[guide.chat] History on snakes by wickapedia
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Snake
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This article is about the animal. For other uses, see Snake
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Snakes
Temporal range: Early Cretaceous - Recent,
112-0 Ma
Pre?
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O
S
D
C
P
T
J
K
Pg
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File:Coast_Garter_Snake
Coast garter snake,
Thamnophis elegans terrestris
Scientific classification
e
Kingdom:
Animalia
Phylum:
Chordata
Class:
Reptilia
Order:
Squamata
Superfamily:
Varanoidea
(unranked):
Pythonomorpha
Suborder:
Serpentes
Linnaeus, 1758
Subgroups
? Alethinophidia - Nopcsa, 1923
? Scolecophidia - Cope, 1864
File:World.distribution.serpentes.1
World range of snakes
(rough range of sea snakes in blue)
Snakes are elongate, legless, carnivorous reptiles of the suborder
Serpentes that can be distinguished from legless lizards by their lack
of eyelids and external ears. Like all squamates, snakes are
ectothermic, amniote vertebrates covered in overlapping scales. Many
species of snakes have skulls with many more joints than their lizard
ancestors, enabling them to swallow prey much larger than their heads
with their highly 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 functional lung. Some
species retain a pelvic girdle with a pair of vestigial claws on either
side of the cloaca.
Living snakes are found on every continent except Antarctica and on most
islands. Fifteen families are currently recognized, comprising 456
genera and over 2,900 species.[1][2] They range in size from the tiny,
10 cm-long thread snake to pythons and anacondas of up to 7.6 metres
(25 ft) in length. The fossil species Titanoboa cerrejonensis was 15
metres (49 ft) long. Snakes are thought to have evolved from either
burrowing or aquatic lizards during the mid-Cretaceous period, and the
earliest known fossils date to around 112 Ma ago. The diversity of
modern snakes appeared during the Paleocene period (c 66 to 56 Ma ago).
Most species are nonvenomous and those that have venom use it primarily
to kill and subdue prey rather than for self-defense. Some possess venom
potent enough to cause painful injury or death to humans. Nonvenomous
snakes either swallow prey alive or kill by constriction.
Contents [hide]
1 Etymology
2 Evolution
2.1 Origins
3 Taxonomy
3.1 Families
4 Biology
4.1 Skeleton
4.2 Internal organs
4.3 Size
4.4 Skin
4.4.1 Moulting
4.5 Perception
4.6 Venom
5 Behavior
5.1 Feeding and diet
5.2 Locomotion
5.2.1 Lateral undulation
5.2.1.1 Terrestrial
5.2.1.2 Aquatic
5.2.2 Sidewinding
5.2.3 Concertina
5.2.4 Rectilinear
5.2.5 Other
5.3 Reproduction
6 Interactions with humans
6.1 Bite
6.2 Snake charmers
6.3 Trapping
6.4 Consumption
6.5 Pets
6.6 Symbolism
6.7 Religion
7 Place names
8 See also
9 References
10 Further reading
11 External links
Etymology
The English word snake comes from Old English snaca, itself from
Proto-Germanic *snak-an- (cf. German Schnake "ring snake," Swedish snok
"grass snake"), from Proto-Indo-European root *(s)neg-o- "to crawl,
creep," which also gave sneak as well as Sanskrit nagá "snake."[3] The
word ousted adder, as adder went on to narrow in meaning, though in Old
English næddre was the general word for snake.[4] The other term,
serpent, is from French, ultimately from Indo-European *serp- (to
creep),[5] which also gave Greek érpo (e?p?) "I crawl."
Evolution
A phylogenetic overview of the extant groups
Modern snakes
Scolecophidia
Leptotyphlopidae
Anomalepididae
Typhlopidae
Alethinophidia
Anilius
Core Alethinophidia
Uropeltidae
Cylindrophis
Anomochilus
Uropeltinae
Macrostomata
Pythonidae
Pythoninae
Xenopeltis
Loxocemus
Caenophidia
Colubridae
Acrochordidae
Atractaspididae
Elapidae
Hydrophiidae
Viperidae
Boidae
Erycinae
Boinae
Calabaria
Ungaliophiinae
Tropidophiinae
Note: the tree only indicates relationships, not evolutionary branching
times.[6]
The fossil record of snakes is relatively poor because snake skeletons
are typically small and fragile, making fossilization uncommon. Fossils
readily identifiable as snakes (though often retaining hind limbs) first
appear in the fossil record during the Cretaceous period.[7] The
earliest known snake fossils come from sites in Utah and Algeria,
represented by the genera Coniophis and Lapparentophis, respectively.
These fossil sites have been tentatively dated to the Albian or
Cenomanian age of the late Cretaceous, between 112 and 94 Ma ago.
However, an even older age has been suggested for one of the Algerian
sites, which may be as old as the Aptian, 125-112 Ma ago.[8]
Based on comparative anatomy, there is consensus that snakes descended
from lizards.[9]:11[10] Pythons and boas-primitive groups among modern
snakes-have vestigial hind limbs: tiny, clawed digits known as anal
spurs, which are used to grasp during mating.[9]:11[11] The
Leptotyphlopidae and Typhlopidae groups also possess remnants of the
pelvic girdle, sometimes appearing as horny projections when visible.
Frontal limbs are nonexistent in all known snakes. This is caused by the
evolution of Hox genes, controlling limb morphogenesis. The axial
skeleton of the snakes' common ancestor, like most other tetrapods, had
regional specializations consisting of cervical (neck), thoracic
(chest), lumbar (lower back), sacral (pelvic), and caudal (tail)
vertebrae. Early in snake evolution, the Hox gene expression in the
axial skeleton responsible for the development of the thorax became
dominant. As a result, the vertebrae anterior to the hindlimb buds (when
present) all have the same thoracic-like identity (except from the
atlas, axis, and 1-3 neck vertebrae). In other words, most of a snake's
skeleton is an extremely extended thorax. Ribs are found exclusively on
the thoracic vertebrae. Neck, lumbar and pelvic vertebrae are very
reduced in number (only 2-10 lumbar and pelvic vertebrae are present),
while only a short tail remains of the caudal vertebrae. However, the
tail is still long enough to be of important use in many species, and is
modified in some aquatic and tree-dwelling species.
