Snakes are elongated, legless, carnivorous reptiles of the suborder Serpentes. Like all different squamates, snakes are ectothermic, amniote vertebrates blanketed in overlapping scales. Many species of snakes have skulls with numerous extra joints than their lizard ancestors, allowing them to swallow prey a great deal large than their heads with their particularly cellular jaws. To accommodate their slender our bodies, snakes' paired organs seem one in the front of the opposite in place of aspect through aspect, and maximum have best one purposeful lung. Some species maintain a pelvic girdle with a couple of vestigial claws on both aspect of the cloaca. Lizards have advanced elongate our bodies with out limbs or with significantly decreased limbs approximately twenty-5 instances independently through convergent evolution, main to many lineages of legless lizards. Legless lizards resemble snakes, however numerous not unusualplace organizations of legless lizards have eyelids and outside ears, which snakes lack, even though this rule isn't universal .
Living snakes are observed on each continent besides Antarctica, and on maximum smaller land masses; exceptions encompass a few massive islands, together with Ireland, Iceland, Greenland, the Hawaiian archipelago, and the islands of New Zealand, and lots of small islands of the Atlantic and principal Pacific oceans. Additionally, sea snakes are good sized for the duration of the Indian and Pacific Oceans. More than 20 households are presently recognized, comprising approximately 520 genera and approximately 3,six hundred species. They variety in length from the tiny, -lengthy Barbados thread snake The fossil species Titanoboa cerrejonensis changed into lengthy. The variety of present day snakes seemed throughout the Paleocene epoch . The oldest preserved descriptions of snakes may be observed withinside the Brooklyn Papyrus.
Most species are nonvenomous and people which have venom use it basically to kill and subdue prey in place of for self-defense. Some own venom powerful sufficient to motive painful harm or demise to humans. Nonvenomous snakes both swallow prey alive or kill through constriction.
Etymology
The English phrase snake comes from Old English snaca, itself from Proto-Germanic snak-an-, from Proto-Indo-European root nēg-o- "to crawl", "to creep", which additionally gave sneak in addition to Sanskrit nāgá "snake". The phrase ousted adder, as adder went directly to slender in meaning, aleven though in Old English næddre changed into the overall phrase for snake. The different term, serpent, is from French, in the end from Indo-European serp-, which additionally gave Ancient Greek hérpō "I crawl".
Evolution
The fossil document of snakes is particularly negative due to the fact snake skeletons are usually small and fragile making fossilization uncommon. Fossils with no trouble identifiable as snakes first seem withinside the fossil document throughout the Cretaceous period. The earliest acknowledged real snake fossils come from the marine simoliophiids, the oldest of that is the Late Cretaceous Haasiophis terrasanctus, dated to among 112 and ninety four million years antique.
Based on comparative anatomy, there's consensus that snakes descended from lizards. Pythons and boas—primitive organizations amongst present day snakes—have vestigial hind limbs: tiny, clawed digits called anal spurs, which might be used to understand throughout mating. Previously, snakes had been a minor thing of the North American fauna, however throughout the Miocene, the range of species and their incidence elevated dramatically with the primary appearances of vipers and elapids in North America and the sizable diversification of Colubridae . An early fossil snake relative, Najash rionegrina, changed into a -legged burrowing animal with a sacrum, and changed into absolutely terrestrial. One extant analog of those putative ancestors is the earless screen Lanthanotus of Borneo . Subterranean species advanced our bodies streamlined for burrowing, and finally misplaced their limbs.
This speculation changed into reinforced in 2015 through the invention of a 113m year-antique fossil of a four-legged snake in Brazil that has been named Tetrapodophis amplectus. It has many snake-like functions, is customized for burrowing and its belly suggests that it changed into preying on different animals. It is presently unsure if Tetrapodophis is a snake or some other species, withinside the squamate order, as a snake-like frame has independently advanced as a minimum 26 instances. Tetrapodophis does now no longer have unique snake functions in its backbone and skull.
An opportunity speculation, primarily based totally on morphology, indicates the ancestors of snakes had been associated with mosasaurs—extinct aquatic reptiles from the Cretaceous—which in flip are concept to have derived from varanid lizards.
In 2016, research stated that limb loss in snakes is related to DNA mutations withinside the Zone of Polarizing Activity Regulatory Sequence, a regulatory location of the sonic hedgehog gene that is severely required for limb improvement. More superior snakes haven't any remnants of limbs, however basal snakes together with pythons and boas do have strains of particularly decreased, vestigial hind limbs. Python embryos actually have absolutely evolved hind limb buds, however their later improvement is stopped through the DNA mutations withinside the ZRS.
