Snakes are the legless elongated, carnivorous reptiles of the suborder Serpentes belonging to order Squamata of class Reptilia, so they are ...
Snakes are the legless elongated, carnivorous reptiles of the suborder Serpentes belonging to order Squamata of class Reptilia, so 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
· Subfamily Sibynophiinae (=Scaphiodontophiinae, see comment in Sibynophis geminatus)
· (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
· Family Xenodermidae (was: Xenodermatidae, see X. javanicus for details)
· 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”.
Literature Cited:
http://www.reptile-database.org/db-info/taxa.html#Ser , retrieved on 1st November, 2018
https://en.wikipedia.org/wiki/Snake retrieved on 1st November, 2018
http://idahoptv.org/sciencetrek/topics/snakes/facts.cfm retrieved on 1st November, 2018
https://www.britannica.com/animal/snake/Form-and-function retrieved on 1st November, 2018
https://defenders.org/snakes/basic-facts retrieved on 1st November, 2018