Modern snakes greatly diversified during the Paleocene. This occurred
alongside the adaptive radiation of mammals, following the extinction of
(non-avian) dinosaurs. The colubrids, one of the more common snake
groups, became particularly diverse due to preying on rodents, an
especially successful mammal group. There are over 2,900 species of
snakes ranging as far northward as the Arctic Circle in Scandinavia and
southward through Australia and Tasmania.[10] Snakes can be found on
every continent (with the exception of Antarctica), in the sea, and as
high as 16,000 feet (4,900 m) in the Himalayan Mountains of
Asia.[10][12]:143 There are numerous islands from which snakes are
absent, such as Ireland, Iceland, and New Zealand.[12]:143
Origins
The origin of snakes remains an unresolved issue. There are two main
hypotheses competing for acceptance.
Burrowing Lizard Hypothesis
There is fossil evidence to suggest that snakes may have evolved from
burrowing lizards, such as the varanids (or a similar group) during the
Cretaceous Period.[13] An early fossil snake, Najash rionegrina, was a
two-legged burrowing animal with a sacrum, and was fully
terrestrial.[14] One extant analog of these putative ancestors is the
earless monitor Lanthanotus of Borneo (though it also is
semiaquatic).[15] Subterranean species evolved bodies streamlined for
burrowing, and eventually lost their limbs.[15] According to this
hypothesis, features such as the transparent, fused eyelids (brille) and
loss of external ears evolved to cope with fossorial difficulties, such
as scratched corneas and dirt in the ears.[13][15] Some primitive snakes
are known to have possessed hindlimbs, but their pelvic bones lacked a
direct connection to the vertebrae. These include fossil species like
Haasiophis, Pachyrhachis and Eupodophis, which are slightly older than
Najash.[11]
File:Naturkundemuseum_Berlin_-_Archaeophis_proavus_Massalongo_-_Monte_Bolca
Fossil of Archaeophis proavus.
Aquatic Mosasaur Hypothesis
An alternative hypothesis, based on morphology, suggests the ancestors
of snakes were related to mosasaurs-extinct aquatic reptiles from the
Cretaceous-which in turn are thought to have derived from varanid
lizards.[10] According to this hypothesis, the fused, transparent
eyelids of snakes are thought to have evolved to combat marine
conditions (corneal water loss through osmosis), and the external ears
were lost through disuse in an aquatic environment. This ultimately lead
to an animal similar to today's sea snakes. In the Late Cretaceous,
snakes recolonized land, and continued to diversify into today's snakes.
Fossilized snake remains are known from early Late Cretaceous marine
sediments, which is consistent with this hypothesis; particularly so, as
they are older than the terrestrial Najash rionegrina. Similar skull
structure, reduced or absent limbs, and other anatomical features found
in both mosasaurs and snakes lead to a positive cladistical correlation,
although some of these features are shared with varanids.
Genetic studies in recent years have indicated snakes are not as closely
related to monitor lizards as was once believed-and therefore not to
mosasaurs, the proposed ancestor in the aquatic scenario of their
evolution. However, more evidence links mosasaurs to snakes than to
varanids. Fragmented remains found from the Jurassic and Early
Cretaceous indicate deeper fossil records for these groups, which may
potentially refute either hypothesis.
Taxonomy
All modern snakes are grouped within the suborder Serpentes in Linnean
taxonomy, part of the order Squamata, though their precise placement
within squamates is controversial.[1]
There are two infraorders of Serpentes: Alethinophidia and
Scolecophidia.[1] This separation is based on morphological
characteristics and mitochondrial DNA sequence similarity.
Alethinophidia is sometimes split into Henophidia and Caenophidia, with
the latter consisting of "colubroid" snakes (colubrids, vipers, elapids,
hydrophiids, and attractaspids) and acrochordids, while the other
alethinophidian families comprise Henophidia.[16] While not extant
today, the Madtsoiidae, a family of giant, primitive, python-like
snakes, was around until 50,000 years ago in Australia, represented by
genera such as Wonambi.
There are numerous debates in the systematics within the group. For
instance, many sources classify Boidae and Pythonidae as one family,
while some keep the Elapidae and Hydrophiidae (sea snakes) separate for
practical reasons despite their extremely close relation.
Recent molecular studies support the monophyly of the clades of modern
snakes, scolecophidians, typhlopids + anomalepidids, alethinophidians,
core alethinophidians, uropeltids (Cylindrophis, Anomochilus,
uropeltines), macrostomatans, booids, boids, pythonids and caenophidians.[6]
Families
Infraorder Alethinophidia 15 families
Family[1]
Taxon author[1]
Genera[1]
Species[1]
Common name
Geographic range[17]
Acrochordidae
Bonaparte, 1831
1
3
Wart snakes
Western India and Sri Lanka through tropical Southeast Asia to the
Philippines, south through the Indonesian/Malaysian island group to
Timor, east through New Guinea to the northern coast of Australia to
Mussau Island, the Bismark Archipelago and Guadalcanal Island in the
Solomon Islands.
Aniliidae
Stejneger, 1907
1
1
False coral snake
Tropical South America.
Anomochilidae
Cundall, Wallach, 1993
1
2
Dwarf pipe snakes
West Malaysia and on the Indonesian island of Sumatra.
Atractaspididae
Günther, 1858
12
64
Burrowing asps
Africa and the Middle East.[9][18][19]
Boidae
Gray, 1825
8
43
Boas
Northern, Central and South America, the Caribbean, southeastern Europe
and Asia Minor, Northern, Central and East Africa, Madagascar and
Reunion Island, the Arabian Peninsula, Central and southwestern Asia,
India and Sri Lanka, the Moluccas and New Guinea through to Melanesia
and Samoa.
Bolyeriidae
Hoffstetter, 1946
2
2
Splitjaw snakes
Mauritius.
Colubridae
Oppel, 1811
304[2]
1938[2]
Typical snakes
Widespread on all continents, except Antarctica.[20]
Cylindrophiidae
Fitzinger, 1843
1
8
Asian pipe snakes
Sri Lanka east through Myanmar, Thailand, Cambodia, Vietnam and the
Malay Archipelago to as far east as Aru Islands off the southwestern
coast of New Guinea. Also found in southern China (Fujian, Hong Kong and
on Hainan Island) and in Laos.
Elapidae
Boie, 1827
61
235
Elapids
On land, worldwide in tropical and subtropical regions, except in
Europe. Sea snakes occur in the Indian Ocean and the Pacific.[21]
Loxocemidae
Cope, 1861
1
1
Mexican burrowing snake
Along the Pacific versant from Mexico south to Costa Rica.
Pythonidae
Fitzinger, 1826
8
26
Pythons
Subsaharan Africa, India, Myanmar, southern China, Southeast Asia and
from the Philippines southeast through Indonesia to New Guinea and
Australia.
