Snakesare elongated, legless,carnivorousreptilesof thesuborderSerpentes[2]that can be distinguished fromlegless lizardsby their lack of eyelids and external ears. Like allsquamates, snakes areectothermic,amniotevertebratescovered in overlappingscales. Many species of snakes haveskullswith several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads with theirhighly mobile jaws. To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one functionallung. Some species retain apelvic girdlewith a pair ofvestigialclaws on either side of thecloaca.

Living snakes are found on every continent except Antarctica, and on most smaller land masses exceptions include some large islands, such as Ireland and New Zealand, and many small islands of the Atlantic and central Pacific.[3]Additionally,sea snakesare widespread throughout the Indian and Pacific Oceans. More than 20familiesare currently recognized, comprising about 500generaand about 3,400species.[4]

HYPERLINK "http://en.wikipedia.org/wiki/Snake" \l "cite_note-NRDB-Cs-5" [5]They range in size from the tiny, 10cm-longthread snaketo thereticulated pythonof up to 6.95 meters (22.8ft) in length.[6]The fossil speciesTitanoboa cerrejonensiswas 13 meters (43ft) long.[7]Snakes are thought to have evolved from either burrowing or aquatic lizards, perhaps during theJurassicperiod, with the earliest known fossils dating to between 143 and 167Maago.[8]The diversity of modern snakes appeared during thePaleoceneperiod (c66 to 56 Ma ago). The oldest preserved descriptions of s