This order represents about 6000 species & is the most successful form of reptiles today. There are 3 sub orders namely Sauria (lacertelia)-lizards, Ophidia (serpents)-snakes, & Amphisbaenia-worm lizards. Amphisbaenia is not found in Sri Lanka.

The most typical modern reptiles showing less modification are the lizards. It’s an agreed fact by the universe that snakes are derived from some lizards & Amphisbaenia that lost their legs. But snakes & lizards have distinctive characters.

Majority of order squamata forms have a highly modifies skull, the quadrate, which in other reptiles is fused to the skull has a joint at its dorsal end as well as its usual articulation with the lower jaw. The joints have loose ligaments & allow movement in several directions. The two halves of the lower jaw are not firmly united. There are joints in the palate & across the roof of the scull that allow the snout to be titled to seize & manipulate their prey. Snakes have highly kinetic skull with these arrangements when compared with lizards, having a freely movable quadrate, which is imparts its motion to the bones of the upper jaw. Paired copulatory organs of a unique type are present in the male & there is a widespread tendency towards limb reduction, in members of lizards & snakes.