Tropidophiidae
Brongersma, 1951
4
22
Dwarf boas
From southern Mexico and Central America, south to northwestern South
America in Colombia, (Amazonian) Ecuador and Peru, as well as in
northwestern and southeastern Brazil. Also found in the West Indies.
Uropeltidae
Müller, 1832
8
47
Shield-tailed snakes
Southern India and Sri Lanka.
Viperidae
Oppel, 1811
32
224
Vipers
The Americas, Africa and Eurasia.
Xenopeltidae
Bonaparte, 1845
1
2
Sunbeam snakes
Southeast Asia from the Andaman and Nicobar Islands, east through
Myanmar to southern China, Thailand, Laos, Cambodia, Vietnam, the Malay
Peninsula and the East Indies to Sulawesi, as well as the Philippines.
Infraorder Scolecophidia 3 families
Family[1]
Taxon author[1]
Genera[1]
Species[1]
Common name
Geographic range[17]
Anomalepidae
Taylor, 1939
4
15
Primitive blind snakes
From southern Central America to northwestern South America. Disjunct
populations in northeastern and southeastern South America.
Leptotyphlopidae
Stejneger, 1892
2
87
Slender blind snakes
Africa, western Asia from Turkey to northwestern India, on Socotra
Island, from the southwestern United States south through Mexico and
Central to South America, though not in the high Andes. In Pacific South
America they occur as far south as southern coastal Peru, and on the
Atlantic side as far as Uruguay and Argentina. In the Caribbean they are
found on the Bahamas, Hispaniola and the Lesser Antilles.
Typhlopidae
Merrem, 1820
6
203
Typical blind snakes
Most tropical and many subtropical regions around the world,
particularly in Africa, Madagascar, Asia, islands in the Pacific,
tropical America and in southeastern Europe.
Biology
File:Snake_Skeletons
When compared, the skeletons of snakes are radically different from
those of most other reptiles (such as the turtle, right), being made up
almost entirely of an extended ribcage.
Skeleton
The skeleton of most snakes consists solely of the skull, hyoid,
vertebral column, and ribs, though henophidian snakes retain vestiges of
the pelvis and rear limbs. The skull of the snake consists of a solid
and complete braincase, to which many of the other bones are only
loosely attached, particularly the highly mobile jaw bones, which
facilitate manipulation and ingestion of large prey items. The left and
right sides of the lower jaw are joined only by a flexible ligament at
the anterior tips, allowing them to separate widely, while the posterior
end of the lower jaw bones articulate with a quadrate bone, allowing
further mobility. The bones of the mandible and quadrate bones can also
pick up ground borne vibrations.[22] The hyoid is a small bone located
posterior and ventral to the skull, in the 'neck' region, which serves
as an attachment for muscles of the snake's tongue, as it does in all
other tetrapods.
The vertebral column consists of anywhere between 200 to 400 (or more)
vertebrae. Tail vertebrae are comparatively few in number (often less
than 20% of the total) and lack ribs, while body vertebrae each have two
ribs articulating with them. The vertebrae have projections that allow
for strong muscle attachment enabling locomotion without limbs. Autotomy
of the tail, a feature found in some lizards is absent in most
snakes.[23] Caudal autotomy in snakes is rare and is intervertebral,
unlike that in lizards, which is intravertebral-that is, the break
happens along a predefined fracture plane present on a vertebra.[24][25]
In some snakes, most notably boas and pythons, there are vestiges of the
hindlimbs in the form of a pair of pelvic spurs. These small, claw-like
protrusions on each side of the cloaca are the external portion of the
vestigial hindlimb skeleton, which includes the remains of an ilium and
femur.
Internal organs
Anatomy of a snake. 1 esophagus, 2 trachea, 3 tracheal lungs, 4
rudimentary left lung, 5 right lung, 6 heart, 7 liver, 8 stomach, 9 air
sac, 10 gallbladder, 11 pancreas, 12 spleen, 13 intestine, 14 testicles,
15 kidneys.
The snake's heart is encased in a sac, called the pericardium, located
at the bifurcation of the bronchi. The heart is able to move around,
however, owing to the lack of a diaphragm. This adjustment protects the
heart from potential damage when large ingested prey is passed through
the esophagus. The spleen is attached to the gall bladder and pancreas
and filters the blood. The thymus gland is located in fatty tissue above
the heart and is responsible for the generation of immune cells in the
blood. The cardiovascular system of snakes is also unique for the
presence of a renal portal system in which the blood from the snake's
tail passes through the kidneys before returning to the heart.[26]
The vestigial left lung is often small or sometimes even absent, as
snakes' tubular bodies require all of their organs to be long and
thin.[26] In the majority of species, only one lung is functional. This
lung contains a vascularized anterior portion and a posterior portion
that does not function in gas exchange.[26] This 'saccular lung' is used
for hydrostatic purposes to adjust buoyancy in some aquatic snakes and
its function remains unknown in terrestrial species.[26] Many organs
that are paired, such as kidneys or reproductive organs, are staggered
within the body, with one located ahead of the other.[26]
Snakes have no lymph nodes.[26]
File:Leptotyphlops_carlae
An adult Barbados threadsnake, Leptotyphlops carlae, on an American
quarter dollar.
Size
The now extinct Titanoboa cerrejonensis snakes found were 12-15 meters
(39-49 ft) in length. By comparison, the largest extant snakes are the
reticulated python, which measures about 9 meters (30 ft) long, and the
anaconda, which measures about 7.5 meters (25 ft) long[27] and is
considered the heaviest snake on Earth.
At the other end of the scale, the smallest extant snake is
Leptotyphlops carlae, with a length of about 10 centimeters (4 in).[28]
Most snakes are fairly small animals, approximately 3 feet in length.[29]
File:Ptyas_gab_fbi
A line diagram from G.A. Boulenger's Fauna of British India (1890)
illustrating the terminology of shields on the head of a snake.
Skin
Main article: Snake scales
The skin of a snake is covered in scales. Contrary to the popular notion
of snakes being slimy because of possible confusion of snakes with
worms, snakeskin has a smooth, dry texture. Most snakes use specialized
belly scales to travel, gripping surfaces. The body scales may be
smooth, keeled, or granular. The eyelids of a snake are transparent
"spectacle" scales, which remain permanently closed, also known as brille.
The shedding of scales is called ecdysis (or in normal usage, moulting
or sloughing). In the case of snakes, the complete outer layer of skin
is shed in one layer.[30] Snake scales are not discrete, but extensions
of the epidermis-hence they are not shed separately but as a complete
outer layer during each moult, akin to a sock being turned inside out.[31]
The shape and number of scales on the head, back, and belly are often
characteristic and used for taxonomic purposes. Scales are named mainly
according to their positions on the body. In "advanced" (Caenophidian)
snakes, the broad belly scales and rows of dorsal scales correspond to
the vertebrae, allowing scientists to count the vertebrae without
dissection.
