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Snakes
Temporal range:
Jurassic–present[1]c. 150–0 mya
Horned rattlesnakeSouthern hognose snakeBlue kraitEmerald tree boaSri Lanka cat snakeRingneck snakeStriped House SnakeBlunthead tree snakeCorn snakeIndian cobraGrass snakePacific gopher snakeGreen vine snakeCoral snakeGreen tree pythonSpiny bush viperFalse coral snakePuffing snake
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Clade: Ophidia
Suborder: Serpentes
Linnaeus1758
Infraorders
Approximate world distribution of snakes, all species

Snakes,otherwise known asserpentsorbasilisks,arereptiles.They are part of theorderSquamata.They arecarnivores,with long narrow bodies and nolegs.There are at least 20families,about 500generaand 3,400speciesof snake.[2][3]

The earliest known fossils are from theJurassicperiod.This was between 143 and 167 million years ago.[4]

Their long, slender body has some special features.[5]They have overlappingscaleswhich protect them, and help them move and climb trees. The scales have colours which may becamouflageorwarning colours.

Many species haveskullswith more joints than the skulls of theirlizardancestors. This allows the snakes to swallowpreymuch larger than their heads. In their narrow bodies, snakes' paired organs (such askidneys) appear one in front of the other instead of side by side. Most have only one workinglung.Some species have kept apelvic girdlewith a pair ofvestigialclaws on either side of thecloaca.They have no eyelids or external ears. They canhiss,but otherwise make no vocal sounds.[verification needed]

They are very mobile in their own way. Most of them live in thetropics.Few snake species live beyond theTropic of CancerorTropic of Capricorn,and only one species, the commonviper(Vipera berus) lives beyond theArctic Circle.[5]They can see well enough, and they can taste scents with their tongues by flicking them in and out. They are very sensitive to vibrations in the ground. Some snakes can sensewarm-bloodedanimals by thermalinfrared.

Most snakes live on the ground, and in the trees. Others live in the water, and a few live under thesoil.Like other reptiles, snakes areectotherms.They control their body temperature by moving in and out of the direct sunshine. That is why they are rare in cold places.[6]

Snakes range in size from the tiny, 10.4 cm (4 inch)-longthread snake[7]to thereticulated pythonof 6.95 meters (22.8 ft) in length.[8]The extinct snakeTitanoboawas 12.8 meters (42 ft) long.[9]

Evolution

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Snakes are thought to have evolved fromlizards-like ancestors approximately 100 million years ago.Before snakes, snakes had legs;they lost their legs over time and developed elongated bodies. This helped them move more efficiently. Fossils of ancestor snakes show that thesnake’s skullhas evolved, become more flexible, and helps to swallow prey as a whole. The evolution of snake bones showcases how these creatures have adapted to their surroundings, enabling them to become successful predators in various ecosystems. The earliest snake fossils are from theLower Cretaceous.[10]A wide range of snakes appeared during thePaleoceneperiod (c66 to 56 million years ago).

Not a clade

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TheSquamataare definitely amonophyleticgroup: it is a sister group to theTuatara.Judged by their fossil record, the squamates were present in theMesozoic,but had a minor place in the land ecology. Three of the six lines are recorded first in the UpperJurassic,the others in theCretaceous.Probably all, certainly the lizards, arose earlier in the Jurassic.[11]TheMosasaursof theUpper Cretaceouswere by far the most successful of all the lizards, becoming the top predator in theirecosystem.

Although snakes and lizards look very different,neither is a properclade.Snakes did descend from early lizards, not once, but many different times.

