ORIGIN, MORPHOLOGY AND LIFESTYLE OF SNAKES
Snakes belong to the suborder serpents which are believed to have evolved from lizards4, 1. Lizards had limbs and snakes evolved by loosing these limbs4. Even though snakes evolved from lizards snakes had to loose their limbs and adapt to crawl on their stomachs. There are various differences that exist between snakes and lizards due to their mobility and their feeding styles4. Lizards tend to have a fixed lower jaw while that the two halves of their lower jaw is united by a ligament and the snakes can swallow bigger prey than the lizards in relation to their head size. In addition snakes have lost the urinary bladder which is present in lizards4. Since snakes don’t have to walk they need not support the limbs and they have lost the pectoral girdle and have their braincases closing on the anterior end and no external ear opening. They have fused eyelids leaving a small slit where the snakes can see from and some have small left lung or none4.
The loss of limbs doesn’t mean that a snake is less active than the lizards. Snake is a name derived from the old English ‘SNACA’ which means to crawl1. Snakes have various ways for movement as they possess muscles that help them in movement. Snakes move by means of lateral undulation movements where they flex their bodies’ from side to side forming a sine wave shape1. Also snakes can make concertina movements which help them move through tunnels and climb trees. In case of climbing trees the snake’s tail coils on a branch and sort of lifts the front side and extends it to the position it needs to move. While moving in tunnels the snake’s body loops severally and moves further by using the tunnels walls to achieve traction. Rectilinear locomotion is similar the caterpillar-like motions where small loops are made. The snake propels itself by using the stomach muscles while still remaining straight and a series of waves move along the belly. This is a means of locomotion used by big snakes like the pythons and vipers1. Side winding is another method of movement used by snakes on slippery surfaces1. All this movements are made possible by snakes having the flank muscles that it uses for this purpose. The scales on the under surface (belly) have a shape as narrow rectangles along the width of the body and overlapping one another with their free edges to the rear and attach themselves to surfaces pushing the snake forward4.
Snakes are carnivorous feeding on small animals including lizard, other snakes, rodents, small mammals, birds, eggs and insects1. The powerful muscles are also used by some species of snakes like boars and pythons to coil around their prey to suffocate it this is known as constriction2. Their lower jaw’s right and left halves are joined by a ligament is an advantage to the snake as they use their mouths to grasp their prey which at times is larger than the size of the head2. It’s also useful in the swallowing process. An interesting feature of snakes is their teeth being curved backwards and they use them to grasp their prey as it is swallowed2. A snake is known to eat prey relatively bigger than the size of the head1, 2. The teeth are also modified to form fangs which are used for killing their prey before ingestion. Fangs can be located in the front of the mouth which also can be fixed or unmovable (mambas and cobras) or moveable/foldable (vipers). Other snakes like the boomslang have fangs at the back of the mouth3, 4. The fangs are specialised teeth that have grooves where the venom (poison) is injected into the prey4.
Some snakes like the rattle snake, python and some boas have a pit located between the nostril and the eye to sense infra-red radiation emitted by prey’s body (radiated heat) and which is also directional1, 4. Snakes have a forked tongue which they use to smell as it has a special organ called the Jacobson’s organ to which particles picked by the tongue are passed1. By moving along the ground snakes are able to pick vibrations and avoid being crashed or escape from enemies. Snakes owing to the shape of their eye have poor eyesight but are able to pick movements1.
All the features that snakes have, has helped them to become more advanced of all the reptiles.
1. Wikipedia contributors. Snake [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 6, 15:39 UTC [cited 2006 May 6]. Available from: http://en.wikipedia.org/w/index.php?title=Snake&oldid=51840544.
2. Porter, K. R. Herpetology. 1972. W. B. Saunders Company
3. Wikipedia contributors. Boomslang [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 5, 06:20 UTC [cited 2006 May 6]. Available from: http://en.wikipedia.org/w/index.php?title=Boomslang&oldid=51641712.4. Knight, R. BCB Biodiversity chapter 2 A Water-Tight Skin and The Shelled Egg (Cited 2006 May 6) http://planet.uwc.ac.za/nisl/biodiversity/Chapter2/page_138.htm
VINCENT MUCHAI WAIRIMU
Biodiversity and Conservation Biology
University of the
Private Bag X17 Bellville