File:Diamond-python_moult_eye-scales
Eye scales visible during the moult of a Diamond Python.
Snakes' eyes are covered by their clear scales (the brille) rather than
movable eyelids. Their eyes are always open, and for sleeping, the
retina can be closed or the face buried among the folds of the body.
Moulting
Moulting serves a number of functions. Firstly, the old and worn skin is
replaced; secondly, it helps get rid of parasites such as mites and
ticks. Renewal of the skin by moulting is supposed to allow growth in
some animals such as insects; however, this has been disputed in the
case of snakes.[31][32]
File:Nerodia_sipedon_shedding
A snake shedding its skin.
Moulting occurs periodically throughout a snake's life. Before a moult,
the snake stops eating and often hides or moves to a safe place. Just
before shedding, the skin becomes dull and dry looking and the eyes
become cloudy or blue-colored. The inner surface of the old skin
liquefies. This causes the old skin to separate from the new skin
beneath it. After a few days, the eyes clear and the snake "crawls" out
of its old skin. The old skin breaks near the mouth and the snake
wriggles out, aided by rubbing against rough surfaces. In many cases,
the cast skin peels backward over the body from head to tail in one
piece, like pulling a sock off inside-out. A new, larger, brighter layer
of skin has formed underneath.[31][33]
An older snake may shed its skin only once or twice a year. But a
younger snake, still growing, may shed up to four times a year.[33] The
discarded skin gives a perfect imprint of the scale pattern, and it is
usually possible to identify the snake if the discarded skin is
reasonably intact.[31] This periodic renewal has led to the snake being
a symbol of healing and medicine, as pictured in the Rod of Asclepius.[34]
Perception
Eyesight
Snake vision varies greatly, from only being able to distinguish light
from dark to keen eyesight, but the main trend is that their vision is
adequate although not sharp, and allows them to track movements.[35]
Generally, vision is best in arboreal snakes and weakest in burrowing
snakes. Some snakes, such as the Asian vine snake (genus Ahaetulla),
have binocular vision, with both eyes capable of focusing on the same
point. Most snakes focus by moving the lens back and forth in relation
to the retina, while in the other amniote groups, the lens is stretched.
Smell
Snakes use smell to track their prey. They smell by using their forked
tongues to collect airborne particles, then passing them to the
vomeronasal organ or Jacobson's organ in the mouth for examination.[36]
The fork in the tongue gives snakes a sort of directional sense of smell
and taste simultaneously.[36] They keep their tongues constantly in
motion, sampling particles from the air, ground, and water, analyzing
the chemicals found, and determining the presence of prey or predators
in the local environment. In water-dwelling snakes, such as the
Anaconda, the tongue functions efficiently under water.[36]
File:Wiki_snake_eats_mouse
Thermographic image of a snake eating a mouse
Vibration sensitivity
The part of the body in direct contact with the ground is very sensitive
to vibration; thus, a snake can sense other animals approaching by
detecting faint vibrations in the air and on the ground.[36]
Infrared sensitivity
Pit vipers, pythons, and some boas have infrared-sensitive receptors in
deep grooves between the nostril and eye, although some have labial pits
on their upper lip just below the nostrils (common in pythons), which
allow them to "see" the radiated heat of warm-blooded prey mammals.[36]
Venom
See also: Snake venom, Venomous snake, and #Bite
File:Red_milk_snake
Milk snakes are often mistaken for coral snakes, whose venom is deadly
to humans.
Cobras, vipers, and closely related species use venom to immobilize or
kill their prey. The venom is modified saliva, delivered through
fangs.[9]:243 The fangs of 'advanced' venomous snakes like viperids and
elapids are hollow to inject venom more effectively, while the fangs of
rear-fanged snakes such as the boomslang merely have a groove on the
posterior edge to channel venom into the wound. Snake venoms are often
prey specific, their role in self-defense is secondary.[9]:243
Venom, like all salivary secretions, is a predigestant that initiates
the breakdown of food into soluble compounds, facilitating proper
digestion. Even nonvenomous snake bites (like any animal bite) will
cause tissue damage.[9]:209
Certain birds, mammals, and other snakes (such as kingsnakes) that prey
on venomous snakes have developed resistance and even immunity to
certain venoms.[9]:243 Venomous snakes include three families of snakes,
and do not constitute a formal classification group used in taxonomy.
The term poisonous snake is mostly incorrect. Poison is inhaled or
ingested, whereas venom is injected.[37] There are, however, two
exceptions: Rhabdophis sequesters toxins from the toads it eats, then
secretes them from nuchal glands to ward off predators, and a small
population of garter snakes in Oregon retains enough toxin in their
liver from the newts they eat to be effectively poisonous to small local
predators (such as crows and foxes).[38]
Snake venoms are complex mixtures of proteins, and are stored in poison
glands at the back of the head.[38] In all venomous snakes, these glands
open through ducts into grooved or hollow teeth in the upper
jaw.[9]:243[37] These proteins can potentially be a mix of neurotoxins
(which attack the nervous system), hemotoxins (which attack the
circulatory system), cytotoxins, bungarotoxins and many other toxins
that affect the body in different ways.[37] Almost all snake venom
contains hyaluronidase, an enzyme that ensures rapid diffusion of the
venom.[9]:243
Venomous snakes that use hemotoxins usually have fangs in the front of
their mouths, making it easier for them to inject the venom into their
victims.[37] Some snakes that use neurotoxins (such as the mangrove
snake) have fangs in the back of their mouths, with the fangs curled
backwards.[39] This makes it both difficult for the snake to use its
venom and for scientists to milk them.[37] Elapids, however, such as
cobras and kraits are proteroglyphous-they possess hollow fangs that
cannot be erected toward the front of their mouths, and cannot "stab"
like a viper. They must actually bite the victim.[9]:242
It has recently been suggested that all snakes may be venomous to a
certain degree, with harmless snakes having weak venom and no fangs.[40]
Most snakes currently labelled "nonvenomous" would still be considered
harmless according to this theory, as they either lack a venom delivery
method or are incapable of delivering enough to endanger a human. This
theory postulates that snakes may have evolved from a common lizard
ancestor that was venomous-and that venomous lizards like the gila
monster, beaded lizard, monitor lizards, and the now-extinct mosasaurs
may also have derived. They share this venom clade with various other
saurian species.
