
Snakes are thought to have evolved from their terrestrial or aquatic lizard ancestors during the Cretaceous period. Modern snakes appeared during the Paleocene period. Majority of the species are non-poisonous and the venomous species use their venom as a measure of self-defence. Some venomous snakes have the potential to kill even humans. Non-venomous snakes either swallow the prey alive or kill it by constriction.
The modern English word snake comes from the Old English word snaca which means to crawl or to creep. Fossil record of snakes is relatively poor as the skeletons are relatively small making fossilization impossible. 150 million year old specimens of snakes have been discovered in South America and South Africa. Fossil records suggest that the snakes have evolved from the burrowing lizards. Primitive snakes among the modern ones are the pythons and the boas.
Snake skeleton is chiefly composed of skull, hyoid, vertebral column, ribs and vestiges of pelvis and hind limbs in the henophidian snakes. Skull consists of a solid braincase to which other bones are loosely articulated making the jaws flexible so that effective feeding and prey capture can commence.
The left and right sides of the lower jaw are joined to a ligament while the posterior end of lower jaw is articulated with the quadrate making the jaw more mobile. Mandibles and quadrate also help in picking sound borne vibrations. Hyoid is a small bone located in the neck region serving for the attachment of the tongue muscles. Vertebral column comprises 200-400 vertebrae. Tail vertebrae fewer and lack ribs. Vertebrae of body bear two ribs. Vertebrae have strong articulation with muscles in order to bring about effective locomotion in absence of limbs. Autotomy is absent in snakes. Pythons and boas have a pair of vestiges of hind limbs in the form of pelvic spurs present on either side of the cloaca made up of the vestiges of ilium and femur.
