Snakes are
the legless, elongated, carnivorous reptiles of
the suborder Serpentes under order Squamata of the class Reptilia, thus they
are often called as serpents. Like all other squamates, snakes are
also ectothermic and amniotic vertebrates which are covered
in with scales.
Most
of the species of snakes have skull containing more joints as
compared to their ancestors (lizard), allowing them to swallow their prey
completely which is much larger in size than their own heads with the help of
their highly mobile jaws. To cope up with their narrow physiques, snakes’
possess paired organs like their kidneys which appear one after the other
instead of having on sides, and have one functional lung only. Some of the
species also retain pelvic girdle having a pair of vestigial claws
on either side of the cloaca.
Existing
snakes are found on every continent of this world excluding Antarctica and some
other minor land masses, where exemptions including some large islands also
viz., Iceland, Ireland, Greenland, Hawaiian archipelago, the atolls of New
Zealand, and the isles of the Atlantic
and central Pacific oceans. Furthermore, sea snakes are common
through the Pacific and Indian Oceans.
More
than 3,709 species of snakes are distinguished by their limbless form,
by their elongated body and tail. Categorized with the lizards in the
same order Squamata, these limbless creatures represent a lizard that
is over the path of advancement, has endured series of physiological modification.
All of the snakes lack external limbs but that does not mean that all legless
reptiles are snakes. Despite the fact, two studies that have been reported in
the year 2016 stated that limb loss in the serpents is connected with mutations
in DNA (in the zone of polarizing activity regulatory sequence), which is a
controlling region of the auditory hedgehog gene, and is critically
essential for the development of limbs. Further most of the modern snakes do
not have any fragments of limbs, but basal serpents such as boas and pythons do
show the remnants of highly reduced vestigial hind limbs. Even embryos of pythons have completely
developed buds of hind limbs but then in their later stages of development
their growth gets stopped by the DNA mutations in the ZRS.
There
are some burrowing lizards that may have front or hind limbs only or may be entirely
legless. Unlike lizards, snakes do not have movable eyelids resulting in a
continuous and often distressing gaze. Snakes also lack an external ear opening
that means they do not listen to tunes. While within, they have lost the
urinary bladder also. The visceral organs of them are elongated,
with the reduction of the left member in relation to the right one, where the
left lung is reduced or even completely lost. However instead of all
these facts snakes have improved and increased number of vertebras, and have advanced
two innovations among the vertebrates viz., a tracheal lung in the neck
region and a venom accompanying system for placating prey.
Furthermore around 24 families of
living snakes have been recognized so far comprising 3,709 species.
Serpents are assumed to have been evolved from the terrestrial lizards during
the Middle Jurassic Epoch (174.1 - 163.5 million of years ago). The
one of the oldest known fossil of snake is “Eophis underwoodi”; it was a small snake species that lived in
southern England around 167 million years ago.
They
range in size from the minute Barbados thread snake (10.4 cm long only)
upto 6.95 meters long reticulated python. The fossil species “Titanoboa cerrejonensis” that once lived
was 12.8 meters long in length.
Phylogeny
of modern serpents according to reptile-database.org
- Ophidian (Serpentes) - Snakes (phylogeny)
- · Superfamily Acrochordoidea
·
Family Acrochordidae (File
Snakes)
- · Superfamily Uropeltoidea s.l. (Pipe snakes and Shield-tailed snakes)
·
Family Anomochilidae (Dwarf
Pipe Snakes)
·
Family Cylindrophiidae (Asian
Pipe Snakes)
·
Family Uropeltidae (Shield-tail
Snakes)
- · Superfamily Pythonoidea s.l. (Pythons and relatives)
·
Family Loxocemidae (Mexican
Burrowing Pythons)
·
Family Pythonidae (Pythons)
·
Family Xenopeltidae (Sunbeam
Snakes)
- · Superfamily Booidea (preliminarily after Vidal & Hedges 2009)
·
Family Boidae (Boas)
·
Subfamily Boinae (Boas)
·
Subfamily Ungaliophiinae (Dwarf
Boas)
·
Subfamily Erycinae
·
Subfamily Calabariinae (or
Calabariidae)
·
Subfamily Candoiinae (or
Candoiidae)
·
Subfamily Sanziniinae (or
Sanziniidae)
·
Subfamily Charininae (or
Charinidae)
- · Superfamily Colubroidea (revised after Pyron et al. 2010, Pyron et al. 2013)
·
Family Colubridae (Colubrids)
·
Subfamily Calamariinae
·
Subfamily Colubrinae
·
Subfamily Grayiinae
·
(Sub-) Family
Dipsadidae (currently as Dipsadinae, following Pyron et al.
2013 and Zheng & Wiens 2016; see squamate phylogeny)
- · Family Lamprophiidae (in Wikipedia currently subsumed under Colubridae)
·
Subfamily Aparallactinae
·
Subfamily Atractaspidinae (Mole
Vipers)
·
Subfamily Cyclocorinae
·
Subfamily Lamprophiinae
·
Subfamily Psammophiinae
·
Subfamily Prosymninae
·
Subfamily Pseudaspidinae
·
Subfamily Pseudoxyrhophiinae
- · Family Natricidae (currently as Natricinae, following Pyron et al. 2013 and Zheng & Wiens 2016)
- · Family Pseudoxenodontidae (Pseudoxenodontinae in Pyron et al. 2013)
- · Family Elapidae
·
Subfamily Elapinae (Cobras, Coral
Snakes, etc.)
·
Subfamily Hydrophiinae (Sea
Snakes)
- · Family Homalopsidae
- · Family Pareidae (was Pareatidae, see P. carinatus for details)
- · Family Viperidae (Vipers and Pit Vipers)
·
Subfamily Azemiopinae
·
Subfamily Crotalinae
·
Subfamily Viperinae
- · Superfamily Typhlopoidea (Scolecophidia)
·
Family Anomalepididae (Dawn
Blind Snakes)
·
Family Gerrhopilidae (Blind
Snakes)
·
Family Typhlopidae (Blind
Snakes)
·
Family Leptotyphlopidae/Glauconiidae
(Slender Blind Snakes)
·
Subfamily Leptotyphlopinae
·
Subfamily Epictinae
·
Family Xenotyphlopidae
- Presently not assigned to any Superfamily:
· Family Aniliidae/Ilysiidae
(Pipe Snakes)
· Family Bolyeriidae (Round
Island Boas)
· Family Tropidophiidae (Dwarf
Boas)
· Family Xenophidiidae
Most
of the species of modern snakes are nonvenomous and those that have venom,
they use it mainly to hunt and placate their prey rather than for self-protection
activities. Those that possess venom are so intoxicating to cause painful
injury leading death to humans if not treated in time. Where in case of nonvenomous
snakes they either swallow their prey alive or kill by constricting the
prey before swallowing.
Etymological
the English word “Snake” originated from the Old
English “Snaca”, which itself derived from Proto-Germanic word
“snak-an-“; from Proto-Indo-European root “nēg-o” which
means "to crawl” or "to creep", & in Sanskrit “nāgá”
means "snake". While the term “Serpent” is from the
French word “Serp” which means “to creep”.
…………………… Coming More……………………
Literature
Cited:
http://www.reptile-database.org/db-info/taxa.html#Ser
https://en.wikipedia.org/wiki/Snake
http://idahoptv.org/sciencetrek/topics/snakes/facts.cfm
https://www.britannica.com/animal/snake/Form-and-function
https://defenders.org/snakes/basic-facts
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