Venomous snakes are classified in two taxonomic families:
? Elapids - cobras including king cobras, kraits, mambas, Australian
copperheads, sea snakes, and coral snakes.[39]
? Viperids - vipers, rattlesnakes, copperheads/cottonmouths, adders and
bushmasters.[39]
There is a third family containing the opistoglyphous (rear-fanged)
snakes (as well as the majority of other snake species):
? Colubrids - boomslangs, tree snakes, vine snakes, mangrove snakes,
although not all colubrids are venomous.[9]:209[39]
Behavior
Feeding and diet
File:Snake_eating_mouse
Snake eating a rodent.
File:Carpet_snake
Carpet python constricting and consuming a chicken.
All snakes are strictly carnivorous, eating small animals including
lizards, other snakes, small mammals, birds, eggs, fish, snails or
insects.[9][1][10][41] Because snakes cannot bite or tear their food to
pieces, they must swallow prey whole. The body size of a snake has a
major influence on its eating habits. Smaller snakes eat smaller prey.
Juvenile pythons might start out feeding on lizards or mice and graduate
to small deer or antelope as an adult, for example.
File:Eierschlange_frisst_Zwergwachtelei
African egg-eating snake.
The snake's jaw is a complex structure. Contrary to the popular belief
that snakes can dislocate their jaws, snakes have a very flexible lower
jaw, the two halves of which are not rigidly attached, and numerous
other joints in their skull (see snake skull), allowing them to open
their mouths wide enough to swallow their prey whole, even if it is
larger in diameter than the snake itself,[41] as snakes do not chew. For
example, the African egg-eating snake has flexible jaws adapted for
eating eggs much larger than the diameter of its head.[9]:81 This snake
has no teeth, but does have bony protrusions on the inside edge of its
spine, which it uses to break shells when it eats eggs.[9]:81
While the majority of snakes eat a variety of prey animals, there is
some specialization by some species. King cobras and the Australian
bandy-bandy consume other snakes. Pareas iwesakii and other snail-eating
colubrids of subfamily Pareatinae have more teeth on the right side of
their mouths than on the left, as the shells of their prey usually
spiral clockwise[9]:184[42]
Some snakes have a venomous bite, which they use to kill their prey
before eating it.[41][43] Other snakes kill their prey by
constriction.[41] Still others swallow their prey whole and alive.[9]:81[41]
After eating, snakes become dormant while the process of digestion takes
place.[44] Digestion is an intense activity, especially after
consumption of large prey. In species that feed only sporadically, the
entire intestine enters a reduced state between meals to conserve
energy. The digestive system is then 'up-regulated' to full capacity
within 48 hours of prey consumption. Being ectothermic ("cold-blooded"),
the surrounding temperature plays a large role in snake digestion. The
ideal temperature for snakes to digest is 30 °C (86 °F). So much
metabolic energy is involved in a snake's digestion that in the Mexican
rattlesnake (Crotalus durissus), surface body temperature increases by
as much as 1.2 °C (2.2 °F) during the digestive process.[45] Because of
this, a snake disturbed after having eaten recently will often
regurgitate its prey to be able to escape the perceived threat. When
undisturbed, the digestive process is highly efficient, with the snake's
digestive enzymes dissolving and absorbing everything but the prey's
hair (or feathers) and claws, which are excreted along with waste.
Locomotion
The lack of limbs does not impede the movement of snakes. They have
developed several different modes of locomotion to deal with particular
environments. Unlike the gaits of limbed animals, which form a
continuum, each mode of snake locomotion is discrete and distinct from
the others; transitions between modes are abrupt.[46][47]
Lateral undulation
Main article: Undulatory locomotion
Lateral undulation is the sole mode of aquatic locomotion, and the most
common mode of terrestrial locomotion.[47] In this mode, the body of the
snake alternately flexes to the left and right, resulting in a series of
rearward-moving "waves."[46] While this movement appears rapid, snakes
have rarely been documented moving faster than two body-lengths per
second, often much less.[48] This mode of movement has the same net cost
of transport (calories burned per meter moved) as running in lizards of
the same mass.[49]
Terrestrial
Terrestrial lateral undulation is the most common mode of terrestrial
locomotion for most snake species.[46] In this mode, the posteriorly
moving waves push against contact points in the environment, such as
rocks, twigs, irregularities in the soil, etc.[46] Each of these
environmental objects, in turn, generates a reaction force directed
forward and towards the midline of the snake, resulting in forward
thrust while the lateral components cancel out.[50] The speed of this
movement depends upon the density of push-points in the environment,
with a medium density of about 8 along the snake's length being
ideal.[48] The wave speed is precisely 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, allowing snakes to move through very dense vegetation
and small openings.[50]
Aquatic
Main article: Sea snake
File:Banded_Sea_Snake-jonhanson
Banded sea krait, Laticauda sp.
When swimming, the waves become larger as they move down the snake's
body, and the wave travels backwards faster than the snake moves
forwards.[51] Thrust is generated by pushing their body against the
water, resulting in the observed slip. In spite of overall similarities,
studies show that the pattern of muscle activation is different in
aquatic versus terrestrial lateral undulation, which justifies calling
them separate modes.[52] 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).[46]
Sidewinding
See also: Sidewinding
File:Crotalus_scutulatus_03
A Mojave rattlesnake (Crotalus scutulatus) sidewinding.
Most often employed by colubroid snakes (colubrids, elapids, and vipers)
when the snake must move in an environment that lacks irregularities to
push against (rendering lateral undulation impossible), 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, resulting in a peculiar "rolling" motion.[53][54] This mode of
locomotion overcomes the slippery nature of sand or mud by pushing off
with only static portions on the body, thereby minimizing slipping.[53]
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 locomotion has very low caloric cost, less than ?
of the cost for a lizard or snake to move the same distance.[49]
Contrary to popular belief, there is no evidence that sidewinding is
associated with the sand being hot.[53]
Concertina
Main article: Concertina movement
When push-points are absent, but there is not enough space to use
sidewinding because of lateral constraints, such as in tunnels, snakes
rely on concertina locomotion.[46][54] In this mode, the snake braces
the posterior portion of its body against the tunnel wall while the
front of the snake extends and straightens.[53] The front portion then
flexes and forms an anchor point, and the posterior is straightened and
pulled forwards. This mode of locomotion is slow and very demanding, up
to seven times the cost of laterally undulating over the same
distance.[49] This high cost is due to the repeated stops and starts of
portions of the body as well as the necessity of using active muscular
effort to brace against the tunnel walls.
