Snake

suborder Serpentes

snake, (suborder Serpentes), also called serpent, any of more than 3,400 species of reptiles distinguished by their limbless condition and greatly elongated body and tail. Classified with lizards in the order Squamata, snakes represent a lizard that, over the course of evolution, has undergone structural reduction, simplification, and loss as well as specialization. All snakes lack external limbs, but not all legless reptiles are snakes. Certain burrowing lizards may have only front or hind limbs or be completely legless. Unlike lizards, snakes lack movable eyelids, which results in a continuous and often disconcerting stare. Snakes also lack external ear openings. Internally, they have lost the urinary bladder. The visceral organs are elongated, with reduction of the left member in relation to the right; the left lung is greatly reduced or even lost entirely. However, snakes possess increased numbers of vertebrae and have developed two novelties among vertebrates: a tracheal lung in the neck region and a venom-conducting system for subduing prey.

Snakes are thought to have evolved from terrestrial lizards as early as the Middle Jurassic Epoch (174.1 million to 163.5 million years ago). The oldest known fossil snake, Eophis underwoodi, was a small snake that lived in southern England about 167 million years ago.