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Historic Background of Reptiles (Part 6)

© Janat Khatoon

Ingenious as these ideas are, they are disregarded by some fossil experts who have discovered significant kinships between snakes and several extinct groups of aquatic lizards, the aigialosaurs, the doliehosaurs and the mosasaurs. These, along with such surviving types as the monitors, the Gila monster and a little known Bornean lizard, make up a group called the Platynota. Unfortunately all platynota are, or were either giant aquatic animals or provided with good functional legs.

Thus, the two prevalent theories of snake origin fail to fit together into a clear pattern of snake history. It would help if a subterranean, blind, limbless monitor or mosasaur could be found, but so far none has turned up. Whatever the derivation of snakes may have been, and whatever the initial value of limblessness to the early snakes, there can be no doubt that an efficient new locomotor system has taken the place of the lost limbs. When they abandoned the fourpoint limb support for their bodies, the early snakes also removed limits to their lengths. They allowed serpentine movements to replace footwork and this laid the groundwork for other modifications as well. Another is the series of tree-climbing adaptations of arboreal species, and the concurrent advantages of having a long body that can be made to look like a twig or branch. Also, the loss of the limbs and girdles and the reduction of the cross-section of the body permitted snakes to go into places like narrow caves and rock crevices that would be closed to a four-legged animal of similar chest expansion. And for aquatic snakes the ability to swim by passing waves of undulation backwards along the body made the loss of the limbs and lengthening of the body not merely inconsequential, but actually a gain.

To the modern snakes the lack of legs is not by any means a handicap to locomotion. Although for sheer speed over smooth ground most men can move faster than most snakes, this is not true in cluttered places. Let the landscape be wooded, rough or scrubby and the snake a whip snake or racer, and a whole posse of men will be left behind in the chase.

Flight, first achieved by the insects in the coal forests millions of years before, was evolved twice during the Age of Reptiles. The first venture was that of the pterosaurs, often called pterodactyls, in the lower Jurassic. These were light-bodied archosaurs which took to the air on leathery wings stretched by their finger bones. The pterosaurs no doubt began as gliders, and some may never have aquired the ability to keep up sustained flapping flight, but others certainly did. It is believed that some pterosaurs fed on the wing, dipping fish out of the sea like modern sea birds. The biggest of them, pteranodon, had a wing-spread of more than 20 feet.

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