Rectilinear
Main article: Rectilinear locomotion
The slowest mode of snake locomotion is rectilinear locomotion, which is
also the only one where the snake does not need to bend its body
laterally, though it may do so when turning.[55] 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.[55] The ribs of the snake
do not move in this mode of locomotion and this method is most often
used by large pythons, boas, and vipers when stalking prey across open
ground as the snake's movements are subtle and harder to detect by their
prey in this manner.[53]
Other
The movement of snakes in arboreal habitats has only recently been
studied.[56] While on tree branches, snakes use several modes of
locomotion depending on species and bark texture.[56] In general, snakes
will use a modified form of concertina locomotion on smooth branches,
but will laterally undulate if contact points are available.[56] 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'.[56]
Gliding snakes (Chrysopelea) of Southeast Asia launch themselves from
branch tips, spreading their ribs and laterally undulating as they glide
between trees.[53][57][58] These snakes can perform a controlled glide
for hundreds of feet depending upon launch altitude and can even turn in
midair.[53][57]
Reproduction
Although a wide range of reproductive modes are used by snakes, all
snakes employ internal fertilization. This is accomplished by means of
paired, forked hemipenes, which are stored, inverted, in the male's
tail.[59] The hemipenes are often grooved, hooked, or spined in order to
grip the walls of the female's cloaca.[59]
Most species of snakes lay eggs, but most snakes abandon the eggs
shortly after laying. However, a few species (such as the King cobra)
actually construct nests and stay in the vicinity of the hatchlings
after incubation.[59] Most pythons coil around their egg-clutches and
remain with them until they hatch.[60] A female python will not leave
the eggs, except to occasionally bask in the sun or drink water. She
will even "shiver" to generate heat to incubate the eggs.[60]
Some species of snake are ovoviviparous and retain the eggs within their
bodies until they are almost ready to hatch.[61][62] Recently, it has
been confirmed that several species of snake are fully viviparous, such
as the boa constrictor and green anaconda, nourishing their young
through a placenta as well as a yolk sac, which is highly unusual among
reptiles, or anything else outside of placental mammals.[61][62]
Retention of eggs and live birth are most often associated with colder
environments, as the retention of the young within the female.[59][62]
Interactions with humans
File:Snake_bite_symptoms
Most common symptoms of any kind of snake bite poisoning.[63][64][65]
Furthermore, there is vast variation in symptoms between bites from
different types of snakes.[63]
Bite
Main article: Snakebite
File:ViperaBerusFang
Vipera berus, one fang in glove with a small venom stain, the other
still in place.
Snakes do not ordinarily prey on humans, and most will not attack humans
unless the snake is startled or injured, preferring instead to avoid
contact. With the exception of large constrictors, nonvenomous snakes
are not a threat to humans. The bite of nonvenomous snakes is usually
harmless because their teeth are designed for grabbing and holding,
rather than tearing or inflicting a deep puncture wound. Although the
possibility of an infection and tissue damage is present in the bite of
a nonvenomous snake, venomous snakes present far greater hazard to
humans.[9]:209
Documented deaths resulting from snake bites are uncommon. Nonfatal
bites from venomous snakes may result in the need for amputation of a
limb or part thereof. Of the roughly 725 species of venomous snakes
worldwide, only 250 are able to kill a human with one bite. Australia
averages only one fatal snake bite per year. In India, 250,000
snakebites are recorded in a single year, with as many as 50,000
recorded initial deaths.[66]
The treatment for a snakebite is as variable as the bite itself. The
most common and effective method is through antivenom (or antivenin), a
serum made from the venom of the snake. Some antivenom is species
specific (monovalent) while some is made for use with multiple species
in mind (polyvalent). In the United States for example, all species of
venomous snakes are pit vipers, with the exception of the coral snake.
To produce antivenom, a mixture of the venoms of the different species
of rattlesnakes, copperheads, and cottonmouths is injected into the body
of a horse in ever-increasing dosages until the horse is immunized.
Blood is then extracted from the immunized horse; the serum is separated
and further purified and freeze-dried. It is reconstituted with sterile
water and becomes antivenom. For this reason, people who are allergic to
horses are more likely to suffer an allergic reaction to antivenom.[67]
Antivenom for the more dangerous species (such as mambas, taipans, and
cobras) is made in a similar manner in India, South Africa, and
Australia, although these antivenoms are species-specific.
Snake charmers
Main article: Snake charming
File:Snake_in_basket
An Indian cobra in a basket with a snake charmer. These snakes are
perhaps the most common subjects of snake charmings.
In some parts of the world, especially in India, snake charming is a
roadside show performed by a charmer. In such a show, the snake charmer
carries a basket that contains a snake that he seemingly charms by
playing tunes from his flutelike musical instrument, to which the snake
responds.[68] Snakes lack external ears, though they do have internal
ears, and respond to the movement of the flute, not the actual
noise.[68][69]
The Wildlife Protection Act of 1972 in India technically proscribes
snake charming on grounds of reducing animal cruelty. Other snake
charmers also have a snake and mongoose show, where both the animals
have a mock fight; however, this is not very common, as the snakes, as
well as the mongooses, may be seriously injured or killed. Snake
charming as a profession is dying out in India because of competition
from modern forms of entertainment and environment laws proscribing the
practice.[68]
Trapping
The Irulas tribe of Andhra Pradesh and Tamil Nadu in India have been
hunter-gatherers in the hot, dry plains forests, and have practiced the
art of snake catching for generations. They have a vast knowledge of
snakes in the field. They generally catch the snakes with the help of a
simple stick. Earlier, the Irulas caught thousands of snakes for the
snake-skin industry. After the complete ban on snake-skin industry in
India and protection of all snakes under the Indian Wildlife
(Protection) Act 1972, they formed the Irula Snake Catcher's Cooperative
and switched to catching snakes for removal of venom, releasing them in
the wild after four extractions. The venom so collected is used for
producing life-saving antivenom, biomedical research and for other
medicinal products.[70] The Irulas are also known to eat some of the
snakes they catch and are very useful in rat extermination in the villages.
Despite the existence of snake charmers, there have also been
professional snake catchers or wranglers. Modern-day snake trapping
involves a herpetologist using a long stick with a V- shaped end. Some
television show hosts, like Bill Haast, Austin Stevens, Steve Irwin, and
Jeff Corwin, prefer to catch them using bare hands.
Consumption
File:Guangzhou-snakes-at-restaurant-0457
A "???" ("sea-leopard snake," supposedly Enhydris bocourti) occupies
a place of honor among the live delicacies waiting to meet their
consumers outside of a Guangzhou restaurant.