There is amonophyleticclade within the Squamata. It is theToxicofera.It includes allvenomoussnakes and lizards, and many related non-venomous species. The evidence for this is in recentmolecular analyses.[12][13][14][15][16][17][18]

Fossil snakes

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The fossil of a primitive snake from theLower Cretaceoushas been found. It lived about 113 million years ago.[19]It had rather small front and rear legs. Several other fossil snakes have been found with small rear legs, but this is the first one with all four legs. The snake,Tetrapodophis amplectus,lived on land and wasadaptedto burrowing. The researcher said there were "a lot of very advanced snake features, including its hooked teeth, flexible jaw and spine – and even snake-like scales. And there's the gut contents – it's swallowed another vertebrate. It was preying on other animals, which is a snake feature".[20]The snake came from theCrato FormationinBrazil,and lay in a private collection for many years. It was re-discovered in a museum atSolnhofen,Bavaria.

Venom

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Most snakes are nonvenomous. Those that havevenomuse it mainly to kill and subdue prey rather than for self-defense. Some have venom potent enough to cause painful injury or death to humans. Nonvenomous snakes either swallow prey alive or kill by squeezing.

Twotaxonomicfamiliesare entirely venomous:

A third family with the "rear-fanged" snakes (and most of the other snake species) is the

Anatomy

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Many snakes haveskullswith morejointsthan their lizard ancestors. This helps them swallowpreymuch larger than their heads. The bones of the head and jaws can move apart to let large prey move into their body. Thethroat,stomachandintestinescan also expand in a most extraordinary manner. In this was, a thin-looking snake can swallow and digest a larger animal.

To fit their narrow bodies, snakes' paired organs (such askidneys) are one in front of the other instead of side by side, and most snakes have only one workinglung.Some species have apelvic girdlewith a pair ofvestigialclaws on either side of thecloaca.This is a relic of the legs which do not appear in modern snakes.

Shedding

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Snakes need to shed their skin regularly while they grow. This is calledmoulting.Snakes shed their skin by rubbing their head against something rough and hard, like a piece of wood or arock.This causes theskin,which is already stretched, tosplitopen. The snake keeps on rubbing its skin on various rough objects until the skin peels off from its head. This lets it crawl out, turning the skin inside out.

Feeding

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All snakes are carnivorous; they eat otheranimals.Some arevenomous;they injectvenomalong grooves in their teeth. Some snakes are constrictors. Constrictors are not venomous, so they squeeze their prey to death. Snakesswallowtheirfoodwhole, and they cannot chew.[23]Because snakes arecold-blooded,they do not have to eat as regularly as mammals. People who own pet snakes feed them as infrequently as once per month. Some snakes can go as long as six months without a good meal.

Snakes have a very flexible lower jaw, the two halves of which are not rigidly attached, and many other joints in their skull. They can open their mouths wide enough to swallow their prey whole, even if the prey is larger in diameter than the snake itself.[24]

Movement

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Not having arms and legs doesn't stop snakes from moving. They have developed several different ways of moving to deal with particular environments. Each type of snake movement is discrete and distinct from the others.[25][26]

Lateral undulation

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Lateral undulation is a snake's only way of moving in water, and the most common way of moving altogether.[26]In this mode, the body of the snake alternately bends to the left and right, resulting in a series of rearward-moving "waves".[25]While this movement appears rapid, snakes have rarely been seen moving faster than two body-lengths per second, often much less.[27]This mode of movement has the same amount of calories burned per meter moved as running in lizards of the same mass.[28]

Terrestrial

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Terrestrial lateral undulation is the most common mode of moving for most snake species.[25]In this mode, the posteriorly moving waves push against contact points in the environment, such as rocks, twigs, irregularities in the soil, etc.[25]The movement is just the same over sand and in water. The movement makes a force against the substrate (ground, sand or water). This gives forward thrust.[29]The speed of the movement depends upon the density of push-points in the environment.[27]The wave speed is the same as the snake speed, and as a result, every point on the snake's body follows the path of the point ahead of it. Snakes move through dense vegetation, small openings, sand and water all quite well.[29]

Aquatic

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See the main article:Sea snake
Banded sea krait,Laticauda

Snakes move forward in water by moving their bodies in a wave-like motion. The waves become larger as they move down the snake's body, and the wave travels backwards faster than the snake moves forwards.[30]Thrust is got by pushing their body against the water.

