Several features of the monitor lizards are not found in other lizards but are found in snakes. For example, the monitor lizards are the only lizards to swallow their prey whole, or if it is too big, pieces of it. Other lizards chew and crush their food before eating. Let’s know more about are snakes really modified lizards.
Another snake-like characteristic is the monitor lizard’s forked tongue, again unknown in other lizards. Finally, monitor lizards are unable to shed their tails, a typical lizard characteristic unknown in snakes. These clues indicate that monitors and snakes probably descended from the same ancestor way back in prehistoric time.
Other lizard families also have snake-like features and we have already seen that the burrowing skinks have long, streamlined bodies with reduced limbs. One lizard often mistaken for a snake is the Slow-worm.
You can tell the Slow-worm, is a legless lizard, however, by the several rows of scales along its belly (snakes have only one row), by the presence of eyelids (snakes have none), and by its notched tongue (snakes have forked tongues).
How do snakes slither?
You might think that, without legs, snakes would have difficulty in moving. However, snakes have developed the art of slithering to a fine degree and grass snakes, for example, can slither as fast as a man can walk. They move along sending waves of contractions alternately along the muscles of either side of the body.
This results in horizontal curves or waves passing from the head of the snake down to the tail. The rear edge of each wave pushes back words, and so if the passage of waves done what snake is checked by bumps and stones on the ground, the snake moves forward. A snake crossing a sandy patch leaves a trill with sand heaped up at the rear of each wave, showing where the thrust was made.
Some snakes move by a variation of this method called ‘concertina locomotion’. The snake throws the front half of its body into waves, grips the ground and draws up the rear half. The rear half then forms waves which push the straightened front half forward.
Heavy, fat snakes tend to creep forward in a straight line. They do this by sending a wave of contraction down the narrow row of overlapping scales on their belly. These scales move forward slightly and then back, and their continued action along the snake puss it forward slowly.
How does a sidewinder move?
If you place a snake on a very smooth surface, the waves passing down its body will not grip and the snake will not move forward. Losses, shifting sand has much the same effect on conventional snake slithering, and so we find a different method of movement in desert snakes.
A side-winding snake throws its head into a sideways loop. It places its neck on the sand and twists the rest of its body of the sand and through the same spot, pushing downwards at the same time. As the body spirals through this point the head makes a new loop and again touches done in front and to the side.
These actions leave a line of parallel ‘J’ shaped in the sand. The curved bottom of the ‘J’ is made by the head touching down, the stem by the body looping through and forwards, and the cross by the tail thrusting off. A sidewinder travels forward even though it is spiraling sideways.
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