Thursday, March 29, 2007

Evolution in Snakes

Snakes of the World Part – 2. - Evolution in Snakes

Image of Vine snake, Ahaetulla nasuta - courtsey:

Snakes v/s Roaches.

All the animals and plants which we see today were quite different in shape and size they sported millions of years ago; they all have undergone many changes and adaptations in accordance with the changes in living conditions. Many have perished as they could not adapt with the changing situations. Dinosaur is a glaring example for the process incidentally it also may be stated that the dinosaurs were closely related to the present reptiles of which the snakes belong. The cockroaches are a special case as they got stabilized in the present form millions of years ago and they undergo no changes yet survive!

Snakes are orchids of the animal kingdom.

Coral snake image courtsey:

Snakes as such are in the process of evolution regardless of the genera or species the present forms of snakes were derived from primitive forms even now the family of snakes have not been stabilized and the process only going on. In that case we can compare the orchids of the plant kingdom with snakes as both are un-stabilized and under going the process of evolution. Wide varieties seen are telling examples in such cases.

Keeping an eye!

1. No eyelids, no problem!

Image courtsey:

When snakes adopted a burrowed life the eye-lids became a trouble! As sand particles got in to it, evolution came to the help and eye-lids were totally replaced by a transparent membrane which allows contact with sand no problem, and the eye freely move under the membrane as if under a watch-glass.

2. All ears not a separate one!

Snakes have no ear holes and they are totally deaf, so they need not be worried about sand particles would enter! But its skin is sensitive to receive turbulences of the earth.

3. Has a sharp tongue

Poor eyesight and lack of ears do not matter as the tongue –which is forked- is able to sense the situations very sharply; this tongue is retractile in to a sheath when not in use. For an animal living in a burrow ears and eye often fail to detect approaching foe but skin does not fail.

4. Limbs a hindrance!

Vestigial (non functional) limbs in phython - Image courtsey:

It has been proved that snakes were once like lizards sported limbs but the necessity to move fast on the land and burrows crawling on legs proved in-efficient and spinal movement (using ribs and muscles) was resorted leaving the limbs un-used and they degenerated when they became only a hindrance to smooth movement. These useless limbs in most species of snakes became extinct leaving only remnants of hind-limbs in certain species of Boas and pythons.

5. Adaptations for feeding.

The jaws of the snake is another point undergone evolution, the nature of swallowing preys without cutting in to pieces required large mouths, rigid bones were a hindrance to this process of swallowing (deglutination), evolution endowed snakes with loosely paired jaw-bones both joined with flexible ligaments.

Changes in teeth and the “glands”

The dentition in snakes also sport evolutionary patterns, swallowing preys as such making teeth without normal functions, along with teeth the poison glands –which are modified salivary glands- also have changed in varying degrees in some species they keep pace in some not.

Snakes shed their teeth occasionally and new ones replace the old quickly. In primitive varieties a uniform dentition with solid teeth is still available as in some species of Colubridae this condition is called aglyphous as in Natrix).

The next stage is the Opsithoglyphae where the grooved posterior teeth with fangs attached to the upper-jaw is visible they are generally harmless to human.

In the front-fanged snakes (sea snakes and the coral snakes) known as Proterglyphae the anterior maxillary teeth are grooved and connected to the poison glands. All these types are poisonous.

Vipers are solenoglypha a further improved version where the fangs are capable of raising and lowering as they are attached to short maxillary bones which are vertically movable.

6. Changing of the costumes!

Image courtsey:

As they crawl on the surface their get bruised very often therefore nature has made it so adaptive such conditions that they change their skin at frequent intervals and get new attire as a gift from the almighty totally free!

7. Oviparous or viviparous? Both!

Image courtsey: shibu bhaskar

The relevance of the snakes in evolutionary process is more evident in its exhibition of both characteristics of procreation as even in same genera there are species showing both features, when pythons lay eggs Boas give birth to young ones. In Vipers most of them give birth to young ones when some of them lay eggs!

Snakes are on a course of evolution and it is the responsibility of human beings to see that the poor reptiles be given a chance to complete it, the present trend if continues there may be no snakes left to evolve, as these reptiles are exterminated in alarming rate either for commercial exploitation or by pure ignorance and superstitions. By saving them man can go long way in saving the earth’s ecology which will serve his own interest too.

Snakes of the World - Part 1

Snakes of the World Part – 2. - Evolution in Snakes

Snakes of the World Part - 3. - Cobra

Snakes of the World Part - 4. - Viper

Snakes of the World Part - 5. - King Cobra

To be continued....

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