Studies show that the pattern of muscle activation is somewhat different in aquatic versus terrestrial lateral undulation.[31]All snakes can laterally undulate forward (with backward-moving waves), but only sea snakes have been observed reversing the motion (moving backwards with forward-moving waves).[25]

Sidewinding

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See the main article:Sidewinding
A Mojaverattlesnake(Crotalus scutulatus) sidewinding

This is most often used by colubroid snakes (colubrids,elapids,andvipers). They use it when the environment lacks anything firm to push against, such as a slick mud flat, or a sand dune. Sidewinding is a modified form of lateral undulation in which all of the body segments oriented in one direction remain in contact with the ground, while the other segments are lifted up. This results in a peculiar "rolling" motion.[32][33]This mode of moving overcomes the slippery nature of sand or mud by pushing off with only static portions on the body, thereby minimizing slipping.[32]The static nature of the contact points can be shown from the tracks of a sidewinding snake, which show each belly scale imprint, without any smearing. This mode of moving has very low caloric cost, less than ​1⁄3of the cost for a lizard or normal snake to move the same distance.[28]

Concertina

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When push-points are absent, but the space is too narrow for sidewinding, such as in tunnels, snakes rely onconcertinamoving.[25][33]In this mode, the snake braces the back part of its body against the tunnel wall while the front of the snake extends and straightens.[32]The front portion then flexes and forms an anchor point, and the back part is straightened and pulled forwards. This mode of moving is slow and very demanding, needing up to seven times the energy of laterally undulating over the same distance.[28]This high cost is due to the repeated stops and starts of portions of the body as well as the need to use the muscles to brace against the tunnel walls.

Rectilinear

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The slowest mode of snake moving is rectilinear moving, which is also the only one where the snake does not need to bend its body laterally, though it may do so when turning.[34]In this mode, the belly scales are lifted and pulled forward before being placed down and the body pulled over them. Waves of movement and stasis pass posteriorly, resulting in a series of ripples in the skin.[34]The ribs of the snake do not move in this mode of moving and this method is most often used by largepythons,boas,andviperswhen stalking prey across open ground as the snake's movements are subtle and harder to detect by their prey in this manner.[32]

Other

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The movement of snakes in trees has only recently been studied.[35]While on tree branches, snakes use several modes of moving depending on species and bark texture.[35]In general, snakes will use a modified form of concertina moving on smooth branches, but will laterally undulate if contact points are available.[35]Snakes move faster on small branches and when contact points are present, in contrast to limbed animals, which do better on large branches with little 'clutter'.[35]

Gliding snakes (Chrysopelea) of southeast Asia launch themselves from branch tips, spreading their ribs and laterally undulating as they glide between trees.[32][36][37]These snakes can perform a controlled glide for hundreds of feet depending upon launch altitude and can even turn in midair.[32][36]

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References

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  1. ↑Hsiang, A.Y.; et al. (2015)."The origin of snakes: Revealing the ecology, behavior, and evolutionary history of early snakes using genomics, phenomics, and the fossil record".BMC Evolutionary Biology.15:87.doi:10.1186/s12862-015-0358-5.ISSN1471-2148.PMC4438441.PMID25989795.
  2. ↑"Serpentes".Integrated Taxonomic Information System.Retrieved3 December2008.
  3. ↑snake species listat theReptile Database.Accessed 22 May 2012.
  4. ↑

    Perkins, Sid (27 January 2015)."Fossils of oldest known snakes unearthed".news.sciencemag.org.Archivedfrom the original on 30 January 2015.Retrieved29 January2015.