File:Snake_meat
Snake Meat, in a Taipei restaurant
While not commonly thought of as food in most cultures, in some
cultures, the consumption of snakes is acceptable, or even considered a
delicacy, prized for its alleged pharmaceutical effect of warming the
heart. Snake soup of Cantonese cuisine is consumed by local people in
autumn, to warm up their body. Western cultures document the consumption
of snakes under extreme circumstances of hunger.[71] Cooked rattlesnake
meat is an exception, which is commonly consumed in parts of the
Midwestern United States. In Asian countries such as China, Taiwan,
Thailand, Indonesia, Vietnam and Cambodia, drinking the blood of
snakes-particularly the cobra-is believed to increase sexual
virility.[72] The blood is drained while the cobra is still alive when
possible, and is usually mixed with some form of liquor to improve the
taste.[72]
In some Asian countries, the use of snakes in alcohol is also accepted.
In such cases, the body of a snake or several snakes is left to steep in
a jar or container of liquor. It is claimed that this makes the liquor
stronger (as well as more expensive). One example of this is the Habu
snake sometimes placed in the Okinawan liquor Awamori also known as
"Habu Sake."[73]
U.S. Army Special Forces trainees are taught to catch, kill, and eat
snakes during their survival course; this has earned them the nickname
"snake eaters," which the video game Metal Gear Solid 3: Snake Eater may
be inferred to draw from.
Snake wine (??) is an alcoholic beverage produced by infusing whole
snakes in rice wine or grain alcohol. The drink was first recorded to
have been consumed in China during the Western Zhou dynasty and
considered an important curative and believed to reinvigorate a person
according to Traditional Chinese medicine.[74]
Pets
In the Western world, some snakes (especially docile species such as the
ball python and corn snake) are kept as pets. To meet this demand a
captive breeding industry has developed. Snakes bred in captivity tend
to make better pets and are considered preferable to wild caught
specimens.[75] Snakes can be very low maintenance pets, especially
compared to more traditional species. They require minimal space, as
most common species do not exceed five feet in length. Pet snakes can be
fed relatively infrequently, usually once every 5-14 days. Certain
snakes have a lifespan of more than 40 years if given proper care.
Symbolism
Main article: Serpent (symbolism)
In Egyptian history, the snake occupies a primary role with the Nile
cobra adorning the crown of the pharaoh in ancient times. It was
worshipped as one of the gods and was also used for sinister purposes:
murder of an adversary and ritual suicide (Cleopatra).
File:Medusa_by_Carvaggio
Medusa by 16th Century Italian artist Caravaggio.
In Greek mythology snakes are often associated with deadly and dangerous
antagonists, but this is not to say that snakes are symbolic of evil; in
fact, snakes are a chthonic symbol, roughly translated as 'earthbound'.
The nine-headed Lernaean Hydra that Hercules defeated and the three
Gorgon sisters are children of Gaia, the earth.[76] Medusa was one of
the three Gorgon sisters who Perseus defeated.[76] Medusa is described
as a hideous mortal, with snakes instead of hair and the power to turn
men to stone with her gaze.[76] After killing her, Perseus gave her head
to Athena who fixed it to her shield called the Aegis.[76] The Titans
are also depicted in art with snakes instead of legs and feet for the
same reason-they are children of Gaia and Ouranos (Uranus), so they are
bound to the earth.
Three medical symbols involving snakes that are still used today are
Bowl of Hygieia, symbolizing pharmacy, and the Caduceus and Rod of
Asclepius, which are symbols denoting medicine in general.[34]
India is often called the land of snakes and is steeped in tradition
regarding snakes.[77] Snakes are worshipped as gods even today with many
women pouring milk on snake pits (despite snakes' aversion for
milk).[77] The cobra is seen on the neck of Shiva and Vishnu is depicted
often as sleeping on a seven-headed snake or within the coils of a
serpent.[78] There are also several temples in India solely for cobras
sometimes called Nagraj (King of Snakes) and it is believed that snakes
are symbols of fertility. There is a Hindu festival called Nag Panchami
each year on which day snakes are venerated and prayed to. See also Naga.
In India there is another mythology about snakes. Commonly known in
Hindi as "Ichchhadhari" snakes. Such snakes can take the form of any
living creature, but prefer human form. These mythical snakes possess a
valuable gem called "Mani", which is more brilliant than diamond. There
are many stories in India about greedy people trying to possess this gem
and ending up getting killed.
The Ouroboros is a symbol associated with many different religions and
customs, and is claimed to be related to Alchemy. The Ouroboros or
Oroboros is a snake eating its own tail in a clock-wise direction (from
the head to the tail) in the shape of a circle, representing
manifestation of one's own life and rebirth, leading to immortality.
The snake is one of the 12 celestial animals of Chinese Zodiac, in the
Chinese calendar.
Many ancient Peruvian cultures worshipped nature.[79] They emphasized
animals and often depicted snakes in their art.[80]
Religion
Main article: Snake worship
File:Simeon_Stylite_Louvre
A snake associated with Saint Simeon Stylites.
Snakes are a part of Hindu worship. A festival Nag Panchami is
celebrated every year on snakes. Most images of Lord Shiva depict snake
around his neck. Puranas have various stories associated with Snakes. In
the Puranas, Shesha is said to hold all the planets of the Universe on
his hoods and to constantly sing the glories of Vishnu from all his
mouths. He is sometimes referred to as "Ananta-Shesha," which means
"Endless Shesha." Other notable snakes in Hinduism are Ananta, Vasuki,
Taxak, Karkotaka and Pingala. The term Naga is used to refer to entities
that take the form of large snakes in Hinduism and Buddhism.
File:Rod_of_asclepius
Rod of Asclepius, in which the snakes, through ecdysis, symbolize healing.
Snakes have also been widely revered, such as in ancient Greece, where
the serpent was seen as a healer, and Asclepius carried two intertwined
on his wand, a symbol seen today on many ambulances.
In religious terms, the snake is arguably the most important animal in
ancient Mesoamerica. "In states of ecstasy, lords dance a serpent dance;
great descending snakes adorn and support buildings from Chichen Itza to
Tenochtitlan, and the Nahuatl word coatl meaning serpent or twin, forms
part of primary deities such as Mixcoatl, Quetzalcoatl, and
Coatlicue."[81] In both Maya and Aztec calendars, the fifth day of the
week was known as Snake Day.
In Judaism, the snake of brass is also a symbol of healing, of one's
life being saved from imminent death (Book of Numbers 21:6-9).
File:Lilith_(John_Collier_painting)
Lilith with a snake, (1892), by John Collier (1892).