    Caldwell, M. W.; Nydam, R. L.; Palci, A.; Apesteguía, S. (2015). "The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution".Nature Communications.6(5996): 5996.Bibcode:2015NatCo...6.5996C.doi:10.1038/ncomms6996.PMID25625704.S2CID205334234.
  5. ↑5.05.1"snake (reptile) -- Britannica Online Encyclopedia".britannica.com.Retrieved4 May2010.
  6. ↑"Snake facts".antiguanracer.org.Archived fromthe originalon 6 January 2010.Retrieved4 May2010.
  7. ↑S. Blair Hedges (2008)."At the lower size limit in snakes: two new species of threadsnakes (Squamata: Leptotyphlopidae: Leptotyphlops) from the Lesser Antilles"(PDF).Zootaxa.1841:1–30.doi:10.11646/zootaxa.1841.1.1.S2CID15584371.Retrieved2008-08-04.
  8. ↑Fredriksson G.M. (2005)."Predation on Sun Bears by Reticulated Python in East Kalimantan, Indonesian Borneo".Raffles Bulletin of Zoology.53(1): 165–168.
  9. ↑Head, Jason J.et al2009 (2009)."Giant boid snake from the paleocene neotropics reveals hotter past equatorial temperatures".Nature.457(7230): 715–718.Bibcode:2009Natur.457..715H.doi:10.1038/nature07671.PMID19194448.S2CID4381423.Retrieved2009-02-05.{{cite journal}}:CS1 maint: numeric names: authors list (link)
  10. ↑Vidal N.et al2009. Snakes (Serpentes). In Hedges S.B. and Kumar S. (eds)The timetree of life.Oxford University Press, 390-397.
  11. ↑Benton, Michael 1997.Vertebrate palaeontology.Chapman & Hall, London, 238.
  12. ↑ Fry B.et al2006 (2006)."Early evolution of the venom system in lizards and snakes".Nature.439(7076): 584–588.Bibcode:2006Natur.439..584F.doi:10.1038/nature04328.PMID16292255.S2CID4386245.{{cite journal}}:CS1 maint: numeric names: authors list (link)
  13. ↑ Fry B.et al2003 (2003)."Molecular evolution and phylogeny of elapid snake venom three-finger toxins".Journal of Molecular Evolution.57(1): 110–129.Bibcode:2003JMolE..57..110F.doi:10.1007/s00239-003-2461-2.PMID12962311.S2CID12358977.{{cite journal}}:CS1 maint: numeric names: authors list (link)
  14. ↑ Fry B.et al2003 (2003)."Isolation of a neurotoxin (α-colubritoxin) from a nonvenomous colubrid: evidence for early origin of venom in snakes".Journal of Molecular Evolution.57(4): 446–452.Bibcode:2003JMolE..57..446F.doi:10.1007/s00239-003-2497-3.PMID14708577.S2CID21055188.{{cite journal}}:CS1 maint: numeric names: authors list (link)
  15. ↑ Fry B. & Wüster W. 2004 (2004)."Assembling an arsenal: origin and evolution of the snake venom proteome inferred from phylogenetic analysis of toxin sequences".Molecular Biology and Evolution.21(5): 870–883.doi:10.1093/molbev/msh091.PMID15014162.{{cite journal}}:CS1 maint: numeric names: authors list (link)
  16. ↑Vidal, Nicolas & S. Blair Hedges 2009. The molecular evolutionary tree of lizards, snakes, and amphisbaenians.Comptes rendus biologies332,(2) 129-139.[1]Archived2013-10-30 at theWayback Machine
  17. ↑Pyron R.A; Burbrink F.T. & Wiens J.J. 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes.BMC evolutionary biology13,(1) 93.
  18. ↑Wiens, John J.et al2012. Resolving the phylogeny of lizards and snakes (Squamata) with extensive sampling of genes and species.Biology letters8,(6) 1043-1046.