In Christianity, Christ's redemptive work is compared to saving one's
life through beholding the Nehushtan (serpent of brass) (Gospel of John
3:14). Snake handlers use snakes as an integral part of church worship
in order to exhibit their faith in divine protection. However, more
commonly in Christianity, the serpent has been seen as a representative
of evil and sly plotting, which can be seen in the description in
Genesis chapter 3 of a snake in the Garden of Eden tempting Eve. Saint
Patrick is reputed to have expelled all snakes from Ireland while
Christianising the country in the 5th century, thus explaining the
absence of snakes there.
In Christianity and Judaism, the snake makes its infamous appearance in
the first book (Genesis 3:1) of the Bible when a serpent appears before
the first couple Adam and Eve and tempts them with the forbidden fruit
from the Tree of Knowledge. The snake returns in Exodus when Moses, as a
sign of God's power, turns his staff into a snake and when Moses made
the Nehushtan, a bronze snake on a pole that when looked at cured the
people of bites from the snakes that plagued them in the desert. The
serpent makes its final appearance symbolizing Satan in the Book of
Revelation: "And he laid hold on the dragon the old serpent, which is
the devil and Satan, and bound him for a thousand years." (Revelation 20:2)
In Neo-Paganism and Wicca, the snake is seen as a symbol of wisdom and
knowledge.
Place names
Various locations in different countries are called for snakes, such as
the Snake River in the United States and Snake Island (Black Sea)
(derived from "Fidonisi," which means the same in Greek).
See also
? Limbless vertebrates
? List of Serpentes families
? List of snakes
? Snake skeleton
? Venomous snake
? Legend of the White Snake
? The New Encyclopedia of Snakes
? Ophiology
? Snake worship
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Further reading
? Behler, John L.; King, F. Wayne (1979). The Audubon Society Field
Guide to Reptiles and Amphibians of North America. New York: Alfred A.
Knopf. pp. 581. ISBN 0394508246.
? Bullfinch, Thomas (2000). Bullfinch's Complete Mythology. London:
Chancellor Press. pp. 679. ISBN 0753703815.
? Capula, Massimo; Behler (1989). Simon & Schuster's Guide to Reptiles
and Amphibians of the World. New York: Simon & Schuster. ISBN 0671690981.
? Coborn, John (1991). The Atlas of Snakes of the World. New Jersey: TFH
Publications. ISBN 9780866227490.
? Cogger, Harold; Zweifel, Richard (1992). Reptiles & Amphibians.
Sydney: Weldon Owen. ISBN 0831727861.
? Conant, Roger; Collins, Joseph (1991). A Field Guide to Reptiles and
Amphibians Eastern/Central North America. Boston, Massachusetts:
Houghton Mifflin Company. ISBN 0395583896.
? Deane, John (1833). The Worship of the Serpent. Whitefish, Montana:
Kessinger Publishing. pp. 412. ISBN 1564598985.
? Ditmars, Raymond L (1906). Poisonous Snakes of the United States: How
to Distinguish Them. New York: E. R. Sanborn. pp. 11.
? Ditmars, Raymond L (1931). Snakes of the World. New York: Macmillan.
pp. 11. ISBN 978-0025317307.
? Ditmars, Raymond L (1933). Reptiles of the World: The Crocodilians,
Lizards, Snakes, Turtles and Tortoises of the Eastern and Western
Hemispheres. New York: Macmillan. pp. 321.
? Ditmars, Raymond L; W. Bridges (1935). Snake-Hunters' Holiday. New
York: D. Appleton and Company. pp. 309.
? Ditmars, Raymond L (1939). A Field Book of North American Snakes.
Garden City, New York: Doubleday, Doran & Co. pp. 305.
? Freiberg, Dr. Marcos; Walls, Jerry (1984). The World of Venomous
Animals. New Jersey: TFH Publications. ISBN 0876665679.
? Gibbons, J. Whitfield; Gibbons, Whit (1983). Their Blood Runs Cold:
Adventures With Reptiles and Amphibians. Alabama: University of Alabama
Press. pp. 164. ISBN 978-0817301354.
? Mattison, Chris (2007). The New Encyclopedia of Snakes. New Jersey:
Princeton University Press. pp. 272. ISBN 978-0691132952.
? McDiarmid, RW; Campbell, JA; Touré, T (1999). Snake Species of the
World: A Taxonomic and Geographic Reference. 1. Herpetologists' League.
pp. 511. ISBN 1893777006.
? Mehrtens, John (1987). Living Snakes of the World in Color. New York:
Sterling. ISBN 0806964618.
? Nóbrega Alves, RôMulo Romeu; Silva Vieira, Washington Luiz; Santana,
Gindomar Gomes (2008). "Reptiles used in traditional folk medicine:
conservation implications". Biodiversity and Conservation 17 (8):
2037-2049. doi:10.1007/s10531-007-9305-0. Retrieved 22 January 2009.
? Romulus Whitaker (English edition); Tamil translation by O.Henry
Francis (1996). ????? ??????????? ????????? (Snakes around us, Tamil).
National Book Trust. ISBN 81-237-1905-1.
? Rosenfeld, Arthur (1989). Exotic Pets. New York: Simon & Schuster.
pp. 293. ISBN 067147654.
? Spawls, Steven; Branch, Bill (1995). The Dangerous Snakes of Africa.
Sanibel Island, Florida: Ralph Curtis Publishing. pp. 192. ISBN 0883590298.
External links
? Media related to Serpentes at Wikimedia Commons
? "Worldwide Snake Species List". Snake Track.com.
? "Bibliography for "Serpentes"". Biodiversity Heritage Library.
? "Serpentes". Integrated Taxonomic Information System.
? "US Snakes". eNature.
? "Snakes of the Indian Subcontinent". Naturemagics Kerala Photo Gallery.
? "About Snake Cell". Snake Cell. (INDIA)
? "Snake World". ReptilesWeb.com.
? "What's That Snake?". OPLIN.
? "Herpetology Database". Swedish Museum of Natural History.
? BBC Nature: Snake news, and video clips from BBC programmes past and
present.
[hide]
v · d · e
Snake families
Chordata ? Reptilia ? Squamata ? Serpentes
Alethinophidia
Acrochordidae ? Aniliidae ? Anomochilidae ? Atractaspididae ? Boidae ?
Bolyeriidae ? Colubridae ? Cylindrophiidae ? Elapidae ? Loxocemidae ?
Pythonidae ? Tropidophiidae ? Uropeltidae ? Viperidae ? Xenopeltidae
Scolecophidia
Anomalepididae ? Leptotyphlopidae ? Typhlopidae
Categories: Snake anatomy | Snakes
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