  19. ↑Martil D.M; Tischlinger H & Longrich N. 2015. A four-legged snake from the early Cretaceous of Gondwana.Science349(6246) 416–419.A four-legged snake from the early Cretaceous of Gondwana | Science
  20. ↑Webb, Jonathan 2015. Four-legged snake ancestor 'dug burrows'.BBC NewsScience & Environment.Four-legged snake ancestor 'dug burrows' - BBC News
  21. ↑21.021.121.2Freiberg, Marcos A.; Walls, Jerry G. (1984).The World of Venomous Animals.Tfh Publications Incorporated.ISBN978-0-87666-567-1.
  22. ↑Mehrtens, John 1987.Living snakes of the world in color.New York: Sterling.ISBN978-0-8069-6461-4
  23. ↑"Snake facts - information on snakes".snakefacts.net.Archived fromthe originalon 16 February 2010.Retrieved4 May2010.
  24. ↑Behler, John L.; King, F. Wayne (1979).The Audubon Society Field Guide to North American Reptiles and Amphibians.Alfred a Knopf Incorporated. p.581.ISBN978-0-394-50824-5.
  25. ↑25.025.125.225.325.425.5Cogger(1991), p. 175.
  26. ↑26.026.1Gray, J. (1946). "The mechanism of locomotion in snakes".Journal of Experimental Biology.23(2): 101–120.doi:10.1242/jeb.23.2.101.PMID20281580.
  27. ↑27.027.1Hekrotte, Carlton (1967). "Relations of body temperature, size, and crawling speed of the Common Garter Snake,Thamnophis s. sirtalis".Copeia.23(4): 759–763.doi:10.2307/1441886.JSTOR1441886.
  28. ↑28.028.128.2Walton, Michael; Jayne, Bruce C.; Bennet, Albert F. (1990-08-03)."The Energetic Cost of Limbless Locomotion".Science.249(4968): 524–527.doi:10.1126/science.249.4968.524.ISSN0036-8075.PMID17735283.S2CID17065200.
  29. ↑29.029.1Gray J. & Lissman H.W 1950. (1950)."Kinetics of locomotion of the grass snake".Journal of Experimental Biology.26(4): 354–367.doi:10.1242/jeb.26.4.354.{{cite journal}}:CS1 maint: numeric names: authors list (link)
  30. ↑Gray, J; Lissman (1953). "Undulatory propulsion".Quarterly Journal of Microscopical Science.94:551–578.
  31. ↑Jayne, B.C. (1988). "Muscular mechanisms of snake locomotion: an electromyographic study of lateral undulation of the Florida banded water snake (Nerodia fasciata) and the yellow rat snake (Elaphe obsoleta) ".Journal of Morphology.197(2): 159–181.doi:10.1002/jmor.1051970204.PMID3184194.S2CID25729192.
  32. ↑32.032.132.232.332.432.5Cogger(1991), p. 177.
  33. ↑33.033.1Jayne, B.C (1986). "Kinematics of terrestrial snake locomotion".Copeia.1986(4): 915–927.doi:10.2307/1445288.JSTOR1445288.
  34. ↑34.034.1Cogger (1991), p. 176.
  35. ↑35.035.135.235.3Astley, H.C.; Jayne, B.C. (2007). "Effects of perch diameter and incline on the kinematics, performance and modes of arboreal locomotion of corn snakes (Elaphe guttata) ".Journal of Experimental Biology.210(Pt 21): 3862–3872.doi:10.1242/jeb.009050.PMID17951427.S2CID18129284.
  36. ↑36.036.1Freiberg (1984), p. 135.
  37. ↑Socha, JJ (2002). "Gliding flight in the paradise tree snake".Nature.418(6898): 603–604.doi:10.1038/418603a.PMID12167849.S2CID4424131.

[1]

Other websites

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Wikimedia Commons has media related toSerpentes.
Wikispecieshas information on:Serpentes.
  1. ↑J. Lesh, Laurie (2024-03-27)."Top 30 Interesting Facts About Snakes".Random Fun Facts Online.Archived fromthe originalon 2024-03-27.Retrieved2024-03-27.
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